8 The Animal Ecology of the Cold Spring Sand Spit 



polyphemus, the largest and most aberrant of our Crustacea, will be seen, especially 

 during June, traveling over the shallow water and occasionally coming to land to lay 

 its eggs in the sand. 



c. The burrowing animals of the submerged zone constitute a remarkable fauna 

 of, for the most part, elongated animals. We have already seen that many molluscs 

 burrow. So do a few sea anemones, such as the white-armed sea anemone, Sagartia 

 leucolena, and the flesh -colored or white Halocampa producta. These sea anemones 

 seem to feed on bits of organic remains, of which the sand is full. The other burrow- 

 ers are here for a similar purpose; the circumpo^r sea cucumber, Synapta inhserens; 

 the worm that shows affinities with vertebrates, fll^^^glossus Kowalevskii; two nem- 

 ertines, Cerebratulus leidyi and Cerebratulus lacteuSf and some seventeen different 

 kinds of jointed worms, Annelida. All these find shelter, moisture, and food in the 

 sand and mud beneath the sea bottom. But their immunity from attack is not com- 

 plete, for as the moles have followed the earthworms and insect larvae into the sub- 

 aerial ground, so have several predaceous Crustacea followed the annelids into the 

 mud. These are: the mantis shrimp, Squilla empusa, which is only a little smaller 

 than the lobster, and Callianassa stimpsoni and Gebia affinis, that are somewhat smaller 

 than a large crayfish. 



d. The swimming animals are partly scavengers and partly predaceous. To the 

 first class belong the prawn Palsemonetes vulgaris, which scours the edge of the tide 

 for floating debris ; and also the swimming crabs, the blue crab, Callinectes hastatus, 

 and the commoner "lady crab," Platyonichus ocellatus. Here, too, we may place the 

 little killifishes, Fundulus, although these pick up many live shore snails. The majority 

 of the fishes are predaceous, feeding on the crawling and even the burrowing 

 species that I have enumerated. The "skates" that lie close to the bottom catch 

 burrowing worms and molluscs and also the snail Lunatia heros. The sand sharks 

 and dogfish (Carcharias littoralis and Mustelus canis) gather in the spider crabs, squil- 

 las, and hermit crabs. The flounders, likewise, living close to the bottom, get Gebia 

 and the prawns. The toad-fish, which lays its eggs in old shoes or in tin cans or 

 under stones, feeds on the mud snail, Nassa, on crabs, and on prawns. Thus we see 

 that in the shallow sea each species that occurs is present on account of particular 

 relations that it bears to other species or to the non-living environment. The pres- 

 ence of the sharks is determined by that of the squillas, the squillas by the worms, the 

 worms by the decaying vegetation, this by the living vegetation, and this by the salts 

 and the nitrogenous food brought down by the creek from the valley above. This 

 microcosm of the submerged zone affects in turn the lower and the upper beaches. 



II. THE FAUNA OF THE LOWER BEACH 



As already stated, the lower beach is a zone where aquatic and terrestrial con- 

 ditions alternate every day. On this account, and on account of the sand, it is an area 

 devoid of all living vegetation excepting the unicellular algae that grow upon the 



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