Austrotheta crassidentata, Criscione & Hallan & Puillandre & Fedosov, 2021

Criscione, Francesco, Hallan, Anders, Puillandre, Nicolas & Fedosov, Alexander, 2021, Where the snails have no name: a molecular phylogeny of Raphitomidae (Neogastropoda: Conoidea) uncovers vast unexplored diversity in the deep seas of temperate southern and eastern Australia, Zoological Journal of the Linnean Society 191, pp. 961-1000 : 986

AUSTROTHETA CRASSIDENTATA SP. NOV.

( FIGS 3H, 6H)

Z o o B a n k r e g i s t r a t i o n: u r n: l s i d: z o o b a n k. org:act: 4EF95055-B0D2-4151-89B1-762BD62DF8DE.

H o l o t y p e: A u s t r a l i a, T a s m a n i a, F r e y c i n e t Commonwealth Marine Reserve, 2820 m, IN2017_ V03_004, (–41.731, 149.12), AMS C.519302.

Distribution: Known only from the type locality.

Etymology: The epithet is composed of the Latin adjectives crassus, thick, and dentatus, toothed, referring to the thick hypodermic tooth.

Description

Shell ( Fig. 3H) (SL = 20.9, SW = 9.6) fusiform, thinwalled, semitranslucent to opaque. Protoconch orange, multispiral (at least 2.5 whorls), with arcuate cordlets on adapical half to two-thirds of whorl, with diagonally cancellate sculpture below. Teleoconch of 4.4 whorls; subsutural ramp distinctly concave in early whorls, in more mature whorls less distinct and with less marked concavity.Whorl profile with prominent shoulder on early teleoconch whorls, situated at adapical third of whorl; in penultimate whorl more rounded, in last adult whorl indistinct; whorl periphery nearly cylindrical in early teleconch,more convex in mature whorls.Early teleoconch whorls with about 12 sharp, weakly opisthocline axials, vanishing well above suture, indistinct in later whorls. Spiral sculpture of dense, slightly undulating striae pronounced throughout last whorl. Microsculpture of collabral growth lines, forming distinct, raised cordlets on subsutural ramp in early whorls, weaker in more mature whorls. Last adult whorl evenly convex below subsutural ramp, with long, slender siphonal canal. Aperture wide, pyriform, about half of shell length. Inner lip with whitish callus, straight. Outer lip thin, unsculptured. Anal sinus shallow, weakly U-shaped.

Head wide, eyes small. Muscular bulb extremely large; proboscis short, wide; radular sac thin, bearing few teeth.

Radula ( Fig. 6H) of thick, straight cylindrical hypodermic teeth exceeding 175 µm in length; two weak distal, lateral barbs; adapical opening short, lateral (i.e. orientation of barbs and adapical opening offset to point of overlap between margins near base); base broad, inflated, with extremely coarse external sculpture ( Fig. 6H); ligament large.

Remarks

Austrotheta crassidentata differs from other raphitomids in the following combined characters: a fusiform shell with sharp, weakly opisthocline axials on early teleoconch whorls and weakly sculptured late teleoconch whorls; slender siphonal canal; thick hypodermic teeth with two weak laterally orientated barbs and a short laterally orientated adapical opening, as well as a broad base with extremely coarse external sculpture.

Based on its shell morphology, A. crassidentata resembles Gymnobela yoshidai (Kuroda & Habe, 1961) , in which strongly shouldered subcylindrical early teleoconch whorls with sharp ribs are succeeded by - in Habe, 1961 evenly convex and finely striate whorls. However, the latter species has a narrower shell with a pointed spire, and a less convex, more elongated shell base, as well as a yellowish staining of the shell. A similar change in the whorl outline and sculptural pattern can be observed in Spergo fusiformis [based on the type series illustrated by Sysoev & Bouchet (2001)], although the latter can be readily differentiated from A. crassidentata by its larger size and narrower, lanceolate aperture. A. crassidentata also has some resemblance to Austrobela rufa , but can be readily differentiated by its diagonally cancellate protoconch, sharp axial ribs, a more convex shell base, and its whitish shell. When compared to T. lyronuclea , it differs in its more elongate shell and in its diagonally cancellate protoconch (which is arcuate in both A. rufa and T. lyronuclea ).