228 THE BIOLOGY OF MARINE ANIMALS 



Cumaceans are bottom-dwelling animals which burrow in sand or mud. 

 In Diastylis a filter current is created by movements of maxillae and maxilli- 

 peds, and this is augmented by the respiratory current. The water currents 

 created by the animal pass through the setous mouth parts (maxillae, 

 maxillipeds), where large particles become deposited and filtered off (21). 



Euphausiids are pelagic in habit and feed upon detritus and small 

 planktonic organisms. The chief food of the antarctic krill Euphausia 

 superba consists of diatoms. That of Meganyctiphanes norvegica is pre- 

 dominantly organic detritus, supplemented by diatoms, flagellates and 

 small crustaceans. Euphausiids appear to feed in a manner similar to 

 mysids (q.v.). The filtering apparatus or food basket is formed by the 

 thoracic limbs which are provided with fringes of setae. Feeding currents 

 are created by lateral movements of the thoracic limbs and by beating of 

 pleopods. Food particles caught in the thoracic basket are transferred to 

 the mandibles to be triturated and swallowed. Meganyctiphanes has also 

 been observed to feed upon suspended matter on the bottom, which is 

 stirred up by the pleopods (61). 



Decapods. These animals are typically omnivores or carnivores, feeding 

 on large food masses, but filter-feeding has been adopted by a few forms, 

 often in conjunction with specialized habits. The peculiar gall crabs 

 Hapalocarcinus and Cryptochirus live in chambers within corals and are 

 dependent upon plankton and suspended matter drawn into the chamber 

 with the respiratory and feeding current (p. 662). The oral region in these 

 animals is screened by a sieve of setae fringing the maxillipeds, while the 

 mandibles, apparently, are also used for sifting food and creating water 

 currents. Spider crabs (Inachus) also consume fine particles. Essentially 

 deposit feeders, they pick up fine material in their chelae and hold it in 

 front of the mouth where it is brushed over the maxillipeds. 



Filter-feeding has been acquired by several groups of anomurans. The 

 hermit crab Eupagwus feeds to a large extent upon bottom detritus and 

 small organisms which are swept up by a terminal brush of setae on the 

 third maxillipeds. In addition the small chela is used to scrape bottom 

 deposits and pick up small masses which are passed to the maxillipeds and 

 thence to the mouth parts. Feeding methods are essentially the same in 

 Galathea which collects finely-divided material from the substratum by 

 sweeping movements of the maxillipeds, but larger pieces of food may also 

 be seized by the chelae and maxillipeds and passed to the mandibles. 

 Porcellana is a particulate feeder and possesses a filter in the form of a 

 fringe of long hairs on the third maxillipeds (Fig. 5.22). These perform 

 regular casting movements, thus entangling suspended particles which are 

 transferred by the second maxillipeds to the mouth. 



Another method of filter-feeding is used by the mud shrimp Upogebia. 

 This animal lives in a burrow through which it draws a feeding current 

 by fanning its swimmerets. The first two pairs of limbs are heavily fringed 

 with hairs so as to form a basket, and as water passes through this filter, 

 detritus and plankton are strained off. The collected food material is 



