Rhynchopygus d’ Orbigny, 1856

Holmes, Francis C., 2004, A new Late Eocene cassiduloid (Echinoidea) from Yorke Peninsula, South Australia, Memoirs of Museum Victoria 61 (2), pp. 209-216 : 210-211

Rhynchopygus d’ Orbigny, 1856

Type species. Cassidulus marmini Agassiz, in Agassiz and Desor, 1847 , by monotypy.

Diagnosis. See Smith and Jeffery (2000: 191)

Remarks. Because of its monobasal apical system ( Fig. 3 ) and lack of known phyllode detail, the new Late Eocene species from South Australia can only tentatively be assigned to the genus; although Smith and Jeffery (2000: 192) suggested that the apical system of Rhyncopygus donetzensis Faas, 1918 , may indeed be monobasal or at least have very reduced genital plates. Rhyncopygus, has been used in the past 150 years as a genus or subgenus to accommodate nearly 40 species, ranging in age from early Late Cretaceous (Turonian) to Recent. Virtually all of these species have subsequently been reassigned to other genera, namely Cassidulus Lamark, 1801 , Eurhodia Haime, 1853 , Procassidulus Lambert, 1918 , Rhyncholampas Agassiz, 1869 , and even the holasteroid Corystus Pomel, 1883 . The type species of all these genera, except Eurhodia , have at some time been assigned to Rhynchopygus . The most recent review of Rhynchopygus ( Smith and Jeffery, 2000) noted that the differently shaped and positioned periprocts of three species included in the genus by Kier (1962), the type species R. marmini , R. lapiscancri ( Leske, 1778) and R. macari ( Smiser, 1935) , preclude uniting them into a single genus-level taxon; referring only to R. marmini and R. donetzensis as belonging to the genus. Although R. donetzensis was listed by Lambert and Thiéry (1925: 588), no reference to this important species was made by Kier (1962). R. lapiscancri has since been assigned by van der Ham et al. (1987) to Procassidulus and R. macari by Smith and Jeffery (2000) to Rhyncholampas . Without comment the latter authors also assigned both Rhynchopygus and Procassidulus to the Faujasiidae , rather than the Cassidulidae .

Both Mortensen (1948: 201) and Kier (1962:161) blame the inaccurate illustrations of d’Orbigny (1856: pl. 927) for the early taxonomic problems in defining Rhynchopygus . While this is unquestionably true, d’Orbigny(1856) and Desor (1855 –1858) did illustrate and refer to the prominent lip-like projection of the test that occurs in interambulacrum 5 adjacent to the periproct; the main feature now considered to distinguish Rhynchopygus from genera which have many other characteristics in common. However, Mortensen (1948) considered this projection to be of no generic value and Kier (1962) did not even mention it in his generic diagnosis, but added to the confusion by describing the periproct opening as either transverse or longitudinal, presumably to accommodate other species then assigned to the genus.

Mortensen (1948) considered Rhynchopygus a synonym of Cassidulus while Kier (1962) regarded the tetrabasal apical system as a major feature separating the two genera. In addition he deemed Procassidulus , a genus retained by Mortensen, to be a synonym of Rhynchopygus .

Figures

Figure 3. Apical plate structure. A and B, Rhynchopygus? janchrisorum sp. nov., Late Eocene holotype NMV P145616; C, R. marmini, Late Cretaceous USNM 19559 from Port Brechay, La Manche, France (drawing adapted from Kier, 1962). Scale bars 1mm.