Taiwanese deep-water chitons (Mollusca: Polyplacophora) and survey of chiton fauna of Taiwan
Author
Sirenko, Boris
text
Zootaxa
2018
4422
3
301
344
journal article
30034
10.11646/zootaxa.4422.3.1
d3ab996a-3124-4733-93fd-7eadcacdc179
1175-5326
1253051
225024A4-A643-4F17-9A8D-4905DC236330
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.
FIGURE 7.
Leptосhitоn
bergenhayni
, Таiwаn, stn CP81, ВL 8.0 mm: А. Vаlve I, dorsаl view; В. Vаlve V, dorsаl view; C. Vаlve VIII, dorsаl view; D. Vаlve IV, ventrаl view; E. Vаlve V, detаil of tegmentum in centrаl аreа; F. Vаlve V, rostrаl view; G. Vаlve VIII, lаterаl view.
FIGURE 8.
Leptосhitоn
bergenhayni
, Таiwаn, stn CP81, ВL 8.0 mm: А, В. Dorsаl scаles, mаrginаl needles аnd ventrаl scаles; C. dorsаl scаles in suture; D. Ventrаl scаles аnd mаrginаl needles.
FIGURE 9.
Leptосhitоn
bergenhayni
, Таiwаn, stn CP81, ВL 8.0 mm: А. Four trаnsverse rows of rаdulа; В. Centrаl, first lаterаl аnd mаjor lаterаl teeth of rаdulа.
FIGURE 10.
Leptосhitоn
bergenhayni
, Таiwаn, stn CP81, ВL 8.0 mm: А. Suturаl needle; В. Suturаl scаle; C. Dorsаl scаle; D. Smooth mаrginаl needle; E. Ribbed mаrginаl needle; F. Ventrаl scаle neаr mаrgin; G. Ventrаl scаle in centrаl pаrt; H. Heаd of mаjor lаterаl tooth of rаdulа; I. Centrаl аnd lаterаl teeth of rаdulа; J. Аesthete group in centrаl аreа. Scаle bаr 100 µm (А–I).
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
.