Shell small, elongate. usually decollate, and pupoid with gibbous midwhorls; teleoconch sculptured with axial ribs, body whorl constricted, Columella with strong internal plait Aperture narrowly ovoid and with expanded outer lip. Operculum corneous, ovoid, paucispiral. with subterminal nucleus.
There are several notable diagnostic shell features of Colina species. This genus is easily identified by its unusual fusiform, frequently slender, pupate shell having inflated midwhorls and a highly constricted body whorl. Early whorls are concave in outline, while adult midwhorls are inflated and usually sculptured with large axial ribs. The bodywhorl is constricted and narrow, relatively weakly sculptured, and has an elongate, ovate aperture. In addition, the upper whorls are frequently decollate and a secondary apex is added as a plug, enhancing the pupate shape.
The truncated apex is a distinctive feature of the shell of Colina species. Although decollation and formation of a secondary apex occurs in shells of Cerithidea species, familx Potamididae ( Houbrick. 1984), this phenomenon is not seen in other genera of the Cerithiidae nor in members of other cerithioidean families.
The protoconch of Colina macrostoma is smooth, comprises one whorl, and is indicative of direct development It differs totally from the elaborately sculptured protoconchs ot litiopids and is unlike those of most Bittium and Cerithium species that have pelagic veliger larvae. However, Cerithium species with direct development have protoconchs similar to those in Colina. Cossmann’s (1989) assertion that the protoconch of Colina was unlike those of cerithiids and more like those ol cerithiopsids such as Lovenella, is probably due to his mistaken notion that the secondary apex of decollate Colina individuals he examined was the real protoconch.
Early whorls of Colina species are sculptured with three to four spiral cords, the two anterior ones being strongest . Kilburn and Rippey noted that "Juveniles resemble very narrow, very high-spired trochids, with a flattened base and short, sharp siphonal spout. “ Immature Colina pinguis shells have a concave outline, and look very much like adult Trochocerithium species .
Of the three Colina species recognised until now, Colina pinguis has the largest, widest shell. In contrast, Colina macrostoma commonly is highly elongate and slender, some morphs attaining almost a nail-like shape . This species also has the most variable shell sculpture within the genus. The shell of Colina selecta has a sculpture that closely resembles Colina macrostoma, but is more finely cancellate