588 



THE BIOLOGY OF MARINE ANIMALS 



tected by its tentacles, and they may even seek protection in the subgenital 

 cavities. The Portuguese man-of-war Physalia is similarly attended by 

 young harvest fish (Peprilus) and man-of-war fishes (Nomeus) (Fig. 14.5 (92)). 

 Echinoderms are another group affording protection and shelter for 

 commensals, and there are many instances of fish, shrimps, crabs, etc., 



Fig. 14.5. Man-of-war Fishes Sheltering among the 

 Trailing Tentacles of Physalia 



Fig. 



14.6. Portion of the Tunnel of the Echiuroid Worm Urechis caupo, 

 which Burrows in Sandy Mud on the Californian Coast 



The sketch shows the worm pumping water through its mucus net, and the position 

 of its commensals. These are a goby Clevelandia ios, a polynoid Harmothoe adventor, 

 and a pinnotherid crab Scleroplax granulata. (From Fisher and MacGinitie (25).) 



occurring in association with sea urchins, starfish and holothurians. In 

 these cases the commensal secures some degree of safety in the shelter 

 of its host (90). 



Endoccism 



There are a vast number of commensals which lurk in the burrows, 

 tubes or other dwellings of various animals, and it is possible to mention 

 only a few of them. A holothurian of muddy bottoms, Labidoplax digitata, 

 has as associates a scale worm Harmothoe lunulata and a bivalve Mysella 

 bidentata, which share the protection afforded by the burrow. Many 

 polynoids are commensals, and additional examples are Gat ty ana cirrosa 

 found in Chaetopterus tubes, and Acholoe astericola occurring in the 



