ZOOGEOGRAPHICAL REMARKS 105 



interest that very few epipelagic species of medusae are common to antarctic and antiboreal waters, 

 the Antarctic Convergence evidently constituting an effective barrier to the distribution of these animals. 

 The number of species found in the West Atlantic tropical region was twenty-six, of which twelve 

 were new to the area; all of them have an extensive geographical distribution. 



Our knowledge of the fauna of medusae off the tropical west coast of Africa was considerably 

 increased by the Danish 'Atlantide' Expedition in 1945-46, twenty-eight species of Hydromedusae 

 being recorded as new to the area (Kramp 1955). Among the few species, which now may be added 

 to the list, only two give occasion for some surprise: Leuckartiara octona which is a predominantly 

 northern species, and Crossota alba which up to now was only known from the northern Pacific. 



The fauna in the waters around South Africa is a mixed fauna ; up to now it was very imperfectly 

 known, but now we can state that it is a rich fauna, as far as the Hydromedusae are concerned. 

 Forty-nine species were found by the Discovery Investigations, and among them no less than thirty- 

 three are new to the region. Most of the finds are not astonishing, considering the complicated hydro- 

 graphical conditions in this area, though several species were found to be distributed considerably 

 farther south than known before. Three species, Heterotiara minor, Zygocanna vagans and Ciinina 

 globosa, were previously known only from Indo-Pacific waters. Of very considerable interest is the 

 occurrence of the four antarctic and subantarctic neritic species, Sarsia gracilis, Halitholus inter- 

 medins, Mitrocomella frigida, and Cosmetirella davisi in the South African coastal area (see, p. 105). 



A series of stations off the tropical east coast of Africa was made in April-May 1935. Twenty-one 

 species of Hydromedusae were found, thirteen of them new to the region. Only two neritic species 

 were found, Leuckartiara annexa, which is a new species, and Octophialucium aphrodite, which was 

 previously known only from the Malayan Archipelago and the Philippines. All the other species 

 found in this series are oceanic, mainly epipelagic, and four of these are now recorded for the first 

 time from outside the Atlantic Ocean (see Table 3). 



The twelve species collected in the Indian temperate region, eight of them new to the area, are 

 all oceanic forms, widely distributed except the two species of Arctapodema, previously known from 

 antarctic waters only. 



The material available from the few hauls in the temperate and warm parts of the Pacific Ocean 

 consists of only six species, one of which is a new species, Ectopleura saccidifera, which was taken off 

 the coast of Ecuador. The others are of no great zoogeographical importance. 



A comparison between the three tables may be summarized as follows : 



Table 2. A considerable number of the neritic species of Leptolina collected by the Discovery 

 Investigations are inhabitants of antarctic or subantarctic seas, where most of them have a circum- 

 polar distribution. A similar number belong to warm or temperate waters; some of these have an 

 extensive distribution from north to south, but only one penetrates into the antarctic region, namely, 

 Staurophora mertensi which is bipolar. On the other hand, several of these species have a compara- 

 tively narrow distribution from west to east, being restricted either to the Atlantic area or to the 

 Indo-Pacific areas; this also applies to some of the subantarctic species. It may partly be due to 

 deficiency of knowledge, but it seems to be characteristic of the neritic forms that many of them 

 occur within restricted areas and, apart from arctic and antarctic species, few of them have a circum- 

 global distribution. In this respect they differ from the oceanic medusae. 



Table 3. The oceanic, epipelagic Leptolina are predominantly warm-water species and do not 

 approach the antarctic waters. 



Most of the epipelagic Trachylina are widely distributed in the oceans; only three species are 

 apparently restricted to the Atlantic. On the other hand, among the twenty species collected by the 

 Discovery Investigations only two, which are very eurythermal, penetrate into the antarctic region. 



D X.XIX 



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