Ischnochiton boninensis Bergenhayn, 1933

Park, Jina, Kim, Yukyung, Putri, Eggy Triana & Park, Joong-Ki, 2024, Revisiting the taxonomy of Korean Ischnochiton species (Polyplacophora, Ischnochitonidae) based on a combined analysis of morphological and molecular data, Biodiversity Data Journal 12, pp. e 134521-e 134521 : e134521-

Ischnochiton boninensis Bergenhayn, 1933

Ischnochiton boninensis Bergenhayn (1933): 10–13, taf. 1, figs. 2, 3, taf. 2, figs. 24–29, 32, textfig. 3; Taki (1938): 369, 373, 375; Kang (1971): 52; Kaas and Van Belle (1980): 18; Kaas and Van Belle (1998): 33; Kira (1982): 183, pl. 67, fig. 2; Saito (1995): 105; Saito (2000): 12, 13, pl. 6, fig. 15; Saito (2017): 732, pl. 4, fig. 11; Slieker (2000): 98, 99, pl. 37, fig. 10; Owada (2016): 5, 6, figs. 4 A – E, 5 A – E; Sirenko and Zhang (2019): 6, fig. 2 B.

Ischnochiton zebrinus Bergenhayn (1933): 13–15, taf. 1, fig. 4, taf. 2, figs. 30, 31, 33–39, textfig. 4; Taki (1938): 375; Taki (1964 a): 342.

Ischnochiton (Ischnochiton) boninensis : Taki (1962): 43; Higo (1973): 6; Yum (1988): 20, 21, pl. 1, fig. 4, pl. 8, pl. 23, figs. 1, 2, pl. 28, fig. 4; Kaas and Van Belle (1990): 184 –186, fig. 83, map 39; Higo et al. (1999): 27; Lee and Min (2002): 94; Min et al. (2004): 70, 71, fig. 8.

Ischnochiton (Ischnochiton) comptus (Gould) forma isaoi: Taki (1964 a): 348, text-figs. 2, 4, 6; Taki (1964 b): 408; Higo (1973): 6; Higo and Goto (1993): 3.

? Ischnochiton (Ischnochiton) zebrinus : Taki (1962): 43; Taki (1964 b): 408; Higo (1973): 6; Higo and Goto (1993): 3; Higo et al. (1999): 27.

Ischnochiton (Simplischnochiton) boninensis : Van Belle (1982): 470; Dell'Angelo et al. (1990): 36, 37.

Materials

Type status: Other material. Occurrence: individualCount: 3; occurrenceID: B04F80DF-C510-566A-9E5A-CEEA8BBADF80; Taxon: scientificName: Ischnochiton boninensis ; Location: country: Korea; locality: Jongdal-ri, Gujwa-eup, Jeju-si, Jeju-do ; verbatimCoordinates: 33°29'16.84"N, 126°54'41.37"E; Event: eventDate: 26 Jan 2015

Type status: Other material. Occurrence: individualCount: 5; occurrenceID: C8673915-9FF2-5CC2-AC00-144DD7F27CAD; Taxon: scientificName: Ischnochiton boninensis ; Location: country: Korea; locality: Jongdal-ri, Gujwa-eup, Jeju-si, Jeju-do ; verbatimCoordinates: 33°29'16.84"N, 126°54'41.37"E; Event: eventDate: 21 Dec 2015

Type status: Other material. Occurrence: individualCount: 1; occurrenceID: 283FB9B8-108F-585F-B330-D280BD77DF60; Taxon: scientificName: Ischnochiton boninensis ; Location: country: Korea; locality: Daejeong-eup, Seogwipo-si, Jeju-do ; verbatimCoordinates: 33°14'27.09"N, 126°13'21.24"E; Event: eventDate: 02 Jul 2016

Type status: Other material. Occurrence: individualCount: 2; occurrenceID: 7BB82550-EA20-5A66-931F-2117EB63AA04; Taxon: scientificName: Ischnochiton boninensis ; Location: country: Korea; locality: Is. Mun, Seogwi-dong, Seogwipo-si, Jeju-do ; locationRemarks: collected by SCUBA-diving; verbatimCoordinates: 33°13'31.06"N, 126°33'54.57"E; Event: eventDate: 26 Mar 2019

Type status: Other material. Occurrence: individualCount: 1; occurrenceID: 8B88C27E-086E-5F4E-B663-D333BF8D776F; Taxon: scientificName: Ischnochiton boninensis ; Location: country: Korea; locality: Is. Mun, Seogwi-dong, Seogwipo-si, Jeju-do ; locationRemarks: collected by SCUBA-diving; verbatimCoordinates: 33°13'35.78"N, 126°34'07.27"E; Event: eventDate: 27 Mar 2019

Type status: Other material. Occurrence: individualCount: 1; occurrenceID: 6A0AE6BA-B86B-5D25-A78E-A730101EC7B8; Taxon: scientificName: Ischnochiton boninensis ; Location: country: Korea; locality: Geumgye-ri, Gogun-myeon, Jindo-gun, Jeollanam-do ; verbatimCoordinates: 34°25'21.32"N, 126°20'56.94"E; Event: eventDate: 14 Dec 2016

