Late Eocene siliceous sponge fauna of southern Australia: reconstruction based on loose spicules record Author Łukowiak, Magdalena text Zootaxa 2015 3917 1 1 65 journal article 36729 10.11646/zootaxa.3917.1.1 39ff92ed-ddb8-4ec4-af8a-19e3288fdbd1 1175-5326 287785 D8CB263D-645B-46CE-B797-461B6A86A98A Family Mycalidae Lundbeck, 1905 Numerous mycalid spicules were found in the studied material. These nail-shaped spicules called exotyles ( Figs. 19 F–L) are 300–400 µm long. They closely resemble spicules of the poecilosclerid sponges of the family Mycalidae . There is some morphological variability of these dermal spicules found in the studied fossil material. Some of them possess a shallow depression at the top of the disc and a small, button-shaped projection in the disc centre (e.g., see Figs. 19 I–L) whereas the others display a flat disc with no button visible (e.g., see Figs. 19 F–H). This variation may suggest that they represent two different species but intraspecific variability cannot be excluded as we know very little about the sponges bearing them. Those with a central depression closely resemble those of the Recent species Mycale (Rhaphidotheca) loricata ( Topsent, 1896 ) (see van Soest & Hajdu 2002 , figs. 13A, B). The 200 µm long spicules described by Topsent do not, however, possess the button at the center of the depression ( Figs. 20 D, E). While the exotyles with a flat disc surface and without the central button may belong to the other sister species (as the sponges bearing exotyles with a flat disc are not known among present-day species), the ones with a central depression may be assigned, most probably, to Mycale (Rhaphidotheca) cf. loricata . The exotyles have already been described from the fossil record from the Late Eocene of Norseman (western Australia ) by Hinde (1910) while Bukry noted similar spicules from the Middle Miocene from around Greenland (1979, pl. 8, fig. 3). There were also some other club-shaped spicules found ( Figs. 30 Q, U) that are very similar to the spicules occurring in Mycale (Rhaphidotheca) marshallhalli ( Kent, 1870 ) (compare with van Soest & Hajdu 2002 , figs. 12C, D). Unfortunately, unquestionable assignment of these spicules to Mycale Gray, 1867a is not possible due to their generalized morphology and the fact that morphologically similar spicules occur in many different demosponge families e.g., Geodiidae [ Geodia ostracomorpha ( Lévi & Lévi, 1989 ) ], Heteroxyidae ( Halicnemia patera Bowerbank, 1864 ), Vulcanellidae ( Sphinctrella porosa Lebwohl, 1914 ), Guitarridae ( Guitarra fimbriata Carter, 1874 ), Placospongiidae ( Placospongia melobesioides Gray, 1867b ), Coelosphaeridae [ Forcepia (Leptolabis) luciensis (Topsent, 1888) ], Pachastrellidae [ Characella ijimai ( Lebwohl, 1914 ) ]. Additionally, there are some other similar, club-shaped spicules ( Figs. 30 N–P) that may belong to the taxa mentioned above but also, in this case, their unquestionable assignment is not possible.