236 THE BIOLOGY OF MARINE ANIMALS 



Caprellids, often found clinging to stems of hydroids, possess large palm- 

 like claws, with which they scrape off diatoms and debris or even attack 

 living hydroid zooids. 



Fishes. The majority of fishes are active carnivores and relatively few 

 species feed upon plants or organic debris. Some exceptions are the grey 

 mullet Mugil and Mulloides, which feed upon sea weeds, bottom mud and 

 detritus. The gill-rakers of the mullet form a sieve-like apparatus prevent- 

 ing fine particulate matter from reaching the gills. The jaw teeth are micro- 

 scopic, pharyngeal grinding teeth are present in Mulloides, and both animals 

 possess strong pyloric gizzards. Some of the parrot-fishes (Scaridae) feed 

 on vegetation or pieces of coral. In these animals the jaw teeth are fused 

 into shearing plates and the pharyngeal teeth form a flat grinding pave- 

 ment. Trunk fishes (Ostraciidae) also feed on bottom algae (2, 42, 57, 82). 



Methods for Seizing Prey 



In this section we shall be dealing with feeding mechanisms principally 

 of carnivores which seize and devour living prey, but we shall have occasion 

 to refer to certain omnivores which are partially scavenging in habit. 

 Yonge shows how such mechanisms may be classified into those concerned 

 with seizing, with seizing and masticating, and with seizing followed by 

 external digestion. These are considered together on a phyletic basis. 



Protozoa. Many protozoa are raptorial, feeding on other protozoans, 

 phytoflagellates, diatoms and even small crustaceans. Amoebae capture 

 small, slow-moving prey which they engulf in a food-cup formed by 

 pseudopodia. In raptorial ciliates the mouth is usually located at the an- 

 terior end and can be widely distended for engulfing large prey. Some 

 species possess special devices for seizing prey, such as proboscides, scoops 

 formed of undulatory membranes and suctorial tentacles. The latter are 

 found in certain parasitic holotrichs which use them to suck out the con- 

 tents of epithelial cells of their host. In suctorians, which feed upon other 

 protozoa, the prey is captured by sticky tentacles which release a paralysing 

 secretion and suck out the contents of the prey (53). 



Coelenterates and Ctenophores. Members of these groups are carnivores, 

 apart from those sedentary species dependent on symbiotic algae (p. 612). 

 With the exception of species making use of ciliary feeding currents, 

 coelenterates usually capture their prey by means of tentacles armed with 

 cnidae capable of discharging adhesive and penetrating filaments. The 

 latter are capable of paralysing small animals. Both hydroids and medusae 

 (Hydrozoa) feed on small Crustacea, worms, eggs, larvae and small fish. 

 In the feeding reaction of tubularians, for example, the proximal tentacles 

 bearing food bend towards the mouth while the manubrium, in turn, 

 bends to meet them. In colonial forms the food is shared among the mem- 

 bers of the colony. The individual polyps initiate digestion of the prey which 

 they capture, and a constriction at the entrance to the stalk allows only 

 the smallest particles and dissolved material to gain ingress into the 

 branches and common stem of the colony, where absorption takes place. 



