Teganium sp.

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 : 9-11

Teganium sp.

Figure 6

Material. NMW.2021.3 G.76, two adjacent specimens, partially overlying.

Description. Two specimens, effectively unweathered, adjacent and pointing in opposite directions ( Figure 6A ); one slightly overlies the other. Information is based primarily on the first ( Figure 6 B-C), which shows a near-complete outline, especially at the apex; the other has damage to apex and edges, but confirms observations based on the first.

The better-preserved specimen is 24 mm tall, conical and slightly sinuous, with maximum width 7 mm, at or near apex, with upper half of approximately even width. Lower half tapers from 5 mm width at mid-height to rounded point. Second specimen also 7 mm wide at apex, total length approximately equal to first, but exact base invisible. Apex narrows in uppermost millimetre such that osculum occupies around 80% of full width of sponge, surrounded by dense array of marginalia, 2 mm long (0.02–0.07 mm thick), converging (and sometimes curving) somewhat inwards.

Wall thickness unclear and irregular, but indicated by dark line at edges (representing more massive preservation of soft tissues; Figure 6C ), approximately 0.5–1.0 mm thick. Mineralised film over body wall shows irregular mottled patterning ( Figure 6 B-C) indicating relatively coarse internal cavernosity with cavities typically 0.5–1.0 mm across and separated by bands of more continuous tissue typically 0.5 mm wide. Finer cavities not visible, but may have been present originally.

Skeletal detail not preserved except for reticulation of dermal skeleton, seen in low-angle light and especially clear in mid-height area of better specimen ( Figure 6C ): a semi-regular grid, roughly longitudinal and transverse, with cell size approximately 0.1 mm or slightly less. Individual body wall spicules not preserved (invisible even when wet). No basalia visible.

Remarks. At present, these two specimens are distinguished from other members of the genus largely by the shape; although internal wall structure also appears to be coarser, it is poorly preserved. It shares the distinctive appearance of the finely reticulate surface with other species, and shares the convergent, dense fringe of marginalia with T. avalonensis sp. nov. The unweathered state of the material obscures many of the fine details of the skeleton, which cannot therefore be compared in detail with other species. The same is true for previously described species (Mouro et al., 2019), however, and the key characters are preserved well enough to allow an unambiguous assignment to the genus. The species is left in open nomenclature because the sample size is too small to reject the possibility of an extreme variation of shape within T. avalonensis sp. nov.

Figures

FIGURE 6. Teganium sp., from the Middle Ordovician Castle Bank Biota, Wales. A, NMW.2021.3G.76i and ii, overall view, with positions of detail images indicated by boxes (all rotated). B, apex of NMW.2021.3G.76i, apex of sponge showing extensive marginalia; C, detail of body wall showing characteristic texture (boxed area enlarged inset); D, apex of NMW.2021.3G.76ii, with oscular margin and trace of marginalia. Scale bars: A equals 10 mm; B–D equal 1 mm.