Stegocephalidae is a little-studied family of amphipods belonging to the suborder Gammaridea.
Description 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.
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.
Distribution and habitat Stegocephalids are found worldwide, almost exclusively on deep and cold waters.
Ecology 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.
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.
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.
They are mostly predators of cnidarians, with the exception of the genus Andaniotes which are scavengers.
Taxonomy Stegocephalidae is the sole member of the superfamily Stegocephaloidea. It includes the following genera and species divided under five subfamilies:
Subfamily Andaniopsinae Berge & Vader, 2001 Genus Andaniopsis Sars, 1895 Andaniopsis africana Berge, Vader & Galan, 2001 Andaniopsis integripes (Bellan-Santini & Ledoyer, 1986) Andaniopsis isaki Berge, 2004 Andaniopsis nordlandica (Boeck, 1871) Andaniopsis pectinata (Sars, 1883) Genus Steleuthera J. L. Barnard, 1964 Steleuthera africana (Berge, Vader & Galan, 2001) Steleuthera ecoprophycaea Bellan-Santini & Thurston, 1996 Steleuthera maremboca J. L. Barnard, 1964 Subfamily Andaniexinae Berge & Vader, 2001 Genus Andaniexis Stebbing, 1906 Andaniexis abyssi (Boeck, 1871) Andaniexis americana Berge, Vader & Galan, 2001 Andaniexis andaniexis Berge & Vader, 2003 Andaniexis australis Barnard, 1932 Andaniexis eilae Berge & Vader, 1997 Andaniexis elinae Berge & Vader, 2003 Andaniexis gloriosae Berge, Vader & Galan, 2001 Andaniexis gracilis Berge & Vader, 1997 Andaniexis lupus Berge & Vader, 1997 Andaniexis mimonectes Ruffo, 1975 Andaniexis oculata Birstein & Vinogradov, 1970 Andaniexis ollii Berge, De Broyer & Vader, 2000 Andaniexis pelagica Berge, Vader & Galan, 2001 Andaniexis spinescens (Alcock, 1894) Andaniexis stylifer Birstein & M. Vinogradov, 1960 Andaniexis subabyssi Birstein & M. Vinogradov, 1955 Genus Andaniotes Stebbing, 1897 Andaniotes abyssorum Stebbing, 1888 Andaniotes bagabag Lowry & Stoddart, 1995 Andaniotes islandica (Thompson, 1882) Andaniotes karkar Lowry & Stoddart, 1995 Andaniotes linearis K. H. Barnard, 1932 Andaniotes lowryi Berge, 2001 Andaniotes pooh Berge, 2001 Andaniotes poorei Berge, 2001 Andaniotes pseudolinearis Berge, 2001 Andaniotes wallaroo J. L. Barnard, 1972 Andaniotes wollongong Berge, 2001 Genus Glorandaniotes Ledoyer, 1986 Glorandaniotes eilae (Berge & Vader, 1997) Glorandaniotes fissicaudata Ledoyer, 1986 Glorandaniotes norae Berge & Vader, 2003 Glorandaniotes sandroi Berge & Vader, 2003 Glorandaniotes spongicola (Pirlot, 1933) Glorandaniotes traudlae Berge & Vader, 2003 Glorandaniotes vemae Berge & Vader, 2003 Genus Mediterexis Berge & Vader, 2001 Mediterexis macho Berge & Vader, 2004 Mediterexis mimonectes (Ruffo, 1975) Genus Metandania Stephensen, 1925 Metandania islandica Stephensen, 1925 Metandania tordi Berge & Vader, 2003 Metandania wimi Berge, 2001 Genus Parandaniexis Schellenberg, 1929 Parandaniexis dewitti Watling & Holman, 1980 Parandaniexis inermis Watling & Holman, 1980 Parandaniexis mirabilis Schellenberg, 1929 Parandaniexis pelagica (Berge, Vader & Galan, 2001) Parandaniexis tridentata Ledoyer, 1986 Genus Stegosoladidus Barnard & Karaman, 1987 Stegosoladidus antarcticus Berge, 2001 Stegosoladidus complex Berge, 2001 Stegosoladidus debroyeri Berge, 2001 Stegosoladidus ingens (Chevreux, 1906e) Stegosoladidus simplex (K. H. Barnard, 1930) Subfamily Bathystegocephalinae Berge & Vader, 2001 Genus