Introduction

The family Canthocamptidae Brady, 1880 is by far the largest family of Harpacticoida G.O. Sars, 1903, comprising in excess of 600 species, being predominantly distributed in freshwater. Representatives of the family can be found in freshwater habitats such as ponds, wetlands, hot springs, glacial melt water, and damp moss. Determining the evolutionary history of the canthocamptids is grossly obstructed by the lack of a coherent scheme of phylogenetic relationships for the family. It has been assumed that the family is almost certainly polyphyletic; therefore, Canthocamptidae is in urgent need of revision and on the other hand, most of the established genera should be carefully diagnosed on the basis of their apomorphic characters (Boxshall and Jaume 2000; Boxshall and Halsey 2004).

Brian (1923) published Mesochra arupinensis as nomen nudum in his study on benthic copepods of Rovinj (Croatia). Later, in another study on the harpacticoid copepods of Rovinj, Brian (1925) validly described Mesochra arupinensis Brian, 1925 as a new species. On the other hand, Gurney (1927) described Pseudomesochra parvula Gurney, 1927 as a new species and created the genus Pseudomesochra Gurney, 1927 by monotypy in the same study. Later Gurney (1932) realized that the genus Pseudomesochra was preoccupied by Pseudomesochra T. Scott, 1902 (family Pseudotachidiidae) and therefore Gurney (1932) created the genus Nannomesochra Gurney, 1932 as a replacement name for the genus Pseudomesochra. Later Monard (1935a) compared the descriptions of N. parvula with that of Mesochra arupinensis and finally reached the conclusion that N. parvula should be accepted as a junior subjective synonym of Mesochra arupinensis. Monard (1935a) also stated that M. arupinensis should be located in the genus Nannomesochra. So, it was Monard (1935a) who first transferred M. arupinensis to the genus Nannomesochra. Lang (1936, 1948) agreed with Monard’s (1935a) decision and this case has been accepted until now. Currently, the genus Nannomesochra contains three valid species (Walter and Boxshall 2022).

During the course of surveys along the Turkish coasts, numerous specimens belonging to the genus Nannomesochra were collected from different locations. Detailed morphological comparisons of the populations as well as the descriptions in the literature revealed the presence of several different morphological species, the descriptions of which are given below. This has also provided us to re-evaluate the taxonomic position of the genus and to review the previous records assigned to N. arupinensis sensu lato.

Material and methods

Several specimens collected from the Turkish coasts (deposited in the collection of Mersin and Balıkesir Universities, Turkey) were re-examined (see details in the results). Differential interference contrast (DIC) attached binocular microscopes (Olympus BX–50 and BX–53) were used to examine and draw the specimens in detail. An Olympus SZX–12 stereomicroscope was used to dissect selected specimens then dissected parts were mounted on several slides in lactophenol mounting medium. The technique of inserting glass fibers between slide and cover slip was used to prevent the whole specimens and dissected appendages from being squashed by the coverslips and to enable rotation and manipulation, permitting observation from all positions. An ocular micrometer was used to take measurements. Total body length was measured from tip of rostrum to posterior margin of caudal rami. Illustrations of the specimens were drawn with Photoshop CS2 or Inkscape v0.91 by using a Wacom Cintiq Pro 13 graphic tablet. Scale bars in illustrations are given in μm. SEM examinations were made with a Zeiss SUPRA 55VP (FESEM) scanning electron microscope at the Mersin University Advanced Technology Education, Research, and Application Centre (MEITAM). A protocol described in Kaymak and Karaytuğ (2014) was followed for SEM study. Entellan (Merck) was used for sealing all dissected specimens prepared for light microscopy after examination; undissected whole specimens were preserved in 70% ethanol in small tubes. The descriptive terminology is adapted from Huys et al. (1996). Abbreviations used in the text are as follows: P1–P6, first to sixth swimming legs; ae, aesthetasc; enp, endopod; exp, exopod. A cladistic analysis was performed on Nannomesochra species. Fifteen morphological characters used in the analysis and their states were listed in Table 1 and the data matrix was given in Table 2. The states of the characters were defined in accordance with the basic principles in the copepod evolution (Huys and Boxshall 1991). Standard coding was used in the matrix: “0” representing a plesiomorphic character state and higher numbers are apomorphies. Unknown values were coded “?”. To construct trees, maximum parsimony (MP) analysis was conducted in PAUP* 4.0a software with a heuristic search option. All material except for the specimens deposited in the Zoology Museum of Adıyaman University (ZMADYU) is incorporated in the collection of Mersin University Biology Department.

Table 1 List of characters used in cladistic analysis (0 is a plesiomorphic state, higher numbers are apomorphic states)
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Table 2 Data matrix used in the PAUP analysis of Nannomesochra species. The character numbers refer to the character list given in Table 1
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Results

Taxonomic account

Order Harpacticoida G.O. Sars, 1903

Family Canthocamptidae Brady, 1880

Genus Nannomesochra Gurney, 1932

Diagnosis. Canthocamptidae. Body slender and more or less cylindrical, slightly tapering posteriorly, without prominent distinction between prosome and urosome, first thoracic somite fused to cephalosome, forming a cephalothorax.. Urosome 5-segmented in female; comprising fifth pedigerous somite, genital double-somite and three free abdominal somites. Genital double somite with internal trace of subdivision ventrally and (dorso)laterally. Rostrum well developed, bell-shaped, anteroventrally directed, fused with cephalothoracic shield, but defined at base by a suture line. Anal operculum straight, distal margin ornamented with fine setules. Urosome 6-segmented in male; comprising fifth pedigerous somite, genital somite and four free abdominal somites. Caudal rami with seven setae, seta II difficult to observe. Antennule short; 7-segmented in female, furnished with aesthetasc on 4th and 7th segments; indistinctly 9-segmented and haplocer, furnished with aesthetasc on 5th and 9th segments in male. Antenna biramous; allobasis with two abexopodal setae; endopod 1-segmented; exopod 1-segmented with two setae. Mandible with well-developed gnathobase; palp represented by a segment with 5 setae. Maxillule with well-developed praecoxal arthrite; exo- and endopod incorporated into basis. Maxilla with two syncoxal endites; allobasis represented by claw. Maxilliped prehensile with syncoxa and basis; endopod with claw and a small seta. P1 with both rami 3-segmented. P2–P4 with 3-segmented exopods and 2-segmented endopods in female; endopod P3 2-segmented in male, second segment with modified inner spine. P5 confluent in both sexes; exo- and endopodal lobes in female with 5–6 and 4 setae respectively; in male endopodal lobe with 2 setae. Female P6 with by 2 setae. Male P6 with 1 seta. Sexual dimorphism in body ornamentation, antennule, endopod of P3, P5 and P6.

Type species. Pseudomesochra parvula Gurney, 1927 = Nannomesochra parvula (Gurney, 1927) (by monotypy).

Other species. N. arupinensis (Brian, 1925), N. zavodniki Petkovski & Apostolov, 1974, N. shermani (Corgosinho & Schizas, 2013) comb. nov., N. gebekumensis sp. nov., N. giziri sp. nov., N. erythraiensis sp. nov.

Species inquirendae. Mesochra arupinensis sensu Brian (1928a, 1928b); Pseudomesochra parvula sensu Willey (1930); Mesochra arupinensis = Mesochra armoricana sensu Monard (1935b); Nannomesochra arupinensis sensu Jakubisiak (1938); Nannomesochra arupinensis sensu Noodt (1953); Nannomesochra arupinensis sensu Vervoort, 1964; Nannomesochra arupinensis sensu Apostolov and Marinov (1988).

