Introduction

Research on parasites associated with vertebrate hosts on islands and archipelagos is of particular interest, as it plays a crucial role in understanding parasitic behavior and ecosystem development in relatively isolated conditions.Among the specialised parasites associated with birds, the quill mites of the family Syringophilidae (Acariformes: Prostigmata: Cheyletoidea) are distinguished by their high morphological specialisation. These mites inhabit exclusively the internal cavities of feather quills, carrying out their entire lifecycle within this unique microhabitat, including feeding and reproduction. The family Syringophilidae represents the most taxonomically diverse group among quill-inhabiting mites, occupying a wide range of habitats in the plumage of their hosts (Kethley, 1970; Skoracki, 2011). Despite their diversity, the taxonomic system of syringophilid mites remains unsatisfactorily developed. Currently, the family comprises approximately 400 described species, and its representatives have been recorded from hosts representing 27 bird orders (Zmudzinski et al., 2023).

The Faroe Islands, an archipelago in the North Atlantic Ocean, consist of 18 volcanic islands. Their unique geological features and geographical location make them a significant habitat for a wide array of seabirds and waders, which either breed on or regularly visit the islands. A comprehensive survey has documented a total of 355 bird species on the Faroe Islands, including subspecies and introduced species (Olofson & Sørensen, 2022). Of these, approximately 150 species are aquatic birds belonging to the orders Anseriformes, Charadriiformes, Gruiformes, Procellariiformes, and Suliformes (Jensen & Sørensen, 2015). Notably, Syringophilidae mites have never been studied in this region before, marking this investigation as particularly pioneering. Consequently, this paper introduces the initial study on syringophilid mites of birds from the Faroe Islands, with a special focus on aquatic birds. The syringophilid mites parasitising this host group comprise approximately 30 species grouped in 16 genera of the subfamily Syringophilinae and three species in two genera of the subfamily Picobiinae (Kethley, 1970; Skoracki, 2011; Glowska & Skoracki, 2011; Glowska, 2015; Skoracki & Zawierucha, 2016; Skoracki et al., 2006, 2016, 2017, 2022; Zmudzinski & Skoracki, 2017; Zmudzinski et al., 2016, 2018). These mite genera have been recorded on birds representing seven orders: Anseriformes, Charadriiformes, Gruiformes, Phoenicopteriformes, Procellariiformes, Suliformes, and Pelecaniformes.

In this paper, we present results of our study of syringophilid mites, based on 75 specimens of 31 species of aquatic birds from the Faroe Islands. We establish a new genus, Sulisyringophilus n. g., based on a newly described species, Sulisyringophilus jenskjeldi n. sp., from the northern gannet, Morus bassanus (Linnaeus) (Suliformes: Sulidae). Furthermore, we describe a new speciesCharadriiphilus lymnocryptes n. sp., from the jack snipe, Lymnocryptes minimus (Brünnich) (Charadriiformes: Scolopacidae). In this study, we also added the new host records for two previously described quill mite species from charadriiform hosts: the semipalmated sandpiper Calidris pusilla (Linnaeus) (Scolopacidae) for Niglarobia ereuneti Kethley, 1970 and the black-legged kittiwake Rissa tridactyla (Linnaeus) (Laridae) for Creagonycha lara Kethley, 1970 (Figs. 1, 2).

Fig. 1
figure 1

Host species infested by quill mites: A, Morus bassanus; B, Lymnocryptes minimus; C, Calidris pusilla; D, Rissa tridactyla. Photos by Jens-Kjeld Jensen (A, C, D), and Ingvar A. Sigurðsson (B).

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Fig. 2
figure 2

Examples of infested feather quills of Lymnocryptes minimus (left), Morus bassanus (right). Photo by Simon Haarder.

