y6 PELAGIC FAUNA 



species were shown to be much more widely distributed than had been 

 supposed. The members of one of the medusa orders, Trachylina, are 

 "holopelagic"; that is to say, they are independent of the coasts and 

 Uve and breed entirely in the open water. In the upper water reaches 

 we found only well-known species of these. The other orders of medusae 

 are "'meropelagic", which means that some stages of their development 

 take place on the sea bed. The eggs hatch into small larvae which descend 

 to the bottom, cling to stones, shells, and similar objects, and grow into 

 fixed polyps which propagate by budding. Often they will form large, 

 branched colonies (hydroids) and develop a new generation of medusae 

 by budding. In many cases we do not know the stages of development, 

 but we presume that this is the way it always happens. Most of these 

 medusae are "neritic", inhabiting coastal regions, and only the larger forms 

 have so long a lifetime that they get carried out to sea by the currents, 

 for though they swim, they do so only slowly. Their occurrence can give 

 valuable information about the course of ocean currents. The majority 

 belong to the small Hydromedusce, and it was chiefly among these that 

 we found many new species. The large medusae (Scyphomedusce) include 

 the RhizostomcE, the numerous genera and species of which nearly all 

 live in the Tropics. Without the single mouth of other medusae, in the 

 middle of the underside, these have eight highly curled oral arms with 

 numerous fine pores, through which the creature pumps water into its 

 canal system along with the tiny animals on which it lives. Belonging to 

 this group is the beautiful brown and violet Crambionella orsini (Fig. p. 

 69). Previously known only from the Red Sea and Arabian Ocean, this 

 proved extremely common all the way over from Africa to India. A 

 Thysanostoma flagellata from Madagascar, with magnificent red stripes 

 on the underside of the bell, was filmed swimming in an aquarium. Near 

 Singapore we caught a Versura anadyomene, which, according to the 

 literature, attains a diameter of 20 centimetres. This one was a giant of 

 60 centimetres, and a swarm of small fish and crabs had found shelter 



The bathy pelagic sea-cucumber Pelagothuria, which lives at depths beyond 1,000 metres. 



