The rare hydroid Clathrozoella drygalskii (Vanhoffen, 1910) is described and recorded for the first time from Australia and New Zealand. It was first discovered in collections from Davis Sea, Antarctica, and assigned by Vanhoffen (1910) to the genus Clathrozoon Spencer, 1890, at that time considered to be an athecate genus. Clathrozoon and the family Clathrozoidae were referred to the Thecata due to the presence of distinct 'false hydrothecae', made up of a mesh of fine tubules, each composed of a peridermal cover of a strand of coenosarc. The genus Clathrozoella was instituted for Vanhoffen's species because of structural differences from Spencer's Clathrozoon wilsoni. The most important point of difference is the presence, in Clathrozoella, of a bottom of peridermal tubules in the tubular 'false hydrotheca', to which the hydranth is attached. In Clathrozoon, as well as in Pseudoclathrozoon Hirohito, 1967, the 'hydrothecae' are open proximally and the hydranths are connected by strands of coenosarc. The mode of reproduction is as yet unknown in Clathrozoella drygalskii, but a small cylinder of tissue next to The hydranth may constitute a gonophore inside the 'false hydrotheca'. In Pseudoclathrozoon Hirohito described a distinct gonotheca containing a well developed gonophore. The differences in structure of the 'false hydrotheca' in Clathrozoella and those in Clathrozoon and Pseudoclathrozoon are so distinct that Clathrozoella may well be kept in the Athecata where its taxonomic position, at least for the present, is with such genera as Hydractinia and Solanderia.
Descriptors: CLATHROZOELLA DRYGALSKII new record; CLATHROZOON; CLATHROZOON WILSONI; PSEUDOCLATHROZOON; HYDRACTINIA; SOLANDERIA
