Syntomodrillia

Syntomodrillia cybele, copyright Korina Sangiouloglou.

Time, I think, for another visit to the often overlooked hotbed of gastropod diversity that is the 'turrids'. As alluded to here and here, these are the less differentiated members of the cone shell superfamily Conoidea, treated in the past as a single family Turridae but now classified into several different families.

Syntomodrillia is a genus in the conoid family Drilliidae. These are small shells, with recent species no more than a centimetre in length (Woodring 1970). Recent species of Syntomodrillia are found only in the American tropics, mostly in the Caribbean and the Gulf of Mexico, with a single species S. cybele (the one shown above) at the Galapagos Islands. The fossil record, however, may indicate a broader range for Syntomodrillia in the past, as Powell (1966) assigned species to this genus from the Oligocene to the Pliocene of Australasia and Okinawa. Syntomodrillia is similar in appearance to another drilliid genus, the somewhat magnificently named Splendrillia, and has been treated by some authors as a subgenus of the latter. Among the features distinguishing the two is the appearance of the longitudinal ribs running down the shell: in Syntomodrillia, the ribs completely cross each whorl, but in Splendrillia they are interrupted on the shoulder. The protoconch (larval shell) also differs between the two, with that of Syntomodrillia being slender with two whorls, whereas that of Splendrillia is broadly rounded and paucispiral (Powell 1966). This may indicate that the larval stage of Syntomodrillia is slightly longer and/or more active than that of Splendrillia.

Radula of Splendrillia, from Kantor & Puillandre (2012); mt = marginal teeth.

As described in an earlier post, the Conoidea have alternatively been known as the 'Toxoglossa' because many conoids have the radula modified for the injection of toxins (taken to the utmost in the cone shells, which may be capable of killing humans). The median and lateral teeth of the radula are reduced or lost, and the marginal teeth turn into disposable syringes. The Drilliidae, however, have not gone down this path: they retain a radula with well-developed saw-like lateral teeth. Though records of drilliid diet are decidedly sparse, they probably hunt soft-bodied prey by actively grabbing and tearing it, in contrast to the more refined eating habits of other conoids.

REFERENCES
Kantor, Y. I., & N. Puillandre. 2012. Evolution of the radular apparatus in Conoidea (Gastropoda: Neogastropoda) as inferred from a molecular phylogeny. Malacologia 55 (1): 55–90.

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

Woodring, W. P. 1970. Geology and paleontology of Canal Zone and adjoining parts of Panama: description of Tertiary mollusks (gastropods: Eulimidae, Marginellidae to Helminthoglyptidae). Geological Survey Professional Paper 306-D: 299–452, pls 48–66.