Ischnochiton comptus ( Gould, 1859 )

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 comptus ( Gould, 1859)

Chiton (Leptochiton) comptus Gould (1859): 163–164; Gould (1862): 117 (partim).

Ischnochiton comptus : Pilsbry (1892): 117 (partim); 1895: 114; Thiele (1909): 111, 114; Taki (1938): 366 –371, pl. 14, figs. 5, 10, pl. 15, figs. 6, 7, pl. 25, figs. 9–16, pl. 27, figs. 6, 7, pl. 29, figs. 11–16 (partim, =? boninensis ); Lee (1956): 11; Kang (1971): 52; Yoo (1976): 146, pl. 35, fig. 9; Kaas and Van Belle (1980): 29; Kaas and Van Belle (1998): 49; Kira (1982): 183, pl. 67, fig. 1; Saito (1995): 105; Saito (2000): 12, 13, pl. 6, fig. 14; Saito (2017): 732, pl. 5, fig. 1; Slieker (2000): 98, 99, pl. 37, fig. 11; Owada (2016): 6, figs. 4 F – J, 5 E – H; Sirenko and Zhang (2019): 6 , 7, fig. 2 C.

Ischnochiton thaanumi Dall (1926): 66 (partim).

Ischnochiton (Ischnochiton) comptus : Taki (1962): 43; Higo (1973): 6; Yum (1988): 18 –20, pl. 1, fig. 3, pl. 7, pl. 22, fig. 5, 6, pl. 28, fig. 3.

Ischnochiton (Ischnochiton) comptus (Gould) forma comptus: Taki (1964 a): 347, text-figs. 1, 3, 5; 1964 b: 408; Okada et al. (1981): 8; Higo and Goto (1993): 3.

Ischnochiton (Haploplax) comptus : Kaas and Van Belle (1994): 70 –72, fig. 28, map. 7; Higo et al. (1999): 27; Lee and Min (2002): 94; Min et al. (2004): 71 –73, fig. 9.

Materials

Type status: Other material. Occurrence: individualCount: 4; occurrenceID: C27ECD33-0416-5309-AEAF-F17C6710DA7D; Taxon: scientificName: Ischnochiton comptus ; Location: country: Korea; locality: Gamsan-ri, Andeok-myeon, Seogwipo-si, Jeju-do ; verbatimCoordinates: 33°14'02.18"N, 126°21'45.60"E; Event: eventDate: 26 Jan 2015

Type status: Other material. Occurrence: individualCount: 3; occurrenceID: 1B2B3AA3-4F11-5273-AA4E-08B84F18B4E2; Taxon: scientificName: Ischnochiton comptus ; Location: country: Korea; locality: Gamsan-ri, Andeok-myeon, Seogwipo-si, Jeju-do ; verbatimCoordinates: 33°14'06.31"N, 126°21'34.21"E; Event: eventDate: 22 Dec 2015

Type status: Other material. Occurrence: individualCount: 2; occurrenceID: CDA06FBD-6774-5AB8-867C-BA22C65B8F5E; Taxon: scientificName: Ischnochiton comptus ; Location: country: Korea; locality: Dokgot-ri, Daesan-eup, Seosan-si, Chungcheongnam-do ; verbatimCoordinates: 36°59'05.79"N, 126°19'50.10"E; Event: eventDate: 22 Mar 2016

Type status: Other material. Occurrence: individualCount: 1; occurrenceID: 50DCB9E7-A1D5-5F61-B1D1-5AF5C4A05326; Taxon: scientificName: Ischnochiton comptus ; Location: country: Korea; locality: Jukbyeon-ri, Jukbyeon-myeon, Uljin-gun, Gyeongsangbuk-do ; locationRemarks: collected by snorkeling; verbatimCoordinates: 37°03'33.85"N, 129°25'42.04"E; Event: eventDate: 08 Sep 2016

Type status: Other material. Occurrence: individualCount: 2; occurrenceID: 1A911F9E-3306-522B-AF9A-26E6BF151A75; Taxon: scientificName: Ischnochiton comptus ; Location: country: Korea; locality: Sagye-ri, Andeok-myeon, Seogwipo-si, Jeju-do ; verbatimCoordinates: 33°13'37.13"N, 126°18'30.92"E; Event: eventDate: 23 Apr 2017

Type status: Other material. Occurrence: individualCount: 1; occurrenceID: 1D4D279E-F639-5747-9CE0-B5B98C3A7CCB; Taxon: scientificName: Ischnochiton comptus ; Location: country: Korea; locality: Hangaechang, 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

Description

Body oval-shaped, less than 25 mm in length (Fig. 2 F and H – J; in examined materials, BL 15.69–19.38 mm, BW 9.9–11.68 mm). Valves overall light green to greyish-green in colour, partially white, cream, pink blotches or dots of various size. Girdle rather narrow, cream in colour with dark brown transverse bands. Gills arrangement holobranchial and adanal on both sides with interspace (Fig. 2 G).

