Cassideus Pessagno, 1969

Dumitrica, Paulian & Zügel, Peter, 2003, Lower Tithonian mono- and dicyrtid Nassellaria (Radiolaria) from the Solnhofen area (southern Germany), Geodiversitas 25 (1), pp. 5-72 : 38-40

Genus Cassideus Pessagno, 1969

TYPE SPECIES. — Cassideus riedeli Pessagno, 1969 ; original designation.

EMENDED DIAGNOSIS. — Dicyrtid, conical, helmetshaped Cuniculiformiidae with two long, three-bladed cephalic horns representing prolongations of apical and ventral spines of the initial spicule. Initial spicule without dorsal spine. Cephalis small, perforate. Thorax conical proximally, flaring distally to form broad thoracic skirt. Boundary between conical thorax and flaring skirt marked at the inner side by an imperforate circumferential ridge. Thoracic wall coarsely perforate, pores alternate, arranged in circumferential rows. Thorax with or without one or more external circumferential ridges. Without thoracic velum.

RANGE. — Tithonian or older to Cenomanian.

REMARKS

The genus Cassideus was erected for two lower Cenomanian species characterised by a dicyrtid, helmet-shaped test with two long primary horns (apical and ventral) and a conical, distally flaring thorax forming broad thoracic skirt. It was originally included within the family Neosciadiocapsidae Pessagno, 1969 but, according to the original remarks, it differed from all other Neosciadiocapsidae genera by possessing two primary horns and by lacking a cephalopyle and a thoracic velum. The absence of the velum was supposed to be due to preservation.

Based on a basal view of a paratype of the type species ( Pessagno 1969: pl. 27, fig. 1), the genus was considered as possessing the dorsal spine. The presence of this spine in Cassideus created initially problems in the assignation of our three new species to this genus because, although their morphology was of Cassideus type, none of them has the D spine. In this situation we were tempted to assign them to the genus Cuniculiformis De Wever, 1982 , but this genus has no thoracic skirt. The best solution would have been to erect a new genus for our species, a genus that would have combined the morphology of the genus Cassideus with the initial cephalic structure of the genus Cuniculiformis , or to make our own investigation of cephalic structure on the two species of the genus Cassideus ( C. riedeli and C. yoloensis ). Our attempt to find in the lower Cenomanian type sample (NSF 350 of Pessagno 1969) the two species failed, but we succeeded in finding two specimens of Cassideus yoloensis in the upper Albian sample NSF 884 of Pessagno (1977b). Their investigation has shown that none of these specimens has the D spine. How then could be interpreted the presence of this spine in C. riedeli , the type species of the genus? Several answers were possible: 1) this species certainly has the D spine; if so, its morphology did not correlate with what we knew from the other species assigned herein to this genus and from the other species of the genus Cuniculiformis , that is especially the presence of the two long cephalic horns; 2) normally C. riedeli has no D spine, its presence in the specimen illustrated is an anomaly; 3) Cassideus riedeli and C. yoloensis are not congeneric; this possibility would have been strange because all the other characters answer perfectly the definition of the genus; and 4) the paratype that shows the D spine and that is illustrated as C. riedeli does not belong to this species and genus.

It is this last possibility that we consider the solution of the problem. The specimen illustrated by Pessagno (1969: pl. 27, fig. 1) in a basal view and which shows a dorsal spine does not represent Cassideus riedeli but Petasiforma glaskockensis Pessagno, 1969 . This is the only neosciadiocapsid species occurring in the type sample and possessing several circumferential ridges similar to those of Cassideus riedeli . In our attempt to solve this problem we found a well preserved specimen of P. glaskockensis in the type sample (NSF 350) and studied it thoroughly. In basal view the cephalic structure is perfectly the one illustrated by Pessagno in what he considered C. riedeli : a well developed dorsal spine and a rather long axobate. There is another argument in favour of our idea. The specimen illustrated by Pessagno shows the apical part of the cephalis broken off. C. riedeli , with its robust apical and ventral horns and ribs on cephalis could not break like that specimen. Only P. glaskockensis , with its thin, fragile cephalic wall, could show such a break.

Thus, the genus Cassideus has no dorsal spine and must be transferred from the Neosciadiocapsidae to the family Cuniculiformiidae . Its definition is herein emended accordingly. It derived probably from the genus Cuniculiformis by acquiring a thoracic skirt and an internal circumferential ridge separating the two segments.