Genus Partecosta Dance & Eames, 1966

(Fig. 3 F–O)

Type species: Strioterebrum wilkinsi Dance & Eames, 1966 (= Terebra fuscobasis E.A. Smith, 1877); OD.

Definition: Includes species with combination of conchological, anatomical and distributional characteristics closely comparable with Strioterebrum wilkinsi, including all species in clade F2 of Modica et al. (2019) and any species proven to be a member of this clade.

Diagnosis: Diagnostic nucleotide combinations in Table 2.

Shell: Small, 10–30 mm, pale or tan, often with spiral bands and dark basal area. Protoconch 1.5–3 whorls. Predominant sculpture of axial ribs spanning whorl height, resulting in even, slightly convex whorl outline, typically interrupted by depression or narrow groove forming subsutural row of nodules. Spiral sculpture indistinct or of fine regular striae. Siphonal canal very short, stout, indistinctly or shallowly notched, with strong fasciole. Aperture wide, pyriform.

Anatomy: Rhynchodeal introvert small; salivary glands and radular sac present; radula of solid curved marginal teeth attached to strong membrane. Venom gland, proboscis and accessory proboscis structure absent.

Distribution: Indian Ocean; intertidal and shallow subtidal.

Remarks: Three clusters with varying sculpture patterns can be recognized:

Partecosta fuscobasis group: sculpture of strong ribs and clearly delineated subsutural band forming distinct nodules at intersections with ribs (Fig. 3 F–I). Closely comparable with New World genus Neoterebra, but can be differentiated by smaller size, wider aperture, usually with wide anterior notch, and solid curved radular teeth.

Partecosta trilineata group: glossy shells sculptured by strong continuous ribs; no distinct spiral sculpture or subsutural band (Fig. 3K, L). Very similar sympatric forms are known in genus Punctoterebra (i.e. Punctoterebra solangeae Bozzetti, 2015 group) that can only be reliably differentiated by anatomical characters (radula lacking in P. solangeae; of solid curved teeth in Partecosta spp.).

Partecosta macleani group: flattened whorl outline, very short robust siphonal canal; very weak sculpture of rounded, indistinct subsutural nodules extended into even less distinct axial folds on whorl periphery (Fig. 3M). Some species of Hastula are close to P. macleani, but are commonly larger, have polished surface and retain distinct ribbing at least on adapical portions of whorls.

Included species:

Partecosta albofuscata (Bozzetti, 2008) 1 n. comb.;

P. bozzettii n. sp. Malcolm, Terryn & Fedosov 1;

P. fuscolutea Bozzetti, 20082 n. comb .;

P. macleani (Bratcher, 1988) 1 n. comb.;

P. nassoides (Hinds, 1844) 1 n. comb.;

P. sandrinae (Aubry, 2008) 1 n. comb.;

P. trilineata (Bozzetti, 2008) 1 n. comb.;

P. varia (Bozzetti, 2008) 1 n. comb.;

P. fuscobasis (E.A. Smith, 1877) 2 n. comb.;

P. fuscocincta (E.A. Smith, 1877) 2 n. comb.;

P. herosae (Terryn & Rosado, 2011) 2 n. comb.;

P. macandrewii (E.A. Smith, 1877) 2 n. comb.;

P. padangensis (Thiele, 1925) 2 n. comb.;

P. tantilla (E.A. Smith, 1873) 2 n. comb.;

P. tenera (Hinds, 1844) 3 n. comb;

P. veliae (Aubry, 1991) 3 n. comb.