the thoracic legs are not shown in the lateral views) are typical in the taxonomy of
small crustaceans. Böttger-Schnack and Huys (2004) regard O. frosti as a species
inquirenda.
(After Heron 2002.)
Typical planktonic copepods are mostly 1–3 mm total length as adults, but some are
smaller and a few, for example, the deep-living genus Bathycalanus, grow to 16 mm.
Sexes are separate throughout the Copepoda, and aspects of sexual reproduction, mate
finding, and development are covered in Chapter 8. However, it can be noted here that
in many copepods the male bears elaborate clamps for catching and then holding the
female during copulation. Males have specially adapted limbs for spermatophore
transfer, the pair of fifth thoracic legs that copepodologists are famous (among
invertebrate zoologists) for studying. The reason for this interest is that characteristics
separating species are most often found on that leg. Separation of species is partly
ensured by the appropriate fit of the male fifth leg to the female’s size and details of
her shape.
(^) Females of some genera (e.g. Euchaeta, Pseudocalanus) carry their eggs in sacs
until hatching; others (e.g. Calanus, Acartia) release them free into the water.
Hatching of the eggs releases small larvae called nauplii (Plate 6.10), which are
rugby-football-shaped and bear three pairs of anterior limbs near a bulky labrum
(mouth cover). Nauplii of some genera are supplied with yolk and do not feed; others
begin to feed at the earliest stages. Nauplii are a significant part of the smaller
heterotrophic plankton, often serving as the diet of larval fish. The six naupliar stages