Unverifiable records: Tunisia (Monard 1935a; Lang 1936); Algeria (Monard 1937); Greece (Monard 1937); Teneriffe (Noodt 1955a); Turkey (Noodt 1955b); Ireland (Roe 1960); Indian Ocean, Aldabra (Wells and McKenzie 1973); Bulgaria (Apostolov 1977); San Diego, USA (Thistle 1982); Italy (Ceccherelli and Mistri 1990); Australia (Halse et al. 2000); United Kingdom (Ventham 2011); Tanzania (Callens et al. 2012); Brazil (Sarmento and Santos 2012). No illustrations.

Nannomesochra arupinensis (Brian, 1925 )

Original description. Mesochra arupinensis Brian, 1925: p.20, Figs. 8–16.

Mesochra arupinensis sp.n. nomen nudum (Brian, 1923): p.130.

Material examined. None

Remarks. N. arupinensis was first published by Brian (1923) as nomen nudum under the name of Mesochra arupinensis in his study on benthic copepods of Rovinj (Croatia). Later, in another study on the harpacticoid copepods of Rovinj, Brian (1925) described Mesochra arupinensis as a new species. Unfortunately, the type material of N. arupinensis sensu Brian (1925) cannot be traced but the detailed comparisons of the original descriptions (Brian, 1925) with those of the successive records revealed that the following combination of the characters easily differentiate N. arupinensis sensu Brian (1925) from other species considered valid of the genus in this study: i) the presence of 6 setae on the third exopod segment of P4 in female; ii) the structure of female P5, i.e. baseoendopodal lobe not exceeds the exopod; iii) the structure of male P5, i.e. the triangle shape of baseoendopodal lobe which exceeds the exopod; iv) the structure of male P3 enp-2. The unusual shape and setation of the male P3 enp-2 are unique within the genus; the modified inner seta on the enp-2 cannot be identified on the figure provided by Brian (1925) but the small/reduced element on the anterior surface of the enp-2 may represent the modified seta. Nevertheless, the P3-enp is very different from that of other species in the genus. Other minor differences compared to those of valid species are summarized in Table 3.

Table 3 Morphological comparison of Nannomesochra species (uk: male unknown, N/A: data not avaliable; **: see description)
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Nannomesochra parvula (Gurney, 1927 )

Original description. Pseudomesochra parvula Gurney, 1927: p.543, Fig. 153 (A–L).

Synonym. Nannomesochra arupinensis (Brian, 1925) sensu Alper et al. (2010).

Material examined. Two ♀♀ (one ♀ dissected on six slides), collected from washings of macroalgae Cystoseira sp., Corallina sp., Halopteris sp. and Laurencia sp., 16 April 2007. Seven ♀♀ in alcohol, collected from washings of macroalgae Cystoseira sp., Corallina sp., Halopteris sp. and Laurencia sp., 23 February 2008. All material collected from the intertidal zone at rocky shore of Gebekum (36.7639833° N, 27.7450000° E), Datça, Muğla/Turkey.

Redescription of the female

Body (Fig. 1a, b) cylindrical, gradually tapering posteriorly; without clear distinction between prosome and urosome; first thoracic somite fused to cephalosome, forming a cephalothorax. Total body length: 498 μm. Greatest width measured at posterior margin of cephalothorax: 124 μm. Surface ornamentation of somites as figured (Figs. 1a, b and 4a). Hyaline frills of somites smooth.

Fig. 1
figure 1

N. parvula, female. a Habitus, dorsal; b Habitus, lateral; c Rostrum, dorsal; d Antennule, dorsal

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Rostrum (Fig. 1c) bell shaped, defined at base; bears two sensilla.

Antennule (Fig. 1d) 7-segmented. Segment-1 ornamented with rows of spinules near posterior margin and a row of robust spinules at distal margin; with a seta at distal corner. Segment-2 with nine setae. Segment-3 rectangular, with six setae. Segment-4 bears one seta and an aesthetasc fused basally to a seta. Segments -5 and -6 are similar in length, with one and two setae respectively. Segment-7 bears five setae and an apical acrothek consisting of an aesthetasc and two setae. Armature formula: 1[1]-2[9]-3[6]-4[1+(1+ae)]-5[1]-6[2]-7[5+acrothek].

Antenna (Fig. 2a). Coxa ornamented with a row of spinules as figured. Allobasis with two abexopodal setae. Exopod 1-segmented, rectangular; armed with two apical setae. Endopod with two lateral robust pinnate spines; distal margin ornamented with spinules as figured; apical armature consists of two pinnate spines, two geniculate setae, and one pinnate spine fused basally to a seta.

Fig. 2
figure 2

N. parvula, female. a Antenna; b Labrum; c Mandible; d Maxilule; e Maxilla; f Maxilliped, anterior; g Maxilliped, posterior

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Labrum (Fig. 2b) large, with bilateral extensions medially. Anterior surface with long spinules subdistally, posterior surface with a row of spinules bi-laterally.

Mandible (Fig. 2c) with well-developed gnathobase that bears a pinnate seta at dorsal corner; cutting edge with series of teeth. Palp 1-segmented, exopod and endopod incorporated into basis, armature consisting of three pinnate setae laterally and two elements (one pinnate spine and one seta) apically.

Maxillule (Fig. 2d). Praecoxa with spinules laterally. Praecoxal arthrite well-developed, with a row of small spinules on posterior surface, with one seta on anterior surface, with nine elements around distal margin. Coxa ornamented with spinular row as figured. Coxal endite bears one pinnate spine and one bare seta. Endopod and exopod incorporated into basis, armature consisting of four setae laterally and, one pinnate spine and three bare setae apically.

Maxilla (Fig. 2e). Syncoxa with two endites; each bears three spines apically, two of which with tubular extensions as figured. Allobasis forming spinous claw, slightly curved distally; accessory armature represented by two setae. Endopod reduced, represented by two setae.

Maxilliped (Fig. 2f and g) subchelate. Syncoxa and basis ornamented with spinular rows as figured. Endopod 1-segmented; armed with long claw, slightly curved apically and with one small accessory seta.

P1–P4 (Fig. 3a, b, c and d). Praecoxae well developed, ornamented with spinules along distal margin. Intercoxal sclerites wider than long. Coxae rectangular; ornamented with row of spinules as figured (P1, P2) or unornamented (P3, P4). Bases ornamented with large spinules along distal margin; with a tube-pore as figured; with one inner seta and one outer seta (P1) or with one outer seta (P2–P4). P1–P4 with 3-segmented exopods; outer margin of exopodal segments ornamented with strong spinules. Exp-1 with naked inner margin (P1–P4). Exp-2 without (P1) or with one inner seta (P2–P4). Exp-3 with two geniculate setae and two outer spines (P1) or with one inner seta, two long apical setae and three outer spines (P2) or with two inner setae, the medial one long and plumose, the sub-distal one short and serrated apically; two apical long setae and three outer spines (P3–P4). Endopod 3-segmented (P1) or 2-segmented (P2–P4); outer margin of endopodal segments ornamented with spinules. Enp-1 with one inner seta, serrated apically (P1, P2, P4); or with one inner bare seta (P3). Enp-2 with one inner seta (P1) or with two inner setae serrated apically, two apical setae (inner one minute, outer one long and plumose) and one outer pinnate spine (P2) or with two inner setae (medial one short and serrated apically, sub-distal one long and plumose), two apical setae (inner one short, outer one long and plumose) and one outer pinnate spine (P3–P4). Enp-3 with one inner naked seta and two apical long, pinnate setae (P1).

