back, then advance in muds. In rough order of numerical abundance among
meiofaunal groups (although varying greatly with sediment type, water depth, and
food availability) are foraminifera, nematodes (and some other worm phyla such as
gastrotrichs), copepods (and a few other microcrustacea), flatworms
(Platyhelminthes), and micro-annelids such as Protodrillus. There is sufficient
convergent evolution in the group that it takes considerable expertise to distinguish,
say, miniscule annelids from the pseudo-segmented nematodes and elongated
copepods that look like annelids.
Fig. 13.10 Examples of elongation of body form of sand-dwelling meiofauna, all to
the same scale (see the sand grains in the left figure). From left to right: a foram, a
polychaete, a harpacticoid copepod, and a nematode. The nematode shows a long,
very thin tail, a feature of sand meiofauna in a number of groups.
(^) (After Giere 2009.)
Fig. 13.11 Three examples of meiofauna from soft sediment, all with epidermal
stiffening by spicules. From left to right: a flatworm, snail, and aberrant mollusk (the
last is an example of Caudofoveata, a group related according to gene similarities to
cephalopods).
(^) (After Giere 2009.)