486 DEPTHS OF THE OCEAN 



upon them. The most noticeable of these is medusa's head 

 {Gorgonocepkalus linckii, see Fig, 345), a brittle-star with ex- 

 tremely branching arms that lives upon the larger gorgonians 

 and sea-trees. A crustacean, GalatJiodes tridentatus, appears 

 also to be intimately connected with the corals, and large 

 quantities are occasionally found upon them. As for the 

 remaining higher forms of crustaceans the fauna consists chiefly 



of prawns, though they are 

 , >• different from the ones in 



the littoral zone,^ but other 



groups are not entirely 



wanting.- 



The large mussel, Lima 

 excavata, is extremely character- 

 istic of the rocky bottom, attach- 

 ing itself by means of its fine 

 silky byssus-filaments. We may 

 further mention a sea-slug {Psolus 

 sqiiajiiatus, see Fig. 346), easily 

 recognisable owing to its abruptly 

 truncated disc with suctorial feet, 

 by which it adheres to stones, 

 shells, etc. ; a crinoid {^Antedon 

 petasus) occurring locally, though 

 often in abundance, especially 

 where there are sponges ; several 

 star -fishes, Pentagonaster granu- 

 laris, Porania pulvillus^ Hippa- 

 sterias phrygiana {plana), which 

 last seems to prefer places where 

 the hard bottom is covered with 

 coarse sand ; a brittle - star 

 {Ophiopliolis aculeata) ; molluscs, 

 as, for instance, species of Pecten ; 

 ascidians, particularly of the family 

 Styelidae ; sea-spiders {NyuipJion strdmi\ etc. At considerable depths 

 there is also the remarkable starfish Brisinga endecacnemos. Some of 

 these are exclusively deep-sea forms, and rarely leave the deeper 

 parts of this zone. Munida te7iuiniana, BatJijplotes tizardi, Brisinga 

 endecacnemos, and Lima excavata do not occur in depths less than 300 

 or 400 metres. 



(3) Other Northern Boreal Coastal Areas. — There are 

 several areas where the littoral zone has been but little studied, 



^ Pandalus pj-opinquus, P. brevirostris, Hippolyte polan's, and H. securifrons. 



- Thus a hermit-crab {Pagurus ptibescetts), which occurs, too, in the littoral zone, is quite 

 common, and so are Munida rugosa, which also inhabits soft bottom, and the stone-crab 

 {Lithodes maja). 



Fig. 344- 

 Serpula verinicttlaris, Mtil 