Bathystegocephalus Schellenberg, 1926 Bathystegocephalus globosus (Walker, 1909) Subfamily Parandaniinae Berge & Vader, 2001 Genus Parandania Stebbing, 1899 Parandania boecki (Stebbing, 1888) Parandania gigantea (Stebbing, 1883) Parandania nonhiata (Andres, 1985) Subfamily Stegocephalinae Dana, 1855 Genus Alania Berge & Vader, 2001 Alania beringi (Berge & Vader, 2001) Alania calypsonis (Berge, Vader & Galan, 2001) Alania hancocki (Hurley, 1956) Genus Austrocephaloides Berge & Vader, 2001 Austrocephaloides australis (K. H. Barnard, 1916) Austrocephaloides boxshalli (Berge, Vader & Galan, 2001) Austrocephaloides camoti (J. L. Barnard, 1967) Austrocephaloides gunnae (Berge & Vader, 2003) Austrocephaloides ingstadi (Berge & Vader, 2003) Austrocephaloides tori (Berge & Vader, 2003) Austrocephaloides tucki (Berge & Vader, 2003) Genus Austrophippsia Berge & Vader, 2001 Austrophippsia unihamata (Berge & Vader, 2000) Genus Bouscephalus Berge & Vader, 2001 Bouscephalus mamillidacta (Moore, 1992) Genus Gordania Berge & Vader, 2001 Gordania minima (J. L. Barnard, 1961) Gordania pajarella (J. L. Barnard, 1967) Genus Phippsia Stebbing, 1906 Phippsia gibbosa (Sars, 1882) Phippsia roemeri Schellenberg, 1925 Genus Pseudo Berge & Vader, 2001 Pseudo bioice (Berge & Vader, 1997) Pseudo pacifica (Bulycheva, 1952) Pseudo pseudophippsia (Bellan-Santini, 1985) Pseudo vanhoeffeni (Schellenberg, 1926) Pseudo viscaina (J. L. Barnard, 1967) Genus Stegocephalexia Moore, 1992 Stegocephalexia penelope Moore, 1992 Genus Stegocephalina Stephensen, 1925 Stegocephalina barnardi Berge & Vader, 2001 Stegocephalina beringi Berge & Vader, 2001 Stegocephalina biofar Berge & Vader, 1997 Stegocephalina boxshalli Berge, Vader & Galan, 2001 Stegocephalina idae Berge & Vader, 1997 Stegocephalina ingolfi Stephensen, 1925 Stegocephalina pacis (Bellan-Santini & Ledoyer, 1974) Stegocephalina trymi Berge, 2001 Stegocephalina wagini (Gurjanova, 1936) Stegocephalina wolf Berge & Vader, 2004 Genus Stegocephaloides Sars, 1895 Stegocephaloides attingens Barnard, 1932 Stegocephaloides auratus (Sars, 1882) Stegocephaloides australis K. H. Barnard, 1916 Stegocephaloides bernardi Berge & Vader, 1997 Stegocephaloides boxhalli Berge, Vader & Galan, 2001 Stegocephaloides christianiensis Boeck, 1871 Stegocephaloides gunnae Berge & Vader, 2003 Stegocephaloides ingstadi Berge & Vader, 2003 Stegocephaloides ledoyeri Berge, Vader & Galan, 2001 Stegocephaloides tori Berge & Vader, 2003 Stegocephaloides tucki Berge & Vader, 2003 Stegocephaloides wagini (Gurjanova, 1936) Genus Stegocephalus Krøyer, 1842 Stegocephalus abyssicola (Oldevig, 1959) Stegocephalus ampulla (Phipps, 1774) Stegocephalus casadiensis (Moore, 1992) Stegocephalus inflatus Krøyer, 1842 Stegocephalus kergueleni (Schellenberg, 1926a) Stegocephalus longicornis (Gurjanova, 1962) Stegocephalus nipoma (J. L. Barnard, 1961) Stegocephalus rostrata K. H. Barnard, 1932 Genus Stegomorphia Berge & Vader, 2001 Stegomorphia watlingi (Berge, De Broyer & Vader, 2000) Genus Stegonomadia Berge & Vader, 2001 Stegonomadia biofar (Berge & Vader, 1997) Stegonomadia idae (Berge & Vader, 1997) Stegonomadia katalia (J. L. Barnard, 1962) Genus Tetradeion Stebbing, 1899 Tetradeion angustipalma (Berge & Vader, 2000) Tetradeion crassum (Chilton, 1883) Tetradeion dampieri (Berge & Vader, 2000) Tetradeion latus (Haswell, 1879) Tetradeion quatro Berge & Vader, 2000 Subfamily incertae sedis Genus Glorandantiotes Glorandantiotes fissicaudata Ledoyer, 1986
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