Teganium, Rauff, 1894

Botting, Joseph P., Muir, Lucy A. & Ma, Junye, 2023, Teganium (Porifera, Hexactinellida) from the Middle Ordovician Castle Bank fauna of Avalonia (Wales, UK), Palaeontologia Electronica (a 21) 26 (2), pp. 1-17 : 4-5

Genus TEGANIUM Rauff, 1894

Diagnosis. (Emended after diagnosis of Teganiella, Finks and Rigby, 2004 .) Sphaeroidal reticulosans with thin wall composed of minute hexactin-based spicules in mostly continuous but irregularly oriented reticulate array, and choanosomal body wall with small, circular internal cavities; circular osculum is in some species lined by dense array of fine marginalia.

Type species. Cyathophycus subsphaericus Walcott, 1879 , by original designation.

Other species. Teganiella heathi Rigby, 1986 ; Tl. ovata Rigby and Mehl, 1994 ; Teganium avalonensis sp. nov.; questionably also Tl. finksi Mouro et al., 2019 .

Remarks. Separation of Teganiella from Teganium is highly problematic and is here considered invalid. The structure of the skeleton and soft tissue in the new species is remarkably similar to that described for Teganium ( Walcott, 1879; Rauff, 1894; Finks and Rigby, 2004), only lacking the presence of abundant prostalia (Hall and Clarke, 1899). The absence of an osculum was stated by Finks and Rigby (2004) to be a defining feature of the genus Teganium . However, the original description of Cyathophycus subsphaericus Walcott, 1879 (the type species of Teganium ), not only states that there is an osculum in many specimens but also gives measurements (9 mm diameter for a 30 mm-diameter sponge). Hall and Clarke (1899) illustrated several specimens that all apparently lack oscules, but the drawings alone are inconclusive. Finks and Rigby (2004) confirmed the nonexistence of an osculum based on only the holotype, and it is likely that in this specimen it is concealed by an awkward angle of flattening. In particular, if the holotype is vertically compressed and viewed from below, this could have both obscured the osculum and potentially also given the appearance of abundant lateral prostalia due to flattening of the radial array of basalia. The original description of Walcott (1879) makes it clear that the type species possesses an osculum and lacks prominent lateral prostalia.

In their species Teganiella finksi, Mouro et al. (2019) noted that although no osculum was visible in the moderately poor material, some specimens have a flattened summit that may indicate its presence and position; this is entirely normal for a laterally compressed reticulosan. Given the requirement for at least one exhalent opening in order for the sponge to function, this apparent lack of any terminal aperture is probably due to inconvenient orientation of compression in a globose sponge with a strongly narrowed osculum, to the extent that it is not clearly visible. It, therefore, appears that Teganium and Teganiella are identical, and given that the latter is well defined and the former (which would be the senior synonym) is more problematic in (according to some authors only) lacking an osculum, the genera should be considered identical and are here formally synonymized.

An assessment of previously known species of Teganiella (here transferred to the senior synonym Teganium ) was provided by Mouro et al. (2019), who erected the species Tl. finksi . The generic definition is revised here, due to some confusion in Finks and Rigby (2004), in which the familial diagnosis contradicts the generic diagnosis in mistakenly requiring the absence of an osculum. The first two named species of Teganiella ( Tl. heathi Rigby, 1986 and Tl. ovata Rigby and Mehl, 1994 ), both show a clear osculum, in at least the latter surrounded by marginalia. The current species is closest to Tl. ovata , which differs in some ways from the type species, but is close enough to support congeneric status.

Stratigraphic range. The genus is previously known from Upper Ordovician, Devonian and Carboniferous rocks of the USA (Laurentia); the new species extend this to the Middle Ordovician of Avalonia.