A medium-sized electric ray with a thick, pear shaped body composed of a sub-circular pectoral disc and a much smaller sub-circular pelvic disc. Snout anterior margin straight, weakly convex, or centrally concave. Pectoral and pelvic fin apices broadly rounded.
Small, narrowly separated eyes and spiracles, positioned close to median. Spiracles oval, with numerous thin papillae. Nostrils small and circular. Mouth large and arched, without labial furrows.
Tail broad based but exytremely small and short. Two overlapping dorsal fins anterior to pelvic fin posterior margin. Caudal fin small with a rounded margin, size sub-equal to dorsal fins. Upper caudal margin straight. Ventral margin broadly convex.
Dorsum greyish brown to dark reddish brown. Occasionally with irregular dark blotches. Ventrum white or yellowish.
Maximum length 63cm. Size at birth 8-11cm.
Temperate to tropical seas. Benthic on sand, mud, sea grass beds, and sometimes estuaries but not into fresh water. Occasionally to 220m on the continental shelf but usually from close inshore to ~80m.
The coffin ray is an Australian endemic, occurring from St Vincents Gulf in South Australia to Timor Reef in the Northern Territory. And from Eden in New South Wales to Heron Island on Great Barrier Reef.
The Coffin Ray (Hypnos monopterygius) is occasionally taken as bycatch by commercial trawlers; post-release mortality is likely to be low as it can survive out of water for hours and is usually discarded alive. Further information is required on its life history, and its full distribution off northwestern Australia. It is assessed as Least Concern given that it is common and widely distributed and is of no interest to fisheries.
Jacobsen, I.P. & Lisney, T.J. 2015. Hypnos monopterygius. The IUCN Red List of Threatened Species 2015: e.T41828A68630121. https://dx.doi.org/10.2305/IUCN.UK.2015-4.RLTS.T41828A68630121.en. Downloaded on 06 June 2021.
Aplacental viviparous. Litter size 4-8.
Capable of stretching its mouth open to ingest fishes almost as large as itself.
The coffin ray can deliver an extremely powerful electric shock to stun or kill large fishes.
Often buries under the sand during the day.
Reaction to divers
Easy to approach. Generally remains motionless or continues moving slowly.
CAUTION: Divers should be careful not to provoke this electric ray due to the severity of the shock it can deliver.
The coffin ray is seen at a great many dive sites around the coast of Australia.
I have seen the western population at Exmouth Navy Pier in WA, and the eastern population at Nelson Bay in NSW.
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The coffin ray is easily distinguished due to its uniquely large disc combined with a very small tail.