Syntomodrillia mellea, 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 : 337

Syntomodrillia mellea , new species

( Plate 174 )

Type material. Holotype 5.6 x 2.2 mm (USNM 1291366); 8 paratypes: 6.0 x 2.4, 5.7 x 2.4 mm (USNM 1291367); 6.1 x 2.5, 5.2 x 2.2 & 5.0 x 2.1 mm (ANSP 464995), 6.4 x 2.4, 5.6 x 2.3 & 5.1 x 2.1 mm (EFG 26619), all from the type locality, E. García! aboard R/V Pelican, 11 Jun 2005.

Type locality. SW of Arcas Cays, Campeche Bay, Mexico, 20°00.35'N, 092°26.10'W, in 73– 77 m.

Other material examined. Four additional specimens were examined: 5.6 x 2.2, 5.6 x 2.1, 5.0 x 2.0 mm (H.G. Lee coll.), & 5.3 x 2.2 mm (EFG 26617), in 77–81 m, W of Triángulos Reef, Campeche Bay, Mexico, 20°52.40'N, 92°24.83'W, E. García! aboard R/V Pelican, 10 Jun 2005.

Range and habitat. Mexico (Campeche Bay). Reported from 73–81 m depth.

Description. Shell very small (to 6.4 mm total length), fusiform, surface glossy, translucent, with up to 7¼ convex whorls with peripheries a little below mid-whorl; last whorl approximately 62% of total length. Whorls sculpted with axial ribs. Aperture narrowly oval, with anal notch near suture posteriorly and moderately long canal anteriorly. Protoconch of 1¾ smooth round whorls. Axial sculpture of curved ribs that run suture-to-suture on spire whorls and evanesce at anterior fasciole on last; recurved, narrower, and lower on shoulders, sigmoid on last whorl. Ribs narrow, crests round; intercostal space about the same as their width; number 9–12 on penultimate and 7–9 on last whorl to varix. Growth striae microscopic, most visible on last whorl. Varix is convex, rib-like, straight, only a little higher and wider than adjacent ribs, positioned about ⅓-turn from edge of outer lip. Spiral sculpture consisting of about 6–7 threads on anterior fasciole and of very faint grooves between ribs on last whorl from below the shoulder to anterior fasciole. Sulcus absent; past positions of the anal sinus marked on whorl shoulder by lower and recurved ribs, most evident on last 2 whorls. Outer lip slightly flattened from the base of the varix; surface with coarse growth striae and 2 weak axial folds near lip’s edge; lip edge traces a curve from anal sinus to anterior canal; stromboid shallow, wide, at the beginning of the anterior canal. Anal sinus a wide, moderately deep notch adjacent to suture, outer side divergent, inner edge lightly flared out. Inner lip narrow, emarginated, erect and thick on columella anteriorly, thinner on parietal wall and forming a weak lobe on parietal side of anal sinus posteriorly. Anterior canal moderately long, open, angled slightly to the right when viewed ventrally; notch shallow; fasciole not swollen. Color light to dark golden brown with whitish shell base and varix.

Remarks. Taxonomy. Syntomodrillia mellea possesses the characteristics of the genus: small size, a fusiform shell sculpted with ribs extending from suture-to-suture and to the anterior fasciole on the last whorl, and a varix about ⅓-whorl from the edge of the outer lip. Spiral grooves between ribs are present in examined specimens but very faint. Variability. 13 specimens have an average total length of 5.55 mm (5.0– 6.4 mm), and an average W/ L ratio of 0.409. Identification. Syntomodrillia mellea is similar to Leptadrillia loria Bartsch, 1934 , Cerodrillia minima , new species, S. socolatea , new species, S. triangulos , new species, and S. lissotropis (Dall, 1881) . From L. loria it differs in having a shorter, straighter anterior canal, a more robust shell, not spindly, and a different colorlight golden brown with whitish shell base and varix, not solid white. From C. minima it differs in possessing whorls whose peripheries are below the whorl midpoints not near the midpoint, in lacking the cuphandle-like varix, in lacking spiral threads on the shell base that cross over the ribs, and in possessing a narrower aperture with a slightly flared anal sinus. From S. socolatea it differs in possessing curved ribs that are also sigmoid on the last whorl not slightly opisthocline, in possessing faint spiral microsculpture on the shell base and somewhat more convex whorls. From S. triangulos it differs in being somewhat smaller (5.55 versus 6.81 mm average total length) with a different color—light golden brown with whitish shell base and varix, not solid white to off white. From S. lissotropis it differs in possessing less convex and lower peripheries on spire whorls.

Etymology. The Honey Syntomodrillia ; named for its golden brown color; from the Latin adjective melleus, feminine mellea , meaning “of honey”.

Figures

PLATE 174. Syntomodrillia mellea, new species. Upper Panel. Figs. 1 – 3: holotype, SW of Arcas Cays, Campeche Bay, Mexico (USNM 1291366). Fig. 1: ventral, lateral & dorsal views; Fig. 2: enlarged view of protoconch; and Fig. 3: apical view, V = varix, L = edge of outer lip. Lower panel. Figs. 4 – 11: paratypes, SW of Arcas Cays, Campeche Bay, Mexico. Figs. 4 – 5: USNM 1291367; Figs. 6 – 8: ANSP 464995; Figs. 9 – 11: EFG 26619. Figs. 12 – 15: W of Triángulos Reef, Campeche Bay, Mexico: Figs. 12 – 14: H. G. Lee coll.; Fig. 15: EFG 26617.