Leptochiton bergenhayni Saito 2011
Creators: name: Sirenko, Boris
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Polyplacophora
Neoloricata
Leptochitonidae
Leptochiton
Leptochiton bergenhayni

description: Leptochiton bergenhayni Saito, 2011
(Figs 7–10, 36G, H)
Leptосhitоn bergenhayni Sаito 2011: 68, figs 2E–F, 4.
Type material. Holotype (NMNS-Mo 77251).
Type locality. Omurodashi Bank, 34°29.8'N, 139°29.3'E–34°30.1'N, 139°29.4'E, 92–95 m.
Material examined. Taiwan, off Tashi, Fishing Boat Chung Tung Long N 26, stn CP81, 24º50.5’N, 121º59.5’E, 205 m, 1 spm, BL 7.5 mm, 0 8.05.2001.
Distribution. Near Japan (Izu Islands and Boso Peninsula) (71–105 m: Saito 2011) and near Taiwan (205 m). The species was found near Taiwan for the first time and this find extends the distribution and depth of this species considerably.The specimen from Taiwan has some differences in color and girdle armature and I decided to give description of it.
Description. Specimen (BL 7.5 mm) elongate oval, shell evenly rounded, moderately elevated (elevation ratio 0.39), tegmentum white in color.
Head valve semicircular, noticeably wider than tail valve, intermediate valve broadly rectangular, two and a half times wider than long, anterior margin slightly concave in jugal area, posterior margin straight, side margin evenly rounded, lateral area not raised, tail valve semicircular, mucro central, postmucronal slope slightly concave.
Tegmentum uniformly sculptured with rounded or oval granules arranged quincuncially, each granule with one megalaesthete and 8 micraesthetes.
Articulamentum moderately developed, apophyses small, widely separated, subtriangular in valves II-VII, more or less trapezoidal in tail valve.
Girdle rather narrow, ca. 0.9 mm wide near valve V, dorsally covered with wide, flattened, slightly curved scales (70 x 42 µm) sculptured with 10–13 ribs. Intersegmental areas with longer scales (90 x 35 µm) of the same type as main dorsal armature, and long smooth needles (150 x 17 µm). Marginal needles of two kinds: long, smooth (213 x 17 µm), and flattened, ribbed on one side needles (100 x 21 µm). Ventral side covered with imbricated, flat, elongate scales (50 x 20 µm), one row near outer margin occupied with larger scales (56 x 30 µm) with two-four riblets in upper half of ventral side of scale.
Ten gills on each side, extending from valve VI to anus.
Radula 3.0 mm long, with 23 transverse rows of mature teeth, rather wide with wide blade, major lateral teeth with unidentate, sharply pointed cusp.
Remarks. The specimen from Taiwan differs from the type material of L. bergenhayni by having a white tegmentum (vs. beige with irregular white maculation in types of L. bergenhayni), long smooth marginal needles (vs. only grooved marginal needles in types of L. bergenhayni), ventral scales near margin with 2–4 ribs in distal part (vs. keeled at distal half in types of L. bergenhayni). Taking into account the difference in habitat depth and distance between the type locality (Japan) and the Taiwan population, I consider these morphological differences within the range of intraspecific variation for L. bergenhayni.
Leptochiton bergenhayni belongs to the group of Leptochiton belknapi Dall, 1878 as defined by Sirenko (2015). It is similar to the species Leptochiton ater Saito, 1997, L. japonicus Thiele, 1909, L. fijiensis Sirenko, 2016 and L. taiwanensis n. sp. Leptochiton bergenhayni differs from L. ater, L. japonicus and L. fijiensis by having nine aesthetes on each granule (vs. 5–7 aesthetes in L. ater, 5 in L. japonicus and 11–13 in L. fijiensis) and 10–12 ribs on dorsal scales (vs. 4–6 ribs in L. ater, 7 ribs in L. japonicus, 6–7 in L. fijiensis). Moreover L. bergenhayni differs from L. ater and L. fijiensis by having central mucro (posterior in L. ater, anterior in L. fijiensis). L. bergenhayni also differs from L. japonicus by having rounded intermediate valve (vs subcarinated in L. japonicus). For the differences separating L. bergenhayni from L. taiwanensis n. sp. see below under Remarks for L. taiwanensis n. sp.
description: Published as part of Sirenko, Boris, 2018, Taiwanese deep-water chitons (Mollusca: Polyplacophora) and survey of chiton fauna of Taiwan, pp. 301-344 in Zootaxa 4422 (3) on pages 308-312, DOI: 10.11646/zootaxa.4422.3.1, http://zenodo.org/record/1253051