Pterodacna, Herbert, 2024

Herbert, David G., 2024, The Vetigastropoda (Mollusca) of Walters Shoal, with descriptions of two new genera and thirty new species, European Journal of Taxonomy 923, pp. 1-119 : 19-20

Genus Pterodacna gen. nov.

urn:lsid:zoobank.org:act:E9BE7547-02C0-4F83-8157-FB4F14BA186C

Type species

Pterodacna boucheti gen. et sp. nov.

Diagnosis

Shell very small (length <2.0 mm), thin and fragile, base evenly elliptical, basal profile flat; apex at ± 0.2 of length from posterior end; anterior slope convex; posterior slope almost straight; interior lacking apical septum. Protoconch elliptical, apical portion long and slender, fused to terminal lip; microsculpture of close-set, irregular, minute pits. Teleoconch with irregular collabral growth-lines and close-set, microscopic, concentric ripples; radial sculpture mostly absent, but anterior third with shallow radial undulation. Radula with rachidian tapering to a narrow cuspless point, innermost lateral broadly trigonal with a blunt vestigial cusp at antero-medial corner; laterals 2–4 with bluntly rounded cusps; fifth lateral large, its cusp with three strong trigonal denticles; inner marginals with simple recurved cusps lacking denticles, middle marginals more slender, their cusps with fine lateral denticles, outer marginals distally spathulate with finely denticulate margins. Animal lacking pigmented eyes, cephalic tentacles well developed, oral disk large; posterior of foot with two small epipodial tentacles.

Etymology

From the Greek “ pteron ” (φτερό) – “a feather” and “ dakno ” (Δάκνω) – “to bite”; in reference to the feeding habits of the animal. Not the fossil Pteradacna Andrusov, 1907 ( Bivalvia: Cardiidae ).

Remarks

The morphology of the protoconch and radula of Pterodacna gen. nov. is typical of taxa referable to the Pseudococculinidae ( Hickman 1983; Marshall 1986). Within this family, the most similar genus is Tentaoculus Moskalev, 1976 , the shell of which is very similar to that of Pterodacna gen. nov., in terms of its shape, sculpture and protoconch morphology. Based on these characters alone, Pterodacna gen. nov. would key out as Tentaoculus using the key to pseudococculinid genera provided by Marshall (1986). However, the radula of Pterodacna gen. nov. differs significantly from that of Tentaoculus . Whereas the rachidian tooth in the radula of Pterodacna gen. nov. tapers to a point and lacks a cusp, that of Tentaoculus retains a finely serrate cusp. Similarly, the cusp of the large innermost lateral tooth has a broad, serrate cutting edge in Tentaoculus and the cusps of laterals 2–4 are also serrate ( Marshall 1986, 1996; Warén & Bouchet 2009), whilst in Pterodacna gen. nov. the innermost lateral has at most a blunt vestigial cusp on its antero-medial corner and the cusps of laterals 2–4 are bluntly rounded and not serrate. Furthermore, the fifth lateral of Pterodacna gen. nov. has a cusp with three strong denticles, in contrast to the more finely serrate fifth lateral cusp found in species of Tentaoculus . Broader comparison shows that some of the features of the radula of Pterodacna gen. nov. are shared with other pseudococculinid taxa; notably the robust tricuspid fifth lateral is shared with Notocrater ponderi Marshall, 1986 and a pointed cuspless rachidian is present in Mesopelex zelandica Marshall, 1986 . The most characteristic features of the radula of Pterodacna gen. nov. include the posterior mid-region dip in the transverse rows of teeth, the very broad, essentially cuspless first lateral tooth and the bluntly rounded cusps on laterals 2–4.

Pterodacna gen. nov., like many small bathyal and abyssal limpets, is associated with a biogenic substrate. Commonly within the Pseudococculinidae this substrate is water-logged decaying wood ( Marshall 1986), but those species of Tentaoculus for which habitat data are available exhibit associations with more unusual substrates, including the carapaces of living stone crabs ( Lithodidae ) and decaying algal holdfasts ( Marshall 1986), as well as chondrichthyan egg cases ( Marshall 1996). The association of Pterodacna gen. nov. with decaying bird feathers represents the first record of a deep-sea limpet living and feeding on such a substrate. In fact, it is the first record of any gastropod subsisting on a substrate of this nature ( Ponder & Lindberg 2020).