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Zoology Publications from Victoria University of Wellington—Nos. 58 to 61



This paper is concerned with the structure and function of the body wall of a hydroid polyp, Syncoryne tenella (Farquhar, 1895). It is one of a series of papers which study the body wall of representative coelenterates, and flatworms (Phylum Platyhelminthes), with the ultimate goal being a consideration of the phylogenetic relationships between these groups.

Most hydroid research in the last 10-15 years has centred on the fresh water genus Hydra, and this animal is used extensively in the teaching of coelenterate and particularly hydroidean morphology and histology. It is, in fact, as Cowden (1965) has stated, difficult to obtain a general account of the histology or cytology of a hydroid other than a representative of the genus Hydra. Indeed, this was the reason which prompted Cowden to study another gymnoblastic hydroid Pennaria tiarella from the histological point of view. The present study on Syncoryne tenella provides further information on the structure of the hydroidean polyp as seen in more a typical member of the Order Hydroida than is Hydra. In addition the various histochemical tests applied give some idea of the page 2 functional relationship of the different components of the tissues present, and the results form the basis for comparison with Pennaria tiarella.

Syncoryne tenella is a colonial gymnoblastic (athecate) hydroid. Although the polyp is without a hydrotheca, the stolons forming the hydrorhiza, and the upright hydrocauli which bear the polyps, are composed of a well defined perisarc surrounding the coenosarc. The general morphology of Syncoryne hydranths has been described (Hyman, 1940). The feeding polyp is elongate, bearing scattered capitate tentacles (Pl. 1, Fig. 1). The base of the polyp is more or less a naked extension of the hydrocaulus and broadens steadily but smoothly into the body of the polyp. This is of uniform diameter throughout in an extended specimen, except at the hypostome which is often slightly swollen. Gonophores bud from the sides of hydranth, between the tentacles. The present paper is restricted to a study of the hydranth, and does not deal with gonophore development, histology or histochemistry.