Hatchling Size and Aspects of Biology in the Deep‐Sea Amphipod Genus Eurythenes (Crustacea: Amphipoda)

Abstract

Records attributed to Eurythenes gryllus are discussed in the light of described morphological variation, and the existence of a third species in the genus is postulated. The presence of five pairs of oostegites in E. gryllus, a character almost unique among the Amphipoda, is confirmed. Brooding females of E. gryllus and E. obesus, captured in deep midwater hauls in the eastern North Atlantic Ocean, are reported for the first time. The 120 mm E. gryllus female carried 237 hatchlings (mean length 11.13 mm) and the 48 mm E. obesus female 47 hatchlings (mean length 7.99 mm). Hatchlings showed variability in size and bodily proportion, and measurements of individual body segments could not be used to predict overall length. Despite this variability, no evidence for more than one instar was found. The hatchlings of E. gryllus are established as a hitherto unrecognized instar in this species. Egg size for E. gryllus and E. obesus is predicted. The biological consequences of the absolute and relative size of hatchling in the two species, and the depths of capture of the E. gryllus female, are discussed.

Extreme food webs: Foraging strategies and diets of scavenging amphipods from the ocean’s deepest 5 kilometers

“…Instead, H. dubia dominates the carrion consumption (Table 3). Moreover, H. dubia appears to prey on S. schellenbergi, which may further deter S. schellenbergi from approaching carrion in this depth range (Thurston and Bett 1995). Uristes sp.…”

“…The larger benthopelagic S. schellenbergi and E. gryllus are thought to rely heavily, if not exclusively, on nekton carrion (Thurston 1990;Kaiser and Moore 1999;) because of the efficiency with which they can locate, ingest, and store large amounts of carrion (SainteMarie 1992). The smaller demersal species Uristes sp.…”

“…This aggressive species certainly appears capable of taking larger prey. They are known to exhibit cannibalistic behavior when maintained in crowded aquaria ) and have been observed attacking live fish that are restrained on a hook and line (Smith and Baldwin 1984;Thurston 1990). Alternatively, the interspecific d 15 N signatures may reflect the changing availability of food with depth, as both detrital quality and hadal biodiversity are thought to decrease with depth (Belyaev 1989;Sokolova 1994).…”

“…Many deep-sea species are adapted to locate and exploit these nutrient hotspots (Smith and Baldwin 1982;Tamburri and Barry 1999;Smith and Baco 2003), and necrophagy as a nutritional strategy becomes more prevalent with depth (Stockton and DeLaca 1982;Britton and Morton 1994). Crustaceous amphipods belonging to the superfamily Lysianassoidea often dominate scavenging assemblages at great depths (Thurston 1990;Gage and Tyler 1996;De Broyer et al 2004), and lysianassoids appear to be the exclusive taxon assuming the role of scavenger in the deep hadal zone (Hessler et al1978;Perrone et al 2002). Hence, scavenging amphipods are key members in hadal food webs (Kamenskaya 1995).…”

“…Current understanding of deep-sea lysianassoid feeding ecology is based on studies detailing their anatomical designs, behavioral displays, and rapid convergence on and sequestering of carrion arriving on the deep-sea floor (Dahl 1979;Thurston 1990;Sainte-Marie 1992). The prevailing view is that deep-sea lysianassoids rely on necrophagy heavily, if not exclusively, for food (De Broyer et al 2004).…”