THE SEA BOTTOM 67 



mud such as the Sipunculids, which have leathery bodies, 

 one end of which can be drawn out into a long proboscis, 

 a feature also of the beautifully coloured Nemertines, which 

 have soft and very extensile bodies, which often break into 

 pieces when handled. The bristle- worms are commonest 

 of all, and include many of the kinds we have already 

 mentioned as well as others only found in this region. 

 The most remarkable of these is the peculiar tube-dwelling 

 Chaetopterus, which lives in sand or mud occupying a 

 parchment-like tube. In the middle of its body are three 

 broad segments which beat rhythmically — even when de- 

 tached from the rest of the body — and maintain a steady 

 current of water through the tube. 



Commonest of all are crustaceans of all sizes. One of the 

 barnacles, Scalpellum, attaches itself to hydroids and is 

 remarkable in that the large specimens are all female, the 

 males being minute creatures which live attached to the 

 females. Various ghost-shrimps and many members of 

 the prawn and lobster family are common on the bottom. 

 Of the latter may be mentioned the Norway lobster 

 {Nephrops), which lives on muddy bottoms (Platens), and 

 the majestic rock lobster {Palinurus) with its handsome 

 brown, sculptured shell but without the large claws of the 

 common lobster (Plate 114). There are also squat-lobsters, 

 such as the small Galathea and the larger Munida, which 

 have long claws and broad, flattened bodies, the tail, 

 normally bent under the body, being straightened out for 

 use in swimming. Various kinds of hermit crabs scavenge 

 over the sea bottom. Of the numerous crabs, there are 

 the large red spiny spider crab {Maia), the largest and most 

 heavily armoured of the spider crabs, and, in more northern 

 waters, the somewhat similar northern stone crab {Lithodes), 

 which is stone grey in colour, and innumerable smaller 

 kinds, some of which live in sand like the angular crab 



