Coelosphaeridae Dendy 1922

Family Coelosphaeridae Dendy, 1922

Among studied acanthoxeas, there are some characteristic enough to assign them to the genus level. These are heavily spined, megasclere-sized (170–300 µm) oxeas with coarse spines that undoubtedly belong to the genus Histodermella Lundbeck, 1910 (Figs. 21 A–D). Besides the acanthoxeas, this genus is also characterized by sigma and isochelae microscleres. The isochelae were not found in the studied samples, probably because of their small size (with a single exception; see Fig. 21 I). However, there are some sigma microscleres recorded (Figs. 21 J, K) but their attribution to the genus Histodermella is uncertain because this morphotype of spicules may also appear in numerous other groups of the order Poecilosclerida.

On the other hand, some of these acanthoxeas (Figs. 21 A, B) are identical morphologically to spicules of the Recent species Histodermella australis Dendy, 1924 (compare with van Soest 2002d, figs. 6F, H; and Fig. 22 A) despite the fact that the recent spicules are more than two times smaller than the Eocene spicules. The other species with similar spicules is H. natalensis (Kirkpatrick, 1903) but it is noted only from African waters while H. australis inhabits currently waters around New Zealand (van Soest 2002d; Bergquist & Fromont 1988). There are no species of the genus Histodermella recorded from Australia today (Atlas of Living Australia). Among the studied acanthoxeas, considering all these arguments, the studied spicules belong to Histodermella australis (Figs. 21 A, B) and Histodermella sp. (Figs. 21 C, D). The spicules of such morphology assigned to Histodermella australis are not known, so far, from the fossil record.