The genus Gyrineum is a compact group of species, all of which have solid, strongly sculptured shells with varices fused into two ridges roughly 180° apart up the whole teleoconch. and a conservative sculptural plan with three or. on some parts of some individuals, four spiral cords on the penultimate whorl, and seven or eight forming low variceal nodules on the last whorl. Gyrineum louisae, with its very different sculptural plan, is separated below in the new genus Halgyrineum. Species of Gyrineum also all have very similar apertures, with a nearly continuous peristome (interrupted by the narrowly open anterior canal) and a ridged, weakly flared inner lip. seven nodules inside the outer lip. and a very similar, lightly curved anterior canal (although the length of the canal varies between species). They also all have similar smooth. globose, turbiniform protoconchs, with protoconchs I and II not differentiated, but in some cases the number of protoconch whorls is a very useful species character.
Counting on apical views of enlarged scanning electron micrographs then produces a reasonably objective figure for each species, although some ambiguity is introduced when the initial hemisphere of the protoconch is very small (e.g. G. lacunatum.; G. bituberculare.: G. concinnum). Counts arrived at by this means are: G. pusillum (sensu stricto), 0.8-0.9 whorls: G. roseum, 1.25-1.3 whorls; G. longicaudatum. 1.3-1.6 whorls: G. lacunatum (= G. pusillum of almost all previous authors). 1.8-2.2 whorls (most specimens), to as many as 2.6 whorls; G. gyrinum, 2.2 whorls; G. hirasei. 1.9-2.2 whorls: G. bituberculare, 2.3-2.4 whorls; G. natator. 2.6 whorls; and G. concinnum. ca 2.7 whorls. Clearly, this criterion separates G. pusillum, G. roseum and G. longicaudatum from all the others most readily, but is of little practical use for distinguishing the other six species.
Criteria used to distinguish the remaining six species are size (G. natator and G. bituberculare reach a considerably larger maximum size than the other species), colour pattern (very consistent in most species, but highly varied in G. longicaudatum. G. lacunatum, and G. bituberculare), length of the anterior canal, and coarseness of the sculpture. Some species have their own unique characters, e.g.. the left margin of the inner lip is raised into a narrow free rim, or collar, in G. longicaudatum only.