. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. MONOGRAPH ON THE HYDROIDA OF SOUTHERN AFRICA 19 velum. ........ ectoderm l-l-l-l -VI -1-1 endoderm HETEROMEDUSOID STYLOID Fig. 11. Types of degenerate medusae (fixed sporosacs). 2. cryptomedusoid. Radial canals absent, but a single layer of endoderm, the endodermal lamella, present lining the exumbrellar ectoderm. Subum- brellar cavity distinct, reduced or absent. 3. heteromedusoid. Endodermal lamella absent. Outer ectoderm two or more- layered, often enclosing the remnant of a subumbrellar cavity. T
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. MONOGRAPH ON THE HYDROIDA OF SOUTHERN AFRICA 19 velum. ........ ectoderm l-l-l-l -VI -1-1 endoderm HETEROMEDUSOID STYLOID Fig. 11. Types of degenerate medusae (fixed sporosacs). 2. cryptomedusoid. Radial canals absent, but a single layer of endoderm, the endodermal lamella, present lining the exumbrellar ectoderm. Subum- brellar cavity distinct, reduced or absent. 3. heteromedusoid. Endodermal lamella absent. Outer ectoderm two or more- layered, often enclosing the remnant of a subumbrellar cavity. This may form an acrocyst for the retention of eggs. 4. styloid. A simple evagination covered with ectoderm and lined with endo- derm; the latter with its cavity forming the spadix. The sex cells develop between the two layers. These stages have a doubtful value in classification since some species are sexually dimorphic, with one sex more reduced than the other, in Tubularia indivisa and T. regalis the male gonophore is cryptomedusoid and the female eumedusoid, and in Eulaomedea flexuosa and E. calceolifera the male gonophore is styloid and the female heteromedusoid. It is, however, important to distinguish between medusae which develop fully and can be keyed out by typical adult characters and those which are degenerate and cannot feed or grow. I therefore propose to follow Rees's dictum (1957) and retain 'separate genera for hydroids with fixed gonophores and for hydroids with free medusae . .'. The term fixed sporosacs will be used for all degenerate medusoid stages, including the four described 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
