Introduction

The apogonid genus Apogon Lacepède 1801 (Apogonidae) is characterized by II, 8 anal-fin rays, predorsal scales present, preopercular flap not extending beyond the vertical edge of the preopercle, and a pale stomach and intestine (Mabuchi et al. 2014). The genus includes several species complexes or groups: Apogon coccineus complex (defined by Greenfield 2001), Apogon erythrinus complex (Greenfield 2001), Apogon talboti group (Greenfield and Randall 2004), and Apogon talboti look-alike group (Greenfield and Randall 2004).

The Ogasawara Islands consist of two major island chains (Bonin and Volcano islands) and three isolated small islands and have never been connected to the Asian Continent and the mainland of Japan. The Bonin Islands, northern island chain, are located about 1,000 km south of Tokyo (Kuriiwa 2018). During an ichthyofaunal survey in the Bonin Islands in 2015, nine unidentified specimens belonging to the A. talboti look-alike group, having two supraneural bones and a membranous flap at the lower corner and along the ventral margin of the preopercle, were collected from the Bonin Islands. Although similar to Apogon caudicinctus Randall and Smith 1988 of the group in color pattern and several other characters, the former differed in their greater number of pectoral-fin rays, greater interorbital width, and a wider blackish band on the caudal peduncle. They are described herein as a new species, and a key to the species belonging to the A. talboti look-alike group is provided. The group includes A. caudicinctus, Apogon deetsie Randall 1998, Apogon dianthus Fraser and Randall 2002, and Apogon rubrifuscus Greenfield and Randall 2004, in addition to the new species.

Materials and methods

Counts and measurements followed Yoshida and Motomura (2016). Measurements were made to the nearest 0.1 mm with needlepoint calipers under a dissecting microscope. Standard and head lengths are abbreviated as SL and HL, respectively. Curatorial procedures for the newly collected specimens followed Motomura and Ishikawa (2013). Institutional codes follow Sabaj (2019). Osteological characters, including vertebral counts, were observed on a radiograph of one specimen of the new species (KAUM–I. 74617, 30.7 mm SL) and two specimens of A. caudicinctus (KAUM–I. 29534, 48.7 mm SL; KAUM–I. 45768, 48.5 mm SL). The formula for the configuration of supraneural bones, anterior neural spines, and anterior dorsal-fin pterygiophores follows Ahlstrom et al. (1976).

Key to the species belonging to the Apogon talboti look-alike group

1a. No blackish band on caudal peduncle ...2

1a. Blackish band on caudal peduncle ...3

2a. Caudal peduncle relatively deep, its depth 11.0–14.8 % of SL; 15 developed gill rakers ... A. dianthus (Indo-West Pacific)

2b. Caudal peduncle relatively shallow, its depth 10.0 % of SL; 20 developed gill rakers … A. rubrifuscus (Easter Island)

3a. Black vertical band on body below second dorsal fin; 13–15 developed gill rakers … A. deetsie (Hawaiian and Tuamotu islands)

3b. No black band on body below second dorsal fin; 8–12 developed gill rakers ...4

4a. 12 pectoral-fin rays; narrower blackish band on caudal peduncle from midpoint to base of caudal fin; interorbital space narrow, its width 6.6–7.9 % of SL... A. caudicinctus (Indo-Pacific)

4b. 13 pectoral-fin rays; wider blackish band on caudal peduncle before midpoint to base of caudal fin; interorbital space wide, its width 9.1–11.1 % of SL ... A. soloriens sp. nov. (Bonin Islands)

Apogon soloriens sp. nov.

(New English name: Rising-sun Cardinalfish; new Japanese name: Asahi-tenjikudai)

(Figs. 1, 2, 5; Table 1)

Table 1 Meristics and morphometrics of Apogon soloriens sp. nov. and A. caudicinctus
Full size table

Holotype. KAUM–I. 74702, 23.5 mm SL, Shika-hama, Ototo-jima island, Bonin Islands, Ogasawara Islands, 27°07ʹ44ʺN, 142°11ʹ01ʺE, 5–25 m depth, hand net, 5 July 2015, T. Yoshida.

