Teganium avalonensis, Botting & Muir & Ma, 2023

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 : 5-9

publication ID	https://doi.org/ 10.26879/1247
publication LSID	lsid:zoobank.org:pub:B66F3F99-3211-416F-BDFD-8583DF0DC844
persistent identifier	https://treatment.plazi.org/id/CF53FD13-A35C-5F79-FED4-794FFC74F8A3
treatment provided by	Felipe
scientific name	Teganium avalonensis
status	sp. nov.

Treatment

Teganium avalonensis sp. nov.

Figures 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5

zoobank.org/ A5C8BA9B-C4D6-4404-8150-CC7C75F6BBDF

Name. After the geographic origin, the palaeocontinent Avalonia.

Diagnosis. Oval to rounded quadrate Teganium with pronounced, slightly inwardly-directed marginalia surrounding broad osculum, and fine skeleton composed of numerous very small hexactins and derivatives; outer (dermal or hypodermal) layer with a semi-regular reticulation and inner layer with numerous, densely-packed, rounded cavities.

Holotype. NMW.2021.3 G.71, large complete specimen with marginalia and basalia, but generally lacking fine skeletal detail.

Paratypes. NMW.2021.3 G.72, pair of sponges with well-preserved marginalia but little fine skeletal detail ; NMW.2021.3 G.73, large complete example; NMW.2021.3 G.74, small partial specimen showing oscular margin; NMW.2021.3 G.77, the largest complete specimen; NMW.2021.3 G.78, three moderate-size specimens; NMW.2021.3 G.79, one small and relatively elongate specimen; NMW.2021.3 G.80, small complete specimen; NMW.2021.3 G.81, cluster of four moderately large specimens; NMW.2021.3 G.82, partial specimen with well-preserved fine detail of body wall.

Description. Sponges are oval, slightly taller than wide, in some cases with somewhat squared outline showing a flattened base ( Figure 2C View FIGURE 2 ). Specimens up to 14 mm wide and 16 mm tall (excluding marginalia). Osculum of holotype ( Figure 2C View FIGURE 2 ) 4 mm wide, and proportionally similar in other specimens, being approximately one-third of maximum width; where basal margin is flattened, this covers approximately half of maximum sponge width. In most cases the specimens are preserved in a thick film of carbon and/or iron minerals, but in some specimens, body wall structure is preserved ( Figure 3C–F View FIGURE 3 ). Wall thickness visible at the lateral margins in several specimens (including holotype, Figure 2C View FIGURE 2 , and in Figure 3C–D View FIGURE 3 ), and is irregular but normally up to 0.5 mm thick.

Internal organisation of wall (preserved as denser brown material representing soft tissue; Figure 3C, F View FIGURE 3 ) with numerous rounded polygonal to circular cavities or exhalent canals (leading into central atrium) on similar scale to primary skeletal grid (c. 0.1–0.4 mm). In most areas (perhaps excluding base and extreme apex), tissue regions between spaces are narrower than the cavities, with a 0.1 mm-thick wall.

Skeleton faintly preserved due to delicate spiculation, but fine dimpled texture reflecting the primary external grid is visible over surface ( Figure 3B View FIGURE 3 ); spicules are visible when wet, but specimens are prone to cracking in contact with water. Dimples, representing spaces between spicules, are 0.1–0.2 mm wide and often arranged in sinuous lines resulting from semi-regular spicule grid. Grid is dominantly diagonal, but irregular. Spicules ( Figure 3D–E View FIGURE 3 ) are simple triaxons, presumed to be hexactins but with gastral and distal rays not confirmed. Ray length typically up to 0.2 mm and extremely fine. The appearance of longer spicules in low-angle light is a result of relief due to locally aligned skeletal grid. Finest spicules appear to be randomly arranged between the larger spicules, including over the spaces within the primary grid, and over cavities preserved in paratype, implying that these occupy an outer layer (probably hypodermal or dermal) overlying internal spaces.

Marginalia ( Figures 2A View FIGURE 2 , C-D and 3A) consistently around 2 mm long (even in largest specimen, implying a maximum length reached early), fine (less than 0.1 mm wide), with bases embedded in body wall; they are either diactins or greatly extended vertical rays of hexactins. Rays are straight and inclined inwards at around 45–60°, forming a barrier around sides of slightly depressed osculum. No lateral prostalia or even projecting distal rays are visible, although the lateral margin of flattened sponges is slightly rough; the preservation is not detailed enough to demonstrate conclusively whether any of the smaller dermal/hypodermal spicules had any rays projecting.

Basalia ( Figure 2C, E View FIGURE 2 ) preserved in holotype as bases of coarse spicules protruding into sediment. Spicules 0.1–0.2 mm wide, extending unknown distance into sediment, and are less well preserved with increasing distance from the sponge body (a documented feature of sponge preservation in, for example, the Anji Biota; see Botting et al., 2020). Basalia appear to have been

PALAEO- ELECTRONICA.ORG numerous, extending into sediment from the entire basal part, equating approximately to the flattened region of the body.

Remarks. A reconstruction of the sponge is shown in Figure 5 View FIGURE 5 . The new species differs from all others that have been assigned to the genus in the pronounced marginalia, and in the rather more quadrate shape, but in other respects most closely resembles Teganium ovata ( Rigby and Mehl, 1994) —including the existence of a similar array of basalia. Teganium heathi ( Rigby, 1986) appears to show no marginalia (a possible taphonomic artefact) and also possessed coarser body wall spicules, and meridional tracts of spicules or spicule rays that are not present in other species. The species described as T. finksi (Mouro et al., 2019) lacks any visible osculum or marginalia and includes much coarser spicules, in some cases up to 2 mm across.

The dense association of multiple specimens on several slabs is typical of the genus ( Rigby and Mehl, 1994) and appears to be a consistent ecological feature. In many (but not all) examples, there is little variation in size in such assemblages at Castle Bank, implying that the sponges were approximately the same age; they may therefore represent a colonisation event, as discussed for other sponges found as similar dense assemblages by Botting (2016) and Botting et al. (2020).

Occurrence. Known only from the Middle Ordovician ( Didymograptus murchisoni Biozone ) of Castle Bank, Llandrindod, UK; Gilwern Volcanic Formation.