Zyzzyzus spongicolus (von Lendenfeld, 1885)

Hydranths solitary, rooted in the canal system of the host sponge by finger shaped hydrorhizal processes.

Hydrocaulus reaching a height of 5-6 mm of which one third is embedded in the sponge. Hydrocaulus stout, covered by a transversely striated transparent sheath of perisarc terminating in a circular groove below hydranth, the coenosarc of the stem divided into about 12 longitudinal canals connecting with the gastral cavity.

Hydranth with 12-16 moderately long aboral tentacles, 0.75-1 mm in length (preserved), and 10-12 shorter oral tentacles. Blastostyles arising just above aboral tentacles, each bearing clusters of up to 6 gonophores in different stages of development, male and female on same blastostyle.

Immature gonophores of both sexes oval with slightly raised and flattened distal end, the male retaining this shape to maturity. Female gonophore cryptomedusoid, containing up to 6 eggs of which 2-3 gonophore rapidly enlarges to accommodate the developing actinulae, the outer envelope becoming transparent and irregular in shape, the actinulae clearly visible within. At this stage a circular orifice with raised collar develops at the distal end, and the spadix is pushed to one side. After escape of the actinulae, the spadix remains within the empty gonotheca. At liberation, the actinulae are 0.25-0.3 mm in width across the body with 10-12 long marginal tentacles.

Nematocysts of four kinds are present:

— Large stenoteles, very abundant, with spherical capsule, 7.5 - 9 x 9.5 µm, butt almost as long as capsule, with 3 large spines.

— Smaller stenoteles, also very abundant, capsule a little more elongate, 5.5 x 3 µm, butt slender, about two thirds length of capsule.

— Basitrichous isorhizas, rare, capsule bean shaped, 8 x 3.5 µm, tube long.

— Heterotrichous anisorhizas, rare, capsule oval, 3 x 5 µm.

Colour: Hydrocaulus and tentacles of hydranth translucent white, body of hydranth dull red, gonophores and actinulae at liberation white, spadix of mature female gonophore deep orange.