478 LAND ANIMALS 



flats in the dry season and become active during the rainy seasons, 

 when they swarm forth in ground-covering numbers. Several species of 

 fishes likewise occupy these mud flats and burrow during the dry 

 season. A number of snails are found, one of which, Littorina angu- 

 lifera, although a gill-breathing snail, has become arboreal and climbs 

 over the mangrove roots, coming down to water only occasionally. 

 In similar mangrove swamps along the shores of the Pacific and 

 Indian oceans may be found Periophthalmus, a bony fish with modified 

 anterior fins by means of which it climbs about the mangrove roots or 

 skips over mud flats, whence the common name of mud skipper. 



In the salt marshes of the Louisiana coastal margin the muskrat 

 [Ondatra rivalicus) is abundant in regions where the tidal influence 

 is not great. The Louisiana seaside sparrow, a marsh wren, the red- 

 wing blackbird, the boat-tailed grackle, the clapper rail, and two species 

 of gallinules and the least bittern nest and feed among the canes and 

 bullrushes. The first four birds mentioned feed in part on insects; 

 other members of the community feed on small crustaceans and fishes 

 as do the herons and snowy egrets which usually nest elsewhere. 

 When the marsh becomes more shallow, it is entered by the raccoon, 

 otter, and the mink. Alligators which abound in neighboring fresh- 

 water marshes are absent in brackish ones. The diamond-backed ter- 

 rapin is limited to these coastal marshes of the Atlantic and Gulf coasts 

 of southeastern North America. 



The seacoast itself, as distinguished from coastal marshes and 

 sounds, has attracted a great variety of the larger animals which take 

 advantage of the coastal invertebrates and fishes for their food supply. 

 The preponderance of wading and swimming birds is again a feature 

 of this environment, and the bird life is further remarkable for its 

 greatest concentrations to the north and south, which compares only 

 with the conditions in the tundra. Mammals are well represented, and 

 there are a few reptiles; but amphibians, which are intolerant of salt, 

 are absent, and as there are only a few midges and the water strider 

 Halobates to represent the insects, it is only the three higher classes 

 of vertebrates which require consideration as the semi-aquatic animals 

 of the marine coast. 



The reptiles of this habitat are few. The large marine iguana, 

 Amblyrhynchus, of the Galapagos Islands is completely adapted to the 

 environmental conditions by its powerful tail for swimming and the 

 strong claws which enable it to land on rocks in the surf, after feeding 

 on the seaweeds exposed at low tide. Two species of crocodile, the 

 East Indian Crocodylus porosus and the American C. acutus, venture 



