Syntomodrillia Woodring, 1928

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 : 316-317

Genus Syntomodrillia Woodring, 1928

Type species: Drillia lissotropis (Dall, 1881) by original designation (Recent, off Bahia Honda, Artemisa Prov., Cuba).

Woodring named Syntomodrillia lissotropis (Dall, 1881) as the type of the genus without designating a specimen or lot as genus type despite Dall having identified six lots from three different localities as this species (Dall, 1881: 58–59; Dall, 1889a: 92) (all listed in the section about S. lissotropis below). To accommodate the specimens of the new lots, Dall emended the description in 1889 to variably include intercostal spiral grooves, which was not mentioned in the original description. Bartsch (1934: 25–26), discovered that Dall’s lots of lissotropis were comprised of more than one species (five different ones are described in this work). Because Woodring had not specified a particular specimen as type of the genus, Bartsch selected a specimen that had distinct intercostal grooves from one of Dall’s lissotropis lots (USNM 87477), which he believed to be representative of the one Woodring intended as type of Syntomodrillia . He named it Syntomodrillia woodringi , and substituted it as the type of the genus. Bartsch believed it to be a different species because Dall’s original 1881 description did not mention intercostal spirals. Woodring (1970: 388–389) later rebutted Bartsch’s action by stating that the presence of spirals was a variable trait, that whether or not S. lissotropis possessed intercostal spirals was unimportant, citing as proof a fossil species that exhibited variability in this trait, and put S. woodringi in synonymy with S. lissotropis , leaving the latter as the type of the genus. Syntomodrillia lissotropis is supported in this work as the valid type of the genus, as intended by Woodring. Bartsch’s action does not fulfill the requirements of ICZN 2000 Article 70 (the type species was not misidentified so substituting another is not allowed). Splendrillia woodringi is shown in this work to be a different but valid species, not a synonym of S. lissotropis .

Diagnosis. According to Woodring (1928: 160), very small slender shell, with numerous ribs, a varix some distance from the outer lip, a short, relatively wide aperture, and short anterior canal with a shallow siphonal notch; fasciole not swollen. Nucleus slender with about 2 smooth whorls. Sculpture of broad axial ribs extending from suture-to-suture, reduced on sulcus. Spiral sculpture of microscopic threads or grooves between ribs on the later whorls and of fine threads on the anterior fasciole. Intercostal spirals may be absent in some species, or variably present (Woodring, 1970: 388–389). Anal sinus broad, with a round apex that adjoins the suture. Outer lip with a shallow stromboid notch. Inner lip narrow, edge detached; a weak parietal callus located posteriorly at junction of outer lip.

Key characteristics. The presence of all the following characteristics is diagnostic of species of Syntomodrillia and separates the genus from other TWA Drilliidae genera:

1. Shell small, slender, glossy, with a moderately long anterior canal. (Although characterized as short by Woodring, the canal is usually longer than in some Fenimorea or Splendrillia , for instance, which are described as short in this work. Relatively speaking, the canal of Syntomodrillia is moderately long but shorter than that of Leptadrillia , which is characterized as long.)

2. Axial ribs that extend from suture-to-suture on spire whorls, to fasciole on last, slightly reduced in height, and recurved on shoulders of later whorls;

3. Spiral sculpture of fine threads or grooves, usually below the periphery of later whorls (absent on shoulder), stronger on shell base, and of ridges on the anterior fasciole. Spiral sculpture may be very faint or variably absent in some species; and

4. A varix (usually not hump-like) approximately ¼- to ⅓-turn from the edge of the outer lip.

Most species in the genus are similar-looking and difficult to distinguish, differing only slightly in shell and whorl profile, size, rib form, and a few other other characteristics, attributes that are not always evident in imperfect specimens. Locality is important because ranges of most Syntomodrillia are very limited.

Nomenclatural notes. There has been a gradual suppression of the use of Syntomodrillia as a genus since Powell (1966) reduced it to a subgenus of Splendrillia . The subgenus has been dropped altogether by Turgeon et al. (1998). However, species in Syntomodrillia are sufficiently different morphologically from Splendrillia (and Leptadrillia ) to merit separation at the genus level (see discussion of similar genera next).

The identification of species of Syntomodrillia has been greatly confused on account of the poor quality and description of most types and similarity of species to each other.

Similar genera. Leptadrillia Woodring, 1928 is most similar to but differs from Syntomodrillia in that it has a long anterior canal and lacks intercostal spiral grooves. Splendrillia Hedley, 1922 differs in the following ways: axial ribs end at the sulcus, not at the suture; ribs are shorter, usually more oblique, evanescing just below the whorl periphery and rarely reaching the anterior fasciole; anterior canal is shorter; shell surface has a microsculpture of spiral lines; and the varix is hump-like. Lissodrillia Bartsch & Rehder, 1939 also has a small glossy shell with ribs that extend from suture-to-suture in some species, but lacks spiral sculpture altogether, most noticeably on the anterior fasciole.

Distribution. Members of the genus Syntomodrillia are largely offshore, soft bottom dwellers, widely distributed throughout the region, though species are individually limited in their range. The genus has apparently undergone a significant radiation based on the number of species discovered to-date, and it is likely that many more are yet to be discovered, especially in areas that have not been thoroughly explored. Because of their habitat preference, and small size, they are easily overlooked and so are uncommon in collections.