Type status: Other material. Occurrence: individualCount: 1; occurrenceID: 5DF8577C-F423-5E58-AF2D-9FB504D98202; Taxon: scientificName: Ischnochiton boninensis ; Location: country: Korea; locality: Gujora Beach, Gujora-ri, Irun-myeon, Geoje-si, Gyeongsangnam-do ; verbatimCoordinates: 34°48'05.58"N, 128°41'28.40"E; Event: eventDate: 12 Jun 2018

Type status: Other material. Occurrence: individualCount: 1; occurrenceID: 1DB2075D-449C-5995-BCB5-B9A6A2EF4C92; Taxon: scientificName: Ischnochiton boninensis ; Location: country: Korea; locality: Haengnam Lighthouse, Dodong-ri, Ulleung-eup, Ulleung-gun, Gyeongsangbuk-do ; locationRemarks: collected by SCUBA-diving; verbatimCoordinates: 37°29'13.48"N, 130°55'00.18"E; Event: eventDate: 30 Oct 2018

Description

Body elongate-oval shaped, medium, less than 30 mm in length (Fig. 2 A and C – E; in examined materials, body length [BL] 14.6–21.76 mm, body width [BW] 7.21–12.23 mm). Valves generally yellowish-green to dark green or wholly whitish or pinkish in colour, brown streaks or cream, yellow, bright pink blotches. Girdle rather narrower in width than valves, dark brown, often with yellow-brown blotches or transverse bands. Gills arrangement holobranchial and adanal on both sides with interspace (Fig. 2 B).

Valves: Head valve semicircular in shape, tegmentum sculpted with about 50 fine radial riblets and a few strong growth lines; radial riblets bifurcate towards margin, but faint towards apex; anterior margin round; posterior margin widely V-shaped (Fig. 3 A). Intermediate valves broadly rectangular in shape, not beaked (Fig. 3 B and C), dorso-ventrally rounded or subcarinated, somewhat high in frontal view, side slope slightly convex (Fig. 3 J; elevation ratio of 0.46 in the 4 th valve); anterior margin nearly straight to slightly convex, except for 2 nd valve (Fig. 3 B; more convex than other intermediate valves, almost triangular); lateral margins somewhat round; posterior margin straight; tegmentum in central area (ca) with rows of densely small, elongate granules in quincunx or zig-zag patterns (Fig. 3 I); lateral area (la) slightly raised, sculpted with 5–7 riblets, dividing to almost double towards margin, similar to head valve (Fig. 3 B and C). Tail valve almost semicircular, as wide as head valve; anterior margin nearly straight (Fig. 3 D); mucro (m) subcentral, not pointed; sculpture of antemucronal area (ama) similar to central area of intermediate valves; postmucronal area (pma) sculpted like head valve; postmucronal slope (pms) weakly concave (Fig. 3 K). Articulamentum light blue, generally red violet in centre, very thin, reflecting colouration and patterns on tegmentum. Apophyses (ap; sutural laminae) short, delicate, triangular in 2 nd valve, but broad rectangular in the other valves; jugal lamina (jl) extremely short; jugal sinus (js) shallow, nearly straight; insertion plate (ip) short, teeth (t) relatively smooth with varying size; slit formula 10–13 / 1 / 9 – 10, slit rays (slr) distinct (Fig. 3 E – H). Eaves (e) narrow, solid (Fig. 3 J).

Girdle: Perinotum scales (ps: length [L] 91–110.8 μm, width [W] 120.3–190.7 μm) small, oval, flat, slightly bent, sculpted with 9–16 fine longitudinal ribs converging to distal tip, densely overlapped, parallel to outer margin (Fig. 7 A and B); peripheral scales of perinotum (pps: L 25.8–56.4 μm, W 33.8–86.5 μm) much smaller than perinotum scales, elongate-oval, with 4–7 fine, flat longitudinal ribs (Fig. 7 A – C); marginal spicules of three types: large one (lmsp: L 67.2–87.6 μm, W 16.9 μm) flat-ovate, narrower to tip, blunt, with weakly longitudinal ribs, middle one (mmsp: L 68.2–80.3 μm, W 7.3–10 μm) long, nearly straight, smooth, rod-shaped with blunt tip and small one (smsp: L 22.1–33.5 μm, W 9.9–11.5 μm) very short, stout with strong radial ribs at tip (Fig. 7 A and C); hyponotum scales (hs: L 56.7 μm, W 14.7 μm) hyaline, smooth, oblong, overlapped, radiated to outline (Fig. 7 D).

Radula: Radula teeth symmetrical (Fig. 8 A). Central tooth (c) small, narrow, keeled from basal, blade broader than stalk, deeply concaved, bent forward; centro-lateral teeth (cl) slightly taller than central tooth, cuspids thickened, convex; head (h) of major lateral teeth (mlt) bicuspid, cuspids sharp, tapering towards tip, inner cuspid longer than outer one; petaloid process (pp; wing) below at head of major lateral tooth, large, rectangular, inner distal concave; major uncinus teeth (mu) long, spatula-shaped with rounded tip; marginal teeth (im, mm, om) flat, increasing in size from inner to outer teeth.

