Connexochiton costatus Sirenko 2021, sp. n.
Creators: name: Sirenko, Boris
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Polyplacophora
Chitonida
Ischnochitonidae
Connexochiton
Connexochiton costatus

description: Connexochiton costatus sp. n.
(Figs. 5–8)
Type material. Holotype (MNHN-IM-2013-67045) now disarticulated, consisting of SEM stub of valves I, II, V, VIII, part of perinotum and radula, mount of part of perinotum and radula and vial with other valves, 4 paratypes (MNHM-IM-2013-49562, MNHN-IM-2013-86086, MNHN-IM-2013-86087, MNHN-IM-2013-86088) and 1 paratype (ZISP 2380).
Type locality. Philippines, Balicasag Island, 9°31.2’N 123°40.7’E, 80–90 m.
Etymology. Latin for ribbed, in reference to the radial ribs on the head valve.
Material examined. Philippines, Balicasag Island, 9°30.9’N 123°40.8’E, 87–111 m, 4 paratypes (MNHN- IM-2013-49562, MNHN-IM-2013-86086, MNHN-IM-2013-86087, MNHN-IM-2013-86088) BL 2.5–3.5 mm, 1 paratype (ZISP 2380) BL 3.5 mm 26.10.2003; 9°31.2’N 123°40.7’E, 80–90 m, holotype (MNHN-IM-2013-67045) BL 4.0 mm, 02.07.2004; West Pamilacan Island, Cerve shoal, 9°29.7’N 123°50.2’E, 110–112 m, 2 spms (MNHN- IM-2013-49560), BL 2.0 mm, 06.07.2004.
Distribution. Philippines, 90– 111 m.
Diagnosis. Head valve with 9 low, wide radial ribs. Tegmentum evenly sculptured with flattened granules in quincuncial pattern, each granule with 9 pores of aesthetes. Pores of megalaesthetes 7 µm in diameter. Tail valve mucro anterior. Dorsal scales with 11–13 longitudinal ribs in distal half. Five gills per side. Major radular lateral teeth with unidentate sickle-shaped cusps.
Description. Chiton of small size, BL up to 4.0 mm, moderately raised (dorsal elevation 0.46 in valve V), back evenly rounded, valves not beaked, color of tegmentum white.
Head valve semicircular with nine low, wide radial ribs; posterior margin widely V-shaped, notched in the middle, noticeably larger than tail valve. Intermediate valves approximately of same length, rather narrow, trapezoidal with narrow, strongly raised lateral areas, anterior margin convex in valve II, almost straight in valves III–VII, curved inwardly towards the rounded sides, hind margin straight, with broken, somewhat swollen apices, lateral areas separated from the central area by diagonal depressions. Tail valve half elliptical, anterior margin straight with slightly protruding sides, mucro anterior, not projecting, anterior slope convex, posterior slope concave.
Tegmentum evenly sculptured with flattened granules in quincuncial pattern, each granule with 9 pores of aesthetes. Pores of megalaesthetes rounded, 7 µm in diameter, most other pores slit-like, 4–5 µm in width.
Articulamentum thin, apophyses short, trapezoidal, connected behind anterior tegmental margin, slit formula 10/1/8.
Girdle of moderate width, 0.3 mm long in holotype (BL 4.0 mm), covered with wide, bent, imbricating scales 50 x 70 µm, sculptured with 11–13 longitudinal ribs in distal half, top of scales rounded, some of these longitudinal ribs tend to form spherule on top of scale. Marginal spicules of two kinds: rare long, smooth needles on short bristle 100 x 8 μm and numerous flattened, sharply pointed spicules 60 x 20 μm with 5 longitudinal ribs on dorsal side. Two rows of ventral scales near margin 45 x 16 μm with 3–4 short ribs in upper half, other ventral scales rectangular, flat, smooth 40 x 15 μm.
Holotype has 5 gills arranged from valve VI to valve VIII on each side.
Radula of the holotype 1.1 mm long with 56 transverse rows of mature teeth. Central tooth slender, elongate, with a small rhomboid blade, longitudinal rib and slightly broadened base. First lateral tooth larger. Major lateral tooth with unicuspid and sickle-shaped head, dorsal part of the head with 2 shallow grooves.
Remarks. The paratype of Connexochiton costatus n. sp. (MNHN-IM-2013-49560) has slit formula 7/1/7. The new species differs from its congeners by having 9 radial ribs on the head valve and flattened granules of the tegmentum (vs. no ribs on head valve and convex granules in all other species of the genus).
description: Published as part of Sirenko, Boris, 2021, Composition of the genus Connexochiton Kaas, 1979 (Mollusca: Polyplacophora Ischnochitonidae), pp. 83-102 in Zootaxa 4950 (1) on pages 90-92, DOI: 10.11646/zootaxa.4950.1.4, http://zenodo.org/record/4643422