. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. MONOGRAPH ON THE HYDROIDA OF SOUTHERN AFRICA 77 Family Eudendriidae Diagnosis. Colonial hydroids with an erect, usually branched stem enclosed in firm perisarc up to the base of the hydranth body. Hydranth large, radially symmetrical, with trumpet-shaped hypostome and one or more whorls of filiform tentacles immediately below it.^ Reproduction by fixed sporosacs borne on the hydranth body below the tentacles; reproductive hydranth often reduced to a blastostyle. Male gonophore usually with several ch
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. MONOGRAPH ON THE HYDROIDA OF SOUTHERN AFRICA 77 Family Eudendriidae Diagnosis. Colonial hydroids with an erect, usually branched stem enclosed in firm perisarc up to the base of the hydranth body. Hydranth large, radially symmetrical, with trumpet-shaped hypostome and one or more whorls of filiform tentacles immediately below it.^ Reproduction by fixed sporosacs borne on the hydranth body below the tentacles; reproductive hydranth often reduced to a blastostyle. Male gonophore usually with several chambers in linear series. Young female gonophore with a single egg encircled by a spadix. Introduction. Members of the Eudendriidae are comparatively easy to recognize, but identification within the family, particularly in the genus Eudendrium, is not at all easy, since most of the macroscopic features vary with age and habitat. The stem may be branched or unbranched, fascicled or unfascicled. It is always covered with firm perisarc which terminates on or below the base of the hydranth. The perisarc is usually smooth or wrinkled with characteristic groups of annulations on the origins of the branches and at other strategic positions. The hydranth is large and distinguished from all other families of the Athecata by the wide, trumpet-shaped hypostome which usually gapes open even in preserved material. Broch (1916) was the first to point out that the endoderm of the hydranth has become differentiated, the cells of the oral part of the hypostome being small and 'indifferent', and the mucous and digestive cells being limited to the lower part of the hypostome and the gastral cavity. The ectoderm is thin over most of the hydranth, but usually there is a shallow groove round the base of the body where the perisarc of the stem terminates and where its growth occurs. The ectoderm below this level is thicker, with a circle of characteristic large cells just below the groove. Mammen (196
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