184 



MARINE ANIMALS 



means of bait, such as a dead fish. Among the annelids, Arenicola is 

 important; its burrows, often closely crowded, are recognizable by the 

 spiral heaps of excrement pushed out of them. Various other annelids, 

 both larger and smaller, occur in the same habitat, among which may be 

 named the primitive Polygordius and Protodrilus, without bristles, 

 and the numerous nearly sessile forms, the terebellids, clymenids, 

 chloraemids, ophelids, maldanids, etc. The latter agree in having rela- 



Fig. 20. — Burrowing crab, Calappa granulata, from 

 the Mediterranean, front view. The arrows indicate the 

 afferent and efferent openings to the gill chambers; 

 the eyes may be seen on each side of the arrow points, 

 and the claws just below the arrows. After Garstang. 

 Fig. 21. — Albunea symnista from Madras, from the 

 dorsal side. An enlarged cross section of the breathing 

 lube formed by the antennae is shown to the right. 

 After Garstang. 



Fig. 21 





tively poorly developed bristle bundles, in connection with their sand- 

 boring habits, and were formerly united into the group Sedentaria. A 

 curious companion of the worms is Balanoglossus (Fig. 22) , a relative 

 of the chordates rather than of the worms, which lives in a U-shaped 

 tube open at both ends, and puts out piles of excrement like those of 

 Arenicola. 



The mollusks of this habitat have much in common. They are 

 uniformly thin-shelled, flat, smooth-surfaced, have a well-developed 

 foot, without a byssus gland, and have siphons formed by the union 

 of the posterior edges of the mantle into more or less elongate tubes, 

 occasionally united, which establish the connection with the surface. 

 The ventral siphon is the intake, bringing in the food and oxygen in 

 the water, while the dorsal cares for the outgoing current with the 



