Figure 2. — Composite diagram o( Balhochordaeus charon . anterolateral 

 view, c, caecum; cp, cheek pouch of epidermis; e, esophagus; g. gonad; gs, gill 

 slit; i. intestme; m, mouth, mb, muscle band; n, notochord; p, pharynx; s, 

 stomach 



great size relative to other larvaceans, whose 

 adult trunk lengths are usually < 5 mm. The pres- 

 ent specimens are the largest collected since 

 Chun's ( 1900) first two giants (Table 1). The ratio 

 of tail length to trunk length ranges from 2.1 to 

 3.9, but damage to the tail and shrinkage after 

 fixation make these figures unreliable. The mean 

 ratio of 3.0 for all 12 intact specimens indicates 

 that, in contrast to other Oikopleuridae.B. charon 

 has a relatively short, broad tail whose width is 

 about one-third its length. The lateral epidermal 

 fin is usually torn or absent, but when present it is 

 widest distally, unique in the Oikopleuridae. The 

 notochord is clearly visible as the central axis of 

 the tail, sandwiched between the two broad mus- 

 cle bands. 



In contrast to other Oikopleuridae, the trunk is 

 strongly compressed dorsoventrally and is nearly 

 as broad as long (Figure 2). The epidermis is thin 

 and often diaphanous, and it protrudes on either 

 side of the oral region as a pair of "cheek" pouches. 

 The mouth, unique in its dorsal and subterminal 

 position, lies atop a low buccal cone and leads into 

 the short, narrow pharynx. The long, spindle- 

 shaped openings of the two stigmata (gill slits) 

 arise from the floor of the pharnyx just behind the 

 level of the dorsal mouth and ventral endostyle. 

 The gut, the only conspicuous internal structure, 

 is light brown in Formalin'-preserved material 

 and lies free in the body cavity. The pharynx opens 



516 



via the esophagus into the large stomach that is 

 expanded laterally as a blind caecum on the left 

 and a right lobe which gives rise to the narrow 

 intestine and rectum. The anus opens ventrally 

 just anterior to the base of the tail . Small masses of 

 gonadal tissue lie in the hemocoel in three of the 

 specimens. In mature individuals the gonad forms 

 a U-shaped mass which protrudes into the cheek 

 pouches. 



Distribution of BjthoihorJtiens charon 



Only one specimen of B. charon was taken with 

 a closing net, thus the depth distribution of the 

 species cannot be determined with certainty. 

 However, all of the remaining 13 specimens were 

 taken well off the bottom in vertical or oblique 

 tows from at least 200 m or in horizontal tows 

 whose time at maximum depth greatly exceeded 

 the time for haulmg in the net. This and the lack of 

 specimens in surface tows support the belief of 

 Chun (1900), Lohmann (1931), and Garstang 

 ( 1937) thatB. charon is a deep-living, mesopelagic 

 species. 



Few specimens have been collected and it is 

 premature to conclusively describe the areal dis- 

 tribution ofB. charon on the basis of known rec- 

 ords (Figure 3). Since the eight previously re- 

 ported specimens came from the North and South 



'Reference to trade names does not imply endorsement by the 

 National Marme Fisheries Service, NOAA 



