Syntomodrillia pusilla, 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 : 342-343

Syntomodrillia pusilla , new species

( Plate 177 )

Type material. Holotype 5.1 x 2.0 mm (SMF 336461).

Type locality. Off Escudo de Veraguas I., Bocas del Toro Prov., Panama, in 201 m, on mud.

Range and habitat. Known only from the holotype.

Description. Shell very small (5.1 mm in total length), glossy, partially translucent, fusiform; with convex whorls with appressed sutures. Whorls number about 7¼, the last approximately 57% of the total length; aperture short, narrowly oval. Protoconch of 1½ translucent, smooth round whorls, the first partially immersed in the second. Axial sculpture of ribs suture-to-suture on spire whorls, to anterior fasciole on last, peripheries at about mid-whorl. Ribs curved on spire whorls, sigmoid on last, number 12 on the penultimate and 12 on the last whorl to the varix. Varix like a swollen rib, about ¼–⅓-turn from edge of outer lip. Lip is re-grown but incompletely developed on holotype. Spiral sculpture of 5 ridges on the anterior fasciole. Microsculpture of distinct intercostal grooves on last and penultimate whorls. Sulcus absent. Prior positions of the anal sinus indicated by recurved ribs on last 2 whorls, and absence of intercostal spiral grooves. Outer lip thin, translucent, without axial ribs on the regrown lip. Edge of lip forms an arc from anal sinus to stromboid notch; stromboid notch is shallow. Anal sinus is a deep notch with a round apex and lies adjacent to suture on shoulder; inner rim of sinus flared out. Inner lip emarginated, lip erect along anterior portion of canal, recumbent elsewhere, narrows to a weak parietal lobe at side of anal sinus. Anterior canal moderately long, open, turned to the right when viewed ventrally, unnotched; anterior fasciole not swollen. Color translucent off-white with a white mid-whorl band.

Remarks. Taxonomy. Syntomodrillia pusilla possesses the combination of characters that are unique to the genus: a small glossy shell, fusiform, sculpted with ribs extending from suture-to-suture and to the anterior fasciole on the last whorl, the presence of intercostal grooves, a short open aperture, and a varix about ⅓-whorl from the edge of the outer lip. Identification. Syntomodrillia pusilla is similar to other small species in the genus. Syntomodrillia triangulos , new species is larger (6.2–7.7 versus 5.1 mm), has weaker intercostal grooves, and is all white, not off-white with a central white band. Syntomodrillia harasewychi , new species is generally larger (6.8– 8.9 versus 5.1 mm), has 2 protoconch whorls, not 1½, and has less convex whorls. Syntomodrillia floridana , new species is larger (7.3–7.8 versus 5.1 mm), has weaker intercostal grooves, 2 protoconch whorls, not 1½, and is white, not off-white. Syntomodrillia cookei (E.A. Smith, 1888) is larger (5.2–8.3 versus 5.1 mm), has weaker intercostal grooves, has less convex whorls, and is a different color. Syntomodrillia woodringi Bartsch, 1934 is larger (7.2–9.7 versus 5.1 mm), has a protoconch with 2–2½ whorls, not 1½, a more tapered last whorl and longer anterior canal, and is white, not off-white. Splendrillia carolinae Bartsch, 1934 has slightly more protoconch whorls (2, not 1½) and a straight anterior canal, not turned to the right. Syntomodrillia lyra , new species is somewhat larger (7.9–8.5 versus 5.1 mm), has slightly more protoconch whorls (2, not 1½), and has a convex anal sulcus.

Although based on only a single specimen, S. pusilla is uniquely different; it does not fit any of the descriptions of similar species as explained above. Also, inasmuch as it is even less similar to other species of Syntomodrillia in the western Caribbean (see Plate 184), and because of the limited range of most species in this genus, describing it as new is felt justified.

Etymology. The Tiny Syntomodrillia , from the Latin adjective pusillus, feminine pusilla , meaning tiny, so named because of its small size for the genus.

Figures

PLATE 177. Syntomodrillia pusilla, new species. Figs. 1 – 3: holotype, off Escudo de Veraguas I., Bocas del Toro Prov., Panama, (SMF 336461). Fig. 1: ventral, lateral & dorsal views; Fig. 2: enlarged view of protoconch (not to scale); Fig. 3: apical view, V = varix, L = edge of outer lip.