Cerodrillia minima, 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 : 71

Cerodrillia minima , new species

( Plate 29 )

Type material. Holotype 4.9 x 2.3 mm, ex coll. H.G. Lee (UF 496651); a total of 18 paratypes: 5 from the type locality (all types E. García! aboard R/V Pelican, 16 Jun 2005): 5.2 x 2.3, 6.0 x 2.4, 6.0 x 2.4, 5.6 x 2.5 mm, ex coll. H.G. Lee (UF 496652), & 5.3 x 2.3 mm (EFG 26620A); 9 spec., 5.7 x 2.4, 5.4 x 2.3, 5.3 x 2.4 mm (USNM 1291331), 5.7 x 2.5, 5.4 x 2.4, 4.5 x 2.1 mm (ANSP 464984), 5.9 x 2.5, 6.0 x 2.5 & 5.5 x 2.3 mm (EFG 26619A), in 73–77 mm, approximately 53 km SW of Arcas Cays, Campeche Bank, 20°00.35'N, 092°26.10'W, E. García! aboard R/V Pelican, 11 Jun 2005; 4 spec., 6.0 x 2.5, 5.7 x 2.6, 5.2 x 2.3 & 4.9 x 2.3 mm, in 77–81 m, 16 km SW of Triángulos Reefs, Campeche Bank, 20°52.40'N, 092°24.83'W, E. García! aboard R/V Pelican, 10 Jun 2005 (EFG 26617A).

Type locality. NW of Arenas Cay, outer Campeche Bank (off Yucatan State), Mexico, 22°16.28'N, 091°30.42'W, in 107– 108 m.

Range and habitat. Mexico (Outer Campeche Bank: SW of Arcas Cays; SW of Triángulos Reefs; NW of Arenas Cay). Reported from on mud at 77– 108 m.

Description. Shell very small (to 6.0 mm), fusiform, mostly translucent, of 6.5–7 convex whorls, the last comprises an average of 60% of total shell length. Protoconch 1¾–2 smooth regularly expanding translucent whorls, the first partially imbedded in the second, producing a blunt apex. Axial sculpture of strong ribs, 9–12 on penultimate, 8–12 on last to varix, curved, running suture-to-suture, sigmoid on base and evanesce at anterior fasciole; round in axial profile with no change in sulcal area. Rib crests ridged in cross section. Very fine growth striae present over entire shell. Varix positioned behind anal sinus, cup-handle-like. Spiral sculpture limited to a few (1–5) spaced spiral threads on base, and indistinct ridges on anterior fasciole. Anal sinus moderately deep, wide, edges slightly divergent; set off a short distance from the suture. Sulcus indistinct; ribs little changed. Outer lip thin, jutting outward from the base of the varix, without strengthening ribs; edge forms a low arc from and congruent with the anal sinus to the anterior canal; stromboid notch not seen in examined specimens. Inner lip erect on canal, thin and unemarginate, or only faintly so on parietal wall, a low callus present at suture. Anterior canal long for the genus, straight, unnotched; anterior fasciole not swollen. Color a uniform light golden brown, protoconch and aperture lighter.

Remarks. Taxonomy. Cerodrillia minima has all the characteristics that define the genus: ribs that extend from suture-to-suture with little change in the sulcal area, a cup-handle-like varix behind the anal sinus, ¼-turn from the edge of the lip, an anal sinus spout-like, and spiral microsculpture restricted to the shell base. It is unique for the relatively long anterior canal and its small size. Variability. The 19 examined shells have an average length of 5.48 mm (4.5–6.0 mm); their average W/ L ratio average is 0.436. Identification. Cerodrillia minima is not easily confused with its congeners; however, its small size, color, and habitat are similar to Syntomodrillia triangulos , new species, and Syntomodrillia mellea , new species. These latter species differ in possessing ribs that “sag” such that the whorl peripheries are below mid-whorl, their varix is not cup-handle-like and is located further away from the edge of the outer lip, and in possessing a narrower aperture with a spout-like anal sinus.

Etymology. The Smallest Cerodrillia . From the Latin minima , feminine form of the adjective minimus, meaning smallest.

Figures

PLATE 29. Cerodrillia minima, new species. Upper panel. Figs. 1 – 3: holotype, NW of Arenas Cay, Campeche Bank, Mexico (UF 496651). 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. Lower panel, paratypes. Fig. 4: off Arcas Cays, Campeche Bank, Mexico (EFG 26619 A); Figs. 5 – 6, 10 – 11: NW of Arenas Cays, Campeche Bank, Mexico (UF 496652); Figs. 7 – 9: off Arcas Cays, Campeche Bank, Mexico (USNM 1291331); Figs. 12 – 15: SW of Triángulos Reefs, Campeche Bank, Mexico (EFG 26617 A).