Fishes of the Western North Atlantic 25 



Amphioxides pelagicus (Giinther), 1889 



Study Material. None. 



Distinctive Characters. Amphioxides larvae differ from adult Lancelets in that they 

 have neither atrial cavity nor oral cirri 5 their mouths are on the left-hand side, and their 

 gill clefts are in a single series. Pelagicus is separable from valdiviae by the facts that its 

 dorsal fin-ray chambers do not extend forward past the first myotome, and that the dorsal 

 fin originates about opposite the 2ist to 25th myotome, while in valdiviae it commences 

 opposite the 32nd to 33rd myotome, or even more posteriorly; pelagicus is separated from 

 stenurus by fewer myotomes (not more than 68 in pelagicus). 



Additional Description.^'^ Caudal fin usually not sharply marked off, although some- 

 times more definitely so, its tip lancet-shaped, usually pointed; notochord tapering to a 

 narrowly pointed tip; dorsal finfold originates about opposite the 2ist to 25th myotome; 

 the ventral farther posterior in some (opposite the 40th myotome), but farther forward in 

 others; the dorsal fin-ray chambers extend forward only to the posterior edge of the first 

 myotome, anterior to which they are replaced by an undivided tapering canal; two cham- 

 bers per myotome anteriorly, increasing to 3 or 4 per myotome posteriorly; gill clefts 16 

 to 18 in specimens of 5 to 6 mm., with 24-26 reported for Bermuda specimens of 8 to 

 10 mm. or longer, and up to 30 for the Indian Ocean form; myotomes usually 63 to 64 

 (50 or 51 preanal and 13 postanal) with totals of 67 also reported from Bermuda, and 

 62 to 68 from Indian Ocean. 



Color. No information available. 



Size. Pelagicus has been recorded up to 16 mm. in length from Bermuda; up to lO 

 mm. from the Indian Ocean." 



Parentage. It is probable that the pelagicus of the Atlantic is the neotenic larva of 

 Asymmetron lucayanum, the pelagicus of the Indian Ocean that of the local representa- 

 tive of lucayanum.^* 



Habits. Nothing positive is known of the habits of this or of any other Amphi- 

 oxides, except that it is planktonic. In the Indian Ocean Amphioxides of the pelagicus 

 type have been taken in abundance at or near the surface and similarly at several locali- 

 ties in the tropical Atlantic. On the other hand, many of the records have been from 

 nets fished at considerable depths.'*^ In most instances, however, there is no certainty that 

 the specimens were actually taken at the depth at which the major part of the haul was 

 made, because the nets also fished while being lowered and hauled up again. Consequently, 

 the depth of chief abundance is still to be learned. We think it probable that the odd speci- 



52. Based on previous descriptions and illustrations. 



53. A 2i-nim. specimen from the Indian Ocean, reported and pictured by Forster-Cooper (in Gardiner, Fauna Geogr., 

 Maldive Laccadive Archip., /, 1903 : 352, pi. 4) was in such poor condition that its specific identity is doubtful. 



54. This identity has been maintained by Gibson (Trans. Linn. Soc. Lond., Zool., [2] /j, 1910: 241). Although 

 Goldschmidt (Biol. Bull. Wood's Hole, 64, 1933: 324) has questioned it, the number of myotomes that he 

 records for the Bermudian felagicus (50 to 51 preanal and 13 postanal, as well as a stated total of 67) falls 

 within the limits reported for lucayanum from the Bahamas (62 to 68). 



55. Ostensibly down even to 1,000 fathoms (1,829 meters). 



