Gomphina undulosa
Similar to Gomphina aequilatera. Gomphina undulosa is distinguishable by its more trigonal, less elongate shape, as well as its rugose nymphs. The lunule of G. undulosa is wider and lanceliform (spear-shaped); whereas, the lunule of G. aequilatera is very narrow. Also, the central tooth (2b) on the left valve if bifid only in G. aequilatera.
Similar to Gomphinella habei. Gomphina undulosa is distinguishable by its more ovate shape, slightly less inflated valves and overall larger size. Also, G. undulosa is typically found in Australia; whereas. G. habei is found in China and Japan (Huber 2010).
The overall shape is trigonal ovate. The posterior margin is slighlty more pointed than the anterior. The anterior dorsal margin is nearly straight, and the posterior dorsal margin is subconvex. The valves are equal in size and shape (equivalve), and there is no gape when they are closed. Sculpture consists of growth lines and very fine comarginal ribs. The lunule is defined by a fine shallow groove and extends 3/4 of the anterior dorsal margin; it is not impressed. The umbo is slightly anterior and the beaks also point slightly to the anterior. The escutcheon is not well defined.
The exterior is white and typically covered with light brown, fine zig-zag patterns. The pattern can also be dark brown. The interior is white.
The ligament is external, extends 1/3 of the posterior dorsal margin and is supported by nymphal ridges. There are three cardinal teeth on the left valve (2a, 2b, 4b), none of which are bifid. The posterior tooth (4b) is fused with the nymph; the shallow groove between the nymph and the appressed tooth has a rugose texture. 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 lightly bifid. The nymph is slightly rugose on the right valve. There are no lateral teeth on either valves. The anterior and posterior adductor muscle scars are similar in area, but the anterior is slightly more elongate in shape. The pallial sinus is rounded and shallow.