Lissodrillia Bartsch & Rehder, 1939

Fallon, Phillip J., 2016, Taxonomic review of tropical western Atlantic shallow water Drilliidae (Mollusca: Gastropoda: Conoidea) including descriptions of 100 new species, Zootaxa 4090 (1), pp. 1-363 : 237

Genus Lissodrillia Bartsch & Rehder, 1939

Type species: Cerodrillia (Lissodrillia) schroederi Bartsch & Rehder, 1939 by original designation (Recent, off Charlotte Harbor, W Florida).

Diagnosis. The following is slightly modified from the diagnosis given by Bartsch & Rehder to include the new species described in this section.

The genus is comprised of very small species that possess a fusiform, partially translucent shell with nearly flat to very round or angular whorls; axial ribs weak to strong; with 2 protoconch whorls; spiral sculpture absent; anal sinus deeply notched, its rim and outer lip edge are congruent, together tracing a reversed “S” when viewed laterally. The outer lip is thin with a weak stromboid notch. Anal sulcus is absent, sinal area on shoulders may have weakened or absent ribs. Inner lip is appressed to the columella; thickened posteriorly into a weak callus. The aperture is short, narrowly oval and ends in a short, distinct canal.

The diagnosis of Bartsch & Rehder of “strong axial ribs that run from the suture and evanesce on the shell base” has been expanded to include species with weak or almost obsolete ribs. The form of the anal sinus in which the outer edge is divergent, and broadly round, its rim and lip edge forming a continuous curve in combination with the outer lip, a reversed “S”, from sinus to stromboid notch is consistent with but a modification of Bartsch & Rehder’s less specific “anal sinus is deep”.

Key characteristics. The following combination of characteristics, in addition to those that characterize the family, distinguish Lissodrillia :

1. Shell very small, glossy, with ribs that extend from suture-to-suture; usually without a sulcus, but ribs reduced or obsolete on the shoulders of some species;

2. Outer edge of anal sinus divergent, such that it and the edge of the outer lip trace a reversed “S” when shell is viewed laterally;

3. Anterior canal distinct but open, short, and without a notch; and

4. Spiral sculpture absent.

Nomenclature. There are three previously described species that have the characteristics of the genus: Lissodrillia schroederi (Bartsch & Rehder, 1939) , L. simpsoni (Dall, 1887) , and L. verrillii (Dall, 1881) . Newly described species fit the diagnosis outlined above but their facies differ sufficiently such that the group may be polyphyletic and require separation when more anatomical or molecular data become available.

Similar genera. Syntomodrillia , which is also comprised of small glossy species with ribs that extend from suture-to-suture, differs principally in having spiral ridges on the anterior fasciole and threads or grooves between ribs. Leptadrillia differs in possessing a long anterior canal and, although lacking on the whorls proper, spiral grooves are present on the anterior fasciole. Inodrillia Bartsch, 1943 (family Pseudomelotomidae) is very similar in that the anterior fasciole lacks spiral grooves but the protoconch of that genus possesses ribs, unlike any of the Drilliidae .

Distribution. Lissodrillia has been recorded principally from around Florida, the Greater Antilles, and Gulf of Mexico. These areas have been more heavily sampled than further afield, so the known species are likely just a fraction of what may exist over the entire region. They are very small, mostly from deeper water, so easily overlooked.