HOLOTHURIOIDEA 357 



coalescence has been observed in specimens lying so close together 

 as to be in contact with each other. 



Parasites occur in no small numbers in the Holothurians. 

 Various Protozoa, Planarians, Nematodes, and Copepods may occur 

 in their body cavity or intestinal canal. Some crabs {Pinnotheres) 

 live in the cloaca or respiratory trees ; another crab, Lissocarcinus 

 orbicularis Dana, lives between the tentacles of various tropical 

 Holothurians. An Actinian, Sicyopus commensalis Gravier, lives 

 on the deep-sea Holothurians Pseudostichopus villosus and 

 Paroriza Prouhoi Her. A Tardigrade, Tetrakentron synaptce 

 Cuenot, lives on the tentacles of Leptosynapta inhcerens ; the 

 Rotifer Discopus synaptce Zel. lives on the skin of Synaptids. 

 Some species of Pol^Tioid w^orms live on the skin of various 

 sea-cucumbers, likewise some molluscs {Eulima). Some very 

 strongly modified Gastropods are found parasitic in Holothurians : 

 Entoconcha mirabilis Joh. Miill. in Labidoplax digitata, En- 

 ter oxenos Oestergreni Bonne vie in Stichopus tremulus, Entocolax 

 Ludwigi Voigt in Myriotrochus Rinkii (and a related form in 

 Myriotrochus Theeli, according to Hj, Ostergren); they are long, 

 w^orm-shaped bodies, very unlike normal Gastropods, but their 

 young are typical larval snails, provided with a normal shell. 

 They are found attached to the oesophagus or intestine {Entocolax 

 to the body v*all), hanging from there free into the body cavity 

 of the Holothurian ; they may also occur free in the body 

 cavity. Also a considerably modified mussel, Entovalva mirabilis 

 Voeltzkow, is found parasitic in the oesophagus of a tropical 

 SjTiaptid. A small fish, Fierasfer, lives in the cloaca and 

 respiratory trees of various larger Aspidochirotes. 



The sea-cucumbers are not much eaten by fishes ; still 

 Thyonidium pellucidum and Psolus phantapus are of some im- 

 portance as food for the cod. It appears that fishes often bite 

 off the tentacles of Dendrochirotes. Sea-stars often devour sea- 

 cucumbers, e.g. Psolus. As food for man the sea-cucumbers play 

 an important role in the Indo-Pacific regions ; various of the 

 larger Aspidochirotes living in shallow w^ater are dried and 

 smoked and, under the name of " Trepang " or " Beche de 

 Mer ", form an important article of commerce ; they are 

 especially a favourite dish with the Chinese. 



On account of the slightly developed skeleton the Holo- 

 thurians are very little fit for being preserved as fossils, and 

 therefore are of very little importance in palaeontology. Only 

 some anchors and wheels of Synaptids are known with cer- 

 tainty in a fossil state. The interpretation of some imprints 



