posterior end of the tube is buried vertically, and the anterior end tips down across the
sediment. The worm has tentacles which search about the surface in the vicinity of the
tube opening, selecting particles and transferring them to the mouth. Terebellid tubes
are nearly fully buried, but the worm partially emerges to search about the
surrounding sediment surface with its tentacles. Sabellids filter particles from flow
over the sediment surface, as do members of several other families. All are mostly
restricted to shallow depths. Predatory polychaetes mostly attack with spinose
eversible proboscides, ingesting prey whole. The Glyceridae (Fig. 13.7d) are perhaps
the best represented family that feeds in this way in the deep sea.
(^) A group of aberrant annelids, the Pogonophora, lack any gut; they have come
strongly to popular attention thanks to Riftia and its relatives, the large and colorful
worms inhabiting sulfide-rich hydrothermal vent areas. However, much smaller
pogonophorans are found in modest numbers in sediments at all depths, particularly
where organic matter is abundant. They live oriented vertically, the lower end
absorbing sulfide from the reducing layers of the sediment to support chemosynthesis
by bacterial symbionts in a trophosome organ. Oxygen to oxidize the sulfide and drive
the chemosynthesis is absorbed above the sediment surface by tentacles. DNA
sequence studies revealed the close relation of pogonophorans to other annelids, and
they superficially resemble the polychaete family Sabellidae in several respects.
Formerly a phylum, they have been “reduced” to family status as Siboglinidae.
(^) While polychaetes are dominant at all depths, there are definite changes in their
character as sampling descends the continental shelf into the abyss. Shallower forms
are larger, more ecologically varied, more colorful. Hartman and Fauchald (1971)
describe the change downward in very strong terms:
(^) “The single most conspicuous feature of the abyssal polychaetes ... is the
uniformly small size and the reduced number of body segments at maturity, as
compared with their shallow water relatives. The body tends to be linear, plain;
parapodia are reduced to small, papillar elevations, with little lamellar
development, and armed with smooth, capillary setae which are rarely coarsely
serrated or spinose along their free lengths. They lack the highly characteristic
modifications uniquely developed in shallow water species. Most species have
muted colors if any, or the body is translucent to dusky or black, with no visible
pattern. Surface or epithelial modifications are rare ... Cephalic eyes are absent,
reduced or variable in occurrence; they are usually small dark pigment spots on
the prostomium.” (...continuing for several more pages, all emphasizing
smallness and simplification).
(^) The arthropod class Crustacea is the second most numerous animal group in deep-
sea sediment, mostly the pericaridean forms that brood their eggs and young in
special pouches and have sessile (as opposed to stalked) eyes. Included are
amphipods, isopods, tanaids, and cumaceans. The egg pouches are constructed from