Valves: Head valve semicircular, tegmentum sculpted with weak microgranules; ca. 50 radial riblets gradually fainter towards apex; growth lines rather distinct; anterior margin round; posterior margin widely V-shaped (Fig. 4 A). Intermediate valves broadly rectangular in shape, hardly beaked (Fig. 4 B and C), dorso-ventrally subcarinated, moderately elevated in frontal view, side slope slightly convex (Fig. 4 J; elevation ratio of 0.43 in 4 th valve); anterior margin nearly straight to slightly convex, except for 2 nd valve (Fig. 4 B; triangular with rounded angle); lateral margins rounded; posterior margin straight; tegmentum in central area (ca) with low oval granules, arranged in quincunx or zig-zag patterns, converging and weaker towards apex (Fig. 4 I); lateral area (la) somewhat raised, sculpted with 4–5 faint radial riblets (Fig. 4 B and C). Tail valve almost semicircular, as wide as head valve; anterior margin convex (Fig. 4 D); mucro (m) subcentral, not projecting; sculpture of antemucronal area (ama) like central area of intermediate valves; postmucronal area (pma) sculpted similarly to head valve, with more pronounced radial ribs; postmucronal slope (pms) straight (Fig. 4 K). Articulamentum light greenish-blue, generally red violet in centre. Apophyses (ap; sutural laminae) short, rounded-angled subtrapezoid in shape, except for that of 2 nd valve, which is triangular; jugal lamina (jl) vert short; jugal sinus (js) shallow, about one-fourth width of valves, almost straight; insertion plate (ip) short, teeth (t) relatively smooth; slit formula 10 / 1 / 10, slit rays (slr) faint (Fig. 4 E – H). Eaves (e) narrow, solid (Fig. 4 J).

Girdle: Perinotum scales (ps: L 114.8–192.5 μm, W 146.7–232.7 μm) large, oval, slightly curved, imbricating, with faint concentric lines and indistinct scratches towards apex, parallel to outer margin (Fig. 7 E and F); peripheral scales of perinotum (pps: L 59.6–73.7 μm, W 64.7–97.2 μm) smaller and narrower than perinotum scales (Fig. 7 E, G); marginal spicules with three types: large one (lmsp: L 93.6 μm, W 20.7 μm) flat-ovate, narrowing towards tip, with fine feather-like grooves, middle one (mmsp: L 50.1 μm, W 11 μm) long, smooth, slightly curved rod-shaped and small one (smsp: L 17.8–26.4 μm, W 6.7–11.1 μm) very short, obese spheroidal (Fig. 7 E, G); hyponotum scales (hs: L 71.2 μm, W 18.5 μm) hyaline, smooth, narrow, oblong, overlapped (Fig. 7 H).

Radula: Radula symmetrical rows (Fig. 8 B). Central tooth (c) narrow, blade wide, bent forward; centro-lateral teeth (cl) wing-like shape, each blade inwardly convex; head (h) of major lateral teeth (mlt) bicuspid, cuspid short, rounded-angled, inner one longer than outer one; petaloid process (pp; wing) small rectangular; major uncinus teeth (mu) tall, curving inwards with broad spatula-like tip; marginal teeth (im, mm, om) flat, with outer one largest.

Distribution

Australia, China, Hong Kong, Indonesia, Japan, Philippines, Taiwan, Vietnam and Korea.

Type locality

Japan: Oushima (Amami Oshima, Kagoshima Prefecture).

Taxon discussion

This species is considered taxonomically challenging due to its extremely high morphological variation, as well as recently discovered cryptic species. Recent studies, based on a combination of morphological and molecular analyses, have uncovered two cryptic species ( Owada 2016, Owada 2018): I. manazuruensis and I. hayamii . They show very similar morphology to I. comptus , but are distinguished by the microstructure of the central area in the intermediate valves and the size of the girdle scales ( Owada 2016, Owada 2018). In I. comptus and I. hayamii , the central area of the intermediate valves is covered with granules arranged in quincunx or zig-zag patterns, whereas I. manazuruensis shows an almost smooth surface in this area. Furthermore, the perinotum scales of I. comptus are similar in size to I. manazuruensis (300–400 μm), but larger than I. hayamii (150–200 μm). This species shows a moderate within-species sequence divergence of the mtDNA cox 1, with a maximum divergence of 1.28 %, but relatively high sequence divergence from their congeneric species compared in this study, ranging from 11.31 % ( I. poppei ) to 16.70 % ( I. hakodadensis ) (Table 3 ).

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 4. Valves of I. comptus from Jeju (NIBR voucher specimen no. NIBRIV 0000863098). 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.