Stenochiton nubilus ( Cochran, 1993 )

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 : 384-386

Stenochiton nubilus ( Cochran, 1993)

( Figures 33A, B , 34–36 )

Ischnochiton (Stenochiton) pallens Ashby, 1900: 86 (pars), pl. 1, fig. 1 (non pl. 1, figs. IB-E).

Ischnochiton (Chartoplax) nubilus Cochran, 1993: 51 , figs. 1–2 (bibliography).

Non: Ischnochiton pallens ; Torr, 1912; Gatliff & Gabriel, 1917 (= Stenochitvn cymodocealis Ashby, 1918 ); Stenochiton pallens ; Ashby, 1920, 1921; Gatliff & Gabriel, 1931 (= Stenochiton cymodocealis Ashby, 1918 ).

Stenochiton nubilus ; Kaas et al. 2006: 43, fig. 11, map 3.

Type material. Holotype ( SAMA 011728 ). Type locality. South Australia , Gulf St. Vincent, dredged.

Material examined. TAS: Tasman Sea, Tamboon, 10 km to SE Lot _60, 37.81°S, 149.0099°E, Benthic dredge, CSIRO, 1 spm ( TMAG, E 45527 ) BL 9.5 x 6.0 mm, 26.11.1996 .

Distribution. South Australia, Gulf St. Vincent and Tasman Sea, 18 m ( Kaas et al. 2006) The latest find significantly expands the range of this species.

Remarks. Cochran (1993) and Kaas et al. (2006) mentioned that this species is more than 2.5 times longer than wide. The specimen collected near Tasmania (TMAG, E 45527) is noticeable shorter than the type specimen. The long body is one of the characteristic features of the species of this genus living on the long leaves of sea grasses. Our specimen has a short body and, apparently, with age, its body rapidly lengthens. It is clearly visible on all valves that growth along the anterior-posterior axis exceeds lateral growth by far. The studied specimen (TMAG, E 45527) has slit formula 0/1–2/ 10, dorsal elevation 0.45, 16 gills per side arranged from valve II to valve VIII.

Figures

FIGURE 33. Stenochiton nubilus, Tasmanian Sea (TMAG, E 45540), BL 9.5 mm: (A, B) and Stenochiton pilsbryanus, Indian Ocean, Western Australia (TMAG, E 45541), BL 13.0 mm: (C, D)

FIGURE 34. Stenochiton nubilus, Tasmanian Sea (TMAG, E 45540), BL 9.5 mm: A. Part of valve I; B. Valve III, dorsal view; C. Valve VIII, dorsal view; D. Part of valve VII, ventral view; E. Valve V, detail of tegmentum in central area; F. Valve III, rostral view; G. Valve VIII, lateral view.

FIGURE 35. Stenochiton nubilus, Tasmanian Sea (TMAG, E 45540), BL 9.5 mm: A. Dorsal and ventral scales; B. Middle part of radula; C. Dorsal scales; D. Central and first lateral teeth of radula.

FIGURE 36. Stenochiton nubilus, Tasmanian Sea (TMAG, E 45540), BL 9.5 mm: A. Dorsal scale; B. Ventral scale; C. Central and first lateral teeth; D. Major uncinal tooth; E, F. Heads of major lateral tooth. Scale bar 100 µm.