| Stegocephalidae | |
|---|---|
 | |
| A stegocephalid amphipod from the eastern Bering Sea | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Malacostraca |
| Superorder: | Peracarida |
| Order: | Amphipoda |
| Superfamily: | Stegocephaloidea |
| Family: | Stegocephalidae Dana, 1852 |
Stegocephalidae is a little-studied family of amphipods belonging to the suborder Gammaridea.
Stegocephalids have smooth and globular bodies with a short and deep head. It has small rostrum and the highly modified mouthparts are arranged into a cone structure. the functions of which are unknown but believed to be either for sucking or piercing. The upper part of the lips has a small notch on the distal side, while the lower lip are tall and lack inner lobes. The mandibular molar and palp may be absent or only present in vestigial forms. On the maxilla, the inner plates are setose and well-developed while the palp is often reduced and consists of only a single segment. The maxillipeds are large, often with an inner cutting edge and slender weakly dactylate palps. The eyes are kidney-shaped when present, but is more often completely absent. The antennae possess short peduncles and flagella, with that on the first pair being somewhat stout with fused flagellar segments near the base. In males the first antennal pair is covered with brushlike setae. [1]
On the first four body segments are four very large, non-overlapping, and deep coxal plates, forming a sort of skirt on the front half of the body. The fourth plates are subovate in shape and are the largest. The gnathopods may are slender and may possess small claws or none at all. The third to seventh pereopods are roughly the same size, with the seventh pair being the shortest. The pleon plates on the sides of the body are deep with strong pleopods. The three uropods possess rami that are about the same size and are lanceolate in shape. Their tips extend past the telson. The telson may be composed of lobes fused at the base and tapering to sharp point; or the lobes may be completely fused together to form a small plate. [1]
Stegocephalids are found worldwide, almost exclusively on deep and cold waters. [1] [2]
Most of the members of the family are believed to be bathypelagic and free-floating, inhabiting the oceanic water columns at depths of thousands of meters below the ocean surface. They are commonly found with oil globules just underneath their carapaces. These are believed to function as aids in making the animals more buoyant, allowing them to float in the water with little energy expenditure. The smooth, globular shape of the body helps in streamlining the animal while drifting in the water currents, further aided by the animal retracting all its appendages within its coxal plates. The more pelagic the habits of the species, the more elongated they seem to be. [1]
Some species, however, may primarily be benthic, inhabiting the surface of the ocean floor in association with megabenthic fauna like sponges. This includes Parandaniexis mirabilis which shows evidence of being a primarily benthic micropredator of polychaetes. Their coxal plates are more reduced with more robust peropods adapted to clinging and walking than that of free-floating stegocephalids. [1]
Stegocephalids extend their legs once resting on a substrate. In observations on captive specimens, they do not seem to have the tendency to burrow into the substrate, though this might only be because of the absence of prey in the laboratory substrates. [1]
They are mostly predators of cnidarians, with the exception of the genus Andaniotes which are scavengers. [1] [2]
Stegocephalidae is the sole member of the superfamily Stegocephaloidea. It includes the following genera and species divided under five subfamilies: [3]
Gammaridea is one of the suborders of the order Amphipoda, comprising small, shrimp-like crustaceans. Until recently, in a traditional classification, it encompassed about 7,275 (92%) of the 7,900 species of amphipods described by then, in approximately 1,000 genera, divided among around 125 families. That concept of Gammaridea included almost all freshwater amphipods, while most of the members still were marine.
Corophiidae is a family of amphipods, containing the following genera:
Dexaminidae is a family of amphipods. It contains the following genera:
Calliopiidae is a family of amphipods, containing the following genera:
Pardaliscidae is a family of amphipods, whose members typically inhabit the deepest parts of ocean basins. It contains the following genera:
Oedicerotidae is a family of amphipods. It comprises the following genera:
Lysianassidae is a family of marine amphipods, containing the following genera:
Eusiridae is a family of amphipods. It contains the following genera:
Leucothoe is a genus of amphipods in the family Leucothoidae. It contains the following species:
Gammaridae is a family of amphipods. In North America they are included among the folk taxonomic category of "scuds", and otherwise gammarids is usually used as a common name.
Talorchestia is a genus of amphipod of the family Talitridae, containing the following species:
Photis is a genus of amphipod crustaceans, containing the following species:
Amphilochus is a genus of crustaceans in the Amphipoda order, containing the following species:
Amphilochidae is a family of amphipod crustaceans, containing the following genera:
Urothoe is a genus of very small marine amphipod crustaceans in the family Urothoidae. Members of the genus are found worldwide.
Nototropis is a genus of amphipod crustaceans, in the family, Atylidae, and was first described by Achille Costa in 1853.
Caprella is a large genus of skeleton shrimps belonging to the subfamily Caprellinae of the family Caprellidae. It includes approximately 170 species. The genus was first established by Jean-Baptiste Lamarck in his great work Système des animaux sans vertèbres (1801) to describe Cancer linearis and Squilla ventricosa.
Epimeria is a genus of amphipods in the family Epimeriidae. There are more than 80 described species in Epimeria.
Maeridae is a family of marine amphipods, which was first described by Taudl Krapp-Schickel in 2008.