23.2 H err e: Philippine Eels 129 



bizarre coloration. The species found in fresh waters and cool 

 seas or in oceanic depths are always of plain and dark or silvery 

 coloration. Many of the reef-dwelling eels strikingly resemble 

 snakes and worms, in both external appearance and habits. 

 They vary greatly in size from those like earthworms or intes- 

 tinal round worms up to huge serpentlike forms more than 3 

 meters in length. Many genera and species have been described 

 but, owing to our very limited knowledge of their breeding 

 habits, larval development, and the changes due to sexual matu- 

 rity and old age, many of the published species are merely nomi- 

 nal or include two or more species. It is my belief that further 

 collecting will increase the number of valid species in the Phil- 

 ippines to seventy-five or eighty. 



Key to the suborders and families of Apodes known from the PhUippims. 



a\ Gill openings well developed, leading to large interbranchial slits ; tongue 



present; opercles and branchial bones well developed; scapular arch 



present and free from the skull Suborder Enchelycephali. 



b\ Skin covered with embedded linear or narrowly oblong scales ; anterior 

 nostrils on top of snout, posterior ones in front of eyes; pectorals 

 well developed as are the vertical fins which are confluent with 

 caudal; lower jaw projecting; tongue with its margins free; teeth 



in cardiform bands on jaws and vomer; eggs minute Anguillidae. 



o\ Scales wholly wanting; eggs of moderate size, so far as known, much 

 as in ordinary fishes; pectorals present or absent; nostrils marginal, 

 lateral, or superior. 

 c\ Tail not greatly shorter than rest of body; heart close behind gills. 

 d 1 . Nostrils lateral or superior. 



e\ Tongue broad, free anteriorly and on sides; dorsal, anal, and 

 caudal well developed and confluent; tail sometimes ending 

 in a long filament; coloration nearly always plain, black- 

 ish, brownish, or silvery, fins often black margined; teeth 

 moderate, 

 f. Pectorals vestigial or absent; snout obtuse, very short, the 

 lower jaw projecting; cleft of mouth strongly oblique; body 

 excessively elongated, depth 48 to 80 in length; needlelike 



teeth in bands Heterocongrid*. 



f. Pectorals well developed; body moderately elongate, depth 14 

 to 26 in length; lower jaw more or less included; teeth in 

 bands, those on sides forming a cutting edge. 



Leptocephalidae. 

 **. Tongue narrow, not free; vomerine teeth usually well developed, 

 often enlarged. Pectoral fins well developed ; dorsal, anal, and 

 caudal well developed and confluent; upper jaw prominent, 

 its rounded tip separated by a notch from rest of snout; 

 vomer with numerous large conspicuous canines. 



Mursenesocidie. 



