Palaeospongillidae Ott and Volkheimer, 1972

Pronzato, Roberto, Pisera, Andrzej & Manconi, Renata, 2017, Fossil freshwater sponges: Taxonomy, geographic distribution, and critical review, Acta Palaeontologica Polonica 62 (3), pp. 467-495 : 477-479

Palaeospongillidae Ott and Volkheimer, 1972 Palaeospongilla chubutensis Ott and Volkheimer, 1972

Fig. 13.

Type horizon: Aptian , Lower Cretaceous .

Type locality: 16 km NNW of Cerro Condor, Patagonia Chubut River Valley, Argentina .

References: Ott and Volkheimer 1972; Racek and Harrison 1975; Volkmer-Ribeiro and Reitner 1991; Manconi and Pronzato 2002.

Description (emended from Ott and Volkheimer 1972; Racek and Harrison 1975; Volkmer-Ribeiro and Reitner 1991; Manconi and Pronzato 2002).—Body shape encrusting-lobose, 2–6 mm thick. Surface smooth even though not well discernible, owing to the calcareous algal cover. Ectosomal skeleton undetected. Choanosomal skeleton a regular, anisotropic meshwork with multispicular (up to 40) ascending primary fibres which, with perpendicular secondary fibres, form a reticulum of square meshes (mesh diameter, 1 mm). Abundant spongin. Megascleres oxeas, straight to feebly curved, of two dimensional classes from stout (230–540 × 10–22 μm) cylindrical abruptly pointed and smooth, rarely bearing 1–2 spines, to abundant slender, fusiform, sharply pointed, finely spiny except at their tips (180–308 × 4–14 μm). Stout oxeas form the main skeleton of central and basal sponge body whereas slender oxeas are more frequent in peripheral skeletal fibres. Microscleres (more abundant above the layer of gemmules), oxeas abruptly pointed, straight to feebly curved, from incipiently to conspicuously spiny (179–190 × 3–4 μm) to smooth (77–147 × 3–10 μm). Gemmuloscleres acanthostrongyles to acanthoxeas dependent on the position of spines at the tips (70–168 × 3.5–8 μm) slender, slightly curved. Spines, scattered along the entire surface, more grouped and recurved at the tips, often with a single spine as prolongation of the axis. Gemmules subspherical (483–644 μm in diameter) scattered in the skeleton, singly or grouped, belonging to two types i.e., armed and unarmed. Unarmed gemmules, that is, without gemmuloscleres, enveloped in a cage of tangential spiny megascleres; gemmular theca bilayered with thin pneumatic layer and conspicuous inner layer, foramen simple without a porous tube. Armed gemmules with gemmuloscleres in one layer, variably arranged and crossing each other at various angles; thick trilayered theca, outer layer ill defined, well developed inner (20 μm in thickness) and pneumatic (100 μm in thickness) layers, nipple-like foramen.

Remarks.— Palaeospongilla chubutensis was described and redescribed in three subsequent papers ( Ott and Volkheimer 1972; Racek and Harrison 1975; Volkmer-Ribeiro and Reitner 1991). Finally, the previous descriptions of P. chubutensis were merged by Manconi and Pronzato (2002). P. chubutensis is represented by a complete and intact skeletal arrangement of megascleres and microscleres, both of two types, as well numerous gemmules with (and without) gemmuloscleres in situ. In the original description ( Ott and Volkheimer 1972) the new species is described as a new genus Palaeospongilla of the family Spongillidae . Racek and Harrison (1975) re-examined the type material and described a single type of gemmule with more or less radially arranged gemmuloscleres suggesting an affinity with the genus Radiospongilla . Volkmer-Ribeiro and Reitner (1991) changed significantly the palaeontological interpretation and re-description of P. chubutensis (partim) describing the new species Spongilla patagonica (see below) and erecting the new family Palaeospongillidae , attributing unarmed gemmules to P. chubutensis and the armed ones to the new species. The decision by Manconi and Pronzato (2002) to declare S. patagonica a junior synonym of P. chubutensis is based on the fact that the production of two gemmular morphs in the same specimen was also known in two genera of Spongillidae i.e., Spongilla and Corvospongilla , both characterised by unarmed and armed gemmules with or without pneumatic layer. Thus the erection of the family Palaeospongillidae , based on the absence of gemmuloscleres, is enigmatic. Further studies are needed.