Leptochiton taiwanensis, Sirenko, 2018

Sirenko, Boris, 2018, Taiwanese deep-water chitons (Mollusca: Polyplacophora) and survey of chiton fauna of Taiwan, Zootaxa 4422 (3), pp. 301-344 : 316-322

Leptochiton taiwanensis n. sp.

( Figs 19–22 )

Type material. Holotype (MNHN IM-2000-33787) now disarticulated consisting of SEM stub with valves I + VIII, parts of intermediate valves, part of perinotum and radula, mount of part of perinotum, radula and vial with other valves.

Type locality. Taiwan, Bashi channel, 22º01.9’N, 120º36.4’E, 246 m (N/O Fishery Researcher 1, “ TAIWAN 2000”, stn DW34, 31.07.2000).

Etymology. Named after Taiwan.

Material examined. Only the holotype is known.

Distribution. Near Taiwan, 264 m.

Diagnosis. Animal small, elevated, valves rounded, mucro of tail valve posterior, antemucronal area

noticeably convex, postmucronal slope sharply concave: tegmentum sculptured by small, low granules, arranged mainly in quincunx, but in jugal area of intermediate valves and in other areas of valves the granules tend to group in radial rows, each granule with one megalaesthete and 6 micraesthetes; dorsal scales wide, sculptured with 10–13 clear riblets on one side, marginal needles with 12 clear riblets around, major lateral tooth of radula with unicuspid dental cup, nine gills on each side.

Description. Holotype (BL 5.5 mm) elongate oval, shell damaged, evenly rounded, moderately elevated, not beaked, tegmentum white in colour.

Head valve semicircular, sculptured by small granules arranged mainly in quincunx, but tend to group in radial rows; intermediate valves rectangular, anterior margin slightly convex, posterior margin straight, lateral area not raised, sculptured like head valve, central area sculptured by small, low granules distributed quincuncially, but in jugal area tend to group in longitudinal rows; tail valve broader than head valve, mucro posterior, antemucronal area noticeably convex, postmucronal slope sharply concave, antemucronal area sculptured like central area of intermediate valves, postmucronal area sculptured like head valve. Each granule contains one megalaesthete and six micraesthetes around it.

Articulamentum moderately developed, white, apophyses small, widely separated, trapezoidal.

Girdle narrow, dorsally covered with imbricated, wide, flattened, obtuse pointed, slightly curved scales (76 x 48 µm) sculptured with 14–16 ribs and interspersed with, ribbed (13–14 ribs) needles (100 x 21 µm). Intersegmental areas with longer scales (140 x 43 µm) of the same type as main dorsal armature. Marginal needles of the same type as sutural ones. Ventral side covered with imbricated, flat, elongate, pointed scales (50 x 20 µm). One row of scales near outer margin occupied with larger, smooth, obtusely pointed scales (77 x 25 µm).

Nine gills on each side, extending from valve VI to near anus.

Radula 2.4 mm long, with 18 transverse rows of mature teeth, central teeth with wide blade, major lateral teeth with unidentate sharply pointed head.

Remarks. This new species belongs to the above mentioned Leptochiton belknapi group ( Sirenko 2015) and has strong similarities with several members of that group, namely: Leptochiton ater , L. fijiensis , L. bergenhayni and L. japonicus . Leptochiton taiwanensis n. sp. differs from these above mentioned species in having a tendency toward an arrangement of the granules in longitudinal rows in the jugal area of intermediate valves and in radial rows in other areas (vs. quincuncially, without this tendency to form rows in the other species). Leptochiton taiwanensis n. sp. is most similar to L. ater in features of radula, aesthete group and shape of tail valve, but differs from the latter in having wide dorsal girdle scales with 10–13 clear riblets (vs. narrow dorsal scales with 4–6 riblets in L. ater ).

The new species differs from L. bergenhayni by having seven aesthetes in each granule (vs. 9 aesthetes in L. bergenhayeni ) and posterior mucro (vs. central mucro in L. bergenhayni ).

Leptochiton taiwanensis differs from L. fijiensis and L. japonicus by having seven aesthetes in granule (vs. 11–

13 aesthetes in L. fijiensis and 5 in L. japonicus ), and 10–13 riblets on dorsal scales (vs. 6–7 riblets in L. fijiensis and 7 in L. japonicus ).

Figures

FIGURE 19. Leptосhitоn taiwanensis n. sp., holotype, Таiwаn, stn DV34, ВL 5.5 mm: А. Vаlve I, dorsаl view; В. Hаlf of intermediаte vаlve, dorsаl view; C. Vаlve VIII, dorsаl view; D. Intermediаte vаlve, detаil of tegmentum in centrаl аreа; E. Intermediаte vаlve, detаil of tegmentum in lаterаl аreа; F. Vаlve VIII, lаterаl view.

FIGURE 20. Leptосhitоn taiwanensis n. sp., holotype, Таiwаn, stn DV34, ВL 5.5 mm: А-C. Dorsаl scаles, mаrginаl needles аnd ventrаl scаles; D. Dorsаl scаles in suture.

FIGURE 21. Leptосhitоn taiwanensis n. sp., holotype, Таiwаn, stn DV34, ВL 5.5 mm: А. Vаlve VIII, detаil of tegmentum in аntemucronаl аreа; В. Rаdulа.

FIGURE 22. Leptосhitоn taiwanensis n. sp., holotype, Таiwаn, stn DV34, ВL 5.5 mm: А. Suturаl scаle; В. Dorsаl needles; C. Dorsаl scаle; D. Ventrаl scаle neаr mаrgin; E. Ventrаl scаle in centrаl pаrt; F. Heаd of mаjor lаterаl tooth of rаdulа; G. Centrаl аnd lаterаl teeth of rаdulа; H. Аesthete group in centrаl аreа. Scаle bаr 100 µm (А–G).