Family URCEOLIPORIDAE Bassler, 1936

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Family URCEOLIPORIDAE Bassler, 1936

Compiler and date details

July 2001 - Dr Philip Bock

Introduction

The small family Urceoliporidae Bassler (1936) is characterised by bushy colonies, basally rooted, in which the branches are made up of two rows of back-to-back alternating zooids. Most samples have been of colonies less than 10 cm high. However, samples obtained off Western Australia using a beam trawl are about 25 cm high, profusely branched, with the branches derived from a main stem. The stem and main branches are constructed of a complex bundle of fine rhizoids, and are up to 8 mm in diameter. The colony forms a strong rootlet system more than 40 mm in diameter in the sandy substratum. The frontal skeletal surface (frontal shield) of the zooid is thin, transparent and imperforate, except for tiny lateral septular pores, hemispherical in cross section, and entirely covered by a thin hypostegal coelom and outer cuticularised epithelium. The orifice has a median sinuosity or distinct sinus in the proximal rim. Articulated oral spines are lacking and there are no avicularia. Ovicells with a pitted ectooecium occur in Urceolipora Macgillivray (1881); in Reciprocus Gordon (1988) ovicells are lacking but zooids are dimorphic, the more swollen female zooids having internal brooding, and porous areas either side of the larger female orifice. A short horn-like projection occurs either side of the orifice in Urceolipora.

One peculiar feature of Urceolipora zooids is a sinuous longitudinal ridge that runs from behind the orifice laterally downwards, to curve round to the frontal side proximally. This ridge divides the zooidal cryptocyst into two fields, a large one that includes must of the frontal shield, and a lateral one that includes some of the septular pores by which the zooidal body cavity communicates with the outer hypostegal coelom. The dividing ridge confers to each zooid the false impression of a twisting of the zooid. Additionally, beyond the distal end of the smaller, lateral, field of the distalmost zooid of a branch element is the budding site of the zooid that begins a new bifurcation. In any internode the zooids are back to back and alternating, but the zooids on either side of a branch do not face strictly in opposite directions, rather slightly obliquely to the same side, so that each internode has a frontal side and an abfrontal side. At bifurcations the two succeeding internodes face somewhat away from each other also. Furthermore, zooids at the bottom of an internode tend to face obliquely away with respect to those at the top of an internode. This varies according to the presence of ovicells, but it is a tendency. It appears related to the disposition of the dorsal connections of each zooid; each (unless at the top or the bottom of an internode) communicates with three others - above, adjacent, and below. Depending on the degree of asymmetry of the dorsal connections, each has the potential to be slightly offset in its orientation with respect to those above and below. Reciprocus zooids lack the longitudinal ridge, but the zooids bear the same positional relationships as in Urceolipora and tend to face more on one side of a branch than another. One significant difference is that, in Reciprocus, branches are separated by uncalcified joints and each succeeding internode is more or less at right angles to the one below.

The family comprises only three species and is entirely Australasian: Urceolipora nana MacGillivray (1881), with granular-surfaced zooids, occurs at Port Phillip Heads and on the Victorian shelf; U. lucida Busk (1884), with longer and smoother zooids, occurs at shelf depths off New South Wales; Reciprocus regalis Gordon (1988) is known only from northeastern North Island, New Zealand.

The affinities of the family are uncertain - it has been allied with the monotypic Miocene Australian family Prostomariidae in the superfamily Urceoliporoidea (Gordon 1990), but its wider relationships to other lepralioid ascophorines remain speculative. A Miocene fossil representative of the family from New Zealand was described as Urceolipora (Cureolipora) miocenica by Gordon (2000).

Diagnosis

Colony erect, branching, biserial, unjointed or jointed, basally rooted. Zooids cryptocystidean, back to back, each communicating with three others dorsally. Orifice with sinus and oral processes, with or without condyles. No avicularia present. Articulated spines absent. Ovicells prominent or recumbent, or absent and zooids dimorphic.