Fig. 3
figure 3

N. parvula, female. Swimming legs. a P1; b P2; c P3; d P4

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Setal formula of swimming legs:

 

Exopod

Endopod

P1

0.0.022

1.1.120

P2

0.1.123

1.221

P3

0.1.223

1.221

P4

0.1.223

1.221

P5 (Fig. 4a) fused medially, forming a bilobate plate with medial incision, bearing a pore and a row of fine spinules on anterior surface. Endopodal lobe extending beyond distal margin of exopod, armed with four pinnate setae. Exopods roundish, armed with five setae (seta-III shortest, spiniform). Outer basal seta with a flagellum.

Fig. 4
figure 4

N. parvula, female. a Urosome and P5, ventral; b Left caudal ramus, dorsal; c Left caudal ramus, lateral

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Caudal rami (Fig. 4a, b and c) slightly wider than long; with a tube-pore at outer distal corner dorsally; with seven setae. Seta I naked; seta II delicate bifid at tip; seta III naked, inserted at outer distal corner. Seta IV and V inserted terminally, with a fracture plane. Seta VI naked. Seta VII located dorsally, tri-articulated at base. A spinular row is present near base of seta VII.

Remarks. As mentioned in the “Introduction” section, N. parvula was synonymized of M. arupinensis and M. arupinensis transferred to the genus Nannomesochra by Monard (1935a). Lang (1936, 1948) agreed with Monard’s (1935a) decision. This case has accepted until now. Some Turkish material of Nannomesochra (named and redescribed in detail above as Nannomesochra parvula) examined in this study is morphologically almost identical with Gurney’s (1927) original description of N. parvula. Comparisons between two species were revealed that N. parvula differs from N. arupinensis by the combination of the following characters: i) P1 endopod equal to exopod in length ii) female P2–P4 bears 5,5,5 and 6,7,7 setae on the distal segments of endo- and exopods respectively; iii) baseoendopodal lobe of female P5 extends beyond distal margin of exopod; iv) seta III on female P5 exopod is short, spiniform; v) spinular row is present near base of seta VII on caudal rami. Other minor differences compared to N. arupinensis and other species of the genus are summarized in Table 3. Because of the characters listed above N. parvula should be considered as a valid species.

Nannomesochra zavodniki Petkovski & Apostolov, 1974

Original description. Nannomesochra zavodniki Petkovski & Apostolov, 1974: Fragmenta Balcanica, 10, 1–8, Figs. 1–3.

Material examined. None.

Remarks. N. zavodniki was originally described from a single female, collected between the algae and stones on Marjan Beach near Split, Croatia (Petkovski and Apostolov 1974), and has not been reported since then. N. zavodniki can be distinguished from the other species of the genus except N. erythraiensis sp. nov. by the combination of the following characters: i) female P5 exopod bears six setae; ii) female P2–P4 bears 5,4,4 and 5,6,6 setae on the distal segments of endo- and exopods respectively. N. zavodniki morphologically differs from N. erythraiensis sp. nov. by the combination of the following characters: i) the inner seta of P1 enp-1 extends to approximately the end of enp-2; ii) P1 enp-1 extends to approximately the middle of exp-2; iii) P2 endopod extends to approximately the middle of exp-2; iv) P4 endopod extends beyond the end of exp-1; v) female P5 exopod with a protuberance between seta I and II; vi) caudal rami without a spinular row near base of seta VII. Other minor differences compared to those of valid species are summarized in Table 3.

Nannomesochra shermani (Corgosinho & Schizas, 2013) comb. nov.

Original description. Archeolourinia shermani Corgosinho & Schizas, 2013 Figs. 1–4.

Synonym. Archeolourinia shermani Corgosinho & Schizas, 2013.

Material examined. None

Remarks. In their study from mesophotic coral ecosystems in southwestern Puerto Rico, Corgosinho and Schizas (2013) described Archeolourinia shermani as a new genus and a new species. As noted by Karaytuğ et al. (2021), the inclusion of the monotypic genus Archeolourinia in the Louriniidae is not justified. Therefore A. shermani is now removed from Louriniidae and transferred to the genus Nannomesochra within the family Canthocamptidae. N. shermani comb. nov. can be distinguished from the other species of the genus by the combination of the following characters: i) female P5 exopod bears five setae; ii) baseoendopodal lobe of female P5 not reaching distal margin of exopod; iii) female P2–P4 bears 5,4,4 and 6,7,7 setae on the distal segments of endo- and exopods respectively. Other minor differences compared to those of valid species are summarized in Table 3.

Nannomesochra gebekumensis sp. nov.

https://zoobank.org/4630FD02-B646-4A31-A6F9-E2FC4A8BBFAE

Synonym. Nannomesochra sp. sensu Alper et al. (2010).

Type locality. Turkey, Muğla province, from intertidal zone at rocky shore of Gebekum/Datça (36.7639833° N, 27.7450000° E).

Type material. Holotype, ♀, collected from washings of macroalgae Cystoseira sp., Corallina sp., Halopteris sp. and Laurencia sp., 16 April 2007; dissected on eight slides (catalogue number: ZMADYU 2007/273). Paratype, ♂, 23 February 2008, dissected on seven slides (catalogue number: ZMADYU 2008/096).

Additional material examined. One ♀ (dissected on six slides) and one ♂ in alcohol, collected from the type locality on 16 April 2007. Three ♀♀, collected from the type locality on 23 February 2008. One ♀ and one ♂ preserved in alcohol; collected from interstitial habitat at Bademlibük beach, İzmir province, Turkey (38.6213333° N, 026.3577778° E), 24 May 2012.

All material collected by S. Sak, A. Alper and S. Sönmez.

Description of the female

Body (Fig. 5a, b) cylindrical, gradually tapering posteriorly; without clear distinction between prosome and urosome; first thoracic somite fused to cephalosome, forming a cephalothorax. Total body length 513 μm. Greatest width measured at posterior margin of cephalothorax: 102 μm. Surface ornamentation of somites as figured (Figs. 5a, b and 9a).

Fig. 5
figure 5

N. gebekumensis sp. nov., habitus. Female. a Dorsal; b Lateral. Male. c Dorsal

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Rostrum (Fig. 6a) bell shaped, defined at base; bears two sensilla.

Fig. 6
figure 6

N. gebekumensis sp. nov., female. a Rostrum, dorsal; b Antennule, dorsal; c Antenna; d Endopod of antenna

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Antennule (Fig. 6b) 7-segmented. Segment-1 ornamented with rows of spinules near posterior margin and a row of robust spinules at distal margin; with a seta at distal corner. Segment-2 with nine setae. Segment-3 rectangular, with six setae. Segment-4 bears one seta and an aesthetasc fused basally to a seta. Segments-5 and -6 are similar in length, with one and two setae respectively. Segment-7 bears five setae and with an apical acrothek consisting of an aesthetasc and two setae. Armature formula: 1[1]-2[9]-3[6]-4[1+(1+ae)]-5[1]-6[2]-7[5+acrothek].

Antenna (Fig. 6c, d). Allobasis with two abexopodal setae. Exopod 1-segmented, rectangular; armed with two apical setae. Endopod with two lateral robust pinnate spines; distal margin ornamented with spinules as figured, apical armature consists of two pinnate spines, two geniculate setae, and one pinnate spine fused basally to a seta.

Labrum (Fig. 7a) large. Anterior surface with long spinules subdistally, posterior surface with a row of small spinules subdistally and with large row of spinules bi-laterally.

Fig. 7
figure 7

N. gebekumensis sp. nov., female. a Labrum; b Mandible, anterior; c Mandible, posterior; d Maxilule; e Maxilla; f Maxilliped, anterior; g Maxilliped, posterior; h P6 and genital area

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Mandible (Fig. 7b, c) with well-developed gnathobase that bears a pinnate seta at dorsal corner; cutting edge with series of teeth. Palp 1-segmented, exopod and endopod incorporated into basis, armature consisting of three pinnate setae laterally and two elements (one pinnate spine and one seta) apically.

