Leptochiton gowlettholmesae, Sirenko, Boris, 2023

Sirenko, Boris, 2023, A small collection of rare and new chitons (Mollusca: Polyplacophora) from the Tasmanian Museum and Art Gallery, Zootaxa 5325 (3), pp. 359-392 : 365-369

Leptochiton gowlettholmesae n. sp.

( Figures 7A, B , 8–14 )

Type material. Holotype ( TMAG, E 45530) and paratype ( TMAG, E 45531), both now disarticulated consisting of SEM stub of valves I, II, IV, V, VIII, part of perinotum and radula, mount of part of perinotum and vial with other valves.

Type locality. Southern Ocean, South of Tasmania, 44.3511°S, 147.2868°E, 1450 m (Huan MP: 744 seamount: stn SS 2008_ VOL _030, Lot 030, dredge CSIRO, 19.01.2008) .

Material examined. Southern Ocean, South of Tasmania, 44.3511°S, 147.2868°E, 1450 m, Huan MP: 744 seamount: stn SS2008_ VOL_030, Lot 030, dredge CSIRO, holotype ( TMAG, E 45530 ) BL 9.0 mm, 19.01.2008 ; 45.1345°S, 146.0161°E, 1520 m, Fracture MP: The Knob stn SS2008_ VOL_037, Lot 037, dredge CSIRO, paratype ( TMAG, E 45531 ) BL 15.5 mm, 22.01.2008 .

Etymology. Named after Karen Gowlett-Holmes, a leading marine biologist of Australia, for her large contribution to the knowledge of Australian marine animals including chitons, and for her beautiful photographs of fishes and invertebrates.

Distribution. Only known from the type material.

Diagnosis. Small to moderately sized chiton, valves lowly elevated, subcarinated, head valve noticeably wider than tail valve. Tegmentum sculptured with small, flattened granules arranged in longitudinal rows in central area of intermediate valves and antemucronal area of tail valve, and in a random manner in other areas. Jugal sinus wide, twice as wide as width of apophyses. Girdle very narrow, about 100–130 μm wide in valve V, covered with pointed, smooth dorsal scales that are very sharp on top. Major lateral radular tooth with long, unidentate cusp.

Description. Small chiton, BL 9.0 mm, elongate oval. Valves only little elevated (dorsal elevation of valve V 0.33), subcarinated, not beaked. Color of tegmentum white.

Head valve semicircular. Intermediate valves broadly rectangular, anterior margin strongly convex in valve II, straight in valves II–VII, posterior margin straight, sides rounded, apex not projecting. Tail valve noticeably narrower than head valve, mucro postmedian, antemucronal slope convex, postmucronal slope slightly concave.

Tegmentum sculptured with small flattened granules arranged in longitudinal rows in central area of intermediate valves and antemucronal area of tail valve and in a random manner in head valve, lateral areas of intermediate valves and postmucronal area of tail valve. Each granule with one megalaesthete and two micraesthetes.

Articulamentum white, weakly developed, apophyses narrow, triangular in intermediate valves, trapezoidal in tail valve, jugal sinus wide, twice wider than width of apophyses in valve V.

Girdle very narrow, about 100–130 μm wide in valve V, dorsally covered with pointed, smooth scales (74 × 20 μm) with very sharp top, and rare smooth needles (100–110× 15 μm). Intersegmental area with long needles (173 × 17 μm). Marginal needles like intersegmental ones but shorter (130 × 16 μm). Ventrally girdle covered with elongate pointed, smooth scales (85–100 × 25 μm).

Radula of holotype 4.1 mm long with 51 transverse rows of mature teeth. Central tooth elongate with narrow blade, major lateral tooth with long, unidentate cusp.

Nine short gills per side arranged from valve VI to anus.

Gut content of both type specimens containing detritus, sand and several foraminifers.

Remarks. The paratype, BL 15.5 mm has radula 6.9 mm long with 51 transverse rows of mature teeth and 11 short gills per side arranged from valve VII to near the anus. Age-related variability was observed: with age, the intermediate valves become more elongated and oval rather than rectangular.

Leptochiton gowlettholmesae n. sp. differs from other species with similar radular teeth and a similar sculpture of the tegmentum ( Leptochiton lascrusesi Sirenko, 2015 , from Chile and L. commandorensis Sirenko, 2017 , from Commander Islands) by having a very narrow girdle with pointed, smooth dorsal scales that are very sharp on top (vs. dorsal scales wide with ribs in both above mentioned species).

Figures

FIGURE 7. Leptochiton gowlettholmesae n. sp. Southern Ocean, South to Tasmania, paratype (TMAG, E 45531), BL 15.5 mm: (A, B) and Belknapchiton australis n. sp. Southern Ocean, South Tasmania slope, holotype (TMAG, E 45527) BL 13.0 mm. (C, D).

FIGURE 8. Leptochiton gowlettholmesae n. sp. Southern Ocean, South to Tasmania, holotype (TMAG, E 45530), BL 9.0 mm: A. Valve I, dorsal view; B. Valve II, dorsal view; C. Valve V, dorsal view; D. Valve VIII, dorsal view; E. Valve IV, ventral view; F. Valve V, detail of tegmentum in central area; G. Valve V, rostral view; H. Valve VIII, lateral view.

FIGURE 9. Leptochiton gowlettholmesae n. sp. Southern Ocean, South to Tasmania, holotype (TMAG, E 45530), BL 9.0 mm: A. Ventral scales and marginal needles; B, C. ventral and dorsal scales and marginal needles; D. Head of major lateral tooth.

FIGURE 10. Leptochiton gowlettholmesae n. sp. Southern Ocean, South to Tasmania, holotype (TMAG, E 45530), BL 9.0 mm: A, B. Middle part of radula.

FIGURE 11. Leptochiton gowlettholmesae n. sp. Southern Ocean, South to Tasmania, holotype (TMAG, E 45530), BL 9.0 mm: A. Sutural needle; B. Dorsal scales; C. Marginal needle; D. ventral scale; E. Aesthete group; F. Head of major lateral tooth; G. Central and first lateral teeth; Scale bar 100 µm.

FIGURE 12. Leptochiton gowlettholmesae n. sp. Southern Ocean, South to Tasmania, paratype (TMAG, E 45531), BL 15.0 mm: A. Valve I, dorsal view; B. Valve II, dorsal view; C. Valve V, dorsal view; D. Valve VIII, dorsal view; E. Valve V, detail of tegmentum in central area; F. Valve V, rostral view; G. Valve VIII, lateral view.

FIGURE 13. Leptochiton gowlettholmesae n. sp. Southern Ocean, South to Tasmania, paratype (TMAG, E 45531), BL 15.0 mm: A. Ventral, and dorsal scales and marginal needles; B. Ventral scales and marginal needles; C. Ventral scales and marginal and sutural needles; D. Radula.

FIGURE 14. Leptochiton gowlettholmesae n. sp. Southern Ocean, South to Tasmania, paratype (TMAG, E 45531), BL 15.0 mm: A, B. Middle part of radula.