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Materials and methods

The birds were collected by Jens-Kjeld Jensen (Nólsoy, Faroe Islands, Denmark) over the period from 1996 to 2024 and were preserved in his private freezer until examination. Their causes of death varied, including natural causes, traffic accidents, predation by feral cats, or hunting. For each bird studied, the majority of the flight, tail, and covert feathers were meticulously removed and examined for the presence of quill mites. Additionally, 10–20 contour feathers from the chest and ventral areas were carefully extracted and analysed. An overview of examined bird species is presented in Table 1.

Table 1 Examined bird species from the Faroe Islands and their quill mites
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Mites found in infested feathers were meticulously removed using fine-pointed tweezers. These specimens underwent a clearing and softening process by being immersed in Nesbitt’s solution at ambient temperature for 24 to 36 hours (Skoracki, 2011). Subsequently, mites were transferred to 70% ethanol for a brief period of approximately 10 minutes and then mounted on microscopic slides using Hoyer’s medium, following the established protocol by Krantz and Walter (2009). The mite specimens were examined using a ZEISS Axioscope light microscope equipped with differential interference contrast (DIC) optics. Illustrations were made using a camera lucida attachment. All measurements are given in micrometres, with the dimension ranges of paratypes presented in parentheses, following the measurements of the holotype. The idiosomal setation nomenclature aligns with Grandjean’s (1939) system as modified for Prostigmata by Kethley (1990), and the leg chaetotaxy follows Grandjean’s (1944) classification. All other morphological terminology follows Kethley (1970) and Skoracki (2011).

Specimen depositories are cited using the following abbreviations: AMU, A. Mickiewicz University, Department of Animal Morphology, Poznan, Poland; NHMD, Natural History Museum of Denmark, Copenhagen, Denmark.


Family Syringophilidae Lavoipierre, 1953

Subfamily Syringophilinae Lavoipierre, 1953


Sulisyringophilus n. g.


Diagnosis


Female. Large-sized syringophilids (total body length 960–1090). Gnathosoma. Lateral hypostomal teeth present. Peritremes M-shaped with clearly visible chambers. Movable cheliceral digit edentate. Stylophore constricted posteriorly, ended by projection. Idiosoma. Six pairs of discernible ornamented propodonotal setae arranged 3–1–2. Propodonotal shield entire, without pocket-like structures, bearing bases of setae vi, ve, si, c1 and se. Hysteronotal shield absent. Hysteronotal setae d1, d2 and e2 long. Setae d1 closer to d2 than to e2. Pygidial shield present. Terminal setae f2 and h2 long, f1 and h1 short. Pseudanal setal series with 2 pairs of setae (ps1–2). Genital setal series represented by 1 pair of setae (g2 absent). Aggenital series with 3 pairs of setae (ag1–3). Legs. Legs I thicker than II–IV. Antaxial and paraxial members of claw pair subequal in size and shape. Coxal apodemes I slightly divergent, not fused to apodemes II. Legs with full complement of setae.

Male. Characteristics as in female except: total body length 660; lateral hypostomal teeth absent; posterior margin of stylophore without projection; all setae on propodonotum smooth; setal pattern of propodonotal region arranged 3–2–1; propodonotal shield bearing bases of setae vi, ve, si and c1; hysteronotal shield fused to pygidial shied; hysteronotal setae short; setae f2 short, h2 long; genital setal series represented by 2 pairs of setae; legs I–IV equal in thickness; coxal apodemes I strongly divergent.

Type-species: Sulisyringophilus jenskjeldi n. sp.

ZooBank registration: The Life Science Identifier (LSID) for Sulisyringophilus n. g. is urn:lsid:zoobank.org:act:E1D3498F-0E1A-4D97-9347-8635FB3524A9

Etymology: The name refers to the order name of the host - Suliformes, and Syringophilus - type genus of the family Syringophilidae.

