THE ERRANT MEGAFAUNA

The large, active forms may be termed errant megafauna as opposed to attached forms which make up the sessile megafauna. The errant megafauna include those forms that have been most easily caught in deep-sea trawls and dredges since the earliest exploratory work in the deep sea. Hence, these species, dominated by the phylum (a major division of the animal kingdom) Echinodermata (usually spiny-skinned animals that include sea urchins and starfish) and, to a lesser extent, decapod crustaceans of the phylum Arthropoda (which includes insects, spiders and crabs) and various bottom-living fishes, are the best known, and their taxonomy the best developed of the benthos and benthopelagic fauna of the deep sea. However, discovery of a scavenging community composed of previously virtually unknown, giant-sized crustaceans called amphi-pods, elsewhere of generally fly-like dimensions, has shown that it is unsafe to assume that most of this errant megafauna will be caught in bottom trawls.

ECHINODERMS: BRITTLE STARS AND BASKET STARS

Of the five large classes of modern echinoderms, the Ophiuroidea (brittle stars and basket stars), Asteroidea (sea stars), Echinoidea (sea urchins) and Holothurioidea (sea cucumbers), make up by far the most important of the errant epifauna. In a relatively well-known area of the deep sea such as the Rockall Trough, the brittle stars make up 27% of the echinoderm species collected, but numerically they far outnumber (63%) the remaining megafaunal catch.