Lissodrillia arcas, 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 : 237-239

Lissodrillia arcas , new species

( Plate 120 )

Type material. Holotype 5.6 x 2.2 mm, D. Steger! aboard M/V Miss Suzanne, Oct 1952 (DMNH 46224); 6 paratypes: 2 spec., 5.8 x 2.1 & 5.6 x 2.3 mm, in 48 m, 32–56 km NNW of Arcas Cays, Campeche Bank, D. Steger! Oct 1952 (DMNH 107187); 4 spec., 6.0 x 2.3 & 5.4 x 2.0 mm (MCZ 279174), 5.3 x 2.2 mm (UF 21573), & 4.6 x 1.9 mm (ANSP 323999) in 44–48 m, 32–40 km NNW of Arcas Cays, Campeche Bank, D. Steger! aboard M/V Miss Suzanne, Oct 1952.

Type locality. 32–56 km NNW of Arcas Cays, Campeche Bank, Campeche Mexico, in 44– 48 m.

Range and habitat. Known only from the type locality.

Description. Shell very small (to 6.0 mm total length) fusiform, translucent, glossy-smooth, whorls convex, peripheries near suture of succeeding whorl such that whorls appear to sag; up to about 7½ total, including protoconch, last whorl about 59% of total shell length. Ribs are the only sculptural element; aperture narrow, only a little wider than the anterior canal at its widest. Protoconch of 1¾ smooth round whorls. Axial sculpture of approximately 9–10 ribs on penultimate and 6–7 on last whorl that run from suture-to-suture and evanesce just below periphery of last whorl, obsolete on lower ⅓ of last whorl; intercostal space as wide as or wider than ribs. Microscopic growth striae present. Varix unremarkable, like adjacent ribs but broader and only a little higher; about ⅓-turn from edge of outer lip. Spiral sculpture absent. Sulcus absent. Ribs slightly lower on shoulder, narrower and slightly recurved on last two whorls. Outer lip thin, without axial folds; edge of anal sinus and outer lip trace a reversed “S”; stromboid notch broad and shallow. Edge of lip from sinus to stromboid notch bent in toward aperture. Anal sinus a deep, broad, U-shaped notch adjacent to the suture; side divergent, aperture not constricted. Inner edge of sinus raised. Inner lip thin, narrow, margined, edge erect anteriorly along columella, recumbent on parietal wall, and formed into a weak callus posteriorly at anal sinus. Anterior canal long for the genus, open, straight, unnotched; anterior fasciole not swollen. Color translucent white.

Remarks. Nomenclature. Multi-specimen lots labeled “ Cerodrillia arcas Steger MS ” were distributed by Dan Steger to museums in anticipation of the publication of his manuscript (around 1970), which never transpired. The whereabouts of his MS is unknown. Lots have been found in ANSP 323999, MCZ 279174, DMNH 107166, DMNH 107187, DMNH 107174, DMNH 46224, and UF 21573 that are this species, in part. They are typically a mix of juvenile and adult specimens, mostly juveniles, with a few juvenile and adult specimens of Cerodrillia porcellana , new species, mixed in. Since some of the specimens were in poor condition, only those clearly identifiable as Lissodrillia arcas , news species are included in the type series. Taxonomy. Lissodrillia arcas has all the characteristics that distinguish Lissodrillia : a very small shell with ribs suture-to-suture, no spiral sculpture, and anal sinus and outer lip edge trace a reversed “S”. It is unique in possessing a longer, more tapering last whorl and anterior canal than most other species in the genus. Variability. The average total length of seven specimens is 5.47 mm (4.6–6.0 mm), and their average W/ L ratio is 0.392. Identification. Lissodrillia arcas is similar to L. verrillii (Dall, 1881) , L. turgida , new species, Syntomodrillia lissotropis (Dall, 1881) , Leptadrillia loria Bartsch, 1934 , Leptadrillia splendida Bartsch, 1934 , and Cerodrillia porcellana , new species. From L. verrillii it differs in having less angular whorl shoulders. From L. turgida it can be distinguished by its more angular, “sagging” whorls, which are evenly round in L. turgida . From the other species it can be distinguished on the basis of differences that separate the genera. Leptadrillia loria and L. splendida have spiral grooves on the anterior fasciole, which are lacking in L. arcas . Cerodrillia porcellana has spiral grooves on the anterior fasciole and a few fine grooves on the shell base. Syntomodrillia lissotropis has spiral grooves on the anterior fasciole and between ribs, although the latter may be almost imperceptible in this species.

Etymology. The Arcas Cays Lissodrillia . Named for Arcas Cays, three small cays 130 km from the mainland west of Campeche State, Mexico. Mr. Dan Steger, the collector of all known specimens, is honored here by retaining his intended minor epithet.

Figures

PLATE 120. Lissodrillia arcas, new species. Fig. 1: holotype, NNW of Arcas Cays, Campeche Bank, Mexico, ventral, lateral & dorsal views (DMNH 46224). Figs. 2 – 6: paratypes, all from the type locality, ventral views. Fig. 2: ANSP 323999; Fig. 3: MCZ 279174; Figs. 4: UF 21573; Fig. 5: DMNH 107187; Fig. 6: MCZ 279174.