94 



CTENOPHORA. 



Pleurobrachia crinita is regarded by Moser as a local form. Though it is as yet known only 

 from the Karajak-Fjord at West Greenland, I do not doubt that it will prove to be widely distributed 

 — whether in the arctic or Atlantic waters nobody can say in the present state of our knowledge. It may 

 have been simply overlooked or confused with other species [PI. pilciisf\ or it may perhaps be a form 

 which generally occurs in greater depths, only occasionally rising to the surface ( — as would appear 

 to be the case with several species of Ctenophores, which are met with only occasionally — ). Upon 

 the whole I am not inclined to believe in the existence of very local species of such eminently plank- 

 tonic organisms as the pelagic Ctenophores. — With the non-pelagic forms the case is, of course, different; 

 thus it is quite possible that Tjalfiella is a very local form, though I would be more inclined to 

 suppose that it will prove to be more widely distributed, probably in tlie warm region of the Atlantic. 

 But as regards the pelagic Ctenophores it is not obvious, how they could avoid being carried along 

 with the currents, getting thus a wide distribution in the waters otherwise affording suitable condit- 

 ions in regard to temperature and salinity. 



These considerations also apply to the Mediterranean fauna of Ctenophores. Moser (Op. cit. 

 p. 178) regards as peculiar to this sea no less than 10 species of Ctenophores, viz. Euchlora rtibra, 

 Euchl. Jiligera, Lesueuria vitrea, Pletirobrachia rhodopis, Hormiphora pluniosa. Lampetia pancerina, 

 Euplokamis stationh, Beroe ovata, Bolina hydatina and Dc'iopca kaloktenofa. Of these I think Pleiirobr. 

 rhodopis and Beroe ovata have been proved above conclusively to be identical with the common At- 

 lantic species, PL pileiis and Beroe ciieiiuiis, and very probably Bolina hydatina is identical with 

 B. infundibulum , while Lesueuria vitrea is evidently only a damaged Bolina (or some other Lobate). 

 The remaining six species have certainly not yet been recorded from the Atlantic; but it can scarcely 

 be doubted that they must be carried out (or in) by the strong current in the Gibraltar strait, so that 

 they will prove to occur at least in the neighbouring regions of the Atlantic, as is the case with the 

 other species found in the Mediterranean, e. g. Vexilluni parallelum, Eurhantpcra vexilligera, not to 

 mention the nearly cosmopolitan Ccstus veneris and Beroe Forskalii. 



Another thing would be, if there are perhaps true deep-sea Ctenophores in the Mediterranean. 

 Such would, probably, be incapable of passing the Gibraltar Strait and thus might represent true 

 local forms. The same would perhaps be the case, if such deep-sea forms should prove to occur in 

 the Polar-Sea. But the existence of deep-sea Ctenophores in these seas remains as yet an unsolved 

 problem. — An almost eqiially interesting problem, viz. the bathymetrical distribution of the pelagic 

 Ctenophores has scarcely been touched as yet. Differential hauls, taken from different depths to the 

 surface, have certainly been made by several expeditions; but reliable results will scarcely ever be 

 reached in that way. The use of closing nets will be needed for the study of this problem. 



As Mertensia ovum must be regarded as a characteristic form of the arctic water, bearing 

 evidence of the distribution of the polar stream, other forms again are unquestionably bound to the 

 warm waters and can afford proof of the intrusion of warm currents, as e. g. the Gulf Stream. The 

 question whether such forms are known from the North Atlantic is answered in the negative by 

 Moser (Op. cit. p. 180). "Der Golfstrom verschleppt offenbar keine einzige Warmwasser-Ctenophore 

 dorthin (viz. the Ice Sea) oder auch nur an die nordeuropaischen Kiisten....; wenigstens ist bisher 

 kein einziger Fund bekannt, der im Sinn einer solchen Verschleppung gedeutet werden konnte". 