Remarks

This new genus is morphologically close to the monotypic genus Procellariisyringophilus Schmidt and Skoracki, 2007. In females of both genera, the movable chericeral digits are edentate; the peritremes are M-shaped; the stylophore is constricted posteriorly; idiosomal setae are stout and strongly ornamented; the hysteronotal shield is absent; the pygidial shield is present; the genital setal series is represented by 1 pair of setae; the pseudanal setal series with 2 pairs of setae, and the coxal apodemes I are weakly divergent. Sulisyringophilus differs from Procellariisyringophilus in the following features: in females of Sulisyringophilus, the lateral hypostomal teeth and leg setae vsII are present. In females of Procellariisyringophilus, the lateral hypostomal teeth and leg setae vsII are absent. Furthermore, the new genus can be easily distinguished from Stibarokris Kethley, 1970, which females also possess strongly ornamented idiosomal setae and lateral hypostomal teeth, by the presence of only 1 pair of genital setae (vs. 2 pairs in Stibarokris).


Sulisyringophilus jenskjeldi n. sp.


Type-host: Morus bassanus (Linnaeus) (Suliformes: Sulidae), northern gannet.

Type-locality: Nólsoy, Faroe Islands.

Type-material: Female holotype, 11 female and 1 male paratypes (reg. no. MS-24-0124-001), 1 September 2021, mites collected by Simon Haarder, bird obtained by Jens-Kjeld Jensen.

Site in host: Quills of contour feathers.

Type material deposition: Female holotype and most paratypes will be deposited in the AMU, except four female paratypes in the NHMD.

ZooBank registration: The Life Science Identifier (LSID) for Sulisyringophilus jenskjeldi n. g., sp. is urn:lsid:zoobank.org:act:A0C755AC-39E3-460F-9AC7-34FB69FE57C6

Etymology: This species is named in the honour of Jens-Kjeld Jensen, the renowned Faroese ornithologist, naturalist and taxidermist.

Description (Figs. 3, 4, 5, 6)

Female. Total body length 980 in holotype (range for 11 paratypes 960–1090). Gnathosoma. Hypostomal apex with pair of strongly sclerotised and blunt-ended hypostomal teeth (Fig. 4A). Each medial branch of peritremes with 8–9 chambers, each lateral branch with 16–17 chambers (Fig. 4B). Stylophore constricted posteriorly, 265 (255–265) long; exposed portion of stylophore apunctate, 200 (200–205) long; posterior margin of stylophore with projection. Movable cheliceral digit, 200 (200) long. Idiosoma. All dorsal setae thick and ornamented, opishonotal setae f1, f2 short and smooth, f2 and h2 long, smooth and whip-like. Propodonotal shield well sclerotised, punctate in anterior half, and slightly concave on anterior margin. Propodonotal setae vi, ve and si subequal in length. Hysteronotal shield absent. Bases of setae d1 situated slightly anterior to level of setal bases d2. Pygidial shield egg-shaped, well sclerotised, densely punctate; bases of setae f1 and f2 not situated on pygidial shield. Bases of setae 1a and 2c situated on same transverse level; bases 3a situated anterior to level of setal bases 3b. Coxal apodemes I slightly divergent, not fused to apodemes II. All coxal fields punctate. Genital plate absent. Both pairs of pseudanal setae (ps1–2) subequal in length. Genital setae short. Body cuticular striations as in Fig. 3. Legs. Femur, genu and trochanter of legs I punctate ventrally. Tarsal claws normally developed, both similar in shape and size (Fig. 4C). Fan-like setae p' and p" of trasi III–IV with reduced number of tines, 5–6. Solenidia ωI and φI equal in length, both slightly longer than σI (Fig. 4D). All tarsal claws without basal angle. Lengths of setae: vi 90 (70–90), ve 100 (80–85), si 90 (80–100), se (230–260), c1 (230), c2 295 (250–285), d1 200 (170–190), d2 (170–180), e2 140 (140–175), f1 50 (50), f2 335 (340–370), h1 50 (50), h2 490 (485–490), g1 25 (30–40), ps1 and ps2 30 (30–35), ag1 220 (180–200), ag2 135 (145–155), ag3 300 (260–275), 1a (165), 3a (110), 3b 50 (50), 4b 55 (45–70), 3c (115–140), 4c 145 (105–145), l'RI (8), l'RII (10), l'RIII 55 (45–50), l'RIV 35 (30–40), tc'III–IV 80 (80–95), tc"III–IV 105 (95–115).

