146 THE BIOLOGY OF MARINE ANIMALS 



water by a series of small openings through which it draws a respiratory 

 current. The Cumacea are burrowing forms with well-developed gill- 

 chambers on either side of the thorax. The inspiratory current is drawn 

 through a posterior opening guarded by a sieve which filters off suspended 

 particles. Anteriorly, the expiratory current is discharged through siphons 

 formed by the first maxillipeds. Burrowing shrimps (Callianassa, Upo- 

 gebia), which inhabit muddy shores, use their pleopods for pumping water 

 through burrows (35, 106). 



The masked crab Corystes cassivelaunus has evolved a siphonal system. 

 Cory st es burrows during the day, and comes to the surface to feed at night. 

 Its antennae, about as long as the body, project upward to the surface 

 when the animal lies buried in the sand. Each antenna bears a double 



Fig. 4.5. Diagrammatic Cross-section through the Sea Mouse Aphrodite 

 aculeata, Showing Respiratory Channels and Chambers Above and Below 



the Body Wall 



Stipple, sand. Overlapping elytra and feltwork of the chaetae cover the animal. (From 

 van Dam (31).) 



row of stiff hairs directed inwards; when the two antennae are apposed the 

 rows of hairs meet and form a functional tube which communicates at its 

 base with the gill chamber. A respiratory current is drawn down the tube, 

 and is passed over the gills from the front of the chamber backwards. 

 This is in reverse to the direction of water currents in surface-living deca- 

 pods, and it is interesting that Corystes maintains a forward-flowing current 

 through its gill chamber when it comes to the surface. 



Tubicoles usually pump water through their tubes, and such mechanisms 

 are particularly characteristic of polychaetes. A eunicid worm Hyali- 

 noecia constructs a quill-like tapering tube provided with valves at either 

 end (Fig. 15.11). When undisturbed, Hyalinoecia emerges from the front 

 end and drags the tube along behind it. The valves are flexible and directed 

 backwards, and when the animal has retreated inside they allow a water- 

 current, created by undulatory waves of the body, to pass through the tube. 



Chaetopterus inhabits a U-shaped tube which is buried in the substratum 

 and open at both ends to the surface. The worm attaches itself to the wall 



