Copepoda Harpacticoida: Biology (Reproduction and post-embryonic development)

Harpacticoid copepods are gonochoristic and fertilization is by copulation involving the attachment of a spermatophore by the male to the copulatory pore of the female. Sperm are stored in the female seminal receptacle, the eggs are fertilized as they emerge into the genital antrum and are united by their outer membranes to form a single or double egg-sac. Brood size varies from about three (in many interstitial species) to over 100 (in some phytal species) with the norm in the range of 15-30 eggs per brood. The number of broods per single copulation varies from 2-15 (in laboratory cultured species) and some species prduce broods throughout the year (most common in phytal habitats) whilst others have a well defined breeding season. Harpacticoids have direct benthic development and pass throughout six naupliar stages followed by a six copepodite stages, copepodite VI being the adult.

Copepoda Harpacticoida: Biology (Ecology)

Harpacticoid copepods are essentially free-living organisms, although a few are planktonic (Microsetella, Euterpina, Clymnestra, Macrpsetella) or found in association with other organisms . In marine sedimente, they are usually the second most abundant meiofaunal taxon afternematodes but tend to become the dominant taxon in coarsed-grained sediments and on marine algae. Generally, there is a reduction in abundance with increasing depth of water. Harpacticoids can be found living in sediment particle interstices, burrowing in the sediments, or living on the sediment surface. Small, vermiform, interstit10al speciesnd broad, slightly flattened, epibenthic species dominate the sand sediments but the former disappear from community when silt/clay content of the sediment exceeds about 10%. In addition to species assemblages being associated with particular substrata, there is both horizontal and vertical zonation of species within the sediment. Harpacticoid is general are known to be intolerant of anaerobic conditions and are therefore confined to the oxygenated layers of the sediment, usually the top 1 cm in muddy sediments but as much as the top 50-100 cm on high energy sand beaches.

Copepoda Harpacticoida: General Structure (Part 4)

The first four pairs of swimming legs (pereiopods P1-P4) are basically biramous with an exopod and endopod. The two members of each leg pair are united into a single functional unit by an intercoxal sclerite. Each ramous is at most 3-segmented. The arrangement of setae and spines on the leg rami is the character most widely used for species identification and a setal formula denotes this arrangement. The fifth pais of legs (pereiopd P5) are each basically biramous and leaf-like, but the endopod and basis remain separated only in a few species. In all other species, the two elements have fused into a single baseoendopod. The sixth pais of legs (pereiopod P6) is the last in both sexes. In males each member is primitively represented by a single plate with three setae. In females, the sixth leg is vestigial and incorporated in the closing apparatus of the genital antrum. Substantial modifications may be found in the shape and structure of the caudal rami. However, a basic pattern of seven (three lateral, one dorsal and three terminal) ramal setae can be recognized.
Males are nearly always smaller than females but are also distinguished by the structure of the antennules, genital somite and the P5 (which is smaller and less ornate than the females)

Copepoda Harpacticoida: General Structure (Part 3)

The antenna (sometimes called the second antenae) have a 2-segmented protopod (coxa and basis) and are biramous with an exopod and an endopod.
The mandibles also have a 2-segmented protopod and are biramous. The endopod is tipically 1-segmented rarely 2-segmented) and the exopod has a maximum of 4 segments. Reduction in obth rami, but usually the exopod, can result in a uniramous, 1-segmented mandibular palp.
The maxillules have a praecoxa with several spines and setae around its distal margin and usually with two setae on the anterior surface (absent in some reduced forms).
The maxillae are uniramous (the exopod absent). The endopod is at most 4- segmented.
The maxillipeds vary considerably throughout the order.

Copepoda Harpacticoida: General Structure (Part 2)

Limbs and/or the body surface are ornamented with various structures. A thorn is a more or less pointed projection of the integument itself. A seta, which is flexible and a spine, which is rigid, are similar in that each is inserted into a hole passing through the integument; each has a central, hollow, core and the position of each is constant for a species and sex. Setules and spines are borne on the outer surface of the integument and leave only tiy scar, nota hole, when they fall off. Spines and seta may each have one or more rows of setules and/or spinules (pinnules) and therefore may be described as unipinnate, bipinnate, tripinnate or multipinnate. Seta with hair-like pinnules are commonly described as plumose. The body surface is often covered with minute sensilla, fine hair-like filaments projecting through the cuticle, and other features as pores, microspinules and microsetules.
The cephalosome bears six (seven if it is a cephalotorax) pairs of appendages? Antennules, antennae, mandibles, maxillules, maxillae and maxillipeds. A rostrum usually projects forward between the antennules from at the anterior margin of the cephalic shield.

Initiating into the Copepoda Harpacticoida's World...

Copepoda

The name copepod is derived from the Greek words kope meaning “oar” and podos meaning “foot” and literally means “oar-footed”. The Order Harpacticoida is one of the ten orders of the sub-classes of the lower Crustacea. At the moment, the order contains well over 3,000 species belonging to 460 genera contained in 50 families. Most species are free-swimming in marine and brackish water, although a few are ectoparasitic or commensal on corals, tunicates, crustaceans, cephalopods or baleen whales. Three families and 945 species are found exclusively in freshwater. Marine harpacticoids are primarily bottom-living copepods, although a few are exclusively planktonic, and are most abundant in soft sediments and on macro-algae. They are small, predominantly less than 1mm long, and are usually the second most abundant group of animals (after nematodes) in benthic meiofauna communities.
Harpacticoids are quite diverse, being difficult to find a typical representative of the Order. Therefore, a figure showing the diversity of forms on their families can be observed below…