248 



A HISTORY OF FISHES 



A little ccl-shapcd fish, related to the Blennies, without pelvic 

 fins and with the anal fin extending forward nearly to the head, 

 is in the habit of sheltering within the bodies of marine animals 

 known as Holothurians or Sea Cucumbers, aUies of the Star- 

 fishes and Sea Urchins. This fish is known as Fierasfer, a name 

 derived from a Gr^ek word meaning sleek and shiny, and has 

 a transparent body with a number of scattered dots of pigment 

 in the skin. When desirous of entering a holothurian the fish 

 searches for the anus with its head, and then bends the tail 

 round, inserts it into the opening, and straightening its body, 



wriggles backwards 

 until completely 

 housed within the 

 body of its host (Fig. 

 95). More than one 

 fish can occupy the 

 same "dwelling," 

 and no fewer than 

 seven have been ob- 

 served to enter a sea 

 cucumber, one after 

 another. By this habit 

 the Fierasfer obtains 

 shelter during the 

 day, and at night 

 sallies forth in search 

 of the small crus- 

 taceans on which it 

 feeds. The unfortun- 

 ate holothurian gets 

 no return for its ser- 

 vices, and its internal organs may even suflfer damage through 

 the presence of its uninvited guest. It is of interest to note 

 that the holothurians living more or less close to the shore 

 are always free from the fishes, whereas those from deeper 

 water generally contain one or more tenants. 



A Japanese species of Fierasfer has been found inside a Star- 

 fish, and on the coast of North America it is not uncommon 

 to find these fishes living inside the Pearl Oysters. This 

 association may be fatal to the fish, however, for it is sometimes 

 imprisoned by the oyster and its body sealed up in a layer of 

 mother-of-pearl. Quite recently a little Cardinal-fish {Apogon- 

 ichthys) has been discovered on the coast of Florida, which 



Fig. 95. 



Fierasfer acus and Holothurians, 

 (After Emery.) 



about ^o 



