Mattaspongia undetermined

? MATTASPONGIA sp.

( Figure 5 View FIGURE 5 A-D)

Material. One fragment from a reef mound block at Niquivil locality Middle Ordovician (Dapingian), CEGH-UNC 27596.

Description. Thin-walled sponge, apparently tubular and with a faintly visible osculum at the top. The sponge fragment is 4 cm long and approximately 2 cm wide. Main body spicules are coarse, predominantly aligned hexactin-type forms, mostly of the same size. This main layer consists of large hexactins arranged in moderately regular quadrate disposition, with rays aligned to form parallel rows. Vertical rays are intercalated to form small quadrules and irregular, somewhat alternating rows. Vertical rows of spicules are commonly between 2 and 3 mm apart. Horizontal spicule rays generally extend below vertical rays of adjacent spicules. Small monaxons ( 0.1–0.3 mm long) are irregularly distributed between the primary rays, most of them horizontally disposed, but some appear perpendicular or with variable angles.

Main spicules are coarse-rayed hexactins, with equal ray size of approximately 2 mm long. Basal ray diameter is 0.3 mm, tapering rapidly to a pointed tip. Dermal ray with a button-like apex or may appear to be absent, possibly due to breakage or awkward angle of preservation. Primary hexactins, seen in a transverse polished section at the base, apparently show a shorter perpendicular ray than the horizontal ones.

Remarks. Interpretation of sponges from fragments is challenging, especially in sectional view. Nonetheless, the main characteristics of Mattaspongia (i.e., a primary layer of coarse hexactins forming a quadrate mesh, vertical rays overlapping to form small quadrules in irregular and somewhat alternating rows, and small monaxons irregularly distributed among quadrules) are seen in our material. However, the presence of conspicuous parietal gaps (or internal canals) in Mattaspongia may indicate separation of the specimen described here from the genus erected by Rigby (1970); this is only likely to be resolved with additional material.