Maxillule (Fig. 7d). Praecoxa with spinules laterally. Praecoxal arthrite well-developed; with a row of small spinules on posterior surface, with one seta on anterior surface, with nine elements around distal margin. Coxa ornamented with spinular row as figured. Coxal endite bears one spine and one seta. Endopod and exopod incorporated into basis, armature consisting of four setae laterally and, one spine and three setae apically.

Maxilla (Fig. 7e). Syncoxa with two endites; each bears three spines apically, two of which with tubular extensions as figured. Allobasis forming spinous claw, slightly curved distally; accessory armature represented by two setae. Endopod reduced, represented by two setae.

Maxilliped (Fig. 7f, g) subchelate. Syncoxa and basis ornamented with spinular rows as figured. Endopod 1-segmented; armed with long claw, slightly curved apically and, with one small accessory seta.

P1–P4 (Fig. 8a, b, c, and d). Praecoxae well developed, ornamented with spinules along distal margin. Intercoxal sclerites rectangular (P1) or squarish (P2–P4). Coxae rectangular; ornamented with row of spinules as figured (P1, P2) or unornamented (P3, P4). Bases ornamented with large spinules along distal margin; with a tube-pore as figured; with one inner seta and one outer seta (P1) or with one outer seta (P2–P4). P1–P4 with 3-segmented exopods; outer margin of exopodal segments ornamented with strong spinules. Exp-1 and exp-2 naked (P1–P4). Exp-3 with two geniculate setae apically and two outer spines (P1) or with 2 apical elements (inner a minute seta, outer a pinnate spine) and 3 outer spines (P2) or with one inner seta serrated apically, two apical elements (inner a minute seta, outer a pinnate spine) and three outer spines (P3) or with one inner long seta serrated apically, two apical setae (inner one minute, outer one long) and three outer spines (P4). Endopod 3-segmented (P1) or 2-segmented (P2–P4); outer margin of endopodal segments ornamented with spinules. Enp-1 with one inner seta, serrated apically (P1–P4). Enp-2 without inner seta (P1) or with one inner setae serrated apically, two apical setae (inner one short, outer one long) and one outer pinnate spine (P2) or with two inner setae serrated apically (proximal one long, distal one short), two distal setae serrated apically (inner one minute; outer one long) and one outer pinnate spine (P3) or with one inner seta, serrated apically, two distal setae (inner one minute; outer one long and serrated apically) and one outer pinnate spine (P4). Enp-3 with one inner minute seta serrated apically and two apical, long, geniculate setae (P1).

Fig. 8
figure 8

N. gebekumensis sp. nov., female. Swimming legs. a P1; b P2; c P3; d P4

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Setal formula of swimming legs:

 

Exopod

Endopod

P1

0.0.022

1.0.120

P2

0.0.023

1.121

P3

0.0.123

1.221

P4

0.0.123

1.121

P5 (Fig. 9a) fused medially, forming a bilobate plate with medial incision, bearing a pore and a spinule row on anterior surface. Endopodal lobe not reaching distal margin of the exopod, armed with four pinnate setae. Exopods ovoid, armed with five setae (seta-III shortest, naked).

Fig. 9
figure 9

N. gebekumensis sp. nov., female. a Urosome and P5, ventral; b Left caudal ramus, dorsal; c Left caudal ramus, lateral

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P6 and genital field (Fig. 7h). P6 represented by a small plate armed with two setae. Copulatory pore located medially, flanked by two secretory tube-pores.

Caudal rami (Fig. 9a, b and c) slightly wider than long; with a tube-pore at outer distal corner dorsally; with seven setae. Seta I naked; seta II delicate, bifid. Seta III inserted at outer distal corner. Seta IV and V inserted terminally; with a fracture plane. Seta VI naked. Seta VII located dorsally, tri-articulated at base.

Description of the male

Body (Fig. 5c) smaller than female. Total body length: 436 μm. Greatest width measured at posterior margin of cephalothorax: 83 μm. Surface ornamentation of somites as figured (Figs. 5c and 10c).

Fig. 10
figure 10

N. gebekumensis sp. nov., male. a Antennule, ventral; b P3 endopod; c Urosome, P5 and P6, ventral

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Sexual dimorphism in body size, sensillar and spinular ornamentation of somites, antennule, Enp-P3, P5, P6.

Antennule (Fig. 10a) haplocer, 9-segmented. Segment-5 with an aesthetasc, fused basally to a seta. Segment-9 with an apical acrothek, consisting of an aesthetasc and two setae. Armature formula: 1[1]-2[9]-3[1]-4[2]-5[4+(1+ae)]-6[1]-7[0]-8[2]-9[4+acrothek].

P3 endopod (Fig. 10b); segment-1 rectangular, longer than female; ornamented with spinules along outer margin, with one inner seta which is shorter than the female. Segment-2 outer margin naked, with two setae apically and with one inner robust, modified spine as figured.

P5 (Fig. 10c) fused medially, forming a bilobate plate with deep medial notch. Endopodal lobe not reaching distal margin of the exopod, armed with two setae. Exopods ovoid. Right exopod with five setae; seta-IV shortest. Left exopod with six elements; the innermost is extra and modified as figured.

P6 (Fig. 10c) fused, forming a bilobate, single plate; armed with 1 pinnate seta.

Variation. In the other male paratype collected from the type locality, the modified innermost extra seta of exp-P5 was observed in the right leg instead of the left leg.

Etymology. The specific epithet “gebekumensis” refers to the type locality.

Remarks. The new species morphologically differs from other members of the genus by the combination of the following characters: i) female P5 exopod bears five setae; ii) baseoendopodal lobe of female P5 not reaching distal margin of exopod; iii) inner margin of P1 enp-2 is naked, which is unique in the genus; iv) female P2–P4 bears 4,5,4 and 5,6,6 setae on the distal segments of endo- and exopods respectively; v) male P3 enp-2, the tip of inner spine modified in form of toggle harpoon. Other minor differences compared to those of valid species are summarized in Table 3.

Nannomesochra giziri sp. nov.

https://zoobank.org/195A4F4F-DD9C-4B1C-AD0F-7516044F6D5A

Type locality. Turkey, Antalya province, from interstitial habitat at Phaselis Beach (36.5270667° N, 30.5514500° E).

Type material. Holotype, ♀, collected on 13 April 2007, dissected on four slides (catalogue number: ZMADYU 2007/274). Paratype, ♂, dissected on four slides (catalogue number: ZMADYU 2012/197); collected from interstitial habitat at Gündoğan Beach, Muğla province, Turkey (37.1306944° N, 27.3450278° E), 20 May 2012.

All material collected by S. Sak, A. Alper and S. Sönmez.

Description of the female

Body (Fig. 11a, b) cylindrical, gradually tapering posteriorly; without clear distinction between prosome and urosome; first thoracic somite fused to cephalosome, forming a cephalothorax. Total body length: 440 μm. Greatest width measured at posterior margin of cephalothorax: 124 μm. Surface ornamentation of somites as figured (Figs. 11a, b and 13c).

Fig. 11
figure 11

N. giziri sp. nov., female. Habitus. a Dorsal; b Lateral

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Rostrum (not illustrated) bell shaped, defined at base; bears two sensilla.

Antennule (Fig. 13a) 7-segmented. Segment-1 ornamented with rows of spinules near posterior margin and a row of robust spinules at distal margin; with a seta at distal corner. Segment-2 with eight setae. Segment-3 rectangular, with four setae. Segment-4 bears an aesthetasc fused basally to a seta. Segments -5 and -6 are similar in length, with one and two setae respectively. Segment-7 bears five setae and with an apical acrothek, consisting of an aesthetasc and two setae. Armature formula: 1[1]-2[8]-3[4]-4[(1+ae)]-5[1]-6[2]-7[5+acrothek].

