. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. A B C Fig. 81. Sertulariidae: structure of hydranth (shown retracted) in diagrammatic A, with blind caecum, Sertularella; B, without caecum, Dynamena; C, with annular fold, , Thyroscyphus. The ectoderm of the hydranth is produced as a lining over the inner wall of the hydrotheca to a varying degree, and in Thyroscyphus may form a 'Decken- platte' below the operculum. To this lining of ectoderm the ectoderm of the hydranth is fastened in certain strategic positions where perisarcal t
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. A B C Fig. 81. Sertulariidae: structure of hydranth (shown retracted) in diagrammatic A, with blind caecum, Sertularella; B, without caecum, Dynamena; C, with annular fold, , Thyroscyphus. The ectoderm of the hydranth is produced as a lining over the inner wall of the hydrotheca to a varying degree, and in Thyroscyphus may form a 'Decken- platte' below the operculum. To this lining of ectoderm the ectoderm of the hydranth is fastened in certain strategic positions where perisarcal thickenings of the hydrotheca may develop. Although Mammen (1965a), following Nutting (1904), speaks of'protractor' and 'retractor' muscles, to the author's knowledge actual muscle fibres have as yet not been identified in these attachments. Nema- tocysts may in certain cases be present in the lining ectoderm or in the 'Decken- platte', and it was on this feature that Splettstosser (1929) based his genus Cnidoscyphus. A peculiar structure is present in Sertularia ligulata (Fig. 100D) and is possibly present in other species too (it has been seen in S. turbinatd). This is the ligula. It consists of a slender outgrowth from the base of the adcauline side of the hydranth and it protrudes as a leaf-shaped process through the mouth of the hydrotheca. It often remains clearly visible after the hydranth has con- tracted. Its function is not clear, but since it is well armed with nematocysts, it may serve as a. nematophore. Although nematothecae do not occur in the Sertulariidae, in Amphisbetia minima certain small pores occur with some regularity on the internodes of the stem and each is usually surrounded by a low collar of perisarc (Fig. 82H). They have sometimes been called nematothecae, but there is as yet no proof of the presence of nematophores. The gonothecae are usually dioecious and sometimes also dimorphic. No special protective structures are developed around them and they a
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
