Chionopsis amathusia

Chionopsis amathusia is a venerid clam that R. A. Philippi described in 1844 under the name Venus amathusia ^[1]. It lives in the tropical eastern Pacific, from the Gulf of California to the far north of Peru, and the annotated checklist of Peruvian bivalves places it on sandy bottoms from the intertidal zone down to 73 m ^[2]. Its shell is ovate-triangular and convex, and well-preserved specimens have an elaborate sculpture ^[3].

Olsson describes an ovate-triangular, convex shell with full, prominent umbones, a somewhat longer posterior side and an anterior margin deeply excavated beneath a wide, heart-shaped lunule; size varies, but it seldom exceeds 58 mm ^[3]. The sculpture is made of numerous raised concentric lamellae tilted backwards, and both the lower face of those lamellae and the spaces between them are engraved with fine radial cords ^[3]. The colour is usually a plain cream, sometimes a muddy brown, with the lunule and escutcheon deep brown ^[3].

The IMARPE guide to recognising commercial bivalves draws it as subtriangular, somewhat inflated and relatively thick, cream on the outside and white inside, with raised, spaced concentric ribs, small radial ribs and small spines alternating on the concentric grooves ^[4]. The same guide gives a maximum size of 74 mm of valve length ^[4].

Olsson treats Chionopsis as a full genus, set apart from Chione in the strict sense by thinner, more convex valves and a larger, deeper pallial sinus, with 3 cardinal teeth in each valve ^[3]. MolluscaBase accepts Chionopsis amathusia as the valid name and regards Chione jamaniana and Venus darwinii as unaccepted synonyms ^[1].

Similar species

• Chionopsis gnidia: According to Olsson, it is similar but larger and heavier, with the concentric lamellae more widely spaced ^[3].

Olsson considers it a common and widely distributed species, ranging from the Gulf of California to northern Peru ^[3]. The annotated checklist by Paredes and colleagues records it from La Paz, Baja California, and the Gulf of California (Sonora, Mexico) to Punta Peña, Tumbes, Peru ^[2]. The IMARPE guide gives the same southern end, under the name Punta Peña Mala ^[4].

According to the annotated checklist, it lives on sandy bottoms, from the intertidal to the sublittoral zone, to a maximum of 73 m ^[2]. The IMARPE guide describes it on soft bottoms of the intertidal zone, down to 75 m depth ^[4]. The two sources differ slightly on the maximum depth ^[2],[4].

The annotated checklist marks the species as commercial in Peru ^[2]. The IMARPE guide includes it among the 34 bivalve species reported in the fishery landings that the institution has recorded in different parts of the coast ^[4]. Neither source gives landing figures for this species ^[2],[4].

Olsson recorded the species in Peru at Tumbes, Zorritos, Boca Pan and Máncora, in a work published in 1961 ^[3]. The 2016 annotated checklist fixes its southern limit at Punta Peña, Tumbes ^[2]. Neither source says whether those places are hard to reach or restricted, or whether the species is seen while diving ^[3],[2].