Ischnochiton hakodadensis P. P. Carpenter, 1893

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 hakodadensis P. P. Carpenter, 1893

Ischnochiton (Ischnoradsia) hakodadensis Carpenter in Pilsbry (1893): 147, pl. 19, figs. 64–66; Pilsbry (1895): 114; Taki (1962): 44; Taki (1964 b): 409; Kaas and Van Belle (1980): 57; Yum (1988): 21, 22, pl. 2, fig. 1, pl. 9, pl. 23, fig. 3, 4, pl. 28, fig. 5.

Ischnoradsia hakodadensis : Taki (1938): 373 –375, pl. 15, fig. 8, pl. 26, figs. 1–5, pl. 27, figs. 1–5, pl. 28, figs. 19–20.

Ischnochiton (Ischnochiton) hakodadensis : Taki (1962): 43; Kaas and Van Belle (1990): 180 –182, fig. 81, map. 31; Dell'Angelo et al. (1990): 34, 35; Higo et al. (1999): 26; Lee and Min (2002): 94; Min et al. (2004): 70, 71.

Ischnochiton (Ischnoradsia) hakodatensis [sic]: Higo (1973): 6; Okada et al. (1981): 8; Higo and Goto (1993): 4.

Ischnochiton hakodadensis : Thiele (1909): 111, 112, taf. 8, fig. 44; Jakovleva (1952): 96, 97, fig. 47, pl. 8, fig. 3; Saito (1995): 103; Saito (2000): 12, 13, pl. 6, fig. 17; Saito (2017): 732, pl. 5, fig. 4; Slieker (2000): 98, 99, pl. 37, fig. 12; Qi (2004): 5, pl. 002 E; Sirenko (2013): 148; Owada (2018): 285 –287, figs. 2 G, 3, 7 B.

Materials

Type status: Other material. Occurrence: individualCount: 6; occurrenceID: D3A30D7C-BDDB-582F-8CA6-CC8D5BE4CF67; Taxon: scientificName: Ischnochiton hakodadensis ; 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: 6CB3AB45-7BDB-55F7-9A0E-21E1F02E87C5; Taxon: scientificName: Ischnochiton hakodadensis ; Location: country: Korea; locality: Buk-ri, Deokjeok-myeon, Ongjin-gun, Incheon-si ; verbatimCoordinates: 37°15'53.09"N, 126°06'00.36"E; Event: eventDate: 18 Apr 2018

Type status: Other material. Occurrence: individualCount: 3; occurrenceID: CBF6FEED-0921-54F9-AA2B-F497D6CA6F3D; Taxon: scientificName: Ischnochiton hakodadensis ; Location: country: Korea; locality: Ayajin-ri, Toseong-myeon, Goseong-gun, Gangwon-do ; locationRemarks: collected by snorkeling; verbatimCoordinates: 38°16'13.35"N, 128°33'28.75"E; Event: eventDate: 14 May 2018

Type status: Other material. Occurrence: individualCount: 4; occurrenceID: 3E051C4B-8B3C-55FC-B092-5897991E6801; Taxon: scientificName: Ischnochiton hakodadensis ; Location: country: Korea; locality: Ayajin-ri, Toseong-myeon, Goseong-gun, Gangwon-do ; locationRemarks: collected by snorkeling; verbatimCoordinates: 38°16'13.35"N, 128°33'28.75"E; Event: eventDate: 22 May 2019

Description

Body shape oval, rarely over 30 mm in length (Fig. 2 K and M; in examined materials, BL 18.63–25.01 mm, BW 10.92–15.66 mm). Valves mostly dark green or greyish-brown, even reddish-brown in colour, with cream, yellow, blackish-brown stripes or blotches of various size. Girdle rather narrow, with alternating light and dark transverse bands. Gills arrangement holobranchial and adanal in both sides with interspace (Fig. 2 L).

