Larvae and juveniles of the deepsea "whalefishes" Barbourisia and Rondeletia (Stephanoberyciformes: Barbourisiidae, Rondeletiidae), with comments on family relationships

Abstract

Larvae of deepsea whalefishes Barbourisia rufa (11: 3.7-14.1 mm nl/sl) and Rondeletia spp. (9: 3.5-9.7 mm sl) occur at least in upper 200 m of open ocean, with some specimens taken in upper 20 m. Larvae of both families are highly precocious, with identifiable features in each by 3.7 mm. Larval Barbourisia have an elongate fourth pelvic ray with dark pigment basally, notochord flexion occurs between 6.5 and 7.5 mm sl, and by 7.5 mm sl body is covered with small, non- imbricate scales with a central spine typical of adult. In Rondeletia notochord flexion occurs at about 3.5 mm sl and elongate pelvic rays 2-4 are most strongly pigmented part of larvae. Cycloid scales (here reported in family for first time) are developing by 7 mm; these scales later migrate to form a layer directly over muscles underneath dermis. By 7 mm sl there is a unique organ, here termed Tominaga's organ, separate from and below nasal rosette, developing anterior to eye. Larvae of two species of Rondeletia can be distinguished by presence or absence of developing spongy bone in pectoral girdle and sphenotic by at least 9 mm and by counts of vertebrae, pelvic-fin rays, and dorsal hypural bones in smaller larvae. The presence of Tominaga's organ in gibberichthyid Gibberichthys suggests that the whalefishes, Barbourisiidae, Rondeletiidae, and Cetomimidae, as a group are paraphyletic, and that Rondeletia and Gibberichthys are sister taxa.