Cassitella, Malinky & Skovsted, 2004

Malinky, John M. & Skovsted, Christian B., 2004, Hyoliths and small shelly fossils from the Lower Cambrian of North-East Greenland, Acta Palaeontologica Polonica 49 (4), pp. 551-578 : 574

Genus Cassitella nov.

Type species: Cassitella baculata sp. nov. Monotypic.

Etymology: From Latin cassis, helmet and Latin Tellus, god of the Earth, for the resemblance of the shell in lateral view to a helmet.

Diagnosis.—Subtriangular to almost circular convex shells with rounded apex displaced towards the higher (proximal) side. Exterior with fine concentric ribs and depressions. Interior with two prominent, widely diverging ridges emanating from proximal edge of shell. Distal termination of ridges free from the shell margin and divided into distinct lobes.

Remarks.—Although at this time poorly understood, the unusual morphology of Cassitella makes this genus distinguishable from all other cap−shaped problematica described from the Early Cambrian. Cassitella resembles a hyolithid operculum and the ridge−like structures on the interior are suggestive of the clavicles ordinarily seen among hyolithids (but see Hyptiotheca ), although there are no cardinal processes associated with them. The lobate distal ends of the “clavicles” are also unusual and have not been documented in any unequivocal hyolithid. Some individuals of Cassitella baculata display a saddle−shaped profile with the shell curving upward between apex and proximal edge. The hyolithid Patholites Marek et al., 1997 (for which the operculum is unknown) from the Middle Cambrian of Morocco possesses an unusual aperture which could have been closed by a saddle−shaped operculum.

There is some resemblance in terms of external morphology between Cassitella and the problematical Ocruranus Liu, 1979 and Eohalobia Jiang in Luo et al., 1982 from the Meishucunian of South China. Shells referable to Ocruranus occur together with Cassitella in the Bastion Formation (Skovsted, unpublished). However, like the Chinese fossils, these shells lack clavicle−like structures on the interior. Ocruranus and Eohalobia appear to be most closely comparable to helcionelloid molluscs, although as Qian and Bengtson (1989) pointed out, they have previously been interpreted variously as brachiopods, bivalves, polyplacophorans or tommotids. At this time, the most likely affinity of Cassitella appear to be to hyoliths, although the presumed conch remain to be discovered.