Tethyidae Gray, 1848

Łukowiak, Magdalena, 2015, Late Eocene siliceous sponge fauna of southern Australia: reconstruction based on loose spicules record, Zootaxa 3917 (1), pp. 1-65 : 27

Family Tethyidae Gray, 1848

A single, spherical microsclere with bulb-shaped, tightly arranged projections ( Fig. 13 E) was found in the studied sample that closely resembles microscleres of Recent Tethya omanensis Sarà & Bavestrello, 1995 (compare with Fig. 14A ). However, micrasters of T. omanensis are about 10 Μm of diameter and the studied Eocene spicule from Australia is much larger, exceeding 80 Μm. Nevertheless, its morphology is almost identical with the discussed Recent microscleres. Unfortunately, the other spicule types characteristic for this species (megasters and other micrasters) have not been found in the studied samples. One has to mention that today Tethya omanensis has been recorded only from Oman and the Western Arabian Sea (van Soest & Beglinger 2008).

There were also numerous oxyasters ( Figs. 13 F–H) found in the studied material and some of them resemble those of Recent Tethyastra oxyaster Burton, 1934 (described as Tethyorrhaphis oxyaster ; see Fig. 14 B). In this case the spicules of this Recent species described by Burton (1934) may be from 200 to 2000 Μm, whereas the ones described here are about 300 Μm in size. The assignment of studied oxyasters to this species or its ancestor seems to be justified not only because of the great morphological resemblance, but also by the fact that T. oxyaster is today noted from all over Australia (van Soest et al. 2013).

Spicules of morphology similar to those of Tethyastra oxyaster were already described from the fossil record e.g., by Hinde & Holmes from the Late Eocene of New Zealand (1892, fig. 14.24) but this is the first fossil occurrence of very characteristic micrasters of Tethya cf. omanensis .

Figures

FIGURE 13. Spicules of sponges of the order Hadromerida; A – D—Different types of selenasters of Placospongia sp., family Placospongiidae; E—Micraster of the Tethya cf. omanensis, family Tethyidae; F – H—Oxyasters of the Tethyastra oxyaster, family Tethyidae.

FIGURE 14. A. Micraster of recent Tethya omanensis (redrawn from van Soest & Beglinger 2008); B—Oxyaster of recent Tethyastra oxyaster (redrawn from Burton 1934).