Distinguishing close relatives

Malacosteus species

Malacosteus niger has a larger postorbital photophore than Malacosteus australis, and differing numbers of other smaller photophores on the rest of the body.

Malacosteus niger

A frontal view of the head of Malacosteus niger illustrating the binocular vision and the lack of floor to the lower jaw.

Closely related genera

Species of Photostomias and Aristostomias are similar to Malacosteus in that they:

  • lack an ethymoid membrane (floor) in their mouths 
  • have no membrane connecting the hinge of the lower jaw to the neck - hence their collective name 'loosejaws'

However Malacosteus can be distinguished as it has pectoral fins (absent in Photostomias) and no chin barbel (present in Aristostomias). 

Pachystomias also closely resembles Malacosteus but has an ethymoid membrane and the lower jaw is connected to the body.

Like Malacosteus, the related genera Pachystomias and Aristostomias are capable of producing red light.

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