Antenna, labrum, mandible, maxillule, maxilla and maxilliped (not illustrated) similar to that of N. parvula.

P1–P4 (Fig. 12a, b, c and d). Praecoxae well developed, ornamented with spinules along distal margin. Intercoxal sclerites wider than long. Coxae rectangular; ornamented with row of spinules as figured (P1, P2) or unornamented (P3, P4). Bases ornamented with large spinules along distal margin; with a tube-pore as figured; with one inner seta and one outer seta (P1) or with one outer seta (P2–P4). P1–P4 with 3-segmented exopods; outer margin of exopodal segments ornamented with strong spinules. Exp-1 with naked inner margin (P1–P4). Exp-2 without (P1) or with one inner seta (P2–P4). Exp-3 with two geniculate setae and two outer spines (P1) or with one inner seta, two long apical setae and three outer spines (P2) or with two inner setae, medial one long and plumose, the sub-distal one short and serrated apically; two apical long setae and three outer spines (P3–P4). Endopod 3-segmented (P1) or 2-segmented (P2–P4); outer margin of endopodal segments ornamented with spinules. Enp-1 with one inner seta, serrated apically (P1–P4). Enp-2 with one inner seta (P1) or with two inner setae serrated apically, two apical setae (inner one minute, outer one long and plumose) and one outer pinnate spine (P2) or with two inner setae (medial one short and serrated apically, sub-distal one long and plumose), two apical setae (inner one short, outer one long and plumose) and one outer pinnate spine (P3–P4). Enp-3 with one inner naked seta and two apical long, pinnate setae (P1).

Fig. 12
figure 12

N. giziri sp. nov., female. Swimming legs. a P1; b P2; c P3; d P4

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Setal formula of swimming legs:

 

Exopod

Endopod

P1

0.0.022

1.1.120

P2

0.1.123

1.221

P3

0.1.223

1.221

P4

0.1.223

1.221

P5 (Fig. 13b) fused medially, forming a bilobate plate with medial incision; bearing a pore and a spinule row on anterior surface. Endopodal lobes extends beyond distal margin of the exopod; armed with four pinnate setae. Exopods squarish, with notch between seta I and II; armed with five setae (seta-III shortest, naked).

Fig. 13
figure 13

N. giziri sp. nov., female. a Antennule, dorsal; b P5; c Urosome and P6, ventral

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P6 (Fig. 13c) represented by a small plate, armed with two setae.

Caudal rami (Figs. 11a,b, 13c) slightly wider than long; with a tube-pore at outer distal corner dorsally; with seven setae. Seta I naked; seta II delicate, bifid. Seta III inserted at outer distal corner. Seta IV and V inserted terminally; with a fracture plane. Seta VI naked. Seta VII located dorsally, tri-articulated at base.

Description of the male

Body (Fig. 14a, b) smaller than female. Total body length: 418 μm. Greatest width measured at posterior margin of cephalothorax: 106 μm. Surface ornamentation of somites as figured (Figs. 14a, b and 16a, c and d). Sexual dimorphism in body size, sensillar and spinular ornamentation of somites, antennule, P3, P5 and P6.

Fig. 14
figure 14

N. giziri sp. nov., male. Habitus. a Dorsal; b Lateral

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Antennule (Fig. 15a, b and c) haplocer, 9-segmented. Segment-1 ornamented with spinules as figured. Segment-5 with an aesthetasc fused basally to a seta. Segment-9 with an apical acrothek, consisting of an aesthetasc and two setae. Armature formula: 1[1]-2[9]-3[1]-4[2]-5[4+(1+ae)]-6[1]-7[0]-8[2]-9[4+acrothek].

Fig. 15
figure 15

N. giziri sp. nov., male. Antennule. a Dorsal; b Ventral; c Ventro-lateral. d P3

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P3 (Fig. 15d) endopod 2-segmented; enp-1 rectangular, longer than in female; ornamented with spinules along outer margin, with one inner seta. Enp-2 without spinular ornamentation along outer margin; armed with one inner spine, tip in form of crochet-hook, and with two setae apically (inner one short, naked; outer one long and plumose, fused basally to segment). Inner sub-distal seta of exp-3 naked.

P5 (Fig. 16a, b) fused medially, forming a bilobate plate, bearing two pores and a spinule row on anterior surface; lobes are not as prominent as in N. gebekumensis sp. nov. Endopodal lobe not extending beyond distal margin of the exopod, armed with two pinnate setae. Exopods squarish, with six setae (seta V shortest).

Fig. 16
figure 16

N. giziri sp. nov., male. a Urosome, P5 and P6, ventral; b P5. Anal somite. c Dorsal; d Lateral

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P6 (Fig. 16a) fused with somite, armed with 1 naked seta.

Etymology. The new species is named in honour of Prof. Dr. Murat Gizir (Mersin University).

Remarks. The new species can be distinguished from the other species of the genus except N. parvula by the combination of the following characters: i) female P5 exopod bears five setae; ii) female P2–P4 bears 5,5,5 and 6,7,7 setae on the distal segments of endo- and exopods respectively; iii) male P3 enp-2, the tip of inner spine modified in form of crochet-hook. N. giziri sp. nov. morphologically differs from N. parvula by the combination of the following characters: i) female A1, segment -2 and -3 with eight and four setae respectively; ii) the inner seta of P1 enp-1 extends well beyond end of the endopod; iii) P1 enp-1 extends to approximately end of the exp-2; iv) female P5 exopod with a notch between seta I and II; v) caudal rami without a spinular row near base of the seta VII. Other minor differences compared to those of valid species are summarized in Table 3.

Nannomesochra erythraiensis sp. nov.

https://zoobank.org/3C3CACEC-0CEC-4C12-8E62-2C53FCC90858

Type locality. Turkey, İzmir province, from interstitial habitat at Ildır village/Çeşme (38.3472222° N, 26.4505000° E).

Type material. Holotype, ♀, collected on 24 May 2012, dissected on seven slides (catalogue number: ZMADYU 2012/198). Paratype, ♂, collected on 24 May 2012, dissected on five slides (catalogue number: ZMADYU 2012/199).

Additional material examined. Three ♀♀ and one ♂, preserved in alcohol, collected from type locality, 24 May 2012. One ♀, preserved in alcohol; collected from Aydın province, Turkey; collected from washings of macroalgae from Pygela Beach (37.9012222° N, 27.2725556° E), 23 May 2012. Two ♀♀, preserved in alcohol; collected from İzmir province, Turkey; collected from washings of macroalgae from Pırlanta Beach (38.2851389° N, 26.2514722° E), 24 May 2012. One ♂, preserved in alcohol; collected from Mersin province, Turkey; from interstitial habitat in front of Eskur-2 Estates (36.1552500° N, 33.4424667° E), 28 August 2007. One ♂, preserved in alcohol; collected from Adana province, Turkey; from interstitial habitat in front of Yonca Estates (36.5825278° N, 35.4061667° E), 09 July 2006.

All material collected by S. Karaytuğ, S. Sak, A. Alper and S. Sönmez.

Description of the female

Body (Figs. 17a, b and 18a, b) cylindrical, gradually tapering posteriorly; without clear distinction between prosome and urosome; first thoracic somite fused to cephalosome, forming a cephalothorax. Total body length: 668 μm. Greatest width measured at posterior margin of cephalothorax: 172 μm. Surface ornamentation of somites as figured (Figs. 17a, b and 19a, b).

