Hintzespongia, Rigby and Gutschick, 1976

Botting, Joseph P. & Muir, Lucy A., 2014, First post-Cambrian records of the reticulosan sponges Valospongia and Hintzespongia from the late Tremadocian of North Wales, Acta Palaeontologica Polonica 59 (1), pp. 241-252 : 249-250

Hintzespongia ? sp.

Fig. 6 .

Material.—NIGP154638, fragment of the body wall preserving detail of both spicule layers, from the Late Tremadocian (early Migneintian), loose block in Ceunant-y-garreg-ddu stream section.

Description.—Fragments of a partial specimen patchily exposed over 24 mm of roughly broken surface, and with spicules often partly replaced by iron oxides. Spicules are distributed through a thickness of matrix, rather than splitting precisely along a plane, producing intermittent overlap of the skeletal mesh from inner and outer layers. The best preserved region displays a dominant diagonal fabric superimposed on a somewhat irregular orthogonal array with major spicule rays visible. Entire individual spicules are difficult to observe, due to the irregular surface and replacement of spicules by iron minerals and reflective films (probably aluminosilicate).

Largest spicules observed with ray length exceeding 3 mm, but no complete rays of largest spicules seen; maximum ray diameter (probably near-basal) approximately 0.20–0.25 mm, but preservation makes exact width difficult to assess.At least three (probably four or five) size orders visible, but few complete spicules. One of the smallest has ray length 0.6 mm and basal diameter around 0.1 mm in broadest ray (around 0.05 mm in narrowest), with rays evenly tapered. These proportions suggest that spicule rays became more elongate as they grew, but better specimens would be required to confirm this. Spicules of orthogonal layer less clearly preserved, but appear to be consistently narrower for given spicule length, with some rays in excess of 1 mm long, but only 0.05 mm in diameter, and not obviously tapering over exposed length. Fewer small spicules are visible in the inconsistently exposed orthogonal array, which may be entirely due to preferential preservation, but might indicate the presence of obscure parietal gaps in that layer. One area ( Fig. 6A , pg) shows what may be the pyritised margin of a parietal gap, around 1 mm in diameter.

Discussion.—The limited material available for this species prevents a categorical assignment even at genus level, but the structure appears to be diagnostic of Hintzespongia . Although normally described with the two planes of spicules clearly distinct (e.g., Rigby and Gutschick 1976), specimens are known in which the layers are less clearly defined and spicules are superimposed ( Rigby et al. 2010). This is a preservational effect that complicates recognition of the sponge, but does not in itself necessitate reconsideration; the specimen was probably originally preserved in a similar manner to the type material, but authigenic aluminosilicate growth during low-level metamorphism is likely to have caused disintegration of particular sedimentary laminations. The preservation is entirely consistent with a regular diagonal layer of spicules overlying a somewhat less regular, sub-orthogonal layer. The only other significant difference from the previously described material is the rarity of obvious parietal gaps in the inner layer, but at least one probable example is visible, and the spicules interpreted as representing that layer in our material are much more sparsely preserved.

The skeletal structure is somewhat similar to that of Valospongia bufo sp. nov., but specimens are in general easily separated by preservational differences; in V. bufo , the most prominently preserved feature is the array of apparent gaps, the margins usually heavily pyritised. In side view these are clearly seen to be mounds in V. bufo , but profile views are not often available due to fragmentation of the sponge skeletons. This difference is not dependent on exact bed; a fragment of V. bufo , preserved in the typical way, is present on the edge of the Hintzespongia ? sp. slab. If only a spicule array is present, there are differences in the spicule dimensions, with the largest spicules in Hintzespongia ? sp. having rays several times longer than the largest seen in V. bufo . Growth stage must be taken into account, but it also appears that parietal gaps in Hintzespongia ? sp. are substantially smaller than the apparent gaps in V. bufo , even when the spicules are substantially larger.

Figures

Fig. 6. The hexactine-bearing sponge Hintzespongia? sp., NIGP154638, Dol-cyn-Afon Formation, upper Tremadocian, Lower Ordovician, Ceunant-ygarreg-ddu stream section, Arenig Fawr, North Wales, UK. A. Overall view of specimen showing several regions with exposed spicules, each revealing skeletal layers interpreted as having originally been dominantly diagonal (d), sub-orthogonal (o) or both (d, o), and with example of possible inner layer parietal gap (pg). B. Detail of central part of specimen, showing both diagonal and sub-orthogonal spicule arrays. C. Camera lucida drawing of region shown in B, with sub-orthogonal series stippled. Scale bars 5 mm. All photographs taken under water.