. Annals of the South African Museum. Annale van die Suid-Afrikaanse Museum. THE GEOGRAPHICAL DISTRIBUTION OF SOUTHERN AFRICAN HYDROIDS 175 have odd distributions which do not fit any of the other categories. There are two possibilities. Either these are newly evolved eurythermic species which are in the process of spreading rapidly and likely to become cosmopolitan, or they are 'peripheral relicts' of fairly primitive forms which were once more widely distributed. Among the scattered species three are interesting because outside southern Africa they are limited to the west and east coasts of
. Annals of the South African Museum. Annale van die Suid-Afrikaanse Museum. THE GEOGRAPHICAL DISTRIBUTION OF SOUTHERN AFRICAN HYDROIDS 175 have odd distributions which do not fit any of the other categories. There are two possibilities. Either these are newly evolved eurythermic species which are in the process of spreading rapidly and likely to become cosmopolitan, or they are 'peripheral relicts' of fairly primitive forms which were once more widely distributed. Among the scattered species three are interesting because outside southern Africa they are limited to the west and east coasts of the tropical Atlantic (Clytia hummelincki, Zyzzyzus solitarius) or to the western tropical Atlantic only {Cladocarpus tenuis). Three others have a similar distribution but also extend further north and/or east (Aglaophenia latecarinata, A. pluma dichotoma, Symplectoscyphus amphoriferus). Cosmopolitan and scattered species with antarctic/subantarctic affinities are included in Table 4. DISTRIBUTION AND DEPTH Figure 6 shows that there are more species present in the shallow water (0-100 m) than at any other level, and although there have been fewer samples from deep water it is not expected that more extensive collecting will alter the picture to any great extent. The shallow water is obviously the optimum zone for hydroids. Most of the species in the littoral area are at the upper edge of 180 -i. 750 1000 1250 DEPTH (m) Fig. 6. The distribution of species according to depth. From range of species 1500. 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 [etc. ] The Museu
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