Fig. 17
figure 17

N. erythraiensis sp. nov., female. a Habitus, dorsal; b Habitus, lateral; c Rostrum and antennule, dorsal; d Antenna; e Maxilliped

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Fig. 18
figure 18

N. erythraiensis sp. nov., female. a Habitus, dorsal; b Habitus, ventral; c Antennule, ventral. d Antennules and rostrum, dorsal; e Antennae and oral region, ventral; e P5 and egg sac, ventral; g Anal operculum and caudal rami, dorsal

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Fig. 19
figure 19

N. erythraiensis sp. nov. Female. a Abdomen and P6, ventral; b Abdomen and P6, lateral; c P5. Male. d P3; e Urosome, P5 and P6, ventral

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Rostrum (Figs. 17c and 18d) bell shaped, defined at base; bears two sensilla.

Antennule (Figs. 17c and 18c, d) 7-segmented. Segment-1 ornamented with rows of spinules near posterior margin and a row of robust spinules at distal margin; with a seta at distal corner. Segment-2 with eight setae. Segment-3 rectangular, with four setae. Segment-4 bears one seta and an aesthetasc fused basally to a seta. Segments-5 and -6 are similar in length, with one and two setae respectively. Segment-7 bears five setae and an apical acrothek consisting of an aesthetasc and two setae. Armature formula: 1[1]-2[8]-3[4]-4[1+(1+ae)]-5[1]-6[2]-7[5+acrothek].

Antenna (Figs. 17d and 18e), labrum, mandible, maxillule, maxilla (not illustrated) and maxilliped (Figs. 17e and 18e), similar to that of N. parvula.

P1–P4 (Fig. 20a, b, c and d). Praecoxae well developed, ornamented with spinules along distal margin. Intercoxal sclerites wider than long. Coxae rectangular; ornamented with row of spinules as figured (P1, P2) or unornamented (P3, P4). Bases ornamented with large spinules along distal margin; with a tube-pore as figured; with one inner seta and one outer seta (P1) or with one outer seta (P2–P4). P1–P4 with 3-segmented exopods; outer margin of exopodal segments ornamented with strong spinules. Exp-1 and exp-2 without inner seta (P1-P4). Exp-3 with two setae apically and two outer spines (P1) or two apical setae (inner one naked, outer one spinulose) and 3 outer spines (P2) or with one inner seta serrated apically, two apical setae (inner one long, outer one spinulose) and three outer spines (P3, P4). Endopod 3-segmented (P1) or 2-segmented (P2–P4); outer distal margin of first endopodal segments ornamented two with spinules except for P4. Enp-1 with one inner seta, serrated apically (P1–P4). Enp-2 with one inner seta (P1) or with two inner setae serrated apically, two apical setae (inner one short, outer one long) and one outer pinnate spine (P2) or with one inner seta serrated apically, two distal setae (inner one short, outer one long) and one outer pinnate spine (P3, P4). Enp-3 with one inner short seta serrated apically, and two apical long setae (P1).

Fig. 20
figure 20

N. erythraiensis sp. nov., female. Swimming legs. a P1; b P2; c P3; d P4. Male. e P2 endopod, tip of distal segment

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Setal formula of swimming legs:

 

Exopod

Endopod

P1

0.0.022

1.1.120

P2

0.0.023

1.221

P3

0.0.123

1.121

P4

0.0.123

1.121

P5 (18f and Figs. 19c) fused medially, forming a bilobate plate with pronounced medial incision than in N. parvula, N. gebekumensis sp. nov. and N. giziri sp. nov. Endopodal lobes not reaching distal margin of the exopod, armed with four pinnate setae. Exopods squarish, armed with six setae (seta-IV shortest, naked).

P6 (Fig. 19a, b) represented by small plate fused to genital segment, armed with two setae.

Caudal rami (Figs. 17a, b, 18g and 19a, b) slightly wider than long; with a tube-pore at outer distal corner dorsally; with seven setae. Seta I naked, seta II delicate bifid at tip, seta III naked, inserted at outer distal corner. Seta IV and V inserted terminally; with a fracture plane. Seta VI naked. Seta VII located dorsally, tri-articulated at base. A spinular row is present near base of seta VII.

Description of the male

Body (Figs. 21a, b and 22a) smaller than female. Total body length: 524 μm. Greatest width measured at posterior margin of cephalothorax: 109 μm. Surface ornamentation of somites as figured (Figs. 19e, 21a, b, 22c, d). Sexual dimorphism in body size, sensillar and spinular ornamentation of somites, antennule, P2, P3, P5 and P6.

Fig. 21
figure 21

N. erythraiensis sp. nov., male. a Habitus, dorsal; b Habitus, lateral; c Antennule

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Fig. 22
figure 22

N. erythraiensis sp. nov., male. a Habitus, ventrolateral; b Antennule, ventral; c P5, ventrolateral; d caudal rami, ventrolateral

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Antennule (Figs. 21c and 22b) haplocer, 9-segmented. Segment-1 ornamented with spinules as figured. Segment-5 with an aesthetasc fused basally to a seta. Segment-9 with an apical acrothek, consisting of an aesthetasc and two setae. Armature formula: 1[1]-2[9]-3[1]-4[2]-5[4+(1+ae)]-6[1]-7[0]-8[2]-9[5+acrothek].

P2 enp-2 distal margin as figured (Fig. 20e). Inner seta longer than in female.

P3 (Fig. 19d) endopod 2-segmented; enp-1 rectangular, longer than female; ornamented with spinules along outer margin, with one inner seta. Enp-2 without spinular ornamentation along outer margin, with one inner, robust spine as figured and with two setae apically (inner one short, naked; outer one long, fused basally to segment). Exopod-3 inner seta shorter than in female.

P5 (Figs. 19e and 22c) fused medially, forming a bilobate plate; medial notch more pronounced than in N. giziri sp. nov. Endopodal lobe not reaching distal margin of the exopod, armed with two pinnate setae. Exopods squarish; with asymmetrical armature, similar to that of N. gebekumensis sp. nov.: Right exopod with five setae; seta-IV shortest. Left exopod with six elements; the innermost is extra and modified as figured.

P6 (Fig. 19e) fused with somite, forming a bilobate single plate; armed with 1 naked seta.

Etymology. The specific name refers to “erythrai” which is the historical name of Ildır village (İzmir, Turkey).

Remarks. The new species can be distinguished from the other species of the genus except N. zavodniki by the combination of the following characters: i) the presence of six setae on the female P5 exopod; ii) P2–P4 bears 5,4,4 and 5,6,6 setae on distal segments of endo- and exopods respectively; iii) male P3 enp-2, the tip of inner spine is blunt. N. erythraiensis sp. nov. morphologically differs from N. zavodniki by the combination of the following characters: i) the inner seta of P1 enp-1 extends to approximately end of the endopod ii) P1 enp-1 extends to approximately end of the exp-2; iii) P2 endopod extends to approximately end of the exp-2; iv) P4 endopod extends to approximately end of the exp-1; v) female P5 exopod without a protuberance between seta I and II; vi) the caudal rami with a spinular row near base of the seta VII on. Other minor differences compared to those of valid species are summarized in Table 3.

A cladistic analysis was performed on Nannomesochra species. The resulted cladogram is shown in Fig. 23. The length of the tree is 23, and the consistency index (CI) and retention index (RI) are 0.7391 and 0.6842, respectively. As a result of the analysis, the genus is divided into two groups. N. parvula and N. giziri sp. nov. are grouped together and formed one of the main groups. The other main group consists of the remaining 5 species and is divided into two subgroups. N. gebekumensis sp. nov., N. erythraiensis sp. nov. and N. zavodniki are clustered in one of the subgroups, while N. arupinensis and N. shermani comb. nov. are clustered in the other sub-group.

