. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. MONOGRAPH ON THE HYDROIDA OF SOUTHERN AFRICA 243 and abcauline edges. The larger valve is adcauline in Amphisbetia and abcau- line in Dynamena and Sertularia. In these forms the adcauline valve may be divided into two by a partition and bent at an angle like a roof. Genera with only one large opercular valve include Diphasia, Idiellana, Abietinaria, Thuiaria and Salacia. The hinge is adcauline in the first three and abcauline in the last two; it is often seated in an embayment of the margin. Sometime
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. MONOGRAPH ON THE HYDROIDA OF SOUTHERN AFRICA 243 and abcauline edges. The larger valve is adcauline in Amphisbetia and abcau- line in Dynamena and Sertularia. In these forms the adcauline valve may be divided into two by a partition and bent at an angle like a roof. Genera with only one large opercular valve include Diphasia, Idiellana, Abietinaria, Thuiaria and Salacia. The hinge is adcauline in the first three and abcauline in the last two; it is often seated in an embayment of the margin. Sometimes the operculum is shed fairly early in development, as in some species of Thyroscyphus, or reduced to a membrane, as in Crateritheca acantho'Stoma, or even lost altogether, as in Stereotheca. These genera thus show relationship to the Syntheciidae, but are retained in the Sertulariidae because of the toothed hydrothecal margin. Naumov (1960) suggests that the number of opercular valves provides an example of the evolutionary process of oligomerization, those with many valves being primitive and those with one or none being advanced. On con- traction the hydranth is completely withdrawn into the hydrotheca and the operculum closed over it. Regeneration of the margin is accompanied by regeneration of the operculum, so that there may be several opercula, one above the ."*. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original South African Museum. Cape Town : The Museum
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
