Decoradrillia, Fallon, Phillip J., 2016

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 : 114-116

Genus Decoradrillia , new genus

Type species: Decoradrillia harlequina , new species (Recent, Devil’s Bay, Grenada).

Diagnosis. Shell small to medium and glossy; fusiform, truncated anteriorly, with a large last whorl comprising 50% or more of the shell’s total length. Whorls strongly convex, sculpted with prominent axial ribs. Protoconch conical, of 1½–2½ smooth whorls that transition to the adult sculpture with a scarcely perceptible margin, the first whorl not usually immersed in the second. Axial sculpture of convex, usually bulging ribs that generally extend from suture-to-suture in an uninterrupted arc, except on the last whorl where they evanesce on the shell base below the periphery of whorl. Ribs reduced on shoulder, narrowed, and slightly recurved in a narrow band adjacent to the suture, but without a distinct sulcal boundary. Growth striae very fine. Spiral sculpture of close microscopic spiral grooves, sometimes faint, sub-equal to the growth striae, but not forming pits by their intersection as in Fenimorea . Fine threads in addition to grooves may be present on later whorls; grooves or threads present on the anterior fasciole. Varix wider, more convex, and higher than proceeding ribs (not hump-like), positioned approximately ¼– ⅓-turn from edge of outer lip. Anal sinus located on the shoulder, U-shaped and deeply notched with a flared inner edge, and offset from the suture by a parietal callus such that the sinus appears somewhat spout-like. Outer lip edge smooth, not toothed, formed into a low arc from anal sinus to a shallow stromboid notch. Inner lip relatively wide, detached from columella anteriorly but adherent in parietal area; formed into a strong parietal lobe posteriorly, positioned over the roof of aperture. Anterior canal short but well defined, turned slightly to the right at its end when viewed ventrally; anterior fasciole may be swollen in older specimens.

Key characteristics. The presence of the following characteristics is diagnostic of species of Decoradrillia and separates the genus from all others in Drilliidae :

1. Spiral sculpture of threads or ridges on anterior fasciole, threads present on some, especially on last whorl. Microsculpture of very fine spiral grooves or threads separated by closely packed finer grooves or threads. Spirals are interrupted by fine growth striae that sometimes give the spirals a wavy or jagged look. Heavier spiral threads, when present, are most pronounced on the last whorl.

2. Anterior canal well defined, short;

3. Axial ribs convex, usually bulging, run suture-to-suture on spire whorls, reduced, lower and slightly recurved in sulcus on whorl shoulders; and

4. Varix wider, higher, and more convex than preceding ribs (not hump-like), positioned approximately ¼ to ⅓- turn from edge of outer lip, usually close behind anal sinus and without a distinct color patch.

Similar genera. Decoradrillia is most similar to Fenimorea Bartsch, 1934 but differs in lacking a welldemarcated sulcus, in possessing ribs that are usually more convex and a varix that is not hump-like. Most importantly, the shell surface microsculpture of Decoradrillia is different. It consists of a repeating pattern of variable numbers of closely set fine threads between heavier threads. This is in contrast with that of Fenimorea , which consists of more widely spaced spiral grooves or ridges intersected by coarse growth striae, with the formation of “pits” between. The pits align in rows bounded by the spiral grooves, and individual pits bounded by axial growth striae. The Decoradrillia pattern is illustrated in the low magnification SEM images appearing in Pl. 51. At higher magnification, as also can be seen in Plate 51 , the threads are seen to have rows of punctae; mostly single rows in the type of the genus, Decoradrillia harlequina , new species, and in a variable number of rows in Decoradrillia pulchella (Reeve, 1845) . The Fenimorea pattern is shown for three different species of that genus in Plate 62. The spiral grooves are seen in both the ridge and groove condition. Punctae, which are visible under higher magnification SEM imagery, are distributed throughout the shell surface, in the pits as well as between.

From Splendrillia Hedley, 1922 Decoradrillia differs principally in that the ribs extend to the suture and do not end at the sulcus. The shell microsculpture differs. Splendrillia usually has a smooth surface, free of the dense spiral sculpture, but may have very fine spiral lines that are more sparsely distributed.

Distribution. Decoradrillia appears to be rare in the Gulf of Mexico (represented so far only by D. pulchella (Reeve, 1845) , but is otherwise found throughout the TWA. D. harlequina , new species and D. pulchella are the most widespread; the remaining species appear limited in distribution.

Etymology. Decoradrillia is derived from the Latin decora (glorious, noble, adjective, feminine form) and Greek drillia (machine). The name was inspired by the striking color patterns exhibited by most of the species discovered to date.

Figures

PLATE 51. Decoradrillia spp. shell surface SEM images. Figs. 1 – 2: Decoradrillia pulchella (Reeve, 1845), Anse Bateau Bay, Tobago I., Trinidad & Tobago (ANSP 338495), 240 x & 930 x, respectively. Figs. 3 – 4: Decoradrillia harlequina, new species: Fig. 3: Indian Cay, Grand Bahama I. (ANSP 366927), 240 x; Fig. 4: holotype, Devil’s Bay, Grenada (USNM 1291335), 1,000 x. Figs. 5 – 6: Decoradrillia interstincta, new species, " Big Rocks ", Utila I., Bay Is., Honduras (ANSP 464986), 250 x & 1,000 x, respectively.