Fig. 23
figure 23

Cladogram generated by the PAUP analysis of the character matrix presented in Table 2

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Discussion

A detailed examination and comparison of the material used in this study as well as the examination of Nannomesochra literature showed that the large variation previously attributed generally to N. arupinensis sensu lato in fact indicates a complex of closely related morphospecies. As a result, seven different morphologically closely related species, three of which being new to science, were recognized and considered valid: N. arupinensis; N. parvula; N. zavodniki; N. shermani comb. nov.; N. gebekumensis sp. nov.; N. giziri sp. nov. and N. erythraiensis sp. nov. The differences between Nannomesochra species are summarized in Table 3. In addition, each species considered valid as well as their synonyms and doubtful records/descriptions are discussed in the respective remarks section in detail above. All other records assigned to N. arupinensis sensu lato are reviewed below.

Brian (1928a) reported Mesochra arupinensis from the islands of Rhodes, Stampalia, Gyali, and Symi in the Aegean Sea but did not specify the exact locality of the material on which the description (Brian 1928a: p.22, figs. 96–99) was made. Brian (1928a) examined female and male specimens but provided only the illustrations of the male P2, P3-enp, P5 and the ventral view of the urosome which may belong to a different species in terms of the structures of P5 and P3-enp in the male.

Willey (1930) reported Pseudomesochra parvula from the brackish Mangrove Lake (Bermuda). The material was collected (June 21, 1928) among intertidal algae attached to roots of mangrove trees in the southern arm of Fairyland Creek, near Agar’s Island. Unfortunately, the description and the illustrations provided by Willey (1930) are incomplete, only the figures of antennule, P2, P3-enp of the female and the antennule, P3-enp and P5 of the male were provided. The female characteristics of the Bermuda population generally matches with N. parvula, unfortunately the male of N. parvula sensu Gurney (1927) is not known in order to make a final decision. This Bermuda population also may represent another distinct species considering the isolated position of Mangrove Lake in the North Atlantic Ocean.

Monard (1935b) reported Mesochra arupinensis in the study of the marine harpacticoid fauna of Roscoff (France), this species being morphologically closely related to N. parvula and N. giziri sp. nov. Monard (1935b) figured only the P5 of the female which strongly resembles the P5 of N. giziri sp. nov. on the basis of the inner lobe of baseoendopod not exceeding the exopod (in N. parvula, this lobe exceeds the exopod) but no further comparisons can be made since the figure lack other minor details such as setal ornamentations. On the other hand, in the descriptive part of the paper Monard (1935b) wrote that the total number of setae/spines on the terminal exopodal segments of the P2–P4 is 6,7,6 but 6,7,7 in N. parvula and N. giziri sp. nov., and the total number of setae/spines on the terminal endopodal segments of the P2–P4 is 6,5,4 but 5,5,5 in N. parvula and N. giziri sp. nov. Monard’s (1935b) material can certainly be assigned to the genus Nannomesochra on the basis of the fused baseoendopod in the midline in the female and a 1-segmented antennary exopod with two setae (Monard 1935b, p. 60), but it cannot be verified at species level. Therefore, it is considered as species inquirenda. In the same paper, Monard (1935b) also described Mesochra armoricana as new to science but later it was accepted as a synonym of N. arupinensis by Lang (1948) who did not provide a clear justification about the synonymy. Lang’s (1948) action was also simply followed by other authors (Marcus and Por 1961; Vervoort 1964; Apostolov and Marinov 1988). The male of this species was partially described by Marcus and Por (1961). But, Wells (2007) rightly removed the species from the synonymy and placed it again in the genus Mesochra.

In the study of the Romanian Black Sea harpacticoids, Jakubisiak (1938) determined Nannomesochra arupinensis and provided only the illustration of the male P3-enp which is insufficient to confirm the specific identity of this Black Sea population.

Noodt (1953) collected six females and three males from the Fastensee (Lake Fasten), a brackish Lake on the northwest side of Fehmarn, Kiel Firth, Germany. This species morphologically mostly resembles N. parvula and N. giziri sp. nov on the basis of setation of the female P2 and P5. They all have an inner seta on the P2 enp-2 and have 6 setae on the terminal exopod segment of P2. The other characteristics of the German material generally matches well N. parvula and N. giziri sp. nov but descriptions of Noodt (1953) are devoid of minor details such as the ventral spinular pattern on the urosome and dorsal spinules on the caudal rami which are important to separate N. parvula from N. giziri sp. nov.

Vervoort (1964) reported one female specimen of Nannomesochra arupinensis on the basis of the material originated from the alga Microdictyon collected at 35–40 ft. depth in the lagoon of Paugob Canoe House at Falarik Islet in the Ifaluk Atoll in the Pacific Ocean. Ifaluk specimens morphologically mostly resembles N. parvula and N. giziri sp. nov on the basis of setation of the female P2 and P5 (a fine distal seta on the terminal endopod segment of P3 and P4 possibly overlooked by Vervoort (1964)). They all have an inner seta on the P2 enp-2 and have 6 setae on the terminal exopod segment of P2. The first segment of the antennule is not a real segment but the base of the antennule, it is highly possible that the second segment drawn by Vervoort (1964) represent the first and second segment. It is possible that Vervoort (1964) overlooked the separation line of these two segments, because of imaging quality of the microscope at that time. Considering the male has not been described and the isolated position of the Ifaluk Atoll in Pacific Ocean, it would not be surprising if this Ifaluk population also represented another distinct species.

Apostolov and Marinov (1988) provided the illustration of Nannomesochra arupinensis from the Bulgarian coast. The setal formula of the swimming legs given by Apostolov and Marinov (1988) indicates that Bulgarian material resembles N. parvula. Yet, the descriptions are devoid of minor details such as the ventral spinular pattern on the urosome and dorsal spinules on the caudal rami.

Alper et al. (2010) reported N. arupinensis from the Turkish coast. This material was reexamined and now verified as N. parvula.

Other reports of N. arupinensis from Salambo, Tunisia (Monard 1935a); Castiglione, Italy (Monard 1937); Tenerife in the Canary Islands, Spain (Noodt 1955a); Sea of Marmara, Turkey (Noodt 1955b); Lough Ine of County Cork, Ireland (Roe 1960); Aldabra, Indian Ocean, Seychelles (Wells and McKenzie 1973); Gulf of Bourgas, Bulgaria (Apostolov 1977); San Diego, USA (Thistle 1982); Valleys of Comacchio and Lesina lagoon, Italy (Ceccherelli and Mistri 1990); Lake McLeod (Blue Holes), western Australia (Halse et al. 2000); East Sussex, United Kingdom (Ventham 2011); Porto de Galinhas coral reefs, northeastern Brazil (Sarmento and Santos 2012) and Nannomesochra sp. from Zanzibar, Tanzania (Callens et al. 2012) do not contain description or sufficient information, therefore these reports cannot be verified at species level and are considered as unverified records.

The characters used in the cladistic analysis of Nannomesochra species in this study were selected by considering the data available in the original descriptions of the previously published species. Although microcharacters such as sensillar and microspinular ornamentations on the body somites and appendages are considered important in the current harpacticoid phylogeny (Galassi et al. 2011; Karanovic et al. 2018), unfortunately, they could not be included in the character set (Tables 1 and 2) since they cannot be discerned from the illustrations or descriptions. Therefore, basic characters such as the armature of swimming legs were mostly used in the analysis. The other characters used in the analysis were related to A1 and furcal rami, as well as the shape and armature of the female P5 (Table 1).