Paratypes. 8 specimens, 18.9–30.7 mm SL, all from Bonin Islands, Ogasawara Islands. KAUM–I. 74505, 27.2 mm SL, off Kita Port, Haha-jima island, 26°41ʹ59ʺN, 142°08ʹ28ʺE, 4 m depth, hand net, 26 June 2015, K. Koeda; KAUM–I. 74,541, 23.8 mm SL, Dobuiso, Chichi-jima island, 27°05ʹ22ʺN, 142°15ʹ08ʺE, 5–45 m depth, hand net, 2 July 2015, S. Chiba et al.; KAUM–I. 74617, 30.7 mm SL, KAUM–I. 74618, 24.8 mm SL, KAUM–I. 74619, 25.0 mm SL, KAUM–I. 74620, 18.9 mm SL, east of Nishi-jima island, 27°07ʹ14ʺN, 142°10ʹ12ʺE, 5–25 m depth, hand net, 3 July 2015, S. Tashiro; KAUM–I. 74701, 27.8 mm SL, Shika-hama, Ototo-jima island, 27°07ʹ44ʺN, 142°11ʹ01ʺE, 26 m depth, hand net, 5 July 2015, K. Koeda; KAUM–I. 74703, 22.0 mm SL, same data as holotype.

Diagnosis. A species of Apogon with the following combination of characters: dorsal-fin rays VI-I, 9; anal-fin rays II, 8; pectoral-fin rays 13; developed gill rakers 8 or 9 (modally 9); total gill rakers (including rudiments) 15–18 (16); interorbital width 9.1–11.1% (mean 9.8%) of SL; supraneural bones 2; membranous flap at lower corner and along ventral margin of preopercle; no black band on body below second dorsal fin; wide blackish band with reddish suffusion on caudal peduncle from before midpoint to base of caudal fin.

Description. Meristics and morphometrics of the type specimens are shown in Table 1. Data for the holotype are presented first, followed by paratype data (if different) in parentheses. Vertebrae 10 + 14; formula for supraneural bones, anterior neural spines and anterior dorsal pterygiophores /00/1/1 + 1/1/1/1/ (based on paratype, KAUM–I. 74617; no data for holotype).

Body rounded, moderately deep, compressed, deepest at first dorsal-fin origin. Dorsal and ventral profiles of head and body convex. Caudal peduncle moderately deep. Head large, compressed. Eye large, round, orbit diameter 3.3 (2.8–3.3) in HL. Mouth oblique, forming angle of ca. 30 degrees to horizontal axis of body. Posterior margin of maxilla slightly concave, extending beyond vertical through anterior margin of pupil. Upper-jaw length 1.9 (1.7–1.9) in HL. Tip of upper jaw anterior to tip of lower jaw. No enlarged caniniform teeth on jaws. A tooth band on both jaws, irregular V-shaped patch of small teeth on vomer, narrow band of teeth rows on palatine, absent on ectopterygoid. Anterior nostril with short oval tube, uppermost margin of opening above level of ventral margin of pupil. Posterior nostril oval, opening vertically, rim absent, uppermost margin below level of dorsal margin of pupil. Gill rakers slender, moderately long. Posterior margin of preopercle serrated with flap. Lateral line well developed, extending from upper end of gill opening to caudal-fin base.

