Douglassia Bartsch, 1934

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 : 129

Genus Douglassia Bartsch, 1934

Type species: Douglassia enae, Bartsch, 1934 by original designation (Recent, off the north coast of Puerto Rico)

Diagnosis. According to Bartsch (1934: 5–6), a medium-sized shell with smooth, round protoconch whorls; teleoconch whorls with a smooth concave sulcus devoid of ribs, remaining portion of whorls convex. Shell base short with a short columella and weak fasciole; aperture large with a deep anterior canal and anal sinus, the latter adjoining the suture. Inner lip recumbent with a parietal lobe posteriorly; outer lip with a strong stromboid notch. Axial ribs extend from sulcus, grow strongest on periphery, and evanesce on base near anterior fasciole; fine growth striae present overall. Whorls marked with fine spiral lines; anterior fasciole with spiral ridges.

Key characteristics. The presence of all the following characteristics, in addition to those that define the family, is diagnostic of species of Douglassia and separates the genus from other TWA drilliid genera:

1. Shell fusiform, stout, (W/L> 0.40), with a short anterior canal.

2. Whorls with a concave sulcus lacking ribs in later whorls; ribs strongly convex below sulcus;

3. Protoconch of 2½–3 smooth round whorls;

4. Spiral microsculpture primarily on shell base and includes incised grooves, threads or ridges that strengthen anteriorly, strongest on anterior fasciole; remainder of shell surface may have microscopic spiral lines, but usually is smooth; and

5. Cup-handle-like varix behind anal sinus (within ¼-turn of outer lip edge, usually less) such that the base of the fully developed shell appears lopsided (skewed to the right) when the shell is viewed ventrally.

Nomenclatural notes. Douglassia is difficult to distinguish from Cerodrillia Bartsch & Rehder, 1939 and these two genera may prove to be congeneric. Some members of both genera have axials that are greatly reduced on the shoulder or, in later whorls of older individual especially, obsolete. The two genera differ principally in the number of protoconch whorls (2½–3 whorls in Douglassia versus 1¾– 2 in Cerodrillia ), and Douglassia usually, but not always, has more angular shoulders.

Gibson (1962: 235) suggests that Douglassia should be synonymized with Splendrillia , presumably because of the absence of ribs in the sulcus and smooth shell, but the two genera have different varices—that of Splendrillia being hump-like about ⅓–turn from the edge of the outer lip. The varix of Douglassia (and of Cerodrillia ) is immediately behind the anal sinus (about ¼-turn or less) and cup handle-like, not hump-like. The type of the genus, D. enae , is morphologically closer to Cerodrillia than to Splendrillia on the basis of the structure of its anal sinus, shell surface microsculpture, and cup-handle-like varix immediately behind the anal sinus.

Similar genera. Cerodrillia Bartsch & Rehder, 1939 is similar and some specimens may be difficult to separate from Douglassia . Differences are discussed under nomenclatural notes above. Some members of two other genera, Viridrillia Bartsch, 1943 and Inodrillia Bartsch, 1943 have an uncanny resemblance to Douglassia (and to Cerodrillia ). Tippett (1995: 134–135) illustrates the radula of Viridrillia williami Bartsch, 1943 and Viridrillia hendersoni Bartsch, 1943 to demonstrate the more appropriate placement of the genus in Crassispirinae , now Pseudomelatomidae Morrison, 1965 (Bouchet et al., 2011) . Earlier, Sysoev, in Taylor et al. (1993: 164) listed Inodrillia as a crassispirine genus on the basis of its radular teeth. Inodrillia has most recently been provisionally placed in Horaiclavidae (Bouchet et al., 2011) . Although very similar, Viridrillia has subtle morphological characteristics not seen in any of the known Douglassia (or Cerodrillia ): an anterior fasciole that lacks spiral ridges, the presence of spiral threads or grooves over the entire shell, not just on the shell base, and a protoconch with obsolete riblets that nonetheless leave a wrinkled look. The protoconch in Douglassia and Cerodrillia is always smooth.

Distribution. The genus Douglassia is distributed throughout the TWA, from North Carolina to northern Brazil. Most species are from water depths of 30 m or greater, an exception being D. antillensis , new species, which is distributed throughout the eastern Caribbean and usually found above this depth.