Hysteroconcha rosea
Similar to Hysteroconcha dione. Hysteroconcha rosea is distinguishable by its less prominent, denser comarginal ribs and fewer anterior lamellar projections. H. rosea also only has one row of posterior spines; whereas, H. dione has two.
Similar to Hysteroconcha lupanaria. Hysteroconcha rosea has less prominent, denser comarginal ribs, fewer anterior lamellar projections and weaker posterior spines. In addition, H. rosea has only one row of posterior spines, and H. lupanaria has two.
The overall shape is elongate, ovate. The anterior, ventral and posterior margins are rounded. The anterior dorsal margin is subconcave, and the posterior dorsal margin is subconvex. The valves are equal in shape and size (equivalve), and there is no gape when they are closed. Sculpture consists of growth lines and erect comarginal ribs. The ribs may split, resulting in more ribs at the posterior than the anterior. The ribs are more prominent anteriorly, and for every 7-8 ribs, one rib is raised, forming a lamellar structure. At the posterior, for every 3-4 ribs, one rib forms a spine. The spines are weak and often broken off. There is only one row of spines at the posterior. The perilunule, lunule and posterior, including the escutcheon, are smoother than the rest of the flank. The lunule is lightly impressed, defined by a fine shallow groove and extends 1/4 the anterior dorsal margin. The umbo is anterior, and the beaks also point slightly to the anterior. The escutcheon is slightly raised, defined by a fine shallow groove and extends 2/3 of the posterior dorsal margin.
The exterior is white with light brown and/or purple coloration covering most of the flank. There is typically a white ray at the posterior, coinciding with the row of spines. The lunule and escutcheon are typically a dark brown or purple. The interior is white with purple coloration at the anterior and posterior dorsal margins, as well as in the pallial sinus.
The ligament is external, extends half the posterior dorsal margin and is supported by nymphal ridges. On the left valve, there are three cardinal teeth, none of which are bifid. The anterior tooth (2a) is weak and the central tooth (2b) is robust; they are joined dorsally, forming an inverted "v" shape. There is also one anterior lateral tooth (A2) on the left valve. On the right valve, there are three cardinal teeth: the anterior (3a) and central (1) teeth are not bifid, and the posterior tooth (3b) is bifid. There are also two anterior lateral teeth (A1, A3), as well as a fine ridge running parallel to the posterior dorsal margin, on the right valve. The posterior adductor muscle scar is slightly larger and rounder than the anterior. The pallial sinus is deep, rounded and extends to the middle of the posterior cardinal tooth in length.
Hysteroconcha rosea is found in the Pacific Ocean, from the Gulf of California in Mexico, to Tumbes in northern Peru (Olsson 1961).