First dorsal-fin origin posterior to vertical through pectoral-fin base; second spine of first dorsal fin longest, its length 2.3 (2.0–2.4) in HL. Posterior end of first dorsal-fin base anterior to vertical through posterior tip of pelvic fin. Second dorsal-fin origin anterior to vertical through anal-fin origin; length of dorsal spine of second dorsal fin 3.6 (3.1–3.6) in HL; first soft ray of second dorsal fin longest, its length 2.0 (1.6–2.0) in HL; all second dorsal-fin rays branched. Posterior end of second dorsal-fin base posterior to vertical through base of seventh anal-fin soft ray. Anal-fin origin below base of first (first or second) soft ray of second dorsal fin; first spine of anal fin short; second anal spine long, its length 3.6 (3.0–4.0) in HL; first soft ray of anal fin long, its length 2.1 (1.7–2.1) in HL; all anal-fin rays branched. Pelvic-fin origin anterior to vertical through origin of first dorsal fin; pelvic-fin spine long, its length 3.0 (2.6–3.0) in HL; first pelvic-fin soft ray longest, its length 1.9 (1.7–2.0) in HL. Posterior tip of depressed pelvic fin reaching to vertical through origin of second dorsal fin. Pectoral fin long, its length 1.6 (1.3–1.7) in HL, posterior tip anterior to vertical through base of fourth (fourth to sixth) dorsal-fin soft ray. Caudal fin forked. Anus closer to anal-fin origin than to pelvic-fin origin.

Color when fresh (Fig. 1). Head reddish orange, with black pigmentation on snout and opercle. Body reddish orange with blackish band suffused with reddish orange on caudal peduncle from before midpoint to base of caudal fin, no black band on body below second dorsal fin. Iris yellowish gold to reddish gold. Black pigmentation scattered on upper part of body from nape to below second dorsal-fin base (sometimes with anal-fin base). Small specimen (holotype, 23.5 mm SL; Fig. 1a) with irregular black patches on scales on upper part of body, anal-fin base and caudal peduncle. Large specimen (30.7 mm SL; Fig. 1b) with black pigmentation at middle of scales on upper part of body and caudal peduncle.

Fig. 1
figure 1

Photographs of fresh specimens of Apogon soloriens sp. nov. a Holotype, KAUM–I. 74702, 23.5 mm SL, Ototo-jima island, Bonin Islands, Ogasawara Islands; b paratype, KAUM–I. 74617, 30.7 mm SL, Nishi-jima island, Bonin Islands, Ogasawara Islands

Full size image

Color in alcohol (Fig. 2). Head and trunk pale. Snout, behind eye, posteroventral margin of orbit, lower part of opercle, upper part of body and caudal peduncle with black pigmentation. Iris black. Fins semi-translucent (sometimes with black pigmentation on first dorsal fin, rarely with black pigmentation on second dorsal and anal fins). Stomach and intestine pale.

Fig. 2
figure 2

Photographs of preserved specimens of Apogon soloriens sp. nov. a Holotype, KAUM–I. 74702, 23.5 mm SL, Ototo-jima island, Bonin Islands, Ogasawara Islands; b paratype, KAUM–I. 74617, 30.7 mm SL, Nishi-jima island, Bonin Islands, Ogasawara Islands

Full size image

Distribution. Restricted to the Ogasawara Islands (Bonin Islands only), Japan. Collection data indicate capture depths of 4–45 m.

Etymology. The specific name “soloriens” is derived from Latin, meaning “Rising-sun”, in reference to the body color.

Comparisons. The new species can be easily distinguished from A. deetsie, A. dianthus, and A. rubrifuscus by having a blackish band on the caudal peduncle (vs. band absent in A. dianthus and A. rubrifuscus), 8 or 9 developed gill rakers (vs. 13–15 in A. deetsie, 15 in A. dianthus, and 20 in A. rubrifuscus), and 15–18 total gill rakers (vs. 19 in A. dianthus and 20 in A. rubrifuscus), and lacking a black band on the body below the second dorsal fin (vs. band present in A. deetsie) (Randall 1998; Fraser and Randall 2002; Greenfield and Randall 2004; Greenfield 2007; this study).

Apogon soloriens is most similar to A. caudicinctus (Figs. 3, 4), both species lacking a black band on the body below the second dorsal fin, but having a blackish band on the caudal peduncle. However, A. soloriens has more pectoral-fin rays (13 vs. 12 in A. caudicinctus; Table 1) and a greater interorbital width [9.1–11.1% of SL (mean 9.8%) vs. 6.6–7.9% (mean 7.3%); Fig. 5]. In addition, the blackish band on the caudal peduncle of A. soloriens is relatively wider than that of A. caudicinctus, in which the band extends only from the midpoint of the peduncle (Figs. 1, 2, 3, 4).

