English. With so many species, marine copepods constitute a large fraction of all
mesozooplankton diversity, and they are abundant, usually over half the specimens in
any net tow and often much of the biomass. In turn, copepodologists constitute a large
fraction of all biological oceanographers, but copepodology is more than an
oceanographic concern. It is a lively discipline in its own right. There is an active
World Association of Copepodologists, and there are several hundred capable
systematists around the world. This is in sharp contrast to most other planktonic
groups. Ostracods, chaetognaths, euphausiids, pteropods, salps, and appendicularians
all have fewer than ten significantly active systematists, and no organizations promote
study of their biology and taxonomy. Mauchline (1998) has provided an extensive
review of planktonic copepod biology and ecology.
(^) The copepod body has two principal sections: the rice-grain-shaped prosome (six
head segments plus, primitively, six thoracic segments) and the urosome that is much
narrower, consisting of four to six tubular segments). Slow swimming is by sculling
movements of the second antennae. Rapid escape swimming is driven by sequential
flapping movements of the thoracic legs on the rear half of the prosome. While the
feeding modes and mouth limbs are diverse, the basic body form and operation of the
thoracic legs are quite uniform, apparently a key and conserved design feature of the
entire group. It makes possible, at least in larger forms, escape velocities greater than
1 m s−1 (200–500 + body-lengths s−1). Many copepods (e.g. Calanus, Acartia,
Oithona) feed by picking or filtering phytoplankton and protists from the water. The
mechanism of particle feeding will be considered in Chapter 7. Predatory copepods
(e.g. Euchaeta, Candacia) impale their prey with large spines on limbs at the back of
the head section, then move them to the mouth. Many mid-water forms (Lophothrix,
Spinocalanus, Tharybis, ...) find and ingest sinking detritus, including marine snow
and fecal pellets from epipelagic plankton. The mandibles in most families bear teeth
for crushing or tearing food. In many species of both particle-feeders and carnivores,
the teeth are tipped with hard, opal caps. Several distinctive families, the Oncaeidae
(Oncaea, Fig. 6.6) and Corycaeidae (Corycaeus), have mouthparts reduced to a small
cluster of pincers, and their antennae and maxillipeds are modified for gripping on
soft surfaces, including gelatinous plankton and marine “snow”, apparently sucking in
nutrition or nipping small bites from them. Oncaea moves over surfaces like
discarded appendicularian houses or pteropod feeding-“balloons”; Corycaeus
probably sucks nutrition from soft-bodied animals (jellyfish, large chaetognaths).
Corycaeus has paired, anterior cuticular lenses focusing light through light guides that
converge to pigmented retinas far back in the prosome. These eyes occupy about half
the body, suggesting that Corycaeus see their hosts and move to them.
Fig. 6.6 Oncaea frosti Heron 2002. Left, 1.0 mm female in dorsal view. Middle, 0.72
mm male in side view, showing maxilliped modified for clipping into soft surfaces.
Paddle-like second thoracic leg to right. Stylized, simplified drawings like this (e.g.