Valves: Head valve semicircular, tegmentum sculpted with ca. 65 fine radial riblets, cut into several distinct concentric growth lines; anterior margin round; posterior margin widely V-shaped; (Fig. 5 A). Intermediate valves broadly rectangular in shape, not beaked (Fig. 5 B and C), dorso-ventrally subcarinated, moderately elevated in frontal view, side slope convex (Fig. 5 J; elevation ration of 0.39 in 4 th valve); anterior margin straight, except for 2 nd valve (Fig. 5 B; convex, nearly triangular); lateral margins almost rounded; posterior margin straight; tegmentum in central area (ca) almost smooth with minute, low granules arranged in quincunx or zig-zag patterns (Fig. 5 I); jugal area (ja) somewhat raised, separated from pleural area (pa) by slightly different elevation; lateral area (la) slightly elevated, sculpted with 6–8 fine radial riblets; concentric growth lines several, distinct across entire tegmentum (Fig. 5 B and C). Tail valve almost semicircular, slightly narrower than head valve; anterior margin nearly straight in centre, convex on the both side (Fig. 5 D); mucro (m) antemedian, not protruding; sculpture of antemucronal area (ama) like central area of intermediate valves; postmucronal area (pma) sculpted similarly to head valve; postmucronal slope (pms) steep, straight (Fig. 5 K). Articulamentum light blue. Apophyses (ap; sutural laminae) short, rounded triangle or subtrapezoid in shape; jugal lamina (jl) very short; jugal sinus (js) shallow, about one-fourth width of valves, straight; insertion plate (ip) short, teeth (t) uneven in size, slightly roughened; slit formula 15 / 2–3 / 17, slit rays (slr) clearly marked (Fig. 5 E – H). Eaves (e) very narrow, solid (Fig. 5 J).

Girdle: Perinotum scales (ps: L 64–122 μm, W 124.9–203.5 μm) small, slightly convex, imbricating, nearly smooth or with faint longitudinal ribs, arranged diagonally to outer margin (Fig. 7 I – K); marginal spicules with three types: large one (lmsp: L 100.5–116.5 μm, W 32.9–40.3 μm) flat-triangular, blunt tip, with fine feather-like grooves, middle one (mmsp: L 63.4–77.4 μm, W 10.5–11.4 μm) slender, smooth, slightly curved rod-shaped and small one (smsp: L 37.2–49.6 μm, W 11.7–14.8 μm) very short, obese rod-shaped with radial grooves on tip (Fig. 7 I, K); hyponotum scales (hs: L 80.7–89.5 μm, W 17–23.2 μm) hyaline, smooth, elongated, rounded-edged rectangular, overlapped, arranged radially (Fig. 7 L).

Radula: Radula symmetrical rows (Fig. 8 C). Central tooth (c) small, narrow, blade slightly bent forward; centro-lateral teeth (cl) taller than central tooth, widening towards tip; head (h) of major lateral teeth (mlt) bicuspid, cuspid short, blunted, outer one shorter, pointed than inner one; petaloid process (pp; wing) short, rectangular with inwardly concave tip; major uncinus teeth (mu) slender with round, spoon-like head; marginal teeth (im, mm, om) flat, widening towards outer.

Distribution

China, Japan, Russia (Vladivostok) and Korea.

Type locality

Japan: Hakodadi (Hakodate, Hokkaido).

Taxon discussion

This species is relatively large in body size (> 30 mm) and easily distinguished from other congeneric species by the following characteristics. I. hakodadensis has 2–3 slits in the intermediate valves (Fig. 5 F and G), whereas other Ischnochiton species have only one slit (Fig. 3 F, G, Fig. 4 F, G, Fig. 6 F and G; Owada (2018)). Additionally, the perinotum scales are arranged diagonally to the outer margin in I. hakodadensis (Fig. 7 I), while they are arranged parallel in other Ischnochiton species (Fig. 7 A, E and M). It is noteworthy that these two morphological features distinguishing I. hakodadensis from other congeneric species are also present in many other Lepidozona species as well. Moreover, previous molecular phylogenetic analysis using four gene regions (COI, 16 S, 18 S and 28 S) revealed that I. hakodadensis was not monophyletic, with some other Ischnochiton species grouped in a separate branch ( Owada 2018). In contrast to the very low individual sequence variation (a maximum of 0.90 %), this species shows very high genetic divergence from other congeneric species, ranging from 15.80 % to 19.93 % (Table 3 ). These findings, based on both morphological and molecular evidence, highlight the need for further studies to clarify the taxonomic position of this species within the family Ischnochitonidae . Furthermore, Owada (2018) described the accessory process of major lateral teeth in the radula, but these characters were not found in Korean I. hakodadensis specimens (Fig. 8 C), requiring further study to confirm this discrepancy.

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 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 5. Valves of I. hakodadensis from Goseong (NIBR voucher specimen no. NIBRIV 0000863046). 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; ja, jugal area; jl, jugal lamina; js, jugal sinus; la, lateral area; m, mucro; pa, pleural area; 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 6. Valves of I. hayamii from Ulsan (NIBR voucher specimen no. NIBRIV 0000863103). 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 using scanning electron microscope. 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 = 2 mm, I = 200 μm, K = 1 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.