Family PASYTHEIDAE Davis, 1934

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Family PASYTHEIDAE Davis, 1934

Compiler and date details

July 2001 - Dr Philip Bock

Introduction

The small family Pasytheidae Davis, 1934 is largely characterised by species with a porous, gymnocystal frontal shield, whose colonies begin growth by ramifying in thin uniserial chains of stolonate zooids across the substratum. Erect zooidal stems arise from some of the encrusting zooids. Additional branches of zooids may arise from the erect stems, sometimes showing a reduction in size. The type species of Pasythea, P. tulipifera (Ellis & Solander) has been described in detail by Marcus (1938; 1939) and Cook (1985). The erect zooids are grouped in triads. The type species of Gemellipora, G. eburnea Smitt, has zooids in opposed pairs, as does the fossil genus Dittosaria. The zooids of the Mexican genus Tecatia Morris (1980) are all encrusting, and uniserial, whereas those of Eutaleia Marcus (1938) are multiserial. All genera have thinly calcified zooids, slightly sinuate orifices, and occasional lateral mucrones (orificial horns). Ovicells, spines, and avicularia are unknown.

Pasythea, Tecatia, and Eutaleia are shallow-water forms, often encrusting algae, but Gemellipora is found in deep to abyssal waters (over 3300 m). Although most records of all genera are from the Atlantic and eastern Pacific, and no pasytheid has been formally recorded from Australian waters, Gemellipora eburnea, which has been recorded from the Kei Islands, Indonesia, and from the Kermadec Ridge, New Zealand (Lagaaij & Cook, 1973; Gordon, 1984), is, however, likely to be encountered in deep water. An undescribed genus occurs epizootically on hydroids and bushy bryozoans in the Darwin area. It is uniserial, with small zooids and relatively large gymnocystal pores. It also has distinctive orificial horns. Erect branches and ovicells have not been encountered in the few specimens seen.

Dating from the Lower Eocene (Taylor 1993), the origins of the Pasytheidae may nevertheless be sought among the encrusting, porous-shielded Cretaceous hippothoids, some of which have been attributed to Tecatia, but are here regarded as distinct from that genus (Voigt, 1981, 1991; Gordon & Voigt, 1996) (see Family Hippothoidae).

Diagnosis

Colony thinly calcified, formed by uniserial chains of creeping, stolonate zooids, which give rise to erect, sometimes nodal stems. Zooids in triads or pairs, elongated with an almost terminal orifice, frontal gymnocystal. Avicularia, spines and ovicells absent.