THE SAND EEL. 
271 
While resident on the Florida Reef, at Fort Jefferson, we discovered a Fierasfer living in 
a large Holothuria. At this time, 1859, this was a novelty to naturalists. Since then species 
have been found in other parts of the world, and in various objects. 
The large Holothuria, or Sea Cucumber of the Reef, is often eighteen inches in length ; 
and it is abundantly spread over the reef in shoal water. The visitor, in sailing leisurely in 
these waters, may reach one easily from his seat in the boat. Lift the creature into a bucket 
of water : he soon exhausts the oxygen of so small amount of water, and there peeps out from 
his mouth another creature that requires more oxygen than is left, and thus asserts his rights 
by leaving. It is a fish, a Fierasfer, that so appears, and a delicate transparent one it is, of 
eight inches in length. Its name Fierasfer is derived from the Greek, meaning sleek and 
SHARP-NOSED EEL . — Anguilla aculirostris. 
shining, in allusion to its great delicacy. Its habit of living protected within the halls of the 
great echinoderm renders its exterior tissues delicate, if indeed it be not originally made so. 
Who can tell ? These cases of parasitic or, more properly, commensal life are, indeed, puz- 
zling. This species is Fierasfer dubius (Putnam), and its locality is recorded as Florida Keys 
to Cuba. 
Another species of this genus, the Sand Eel, or Hornels (. Ammodytes tobianus ), is 
sometimes mistaken for the preceding species, from which, however, it may be distinguished 
by its greater size, its larger head, the farther setting back of the dorsal fin, the browner color, 
and more opaque body. When full-grown, the Sand Eel will reach the length of a foot or 
thirteen inches. 
