Cyathidium Steenstrup, 1847

Martinez-Soares, Pablo, Roux, Michel, Giusberti, Luca, Gatto, Roberto, Eléaume, Marc & Améziane, Nadia, 2024, New Eocene species of the crinoid genera Holopus and Cyathidium (Cyrtocrinida: Holopodidae) from north-eastern Italy, Zootaxa 5541 (4), pp. 401-437 : 413

Genus Cyathidium Steenstrup in Michaelis & Scherk, 1847

Type-species. Cyathidium holopus Steenstrup in Michaelis & Scherk, 1847, by monotypy.

Synonymy. Cyathidium ( Steenstrup 1847) in Michaelis & Scherk, 1847: 119, 150; Micropocrinus Michelin, 1851: 93 ; Sieverts, 1931:173; Pseudocupressocrinus Valette in Lambert & Valette, 1934: 59; Cyathidium Sieverts-Doreck, 1938: 29 ; Micropocrinus Biese & Sieverts-Doreck, 1939: 117 ; Cyathidium Rasmussen, 1961: 238–239 ; 1978: T839.

Remarks. Žítt et al. (2014) thoroughly described the wide range of shape variation in a lower Turonian population of 136 aboral cups attributed to Cyathidium aff. depressum . The ratio H/D varies from 0.2 to c. 1.0 and usually increases during growth ( Fig. 7 ). The cup curvature is also greatly variable with H/h from 1 to 2.7. Details of characters discriminating the extant species such as interradial morphology and fulcral ridge arrangement ( Améziane et al. 1999) are only preserved in a few specimens, and only parts of the external surface show growth lines and peculiar ornamentation. Therefore, attribution to a new species or to previously described species merely based on aboral cups requires well-preserved specimens and discriminating qualitative characters. Intact fossil specimens with a retracted crown are known exclusively in C. holopus ( Baumiller & Gaździcki 1996; Donovan & Jakobsen 2004; Hess & Messing 2011; Nielsen 1913; Rasmussen 1961). The vault covering the distal arm series is composed solely of IIBr1, their height being substantially greater than their width. IIBr have not yet been described from the large species Cyathidium vlieksi Jagt, 1986 , but are known (Jagt pers. comm.). This species has an aboral cup seemingly very similar to some specimens of C. holopus . Intraspecific variation of the aboral cup in C. holopus and C. vlieksi show two extreme morphotypes: one very depressed, like in C. depressum , and another as high or taller than wide with conspicuous growth lines. The lower Santonian species, C. senessei , differs from all other known congeners in having a stout and tumid curved IBrax, with relatively small distal articular facets facing inwards and subperpendicular to the upper plan of the IBr circlet ( Améziane et al. 1999; Heinzeller et al. 1996; Rasmussen 1961). The central space provided by the IBrax circlet ( Rasmussen 1961, pl. 34 fig. 7c) probably houses IIBr1 keystone plates, but these have not yet been described. Žítt et al. (2014) figured the main discriminating characters of dissociated brachials of C. aff. depressum from the lower Turonian. Unfortunately, IIBr were not available in the original description of C. depressum from the upper Cenomanian but IBr1 were illustrated ( Rasmussen 1961). The presence of granulation on the aboral cup appears highly variable among fossil assemblages and cannot be used as a specific discriminating character except when there are sufficient ossicles to demonstrate the stability of this trait. Another early Campanian form from southern England and north-west France will be published soon (Gale & Jagt, in press).

Included fossil species and occurrence. Cyathidium chiampoensis sp. nov. (lower Lutetian of Chiampo valley, north-eastern Italy), C. depressum including C. aff. depressum first described by Žítt 1996 (upper Cenomanian–lower Turonian, Germany and Bohemia), C. gastaldii (Middle Miocene near Turin, northwestern Italy), C. holopus (upper Maastrichtian of Netherlands, Danian of Denmark and Sweden, lower Eocene of Seymour Island, Antarctica), C. senessei (lower Santonian of Bugarach, southern France), C. vlieksi (Maastrichtian of Belgium, Netherlands), C. sp. nov. (Gale & Jagt, in press; lower Campanian, north-western France and southern England).

Stratigraphic distribution. Upper Cenomanian–Recent.

Figures

FIGURE 7. Main quantitative characters of aboral cup and IBrax in fossil Holopodidae. S: Cyathidium holopus from Seymour Island. Straight lines: values of H/D and H/Wd. Other values in mm.