Figure 3. — Known collection sites oi Bathochordaeus charon Numbers correspond to specimen number listed in Table 1. 



Atlantic, Indian, and southwestern Pacific 

 Oceans, this report represents the first clearly es- 

 tablished record of the species in the eastern 

 Pacific Ocean. On the basis of the known material, 

 it appears thatB. charon has a circumglobal dis- 

 tribution in tropical and subtropical oceanic wa- 

 ters between lat. 35° N and 35° S. Forneris ( 1957) 

 classified it as a "eurythermic thermophile," but 

 such a characterization seems unwarranted, as it 

 was based on only eight specimens obtained from 

 widely separated local ities and without associated 

 physical oceanographic data. 



D 



iscussion 



All known larvacean species secrete a mucous 

 feeding device, the house. The structure of the 

 house varies considerably among the three larva- 

 cean families, but in the Oikopleuridae it contains 

 mucous filters which remove particulate matter 

 from the water. Periodically, when the filters be- 

 come clogged, the animal abandons the old house 

 and within a few minutes produces a new one from 

 a mucous rudiment secreted while in the old 

 house. The type of house produced byB. charon is 

 not yet known. Chun (1900) believed it was as 

 large as a pumpkin and that it completely enclosed 

 the animal, as in other Oikopleuridae. Lohmann 

 (1931)believed that the house was probably of the 

 "nose bag" type, as in Fritillariidae, in which a 

 mucous net is cast out from the buccal region and 

 the animal is free in the water. 



Barham (1969) observed spherical, mucous 

 structures, at least 25 to 50 cm in diameter, from 

 deep submersibles off San Diego, Calif., at about 

 200 m. Inside some of these structures, the swim- 

 ming motions of a large, tadpolelike animal were 

 visible. The structure and size of these "busted 

 balloons" leave little doubt that they were oc- 

 cupied and abandoned larvacean houses, very 

 likely those of S. charon . Because the houses have 

 not been collected in nets, Barbara's account rep- 

 resents the only observation of them. Studies of 

 photographs from such in situ observations and of 

 the secretory apparatus of the animals themselves 

 may elucidate the structure of the house of B. 

 charon. 



Bathochordaeus charon is considered to be rare 

 because of sparse records obtained since its discov- 

 ery in 1900. However, current evidence indicates 

 that the animals and their houses may be rela- 

 tively common, comparable with other species of 

 similar, large size, at least at certain depths, loca- 

 tions, or times. Barbara^ estimated the densities of 

 presumed giant larvacean houses off Cape Cor- 

 rientes, Mexico, to be on the order of 1 to 3/m'' 

 within narrow layers near the thermocline, be- 

 tween about 50 and 300 m. At least six of the 

 known specimens occurred in pairs in the same 

 plankton sample. Thus, despite their large size, 



^Eric G. Barham, Southwest Fisheries Center, National 

 Marine Fisheries Service. NOAA, P.O. Box 271, La Jolla, CA 

 92038, pers. commun. March 1978. 



517 



