Family TENDRIDAE Vigneaux, 1949

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Family TENDRIDAE Vigneaux, 1949

Compiler and date details

July 2001 - Dr Philip Bock

Introduction

The family Tendridae was introduced by Vigneaux (1949), for the genus Tendra, which occurs in waters of lowered salinity in the Black Sea. The larva of Tendra zostericola Nordmann (1839), the type species, is of a coronate type, and is brooded in a chamber formed by marginal spines which overarch the frontal membrane of the zooid distal to the maternal zooid. Several larvae may be brooded at once in this structure, which is sometimes called an 'acanthostegous ovicell'. The autozooids of T. zostericola resemble those of Electra, with a well developed gymnocyst, and 3-5 marginal spines, the most proximal being enlarged. A cyphonautes larva has been reported in Tendra repiachowi Ostroumoff (1886), but this species does not develop any form of brood chamber and is referable to the genus Electra (Occhipinti-Ambrogi & d'Hondt 1981). They reported that T. zostericola also occurs in lagoons in the northern Adriatic. Although its larvae may have a fully developed gut (Zimmer & Woollacott, 1977), T. zostericola seems to belong to the Neocheilostomina, even though it has many of the characteristics of the Malacostegina.

Another genus with a somewhat similar acanthostegous ovicell structure is found only in Australia and was introduced, as Heterooecium, by Hincks (1892), for a species he had first described as Membranipora amplectens in 1881, from Western Australia, 'creeping over an alga' (Hastings 1966).

H. amplectens has autozooids which resemble those of Electra and Tendra, and brooding zooids in which the distal part of the zooid is expanded, and has a frontal membrane covered by overarching marginal spines. The operculum of this zooid is proximal to the spinous cover, and just distal to the edge of the short gymnocyst. The larvae have not been described.

MacGillivray (1889) illustrated specimens from Port Phillip as Electra amplectens, and Levinsen (1909) compared the structure of the ovicells in both Tendra and Heterooecium. Colonies form delicate, white or semi-transparent encrustations, particularly on red algae. The zooids are usually uniserial, the enlarged brooding zooids occurring between two new series of zooids at a bifurcation.

Diagnosis

Colonies encrusting, weakly calcified, of chains of disjunct zooids. Frontal area oval with marginal spines, gymnocyst extensive. Brooding zooids dimorphic, expanded distally, with a frontal cover of fused spines.