Saccopharyngiformes
Habitat: deep in the ocean, down to 500 to 1800 meters deep.
Region: all oceans; Neoceymatidae in Atlantic Ocean.
Zoology
Fish; deep-dwelling; rarely seen; known from only a handful of specimens;
they lack symplectic bone, operclular bones, ribs, swim bladders, scales, pelvic fins; myomeres are V shaped instead of W shaped as in all other fishes; their lateral lines have no pores, but groups of elevated tubules; jaws are quite large, lined with small teeth, able to consume fish larger than themselves; some are bioluminescent.
Reproduction: sexual dimorphism; larvae are leptocephalus, have remarkably deep bodies, long lower jaws, unique pigmented swellings at the ends of the gut.
Taxonomy
Until recently, the order "Saccopharyngiformes" was accepted as a separate order from Anguilliformes, based on their distinct morphological differences from the rest of the "true eels". Genetic work over the past few years has shown that it is instead a derived lineage within the Anguilliformes.
Families
Suborder Cyematoidei
• Cyematidae: Bobtail snipe eels.
Suborder Saccopharyngoidei
• Eurypharyngidae: Gulpers.
• Monognathidae : One-jaws.
• Saccopharyngidae : Swallowers.
• Neocyematidae.