Ischnochiton hayamii Owada, 2018

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 hayamii Owada, 2018

Ischnochiton hayamii Owada (2018): 287, figs 2 A – F, 4, 7 A.

Materials

Type status: Other material. Occurrence: individualCount: 2; occurrenceID: 5C753217-14FB-5D05-9BCF-8E0933B7989D; Taxon: scientificName: Ischnochiton hayamii ; Location: country: Korea; locality: Sinam-ri, Seosaeng-myeon, Ulju-gun, Ulsan-si ; verbatimCoordinates: 35°20'16.35"N, 129°19'10.12"E; Event: eventDate: 24 Nov 2016

Description

Body oval-shaped, small to medium in size (Fig. 2 N; in examined material, BL 15.28 mm, BW 9.04 mm). Valves dark olive-green in colour, with small spots or large blotches of variable colours; cream, yellow, pink and brown. Girdle rather narrow, alternating with transverse bands of yellowish-brown and light yellow. Gills arrangement adanal and holobranchial on both sides with interspace (Fig. 2 O).

Valves: Head valve semicircular in shape, tegmentum almost smooth with faint growth line; anterior margin round; posterior margin widely V-shaped (Fig. 6 A). Intermediate valves broadly rectangular in shape, hardly beaked (Fig. 6 B and C). Intermediate valves dorso-ventrally carinated, moderately elevated in frontal view and side slope nearly straight (Fig. 6 J; elevation ratio of 0.4 in 4 th valve); anterior margin slightly convex, except for 2 nd valve (Fig. 6 B; more convex than other intermediate valves, even appearing triangular); lateral margins somewhat round; posterior margin almost straight; tegmentum of central area (ca) densely arranged minute granules in quincunx or zig-zag patterns (Fig. 6 I); lateral area (la) hardly raised, almost smooth like head valve (Fig. 6 B and C). Tail valve semicircular, as wide as head valve; anterior margin straight (Fig. 6 D); mucro (m) subcentral, slightly elevated; sculpture of antemucronal area (ama) same as central area of intermediate valves; postmucronal area (pma) nearly smooth such as head valve; postmucronal slope (pms) concave (Fig. 6 K). Articulamentum light blue, central part of articulamentum red violet in colour. Apophyses (ap; sutural laminae) rectangular in shape, short, fragile and separated with very short jugal lamina (jl); jugal sinus (js) shallow, about one-third of tegmentum width; insertion plate (ip) teeth (t) uneven in size; slit formula 10 / 1 / 10, slit rays (slr) fine, but relatively distinct (Fig. 6 E – H). Eaves (e) very narrow, solid (Fig. 6 J).

Girdle: Perinotum covered with flat, oval, slightly bending, nearly smooth and overlapping scales (Fig. 7 M, N; ps: L 108.2–157.6 μm, W 152.6–184.8 μm), scales arranged parallel to margin; peripheral scales of perinotum (pps: L 18.8–59.8 μm, W 79.5–92.9 μm) much smaller than perinotum scales, with 8–15 fine, flat longitudinal ribs (Fig. 7 M – O); marginal spicules with three types: large one (lmsp: L 77.7–95.6 μm, W 23–27.34 μm) long, flat-ovate, narrower to tip, obtuse, with 5–7 weak longitudinal ribs; middle one (mmsp: L 97.7–100.9 μm, W 8.8–11.7 μm) long, slender, smooth, blunt rod-shaped; small one (smsp: L 18.3–21.6 μm, W 14.7–15.3 μm) very short, obtuse with strong radial ribs (Fig. 7 M and O); hyponotum covered with hyaline, smooth, oblong and overlapping scales (Fig. 7 P; hs: L 70.6–75.6 μm, W 11.3–17.5 μm).

Radula: Radula symmetrical rows with 17 teeth per transverse row (Fig. 8 D). Central tooth (c) narrow oblong shape with forward bent blade; each centro-lateral tooth (cl) taller than central tooth, with wide inwardly convex cuspid; head (h) of major lateral teeth (mlt) bicuspid, inner cuspid rounded, outer one shorter and more angled than inner one; petaloid process (pp; wing) near base of major lateral tooth, blunt rod-shape, protruding slightly more than cuspids of major lateral tooth directed towards the centre; major uncinus teeth (mu) tall, slender, curving inwards with round spoon-like tip; marginal teeth (im, mm, om) flat, increasing size from inner to outer teeth.

Distribution

Japan (Zushi, Shimoda, and Hakodate) and Korea (Ulsan).

Type locality

Japan: Zushi, Kanagawa Prefecture.

Taxon discussion

Previously, three Ischnochiton species have been reported in Korea ( National list of species of Korea 2022): Ischnochiton boninensis , Ischnochiton comptus and Ischnochiton hakodadensis . I. boninensis and I. comptus are very similar in overall morphology and typically co-occur in sympatric regions in intertidal and subtidal habitats ( Taki 1938). Owada (2018) noted that I. hayamii shares morphological similarities with these species in their overall appearance, moderated elevation and sculptures of the central area in the intermediate valves. Nevertheless, I. hayamii is distinguished from the other three Korean Ischnochiton species by their morphological differences in body size, back shape and sculptures of the lateral areas (see Table 2 for detailed comparison). Amongst the four Korean Ischnochiton species, I. hayamii is the smallest in adult body size (<15 mm in length), whereas the other three species typically have larger sizes ( I. boninensis and I. comptus range from 15–30 mm and I. hakodadensis is the largest species> 30 mm) ( Kaas and Van Belle 1990, Kaas and Van Belle 1994, Owada 2016, Owada 2018). The dorsal back shape of I. hayamii is carinated (Fig. 6 J), while it is rounded in I. boninensis (Fig. 3 J) and subcarinated in both I. comptus and I. hakodadensis (Fig. 4 J and Fig. 5 J) ( Pilsbry 1893, Kaas and Van Belle 1990, Kaas and Van Belle 1994, Owada 2018). In microstructures of the valves, the lateral areas are almost smooth with faint radial ribs in I. hayamii (Fig. 6 B and C), whereas the other three species possess 5–8 bifurcating radial ribs (Fig. 3 B, C, Fig. 4 B, C, Fig. 5 B and C) ( Taki 1938, Kaas and Van Belle 1990, Kaas and Van Belle 1994, Owada 2016, Owada 2018).

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.