Fig. 3
figure 3

Photographs of fresh specimens of Apogon caudicinctus. a Non-type, KAUM–I. 99992, 27.7 mm SL, Iwo-tou island, Volcano Islands, Ogasawara Islands; b non-type, KAUM–I. 21765, 32.9 mm SL, Yaku-shima island, Osumi Islands

Full size image
Fig. 4
figure 4

Photographs of preserved specimens of Apogon caudicinctus. a Holotype, BPBM 13002, 50.0 mm SL, Rapa, Bass Islands, French Polynesia; b non-type, KAUM–I. 99992, 27.7 mm SL, Iwo-tou island, Volcano Islands, Ogasawara Islands; c non-type, KAUM–I. 21765, 32.9 mm SL, Yaku-shima island, Osumi Islands

Full size image
Fig. 5
figure 5

Relationship of interorbital width (% of SL) to SL (mm) in Apogon soloriens (open circles) and A. caudicinctus (closed triangles)

Full size image

Apogon caudicinctus has been recorded from Réunion Island, Indian Ocean, as well as from the following Pacific Ocean localities: Pitcairn Islands, Marquesas Islands, Rapa, Fiji, and Japan (Randall and Smith 1988; Randall 2005; this study). In the Ogasawara Islands, A. soloriens and A. caudicinctus have been collected only from the Bonin (northern island chain) and Volcano islands (southern island chain), respectively. Although comprehensive surveys of specimens of Apogon in museum collections have been made by the authors, no additional examples of the new species from beyond the area of the Bonin Islands were located, suggesting that A. soloriens is most likely endemic to the Bonin Islands.

Comparative material. Apogon caudicinctus (9 specimens, 27.7–63.6 mm SL): BPBM 7398, paratype, 49.8 mm SL, Ishigaki-jima island, Yaeyama Islands, Japan, 6–11 m, 22 May 1968, J. Randall and A. Banner; BPBM 13002, holotype, 50.0 mm SL, south side of Mei Point, Rapa, Bass Islands, French Polynesia, 14 Feb. 1971, J. Randall and D. Cannoy; BPBM 16799, 2 paratypes, 51.9–63.6 mm SL, Big Pool, St. Paul’s Point, southeastern Pitcairn Island, Pitcairn Islands, 0.6 m, 7 Jan. 1971, J. Randall et al.; KAUM–I. 21765, 32.9 mm SL, west of Kamazeno-hana, Kurio, Yaku-shima island, Osumi Islands, Japan, 30°16ʹ03ʺN, 130°24ʹ48ʺE, 0–4 m depth, hand net, 30 July 2009, KAUM fish team; KAUM–I. 29534, 48.7 mm SL, off south coast of Iwo-jima island, Osumi Islands, Japan, 30°46ʹ32ʺN, 130°16ʹ43ʺE, 10–60 m depth, hand net, 26 May 2010, KAUM fish team; KAUM–I. 45768, 48.5 mm SL, off Tomori Fishing Port, Yoron-jima island, Amami Islands, Japan, 27°01ʹ54ʺN, 128°24ʹ29ʺE, 5–10 m depth, hand net, 15 Apr. 2012, M. Yamashita and T. Yoshida; KAUM–I. 99992, 27.7 mm SL, off Mount Suribachi, Iwo-tou island, Volcano Islands, Ogasawara Islands, Japan, 24°44ʹ38ʺN–24°44ʹ46ʺN, 141°17ʹ02ʺE–141°17ʹ13ʺE, 13–17 m depth, hand net, 6 June 2017, T. Yoshida; WAM P.29385-001, paratype, 52.2 mm SL, Marotiri, Austral Islands, French Polynesia, 0–1.5 m, 20 Feb. 1971, A. Sinito et al.