Distribution

China, Hong Kong, Japan, Vietnam and Korea.

Type locality

Japan: Sagami Misaki and Bonin Islands (Ogasawara).

Taxon discussion

This species is morphologically similar to I. comptus ( Gould, 1859) , but easily distinguished by the size and microstructure of its perinotum scales (Table 2 ). I. boninensis has small perinotum scales sculpted with conspicuous fine longitudinal ribs (Fig. 7 A and B), while I. comptus displays relatively large, smooth, glossy scales (Fig. 7 E and F). In contrast to the markedly high individual variations in tegmentum colour and pigmentation patterns, the mtDNA cox 1 sequences of this species showed moderate within-species variations, less than 1.8 % (Fig. 2 A and C – E, Table 3 ), even amongst individuals sampled from different geographic regions (i. e. Japan and Korea).

Figures

Figure 2. External view of Korean Ischnochiton species. A I. boninensis from Jeju, dorsal view; B I. boninensis from Jeju, ventral view; C I. boninensis from Ulleng (NIBRIV 0000863007), dorsal view; D I. boninensis from Jeju, dorsal view; E I. boninensis (= I. zebrinus) from Jeju (NIBRIV 0000863047), dorsal view; F I. comptus from Jeju (NIBRIV 0000863098), dorsal view; G I. comptus from Jeju (NIBRIV 0000863098), ventral view; H I. comptus from Jeju, dorsal view; I I. comptus from Jeju, dorsal view (NIBRIV 0000863020); J I. comptus from Uljin, dorsal view (NIBRIV 0000863048); K I. hakodadensis from Goseong (NIBRIV 0000863028), dorsal view; L I. hakodadensis from Goseong (NIBRIV 0000863028), ventral view; M I. hakodadensis from Goseong, dorsal view; N I. hayamii from Ulsan (NIBRIV 0000863103), dorsal view; O I. hayamii from Ulsan (NIBRIV 0000863103), ventral view. Scale bars: A – O = 5 mm. The NIBR voucher specimen numbers are provided in parentheses.

Figure 3. Valves of I. boninensis from Jeju (NIBR voucher specimen no. NIBRIV 0000863097). A head valve, dorsal view; B 2 nd valve, dorsal view; C 4 th valve, dorsal view; D tail valve, dorsal view; E head valve, ventral view; F 2 nd valve, ventral view; G 4 th valve, ventral view; H tail valve, ventral view; I 4 th valve, detail of tegmentum surface of central area using scanning electron microscope; J 4 th valve, frontal view; K tail valve, lateral view. Abbreviations: ama, antemucronal area; ap, apophyses; ca, central area; e, eave; ip, insertion plate; jl, jugal lamina; js, jugal sinus; la, lateral area; m, mucro; pma, postmucronal area; pms, postmucronal slope; sl, slit; slr, slit ray; t, tooth. Scale bars: A – H, J = 5 mm, I = 200 μm, K = 2 mm.

Figure 7. Microstructure of girdles in Ischnochiton species using scanning electron microscope. A – D I. boninensis; E – H I. comptus (NIBRIV 0000863098); I – L I. hakodadensis (NIBRIV 0000863046); M – P I. hayamii (NIBRIV 0000863103); A perinotum scales and marginal spicules of I. boninensis; B perinotum scales of I. boninensis; C marginal spicules of I. boninensis; D hyponotum scales of I. boninensis; E perinotum scales and marginal spicules of I. comptus; F perinotum scales of I. comptus; G marginal spicules of I. comptus; H hyponotum scales of I. comptus; I perinotum scales and marginal spicules of I. hakodadensis; J perinotum scales of I. hakodadensis; K marginal spicules of I. hakodadensis; L hyponotum scales of I. hakodadensis; M perinotum scales and marginal spicules of I. hayamii; N perinotum scales of I. hayamii; O marginal spicules of I. hayamii; P hyponotum scales of I. hayamii. Abbreviations: hs, hyponotum scale; lmsp, large marginal spicule; mmsp, middle marginal spicule; pps, peripheral perinotum scale; ps, perinotum scale; smsp, small marginal spicule. Scale bars: A – P = 50 μm. The NIBR voucher specimen numbers are provided in parentheses.

Figure 8. Microstructure of radula of Ischnochiton species using scanning electron microscope. A I. boninensis (NIBRIV 0000863095); B I. comptus (NIBRIV 0000863098); C I. hakodadensis; D I. hayamii (NIBRIV 0000863103). Abbreviations: c, central tooth; cl, centro-lateral tooth; h, head of major lateral tooth; im, inner marginal tooth; isl, inner small lateral tooth; mlt, major lateral tooth; mm, middle marginal tooth; mu, major uncinus tooth, om; outer marginal tooth; osl, outer small lateral tooth; pp, petaloid process. Scale bars: A – D = 100 μm. The NIBR voucher specimen numbers are provided in parentheses.