As a result of the cladistic analysis, the genus was divided into two major groups (Fig. 23). N. parvula and N. giziri sp. nov. were grouped together and took place in the first group. One of the significant characters connecting the two species and separating them from the other species in the genus is the length of the female P5 baseoendopodal lobe. A baseoendopodal lobe extending beyond the distal margin of the exopod (character 14 in Tables 1 and 2) is considered a synapomorphy for N. parvula and N. giziri sp. nov. In contrast, the presence of only one seta, i.e. the reduction of one seta on the inner margin of the P4 endopod (character 9 in Tables 1and 2) is considered here as a synapomorphy for all remaining Nannomesochra species, whilst N. parvula and N. giziri sp. nov. retain the plesiomorphic state (the presence of two setae). The presence of a notch between seta I and II on the female P5 (character 12 in Tables 1 and 2) is an autoapomorphy for N. giziri sp. nov.

The second major group was divided into two sub-groups. The first sub-group consisted of N. gebekumensis sp. nov., N. erythraiensis sp. nov. and N. zavodniki. The bare inner margin of P2–P4 (characters 6, 8 and 10 in Tables 1 and 2) is defined as synapomorphies for this sub-group. The presence of a protuberance between seta I and II on female P5 (character 13) is an autoapomorphy for N. zavodniki. The P1 enp-2 with bare inner edge and the P2 enp-2 with one inner seta (characters 4 and 5 in Tables 1 and 2) are autoapomorphies for N. gebekumensis sp. nov. The presence of a spinular row near the base of the seta VII on the caudal rami (character 15 in Tables 1 and 2) is considered as an autoapomorphy for N. erythraiensis sp. nov.

The other sub-group includes N. arupinensis and N. shermani comb. nov. which are characterized by longer P1 endopods (character 3 in Tables 1 and 2) than in other species of the genus. A basoendopodal lobe reaching the distal edge of the exopod (character 14 in Tables 1 and 2) is considered as an autopomorphy for N. arupinensis.

Phylogenetic position of Nannomesochra within Hemimesochrinae

Gurney (1927) put some reservations about the monophyletic status of the genus by stating that none of the differences may have had a generic value for Pseudomesochra (= Nannomesochra). On the other hand, Gurney (1927) assumed that the justification for treating Pseudomesochra as sufficiently distinct genus within the family Canthocamptidae may be justified by the peculiar/characteristic structure of the female P5. Since Gurney (1927), several new genera have been added to the family Canthocamptidae and the family was divided into two subfamilies Canthocamptinae Brady, 1880 and Hemimesochrinae Por, 1986 (Wells 2007). The genus Nannomesochra belongs to the Hemimesochrinae and seems to be phylogenetically closely related to Bathycamptus Huys & Thistle, 1989, Pusillargillus Huys & Thistle, 1989 and Heteropsyllus T. Scott, 1894. However, Nannomesochra can easily be distinguished from Bathycamptus by its fifth pair of legs with medially fused baseoendopods in the female and a 2-segmented P3 endopod with three elements (two elements apically and a modified inner seta) on the distal segment in the male (3-segmented with an apophysis on the middle segment in Bathycamptus). Within the subfamily, the 2-segmented P3 endopod is only found in the males of Nannomesochra, Pusillargillus and Heteropsyllus and can be considered as a synapomorphy of the three genera. Pusillargillus can easily be differentiated from Nannomesochra in having a 5-segmented antennule and a 2-segmented P1-enp in the female, and Pusillargillus bears an apophysis on the outer distal corner and three setae (two setae apically and an unmodified inner seta) on the second segment of the male P3 endopod. Heteropsyllus differs from Nannomesochra by having an antennary allobasis with a l-segmented trisetose exopod and a 5-segmented antennule in the female and Heteropsyllus bears an apophysis on anterior side and four setae (two setae apically and two unmodified inner seta) on the second segment of the male P3 endopod.

A key to subfamily Hemimesochrinae

  • 1. Antennary exopod with 1 seta ……………………………..…………………..……………………..……….....….Dahlakia

  • Antennary exopod with 2 setae …………………………………............…………....……………..……….……………….2

  • Antennary exopod with 3 setae ……………………………….………………..…………………..................................……7

  • 2. P1-enp 1-segmented. P2–P4 endopod absent …………..…………….........…….......…….......…….......……….Isthmiocaris

  • P1-enp 2-segmented ………………………..………………….…………….………….......…….......……..…...…….…….3

  • P1-enp 3-segmented ………………………..………………………………………….......…….......……...…...……..…….4

  • 3. Baseoendopod and exopod of P5 not fused in female; exopod with 5 setae………….......……..........…...…….Pusillargillus

  • Baseoendopod and exopod of P5 fused in female; exopod with 4 setae…………….........................……...……Boreolimella

  • 4. P2 and P3 endopod 3-segmented ……………………………………….......…….......…….......…….......…….......……..…Poria

  • P2 and P3 endopod 2-segmented ………………...……….......……...........................................................…………………..5

  • 5. Male P3 endopod 2-segmented …………………...……….......…….......…….......…….......…….......…….Nannomesochra

  • Male P3 endopod 3-segmented ………….…………………….......…….......…….......…….......….…………….………….6

  • 6. Antennule 6-segmented; sexual dimorphism in Pl–P2. ……….......…….......…….......….…….…...………..Psammocamptus

  • Antennule 7-segmented; no sexual dimorphism in Pl–P2 …….......…….......……........…………………....….Bathycamptus

  • 7. P4 endopod absent ……………………………...…………….......…….......…….......…….......…….......…..…Perucamptus

  • P4 endopod 2-segmented …………………………………….......……........…….......……………….……………..……….8

  • 8. Antennule 6-segmented ……………………………..…..……….......…….......…….......…….......……..........…Mesopsyllus

  • Antennule 5-segmented ………………………………………….......……..................……………….………..…..………..9

  • 9. P1 endopod 3-segmented ………………………………………….......…….............................................……..Heteropsyllus

  • P1 endopod 2-segmented ……………………………...….………………………….......…….......…….........Hemimesochra

A key to the species of the genus Nannomesochra

  • 1. P1 enp-2 with 1 inner seta, P2 enp-2 with 1 inner setae……………....…………………..……….N. gebekumensis sp. nov.

  • P1 enp-2 with 1 inner seta, P2 enp-2 with 2 inner setae…………….…….….…………………..............………..………….2

  • 2. Female, P5 exp with 6 setae …………………………………….……………………………………………………………3

  • Female, P5 exp with 5 setae ...……………………………………...……………..……………….……….…….……..……4

  • 3. Female, caudal ramus without a spinular row near base of seta VII. P5 exp roundish, with protuberance between seta I and II. A2 exp with two setae unequal in length………..……..….......….………………………………………………..N. zavodniki

  • Female, caudal ramus with a spinular row near base of seta VII. P5 exp squarish, without protuberance between seta I and II. A2 exp with two setae equal in length………………...….…………………………………............N. erythraiensis sp. nov.

  • 4. Female, P3–P4 enp-2 with 4 setae ……….……………………………………………………………………………..…….5

  • Female, P3–P4 enp-2 with 5 setae ……………………………………….……………………………………………..…….6

  • 5. Female, P5 baseoendopodal lobe triangular, reaching to distal margin of the exopod ...........………………....N. arupinensis

  • Female, P5 baseoendopodal lobe not triangular, not reaching distal margin of the exopod …………N. shermani comb. nov.

  • 6. Female, caudal ramus with a spinular row near base of seta VII. The length of distal seta on the inner margin of P4 exp-3 equal/shorter than the segment. P5-exp without a notch between seta I and II; seta III spiniform. ………............…..…..N. parvula

  • Female, caudal ramus without a spinular row near base of seta VII. The length of distal seta on the inner margin of P4 exp-3 longer than the segment. P5-exp with a notch between seta I and II; seta III slender. ………………………N. giziri sp. nov.