D VIII+30-31; A 27-31; P 29-32; V 29-33; C 20-25/35-38/21-22; LL 94-104; gills 4; gill rakers replaced by spiny tooth-plates. Head naked, the opercular bones exposed; gill cover expanded posteriorly and ventrally as a thick flap of skin; lower jaw with two large, overlapping gular plates; teeth conical, set on bony plates attached to palatines, ectopterygoids, and dentaries; maxilla absent (the structure at the side of the upper jaw that appears to be a maxillary bone is a thick fold of skin connecting the upper jaw to the rear of the lower jaw).Swim bladder elongate, filled with fat; intestine with spiral valve; osmoregulation involves retention of urea and trimethylamine oxide in the blood, but urea is not resorbed by the kidneys and excess salts are excreted by the rectal gland. In adults the brain is incredibly small, occupying only about 1% of the cranial cavity; but in the smallest juveniles, the brain completely fills the cranial cavity.Color in life: dark metallic blue, the head and body covered with irregular white or pale bluish spots. After death, the bluish color fades to dark brownish black.
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