Murraypneustes, Holmes & Yee & Krause, 2005

Holmes, Francis C., Yee, Christopher Ah & Krause, Janice, 2005, Two new Middle Miocene spatangoids (Echinoidea) from the Murray Basin, South Australia, Memoirs of Museum Victoria 62 (1), pp. 91-99 : 92-93

Murraypneustes gen. nov.

Type and only known species. Murraypneustes biannulatus sp. nov.

Diagnosis. Large ovoid spatangoid with centrally depressed adapical surface, apex well posterior of centre. Apical system ethmolytic with 4 gonopores. Aboral primary tubercles of 2 distinct sizes, small and randomly spaced, the larger proximal to the ambitus. Labrum long, narrow, partially tuberculate, extending to third ambulacral plate. Two ‘peripetalous’ fascioles present; one marginal, passing above the periproct (pseudolateral); the second, rudimentary, non re-entrant and clear of the distal ends of paired petals. Intermittent horizontal fasciole bands also occur between the 2 ‘peripetalous’ fascioles. Subanal fasciole in contact with marginal periproct.

Etymology. For the Murray River cliffs, the origin of the fossils, and “pneustes”, a common suffix used for spatangoid echinoids. Gender masculine.

Remarks. The following analysis of morphological features of genera similar to Murraypneustes gen. nov. is based primarily on Mortensen (1950a) and Smith et al. (2003). Although approximately 30 genera within the Micrasterina have been investigated, only eight warranted further scrutiny; four currently unassigned to a family by Smith et al. (2003), Elipneustes Koehler, 1914 , Eurypatagus Mortensen, 1948 , Linopneustes A. Agassiz, 1881 , and Platybrissus Grube, 1865 ; three belonging to the Maretiidae ( Lambert, 1905) , Eupatagus L. Agassiz, 1847 , Mazzettia Lambert and Thiéry, 1915 and Spatagobrissus H. L. Clark, 1923 ; and Macropneustidae genus Lajanaster Lambert and Sanchez Roig, 1924 .

Using a broad comparison of 38 features, Linopneustes stands out from the other seven genera as having closest affinity with Murraypneustes ; four of its recorded six species, L. longispinus (A. Agassiz, 1878) , L. fragilis (de Meijere, 1903) , L. spectabilis (de Meijere, 1903) , and L. brachipetalus Mortensen, 1950b having distinct marginal peripetalous fascioles passing above the periproct. In the other two, L. murrayi (A. Agassiz, 1879) and L. excentricus de Meijere, 1903 , the peripetalous fasciole is not marginal but somewhat higher up on the test ( Mortensen, 1950a: 221). Although L. fragilis has multiple fasciole bands around the ambitus, L. murrayi a rounded margin (Smith, pers. com. 2005) and L. longispinus relatively short closing petals; Murraypneustes is distinguished by its centrally depressed aboral surface forming four apices (domed on Linopneustes ) with the highest point of the test posterior to the apical disk (anterior in Linopneustes ), the presence of two ‘peripetalous’ fascioles and intermittent horizontal fasciole bands, two distinct sizes of small randomly spaced aboral primary tubercles, the larger restricted to the area outside the upper ‘peripetalous’ fasciole, and a prominent angular subanal fasciole.

Based on the same criteria, three other genera show a moderate degree of morphological similarity to Murraypneustes , namely Elipneustes , Mazzettia , and Eupatagus .

Elipneustes , however, can be distinguished by its very long, parallel-sided, open-ended, flush petals with conjugate pore pairs; single, narrow, marginally situated peripetalous fasciole; peristome situated immediately below the apical disk; small thickset plastron with minimal posterior swelling; and much larger primary tubercles scattered over all the aboral interambulacra.

Mazzettia , a poorly known fossil genus, has an elongated heart-shaped test with a low sharp margin, very long weaklybowed petals closing distally, no recorded peripetalous fasciole and only occasionally a weak shield-shaped subanal fasciole, an elongated labrum just reaching the relatively small plastron, and random but closely spaced coarse tubercles aborally.

Eupatagus , although possessing well developed peripetalous and subanal fascioles is easily categorised by its lack of an anterior sulcus, predominately short lanceolate closed petals, primary tubercles of varying density restricted to the area within the peripetalous fasciole in aboral interlambracra 1–4, and very small evenly spaced tubercles distally over the remainder of the aboral surface. Comparison of other features is difficult because of variability among the very large number of described species. In particular, the eight Australian fossil species vary considerably in profile, are generally more rounded, and have an extremely wide range of primary tubercle densities when compared with the type species on which the generic description is based.

Two other genera, Platybrissus and Eurypatagus , are distinguished by their complete lack of fascioles, although the former may have a subanal fasciole present in juvenile specimens.

Lajanaster , although depressed aborally, has no anterior sulcus, a relatively sharp ambitus, a markedly narrow plaston, and primary tubercles confined to the posterior column of anterior and lateral interambulacra within the peripetalous fasciole.

Spatagobrissus was included in the comparative analysis, primarily as a new species of the genus occurs at the same locality ( PL 3203) as Murraypneustes . In most respects the former is very similar to Eupatagus but has shorter petals and only small tubercles over the whole of the aboral surface.