Research project: Deep sea whalefishes (Cetomimidae): ontogeny, morphology, biology and relationships

Dates

Start date:
2002

Museum investigators

External investigators

  • G. David Johnson, Smithsonian Institution

Description

Female cetomimid whalefishes have been known for more than 100 years, with adults living between 1500 and 3500 metres in the bathypelagic zone of the oceanic midwaters. Neither males nor larvae of this family had been authenticated previously. Our recent paper united two other families of greatly different morphology, one of larvae (Mirapinnidae) and one of males (Megalomycteridae) with the females. Evidence included the recent fortuitous collection of a transforming female and recognition of transforming males, coupled with DNA from all three life stages from recent specimens.

Current research involves linking the various taxa of all three life stages (9 genera and at least 15 species of females are recognised, but only 6 species of larvae and males), challenging due to the greatly differing morphologies and the rarity of fresh specimens. It is hoped that detailed descriptions of the elongated tail streamers of the tapetail larvae will elucidate how the larvae can swim and catch copepods with a streamer up to 10 times the length of the fishes. Some of these streamers resemble siphonophores, and their function is unclear.

Detailed description of bignose male internal anatomy is underway, as males have just been found to cease feeding after larval transformation and subsist on a greatly enlarged liver. Presumably the females produce pheromones, as all males have very large nasal organs; the search for pheromone-producing tissue is also underway. Study of the more conservative skeletal elements of all three life stages will provide characters to reanalyse relationships within the family, as well as those with other families in the order Stephanoberyciformes. A review of available DNA data will be included in the reanalysis.


Dr John Paxton , Senior Fellow
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