Fig. 3
figure 3

Sulisyringophilus jenskjeldi n. sp. Female. A, Dorsal view; B, Ventral view. Scale-bar: 100 µm.

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Fig. 4
figure 4

Sulisyringophilus jenskjeldi n. sp. Female. A, Gnathosoma in ventral view; B, Peritremes; C, Tarsus II; D, Solenidia of leg I. Scale-bar: 20 µm.

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Male. Total body length 660 (in 1 paratype). Gnathosoma. Hypostomal apex rounded, without protuberances (Fig. 6A). Infracapitulum apunctate, 140 long. Stylophore rounded posteriorly, 220 long; exposed portion of stylophore apunctate, 190 long. Each medial branch of peritremes with 8–9 chambers, each lateral branch with 17–20 chambers (Fig. 6B). Idiosoma. Propodonotal shield well sclerotised, concave on anterior margin, punctate, bearing bases of setae vi, ve, si and c1. Bases of setae c2 situated posterior to level of setal bases si and anterior to bases of setae se. Setal bases se situated anterior to c1. Hysteronotal shield apunctate, fused with pygidial shield, reaching anteriorly above level of setal bases e2, bearing only bases of setae f2 and h2. Bases of setae d1 situated closer to d2 than to e2. Bases of setae 1a situated slightly anterior to level of setal bases 2c, bases 3a situated slightly anterior to level of setal bases 3b. Coxal fields I–IV well sclerotised, apunctate. Three pairs of aggenital setae present. Setae g1 and g2 subequal in length and situated on same transverse level (Fig. 6C). Setae ps2 longer than ps1. Cuticular striations as in Fig. 5. Legs. Both tarsal claws of legs I–IV of same size and shape. Lengths of setae: vi 90, ve 100, si 60, se 140, c1 135, c2 longer than 100, d1 20, d2 30, e2 20, f2 20, h2 230, ag1 65, ag2 35, ag3 85.

Fig. 5
figure 5

Sulisyringophilus jenskjeldi n. sp. Male. A, Dorsal view; B, Ventral view. Scale-bar: 100 µm.

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Fig. 6
figure 6

Sulisyringophilus jenskjeldi n. sp. Male. A, Gnathosoma in ventral view; B, Peritremes; C, genito-anal opening. Scale-bar: 20 µm.

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Charadriphilus lymnocryptes n. sp.


Type-host: Lymnocryptes minimus (Brünnich) (Charadriiformes: Scolopacidae), jack snipe.

Type-locality: Tórshavn, Faroe Islands.

Type-material: Female holotype and 13 female and 5 male paratypes (reg. no. MS-23-0808-001), 13 September 2019, mites collected by Simon Haarder, bird obtained by Jens-Kjeld Jensen.

Site in host: Quills of secondaries.

Type material deposition: Holotype and most paratypes will be deposited in the AMU, except 5 female and 2 male paratypes in the NHMD.

ZooBank registration: The Life Science Identifier (LSID) for Charadriphilus lymnocryptes n. sp. is urn:lsid:zoobank.org:act:8DC86654-42F8-4631-A64D-17EC50FF4A5E

Etymology: The species name “lymnocryptes” is taken from the generic name of the host.

