Cambraster tastudorum Jell, Burrett, and Banks 1985

Zamora, Samuel, Sumrall, Colin D. & Vizcaïno, Daniel, 2013, Morphology and ontogeny of the Cambrian edrioasteroid echinoderm Cambraster cannati from western Gondwana, Acta Palaeontologica Polonica 58 (3), pp. 545-559 : 554-555

Cambraster tastudorum Jell, Burrett, and Banks 1985

Fig. 6 .

Material.—Several latex casts obtained from the Museum of Victoria Palaeontological Collection including specimens NMVP107060, NMVP107061, and NMVP107063A, B. See Jell et al. 1985 for aditional information.

Diagnosis.—Small to medium Cambraster bearing relatively few epispires at maturity, spiny peripheral skirt, proportionately longer ambulacra at maturity, and well−organized central ventral disk with large, radially arranged plates.

Discussion.— Cambraster tastudorum Jell, Burrett, and Banks, 1985 conforms well to Cambraster cannati and these taxa are considered congeneric. Jell et al. (1985) listed two characteristics as diagnostic of Cambraster tastudorum : epispires developed on the central part of the oral surface in the interambulacra, and a circlet of large, radially arranged contiguous plates surrounding a small number of tiny plates on the aboral surface. Of these characteristics, we consider only the second one as clearly diagnostic of the species. Most of the described specimens of C. tastudorum are generally small, and only a few epispires are present in the largest ones. The relative paucity of epispires is also noted for similar sized specimens of C. cannati where small specimens lack epispires, medium−sized specicannati

Cambraster mens have relatively few, and large specimens have very large numbers. If known specimens of C. tastudorum represent the mature condition for the species, than paucity of epispires is a valid taxobasis. If, however, known specimens are submature, and epispires are added later in ontogeny, this feature is non−diagnostic.

As mentioned above, the plating of the aboral surface of a large Cambraster tastudorum ( Fig. 6D ) shows a similar arrangement to only the smallest known specimens of Cambraster cannati suggesting heterochronic evolution. Unfortunately, there is no data to polarize this transformation to determine if C. tastudorum is paedomorphic with respect to C. cannati or if C. cannati is peramorphic with respect to C. tastudorum . Regardless, the relative juvenilization of the aboral surface of C. tastudorum serves to separate the two species.

However, the tips of the ambulacra are proportionately longer in C. tastudorum than they are in similar−sized specimens of. cannati (see below). If interpreted as heterochrony, the polarity of this transformation is in the opposite direction as the development of the aboral surface being more developed in C. tastudorum with respect to C. cannati . This feature is consistent between specimens of both species and serves to distinguish the two taxa.

Stratigraphic and geographic range.—Cateena Group, middle Cambrian (Cambrian series 3, Drumian), road cutting just S of Gawler River on Isandula Road, 8 km south of Ulverstone, N Tasmania, Australia.

Figures

Fig. 6. Edrioasteroid echinoderm Cambraster tastudorum Jell, Burrett, and Banks, 1985 from the Cambrian Cateena Group, Australia. A. NMVP107063B, oral view of a complete specimen. B. NMVP107061, oral view of a complete specimen. C. NMVP107060, oral view of a nearly complete specimen showing the peristome bounded by interradial plates (mfp), flooring plates (fp), and apertures for the water vascular system (p). General view (C1) and detail of the oral plating showing the interradial elements constructing the mouth frame (C2). D, E. Aboral view of two specimens showing the plating pattern with large radial elements (rap). NMVP107068 (D) and NMVP107063A (E). Scale bars 2 mm.