Asperdaphne, I Don't Know Who You Are Any More

A true Asperdaphne: the type species A. versivestita, photographed by Des Beechey.

The subject of today's post has been going through something of an identity crisis recently. Asperdaphne was listed by Powell (1966) as a genus of small conoid gastropods found in Australia, New Zealand and the Pacific coast of Asia, with a fusiform shell and coarse clathrate (lattice-like) ornamentation. This remains the sense in which it has been most commonly recognised. However, in a paper published just last year, Beu (2011) revealed that this picture of Asperdaphne was a fraud. The majority of species assigned to Asperdaphne by Powell (1966) were not members of the same genus as the type, A. versivestita. Instead, they belonged to another genus, Pleurotomella, the type species of which Powell had not been familiar with. Meanwhile, A. versivestita was more appropriately placed with what Powell had called Tritonoturris, an Indo-Pacific genus of larger conoids with a more ovate shell shape. As Asperdaphne was an older genus name than Tritonoturris, this meant that what had been Tritonoturris was now Asperdaphne, while what had been Asperdaphne was now Pleurotomella. The identity of the two east Asian species assigned to Asperdaphne by Powell (1966) was not discussed by Beu (2011).

Not an Asperdaphne: Pleurotomella hayesiana, also photographed by Des Beechey.

We have encountered this paper of Beu's before, when I cited it in the post on another conoid genus, Kuroshioturris. As with that genus, the recognition of Asperdaphne had been confused by differences in protoconch morphology related to larval nutrition. Species assigned to 'Tritonoturris' had a tall conical protoconch, indicating a planktotrophic (feeding on plankton) lifestyle as a larva, while Asperdaphne versivestita has a blunt-tipped paucispiral protoconch, indicating that its larvae are lecithotrophic ('fed' by energy reserves in the yolk).

Diagram of the foregut of 'Tritonoturris' subrissoides, from Fedosov (2008).

Slightly more mysterious are Asperdaphne's feeding habits as adults. Foregut structure has been investigated for one presumed Asperdaphne species, under the name Tritonoturris subrissoides (Fedosov 2008). T. subrissoides is one of a number of members of the family Raphitomidae to show a reduction in foregut structures, and has lost the radula and venom gland of most conoids. Instead, it has a large introvert (extendable proboscis) that probably functions in prey capture. However, the roof of the introvert has a large and elongate outgrowth, unlike any found to date in any other conoid, with a well differentiated muscle system indicating that it is capable of complex movement. Presumably, this outgrowth functions somehow in prey capture (perhaps as a grasping 'finger'?) but its exact purpose remains unknown.

REFERENCES

Beu, A. G. 2011. Marine Mollusca of isotope stages of the last 2 million years in New Zealand. Part 4. Gastropoda (Ptenoglossa, Neogastropoda, Heterobranchia). Journal of the Royal Society of New Zealand 41 (1): 1-153.

Fedosov, A. E. 2008. Reduction of the alimentary system structures in predatory gastropods of the superfamily Conoidea (Gastropoda: Neogastropoda). Doklady Biological Sciences 419: 136-138.

Powell, A. W. B. 1966. The molluscan families Speightiidae and Turridae: an evaluation of the valid taxa, both Recent and fossil, with lists of characteristic species. Bulletin of the Auckland Institute and Museum 5: 1-184, pls 1-23.