Description (Figs. 7, 8)

Female. Total body length 725 in holotype (range for 13 paratypes 700–730). Gnathosoma. Infracapitulum apunctate. Hypostomal apex rounded and smooth; 2 pairs of large hypostomal lips present (Fig. 8A). Movable cheliceral digits 160 (160–165) long. Stylophore constricted posteriorly, 200 (200–220) long; exposed portion of stylophore apunctate, 155 (155–165) long. Each medial branch of peritremes with 3 chambers, each lateral branch with 9 chambers (Fig. 8B). Idiosoma. Propodonotal shield punctate laterally, weakly sclerotised, concave on anterior margin, bearing bases of all propodonotal setae except c2. Bases of setae c1 and se situated on same transverse level. Length ratio of setae vi:ve:si 1:1.4–1.5:2.8–3. Hysteronotal shield fused with pygidial shield, weakly sclerotised in anterior part and between bases of setae e2 and f2, apunctate, bearing bases of setae d1, f1 and f2. All coxal fields apunctate. Length ratio of setae ag1:ag2:ag3 1.3–1.7:1:1.7–1.9. Both pairs of genital setae subequal in length and situated on genital plate. Cuticular striations as in Fig. 7. Legs. Fan-like setae p' and p" of legs III–IV with 6–8 tines (Fig. 8C). Solenidia of legs I as in fig. 8D. Lengths of setae: vi 25 (25–30), ve 35 (40–45), si 75 (70–75), se 180 (170–180), c1 180 (175–190), c2 180 (180–185), d1 170 (150–175), d2 180 (150–170), e2 170 (150–170), f1 35 (25), f2 325 (275–300), h1 35 (25), h2 (410–470), ag1 120 (100–115), ag2 70 (75–80), ag3 130 (135), g1,2 30 (20–30), ps1,2 20 (20), l'RIII 35 (40–45), l'RIV 35 (30–40), 3b 40, 4b (30), 3c 110, 4c 110 (90–100).

Fig. 7
figure 7

Charadriphilus lymnocryptes n. sp. Female. A, Dorsal view; B, Ventral view. Scale-bar: 100 µm.

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Fig. 8
figure 8

Charadriphilus lymnocryptes n. sp. Female (A–D). A, Hypostomal apex in dorsal view; B, Peritreme; C, fan-like seta p'III; D, solenidia of leg I. Male (E–J). E, Hypostomal apex in dorsal view; F, Peritreme; G, solenidia of leg I; H, genito-anal opening; I, opisthosoma in ventral view; J, Body in dorsal view. Scale-bars: 20 µm (A–H), 100 µm (I, J).

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Male. Total body length 600–620 (in 5 paratypes). Gnathosoma. Infracapitulum apunctate. Hypostomal apex rounded, without protuberances (Fig. 8E). Movable cheliceral digits 140–145 long. Each medial branch of peritremes with 3 chambers, each lateral branch with 10 chambers (Fig. 8F). Stylophore constricted posteriorly, 180–185 long; exposed portion of stylophore apunctate, 135–140 long. Idiosoma. Propodonotal shield punctate laterally, weakly sclerotised, slightly concave on anterior margin, bearing bases of all propodonotal setae except se and c2. Bases of setae se situated anterior to level of c1 setal bases. Length ratio of setae vi:ve:si 1:1.4–1.8:2.6–3.3. Hysteronotal shield fused with pygidial shield, apunctate, bearing bases of setae d1, f2 and h2, bases of setae e2 on or near this shield. Setae d2 variable in length but always longer than d1 and e2. All coxal fields apunctate. Length ratio of setae ag1:ag2:ag3 3:2:1. Setae g1 situated anterior to bases of setae g2 (Fig. 8H). Cuticular striations as in Figs. 8J. Legs. Solenidia of legs I as in Fig. 8G. Lengths of setae: vi 30–45, ve 50–65, si 90–115, se 180–210, c1 150–180, c2 195–210, d1 25–30, d2 variable 80–170, e2 25–30, f2 25–30, h2 295–330, ag1 90–105, ag2 55–65, ag3 30–35, l'RIII 40–45, l'RIV 25–30, 3c 100–105, 4c 85–95.

