Coffin Ray - Biology and Ecology

Biology and Ecology

The coffin ray is a slow and weak swimmer that moves forward with a jerky, fluttery motion. It is nocturnal and spends most of the day buried in sediment with only its spiracles showing. When disturbed, it has been observed performing a possible defense behavior, wherein it erupts from the bottom and swims in a loop with its mouth agape. This species is sometimes stranded on land by the ebbing tide, but can survive out of water for hours. Like in other electric rays, the coffin ray's electric organs are derived from muscle tissue and consist of numerous vertical columns, each formed from a stack of jelly-filled "electric plates" that essentially acts as a battery. It is capable of generating up to 200 volts of electricity and delivering 50 shocks over span of ten minutes, with each successive shock weakening. The coffin ray employs electricity both to subdue prey and deter predators.

The diet of the coffin ray consists mostly of benthic bony fishes, but also includes cephalopods and on occasion crustaceans and polychaete worms. Penguins and rats have also been recorded from the stomachs of this species. The coffin ray ambushes prey from the substrate, and swallows them whole head-first before re-burying. It often takes extremely large prey relative to its size; one observed individual 60 cm (24 in) long had swallowed a flathead (Platycephalus sp.) 70 cm (28 in) long, and the tail of the prey fish was still protruding from its mouth. Dead specimens have been recovered that had apparently choked trying to swallow too-large prey. The coffin ray is aplacental viviparous, in which the developing embryos are nourished by yolk, later supplemented by histotroph ("uterine milk") secreted by the mother. Females give birth to litters of 4–8 pups in summer; the newborns measure approximately 8–11 cm (3.1–4.3 in) long. Males and females both attain sexual maturity around 40–48 cm (16–19 in) long. This species is known to be parasitized by the tapeworms Acanthobothrium angelae and Lacistorhynchus dollfusi, and the nematode Echinocephalus overstreeti.