Biconitoma cretosa, 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 : 981-982

BICONITOMA CRETOSA SP. NOV.

( FIGS 3D, 6G)

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: 49AFD1E4-21AD-473C-A983-1504F5AAA623.

Holotype: Australia, NSW, off Byron Bay , 2587 m, I N 2 0 1 7_ V 0 3_0 9 0, (–2 8.6 7 7, 1 5 4.2 0 3), A M S C.482313.

Paratype: Australia, NSW, off Byron Bay , 3825 m, IN2017_ V03 _ 099, (–28.371, 154.649), one wet ( AMS C.482288) .

Distribution: Known from two adjacent localities off Byron Bay, northern New South Wales.

Etymology: The epithet is derived from the Latin adjective cretosus, chalky, referring to the somewhat chalky appearance of the shell.

Description

Shell ( Fig. 3D) (SL = 24.6, SW = 12.9) fusiformbiconical, opaque. Protoconch eroded. Teleoconch of about five uniformly whitish, chalky whorls; suture impressed. Whorls broad, with wide, flat to lightly concave subsutural ramp and rounded to subcylindrical periphery. Shoulder situated slightly below half-height of whorl, severely eroded in early teleoconch whorls. Axial sculpture of 15 or more rounded opisthocline folds below subsutural ramp, roughly half to one-third width of their interspaces, becoming indistinct toward suture and obsolete toward base of last whorl. Spiral sculpture of fine but distinct threads on subsutural ramp, and prominent cords subsequently (totalling about ten on penultimate whorl,> 30 on last whorl). Microsculpture of indistinct collabral growth lines. Last adult whorl evenly convex below subsutural ramp, constricted towards stout, tapering siphonal canal. Aperture elongate, a little over half of shell length; outer lip thin, unsculptured. Inner lip whitish, straight, gently recurved, with distinct callus. Anal sinus wide, deep, U-shaped.

Animal uniform cream. Head broad, blunt. Cephalic tentacles of moderate length, slightly tapering toward blunt tip. Eyes absent. Penis long, slender, cylindrical, with small seminal papilla situated distally; anterior vas deferens long, undulating, visible through epidermis.

Introvert short; rhynchostomal sphincter thick, muscular. Proboscis long, narrow, pointed, coiled counterclockwise; venom gland of medium length; muscular bulb elongate, lustrous.

Radula ( Fig.6G) of straight, tightly rolled hypodermic teeth attaining 135 µm in length; no ventral barb; dorsal blade sharp, approximately one-sixth of length of shaft; adapical opening elongate-triangular, about one-tenth of length of shaft. Base moderately broad, with weak lateral process; exterior of base with coarse texture; basal opening large. Ligament large, broad.

Remarks

This new taxon can be differentiated from other known raphitomids by its biconical shell with distinct spiral cords; the absence of eyes; a long penis with small distal seminal papilla, and comparatively short, tightly rolled, hypodermic teeth with subtriangular adapical openings. In terms of shell morphology, this species can be difficult to differentiate from Aplotoma brevitentaculata ( Fig.3C), despite their difference in radular features ( Fig. 6A, F) and their demonstrated genetic distinctiveness. However, the latter possesses a distinctly more convex shell base, a more acutely shouldered whorl profile with narrower subsutural ramp and its axial sculpture consists of considerably narrower ribs.