| Family | Scientific Name | Author | Year | Common Name |
| Synaphobranchidae | Synaphobranchus affinis | Gùˆnther | 1877 | Grey Cutthroat Eel |
Family Synaphobranchidae — Teeth usually small and conical, in 1 to several rows on jaws and vomer; some species have enlarged, compound teeth on vomer, but large fangs never present. Gill openings low on body, below pectoral fins (when present); sometimes the gill openings of the 2 sides united in a ventral slit. Dorsal and anal fins well developed, confluent with caudal fin. Pectoral fins present or absent. Scales present or absent.
Synaphobranchus affinis
Unique Characters: Gill openings on the 2 sides united as a longitudinal slit on ventral midline. Scales present. Scales oval, not so regularly arranged. Dorsal-fin origin at or just posterior to level of anus. Vomerine teeth uniserial.
Similar Species:
Northern Cutthroat Synaphobranchus kaupi
Shortbelly Eel
Dysomma anguillare
Northern Cuthroat Eel Synaphobranchus kaupi. Gill openings on the 2 sides united as a longitudinal slit on ventral midline. Scales present. Scales very elongate (3-4 times as long as wide), small, regularly arranged in aligned clusters of 4 or 5 set at right angles to other such groups. Dorsal-fin origin well behind level of anus. Vomerine teeth uniserial but zig-zag anteriorly.
Shortbelly Eel Dysomma anguillare. Gill openings separate, although they may be closely approximated. Scales absent.
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