Remarks

Charadriphilus lymnocryptes n. sp. is morphologically similar to Ch. ludmilae Bochkov and Chystiakov, 2001 found on the Eurasian woodcock Scolopax rusticola Linnaeus (Scolopacidae) from Russia (Bochkov and Chystiakov 2001). In females of both species, setae si are distinctly longer than vi; each medial branch of the peritremes has 3 or 4 chambers, the propodonotal shield is concave on the anterior margin; all coxal fields are apunctate, and fan-like setae of legs III and IV have 6–8 tines. This new species differs from Ch. ludmilae in the following features: in females of Ch. lymnocryptes, the infracapitulum is apunctate; each lateral branch of the peritremes has 9 chambers, and the lengths of setae ve and si are 35–45 and 70–75, respectively. In females of Ch. ludmilae, the infracapitulum is densely punctate; each lateral branch of the peritremes has 14–15 chambers, and the lengths of setae ve and si are 65 and 130, respectively.


Niglarobia ereuneti Kethley, 1970


Niglarobia ereuneti Kethley, 1970: 44, figs. 25, 26. Skoracki, 2011: 290 [in key].


This species was originally described based on the mite material collected from the semipalmated sandpiper, Calidris pusilla (Linnaeus) (Charadriiformes: Scolopacidae) in the USA (Kethley, 1970), and so far, there have been no other records of this mite species. Below, we present a new host species and locality for this parasitic mite - the purple sandpiper Calidris maritima (Brünnich) from the Faroe Islands.

Material examined: 18 females and 5 males from quills of contour feathers from Calidris maritima (Charadriiformes: Scolopacidae), Nólsoy, Faroe Islands, 27 May 1996, mites collected by Simon Haarder, bird obtained by Jens-Kjeld Jensen – all specimens are deposited in the AMU, except 8 females and 3 males in the MNHD. 10 females and 2 males from quills of upper wing coverts from same host species; Nólsoy, Faroe Islands, 15 April 1996 – all specimens are deposited in the MNHD.


Creagonycha lara Kethley, 1970


Creagonycha lara Kethley, 1970: 36, figs. 20, 21. Skoracki, 2011: 275 [in key].


This species was originally described based on specimens collected from the ring-billed gull, Larus delawarensis Ord (Charadriiformes: Laridae) in the USA (Kethley, 1970). Since its original description, no further records of this species have existed. Below, we record a new host species for this parasite, the black-legged kittiwake, Rissa tridactyla (Linnaeus), and a new locality, the Faroe Islands.

Material examined: 11 females and 1 male from quills of secondaries from Rissa tridactyla (Charadriiformes: Laridae), Nólsoy, Faroe Islands, 28 December 2007, mites collected by Simon Haarder, bird obtained by Jens-Kjeld Jensen. All specimens are deposited in the AMU, except 4 females in the MNHD.


Prevalence


A total of 31 species and 75 specimens of aquatic birds from the Faroe Islands were investigated for quill mites during this study (Table 1). Generally, only a few specimens of each bird species were examined for quill mites. Quill mites were found on five bird specimens (6%), a finding consistent with reports indicating a generally low prevalence of quill mites in avian wild populations (e.g. Skoracki et al., 2010; Skoracki, 2011). However, aquatic birds have received very little attention regarding the prevalence and intensity of quill mite infestations. Both examined specimens of the purple sandpiper (Calidris maritima) were infested by the quill mite Niglarobia ereuneti Kethley, 1970, albeit in two different microhabitats, whereas only one specimen of the northern gannet (Morus bassanus) was sampled for quill mites. Quill mites were recovered from one specimen of the jack snipe (Lymnocryptes minimus), out of three examined. Only one of the black-legged kittiwake (Rissa tridactyla) was found to harbour quill mites. This specimen was caught in December 2007, while the remaining kittiwakes in this study were obtained in July 2014 (1 specimen) and January 2024 (18 specimens). Further examination of additional bird specimens is imperative to attain a comprehensive understanding of the actual occurrence status of these underexplored mites on aquatic avifauna. Finally, future investigations could focus on elucidating the relationships between the presence of quill mites and seasonal fluctuations, as well as the health status, age, and sex of the host avian species.