A RARE HYDROID, CLATHROZOELLA-DRYGALSKII (VANHOFFEN, 1910) IN THE WATERS OF AUSTRALIA AND NEW-ZEALAND

The rare hydroid Clathrozoella drygalskii (Vanhoffen, 1910) is describ ed and recorded for the first time from Australia and New Zealand. It was first discovered in collections from Davis Sea, Antarctica, and as signed by Vanhoffen (1910) to the genus Clathrozoon Spencer, 1890, at that time considered to be an athecate genus. Clathrozoon and the fami ly Clathrozoidae were referred to the Thecata due to the presence of d istinct 'false hydrothecae', made up of a mesh of fine tubules, each c omposed of a peridermal cover of a strand of coenosarc. The genus Clat hrozoella was instituted for Vanhoffen's species because of structural differences from Spencer's Clathrozoon wilsoni. The most important po int of difference is the presence, in Clathrozoella, of a bottom of pe ridermal tubules in the tubular 'false hydrotheca', to which the hydra nth is attached. In Clathrozoon, as well as in Pseudoclathrozoon Hiroh ito, 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 n ext to The hydranth may constitute a gonophore inside the 'false hydro theca'. In Pseudoclathrozoon Hirohito described a distinct gonotheca c ontaining a well developed gonophore. The differences in structure of the 'false hydrotheca' in Clathrozoella and those in Clathrozoon and P seudoclathrozoon are so distinct that Clathrozoella may well be kept i n the Athecata where its taxonomic position, at least for the present, is with such genera as Hydractinia and Solanderia.