Hanleyella henrici, Sigwart & Chen, 2018

Sigwart, Julia D. & Chen, Chong, 2018, A new deep water chiton (Mollusca: Polyplacophora) from hydrothermal vent ecosystems in the Okinawa Trough, Japan, Zootaxa 4531 (3), pp. 430-436 : 431-433

Hanleyella henrici n. sp.

Figs. 1–3

Type material. Holotype: NSMT-Mo 79005, Aki site, Iheya North hydrothermal vent field (27°46.122’N 126°54.178’E), Okinawa Trough , 1080 m deep, taken by ROV Hyper-Dolphin during dive #1616 using a scoop on-board R/ V Kaiyo cruise KY14-01, 2014/i/25, fixed and stored in 99% ethanol. Paratype #1: NSMT-Mo 79006, Iheya North Original site, Iheya North hydrothermal vent field (27°47.240’N 126°53.906’E), Okinawa Trough , 950 m deep, taken by ROV Hyper-Dolphin during dive #1861 using a suction sampler on-board R/V Natsushima cruise NT15-13, 2015/viii/3, fixed and stored in 99% ethanol. NCBI GenBank accession: MH 349538 . Paratype #2: NSMT-Mo 79007, Fukai site ( Chen et al. 2017), Higashi-Ensei hydrothermal vent field (28°26.2197’N 128°11.3131’E), Okinawa Trough , 1178 m deep, taken by ROV KAIKO during dive #724 on-board R/ V Kairei cruise KR16-16, 2016/xii/4, fixed and stored in 99% ethanol. NCBI GenBank accession: MH 349539 .

Etymology. Named in honour of Henry Schwabe, who shares the Latin form of his name with his father Enrico.

Material examined. Known only from the type series.

Distribution. Known only from the localities of the type series; deep-sea hydrothermal vents of the Okinawa Trough.

Diagnosis. Valves moderately elevated, not beaked. Intermediate valves side margins rounded, anterior margins straight, posterior margins slightly convex, lateral areas slightly inflated. Tail valve mucro anterior of central, postmucronal slope slightly concave. Tegmentum with pronounced longitudinal ridges formed of fused flattened round granules in central areas, lateral areas with occasional strongly pronounced raised spherical granules. Aesthete caps not projecting. Girdle narrow, dorsally with ribbed bluntly pointed scales, ventrally with smooth flat scales. Gills seven per side. Radula major lateral teeth with tridentate cusps.

Description. Holotype 8.9 x 4.3 mm. Shell carinated, moderately elevated (elevation ratio 0.43 in valve II of holotype), valves not beaked. Colour of tegmentum white, in holotype valves and girdle covered dorsally with brown mineral deposits, pale newer growth visible on distal edges of valves.

Head valve slightly more than semicircular, slightly more than 10% wider than tail valve. Intermediate valves rectangular, lateral areas slightly inflated, anterior margins nearly straight, except margin of valve II convex, posterior margins slightly convex. Tail valve with mucro anterior of centre, anterior margin of jugal area straight except in valve II, postmucronal slope slightly concave.

Tegmentum of central areas and antemucronal area with elongate round granules (approx. 100 × 65–75 µm) fused to form pronounced longitunidal ribs, about 15 ribs per side in intermediate valves. Ribs becoming more irregular and closer set toward jugum; on distal pleural areas, ribs curving inward as they join lateral area. Lateral areas, head valve, and postmucronal area of tail valve sculpted with distinctive, highly raised irregularly arranged spherical granules (approx. diameter 100 µm). Some growth marks visible especially on the postmucronal area and head valve, and lateral areas continuing into central areas of intermediate valves.

Each granule with one megalaesthete (7 µm diameter) surrounded by 4–6 slightly smaller micraesthetes (4–5 µm), irregularly arranged. Single aesthete pores (7 µm diameter) arranged in spaces between spherical granules on lateral areas.

Articulamentum well developed, eaves of intermediate valves spongy and porous texture to jugal area and lateral area where tegmentum overhangs the primordium of an insertion plate; apophyses small, widely separated, anteriorly rounded with long straight slope to jugum.

Girdle narrow, dorsally covered in blunt scales with 4–5 ribs, scales 60 × 30 µm, longer toward valve interstices. Occasional marginal spicules, cylindrical, smooth, over 130 µm long. Ventrally, girdle covered in elongate, smooth, flat, bluntly pointed scales 60 × 24 µm, with four short ribs at tip on one side only.

Radula major lateral teeth flat and wide with tridentate heads, interior denticle slightly longer than the exterior denticle; outer denticle well formed but worn. Central tooth flat, with a short blade that forms a curled edge extending down both lateral edges of the tooth. First laterals short, pointed.

Gills seven per side, without interspace, extending posteriorly to the anus. Schwabe organ ( Sigwart et al. 2014) present under the corner of the mouth lappets, dark and triangular ( Fig 1A ).

Figures

FIGURE 1. Hanleyella henrici n. sp., live images of the holotype (NSMT-Mo 79005), body length 8.9 mm. A. Underside of the head showing Schwabe organ. B. Side view. C. In natural position, live animal collected on shell material and re-attached to a rock post-sampling.

FIGURE 2. Hanleyella henrici n. sp., SEM of the valves of the holotype (NSMT-Mo 79005). A. From top to bottom, head valve, ventral side of valve II, dorsal view of intermediate valve, and tail valve. B. Close of up granules in intermediate valve showing aesthete pores and the coalescing chains of granules on distal part of the central area. C. Higher magnification view of round, raised granules on lateral areas in intermediate valve shown in A.

FIGURE 3. Hanleyella henrici n. sp., SEM of elements from the holotype (NSMT-Mo 79005). A. Perinotum section, showing dorsal (top) and ventral (bottom) scales. B. Higher magnification view of ribbed dorsal scales. C. Anterior portion of the radula.