Leptochiton ibanezi, Sirenko, Boris & Sellanes, Javier, 2016

Sirenko, Boris & Sellanes, Javier, 2016, Update of the genus Leptochiton (Mollusca: Polyplacophora) in Chilean deep waters: three new reports and description of two new species, Zootaxa 4173 (3), pp. 259-279 : 271-274

Leptochiton ibanezi sp. nov.

( Figs 1 G, H, 12–14)

LSID [urn:lsid:zoobank.org:act:E2ED20F2-AF06-4041-A114-2DA955FD67AC] Type material. Holotype (MNHNCL 400187), now disarticulated, consisting of SEM stub of valves I, V, VIII, part of perinotum and radula, mount of part of perinotum and radula and vial with other valves, and two complete paratypes (ZISP 2265, MNHNCL 400188).

Type locality. Chile, 36.0023– 36.0058°S, 73.3841 –73.3706°W, 922–1013 m depth (RV AGOR Vidal Gormáz, VG 07-07, AGT-08).

Etymology. Named after our friend Christian M. Ibáñez, Universidad Andrés Bello, Chile, who made a major contribution to the knowledge of the biogeography of Chilean mollusks including chitons.

Material examined. Off Chile, RV AGOR Vidal Gormáz, VG 07-07, AGT-10, 36.2210– 36.2218°S, 73.4310 –73.4285°W. 764–843 m, 5 spms (SCBUCN 4141), BL— 15–25 mm, 02.10.2007; VG 07-07, AGT-08, 36.0023–36.0058°S, 73.3841–73.3706°W, 922–1013 m depth, holotype, BL— 21 mm, 1 paratype (MNHNCL 400190) BL— 25 mm and 1 paratype (ZISP 2265), BL— 25 mm, 07.10.2007; VG 07-08, AGT-13, 36.2179–36.2237°S, 73.4338–73.4266°W, 737–855 m depth, 2 spms (SCBUCN 4142), BL— 12–25 mm, 0 7.10.2007.

Distribution. Off Chile, 36.0– 36.2°S, 737–1013 m depth.

Diagnosis. Animal of moderate size up to 25 mm, valves highly elevated, subcarinated, not beaked. Intermediate valve short and wide, trapezoidal, anterior margin of intermediate valves splayed laterally, posterior margin straight, lateral areas slightly raised. Tail valve wider than head valve, with subcentral mucro. Tegmentum sculptured with weakly raised, round granules arranged in longitudinal rows in central areas of intermediate valves and antemucronal area of tail valve and in radial rows in other areas. Each granule with one megalaesthete and two micraesthetes in front. Girdle dorsally covered with narrow, sharply pointed scales with two ribs. Major lateral teeth with bidentate cusp, inner denticle much smaller then outer one. Twelve gills per side, arranged from valve VI to anus.

Description. Holotype 21.0 x 10.1 mm. Valves elevated (elevation ratio 0.49 in valve V), subcarinated, not beaked. Color of tegmentum white. Head valve semicircular. Intermediate valves short, wide (ratio of width to length of valve V 2.5), trapezoidal, anterior margin splayed laterally in pleural areas, lateral margins rounded, posterior margin straight, lateral areas weakly raised. Tail valve slightly wider than head valve, antemucronal slope convex, postmucronal slope concave, mucro subcentral.

Tegmentum sculptured with weakly raised round granules arranged in longitudinal rows on central areas of intermediate valves (about 70 rows on valve V) and antemucronal area of tail valve, and in radial rows on other areas. Each granule with one megalaesthete and two micraesthetes in the front.

Articulamentum well developed, apophyses small, jugal sinus rather narrow, ratio width of jugal sinus to width of apophyses 1.28 in valve V.

Girdle narrow (about 1.1 mm wide near valve V), dorsally, covered with sharply pointed scales (63– 68 x 20–22 µm) with two ribs, and scattered long, smooth needles (100–200 x 20 µm). Intersegmental area with long needles (249 x 20 µm). Marginal needles same shape but shorter (120 x 15 µm). Ventrally girdle covered with elongate, pointed, smooth scales (85–104 x 20–22 µm).

Radula 6 mm long with 43 transverse rows of mature teeth. Central teeth long and narrow, first lateral tooth narrow, bearing an elongate exteriorly curved blade, major lateral tooth with bidentate cusp, inner denticle much smaller than outer one, third uncinal tooth long, lanceolate.

Twelve gills per side arranged from valve VI to anus. Gonopore between tenth and eleven gills and nephropore between ninth and tenth gills counted from anus. Gut content was composed of detritus and sand.

Remarks. Leptochiton ibanezi sp. nov. belongs to the L. sykesi (G. B. Sowerby III, 1903) group, defined by the similar features of shell, girdle and radula, and is comparable to this species by having a laterally splayed anterior margin of intermediate valves. The new species differs from L. sykesi by having 3 aesthetes in the aesthete group (vs. 5 aesthetes in L. sykesi ), 2 ribs on dorsal scales (vs. 3 ribs in L. sykesi ) and radial rows of granules in lateral areas of intermediate valves and postmucronal area of tail valve (vs. granules arranged in a random manner in L. sykesi ). Leptochiton ibanezi sp. nov. is also similar to L. batialis Sirenko, 1979 and L. laurae . It differs from L. batialis in having trapezoidal shaped intermediate valves (vs. rectangular in L. batialis ), lateral and postmucronal areas with radial ribs of granules (vs. in a random manner in L. batialis ), jugal sinus narrower than the apophyses on valve VIII (vs. jugal sinus wider than the apophyses in L. batialis ), dorsal scales with 2 ribs (vs. 1 rib in L. batialis ). Leptochiton ibanezi sp. nov. differs from L. laurae in having wider intermediate valves (ratio of width/length of valve V 2.5) (vs. 1.9 in L. laurae ) and a trapezoidal shape of the intermediate valves (vs. rectangular in L. laurae ).

Figures

FIGURE 1. Complete specimens of Leptochiton belknapi Dall, 1878. BL— 23 mm, RV Melville, st. INSPIRE, AGT- 3 _ 533, 724 m, SCBUCN 4136 (A, B), Leptochiton sigwartae Sirenko, 2015. BL— 33 mm, RV Sonne, st. SO- 156. 7176 - 5, 502 m, ZISP 2275 (C, D), Leptochiton laurae Schwabe & Sellanes, 2010. BL— 11,5 mm, RV Melville, st. INSPIRE, AGT- 2, 583. 497 – 574 m, ZISP 2276 (E, F), Leptochiton ibanezi sp. nov., holotype, BL— 21 mm, MNHNCL 400187 (G, H). A, C, E, G. Dorsal view; B, D, F, H. Lateral view. Scale bars 2 mm.