expedition, say yes.
Megafauna – Largest Denizens of the Deep
(^) Swimming along the deep-sea bottom and sometimes resting on it are specialized fish,
particularly the grenadiers (Macrouridae, also called rat-tails) (Fig. 13.1), part of an
animal assemblage sometimes termed the “suprabenthos”. Grenadiers have large
heads with large eyes (although what they can see in the total dark is a mystery), a
wide, deep mouth, and a tall dorsal fin. The body tapers posteriorly, with the tail fin
continuous around a narrow, tubular tail with the long, deep ventral fin. Pectoral fins
are large; pelvic fins are small. Grenadiers cruise slowly, seeking scent from deadfalls
(see ahead) at which they are among the first arrivals. Other fish such as Liparidae,
snail fish, lead somewhat similar lives, picking at animals in the sediment. Some
deep-sea octopus species move close over the bottom. Particularly at shelf and upper-
slope depths, the epifauna or suprabenthos includes crabs and shrimp. Shrimp that rest
and feed on the bottom often swim up into the water column.
(^) Trawl catches from all depths include crabs, squat lobsters, and shrimp, but, in the
deep sea, the bulk of the megafauna are echinoderms (Figs. 13.4, 13.5d), including
brittle stars (Ophiuroidea, as much as two-thirds of the megafauna by numbers), sea
stars (Asteroidea), sea cucumbers (Holothuroidea), sea urchins (Echinoidea) and, in
places, both stalked (usually attached to rock) and free-living sea lilies and feather
stars (Crinoidea). Brittle stars can break away from a limb when it is grabbed by a
predator, hence their common name. They are very heavily calcified, both at the
surface of the central disk, which bears the mouth ventrally, and in the chains of hard
rings armoring the five limbs. The spacing of the rings allows sharp bending of the
limbs and great flexibility. Sea stars are also flexible, but body bending is slower and
stiffer. The internal organs of sea urchins are enclosed in a strongly calcified case or
test, only an array of surface spines and ventral tube feet are movable. Many sea
cucumbers are tubular, as their common name implies, but body designs with flaps
and rather extended “legs” are also found. A diverse suite of holothurians, more than
20 species, principally in four families (Sars 1867; Miller & Pawson 1990), are
documented as regular swimmers. Evidently this capability evolved repeatedly. All
echinoderms move over the seabed by the action of hundreds of tubular feet, tipped
with suction cups in some groups, and moved by internal hydraulic pressure. Some
ophiuroids can also move by stepping forward with lifted limbs.
Fig. 13.4 Typical epibenthic echinoderms photographed in situ: (a) brittle star or
ophiuroid; (b) sea star or asteroid; (c) sea cucumber or holothurian; and (d) sea urchin
or echinoid.
(^) (All originally by A.L. Rice, courtesy of the UK National Oceanography Centre, and previously published in Gage