urn:lsid:zoobank.org:act: 85ED0CCE-6EB7-4010-AFB3-29894C55616C
Figs 222–228
Xestus, -a, -um is a Latinization of the Greek adjective ξεστός, which means smooth or polished. The name alludes to the smooth body surface of the species.
Holotype
RV Polarstern cruises:
SOUTHERN OCEAN: dissected ♀, cruise PS14, ANT-VII/4, EPOS leg 3, stn 226, eastern Weddell Sea, 75°15.9ʹ S, 25°58.3ʹ W to 75°15.7ʹ S, 25°54.2ʹ W, 569–574 m, bottom trawl, 28 Jan. 1989, coll. C. De Broyer (RBINS, INV. 132946).
Paratypes
RV Polarstern cruises:
SOUTHERN OCEAN: 1 juv., cruise PS14, ANT-VII/4, EPOS leg 3, stn 226, eastern Weddell Sea, 75°15.9ʹ S, 25°58.3ʹ W to 75°15.7ʹ S, 25°54.2ʹ W, 569–574 m, bottom trawl, 28 Jan. 1989, coll. C. De Broyer ( RBINS, INV. 132947); 2 adult specs, cruise PS14, ANT-VII/4, EPOS leg 3, stn 226, eastern Weddell Sea, 75°15.9ʹ S, 25°58.3ʹ W to 75°15.7ʹ S, 25°54.2ʹ W, 569–574 m, bottom trawl, 28 Jan. 1989, subsample, coll. C. De Broyer ( RBINS, INV. 132948); 1 ovigerous ♀, cruise PS14, ANT-VII/4, EPOS leg 3, stn 226, eastern Weddell Sea, 75°15.9ʹ S, 25°58.3ʹ W to 75°15.7ʹ S, 25°54.2ʹ W, 569–574 m, bottom trawl, 28 Jan. 1989, coll. C. De Broyer ( RBINS, INV. 132949); 3 very large specs, presumably including specimen photographed on board, cruise PS39, ANT-XIII/3, EASIZ I, no locality, aquarium, 3 Mar. 1996, coll. C. De Broyer and G. Chapelle ( RBINS, INV. 132994); 1 spec., previously mixed with 9 E. inermis, misidentified as E. georgiana and used for gut content analysis, cruise PS39, ANT-XIII/3, EASIZ I, stn 12, GSN 5, eastern Weddell Sea, 73°18.10ʹ S, 21°10.10ʹ W to 73°17.10ʹ S, 21°08.20ʹ W, 457–459 m, bottom trawl, 14 Feb. 1996, coll. C. De Broyer and G. Chapelle ( RBINS, INV. 132997); 1 large spec., misidentified as E. georgiana and used for gut content analysis, cruise PS39, ANT-XIII/3, EASIZ I, stn 29, BPN 4, eastern Weddell Sea, 71°31.50ʹ S, 12°25.50ʹ W to 71°30.30ʹ S, 12°27.80ʹ W, 504–529 m, 28 Feb. 1996, coll. C. De Broyer and G. Chapelle ( RBINS, INV. 132998).
ROSTRUM. Medium-sized, overreaching tip of article 1 of peduncle of antenna 1, anteriorly weakly curved, ventrally straight, subacute in lateral view; of medium width and with nearly straight converging borders in frontal view.
EYE. Very large, broadly elliptic.
PEREION– PLEOSOME TOOTH PATTERN. Pereionites 1–3 smooth; pereionite 4 to pleonite 3 with very low and very blunt mid-dorsal carina; profile of carinae of pereionites 4–7 weakly and regularly curved; profile of carinae of pleonites 1–2 straight, profile of carina of pleonite 3 straight with anterior low protrusion followed by shallow notch, then nearly straight (slightly irregular), posteriorly blunt; dorsolateral ornamentation absent.
COXAE 1–3. Weakly carinate and distally subacute.
COXA 4. Anterodorsal border nearly straight (very slightly concave), anteroventral border slightly but distinctly concave, these two borders being joined by a very large rounded lobe (anterior corner), which is weakly projecting forward; ventral corner forming a blunt squared angle (ventral projection well developed); lateral carina very obtuse, parallel and close to posteroventral border; posteroventral border distinctly concave.
COXA 5. Broad, with surface smooth, with posteroventral corner forming a blunt-tipped nearly squared angle, not expanded laterally, not forming an angle in dorsal view (scarcely visible in dorsal view).
COXA 6. With posteroventral corner broadly rounded, with low projection arising from its surface (forming a very low indistinct lobe in dorsal view).
COXA 7. Posteriorly rounded.
EPIMERAL PLATES 1–3. Posteroventral angle very obtusely rounded in plate 1, produced into a small tooth in plate 2 and into a medium-sized tooth in plate 3.
UROSOME TOOTH PATTERN. Urosomite 1 with very low dorsal process: anteriorly nearly straight, apically very blunt, posteriorly regularly convex large and sharp narrow tooth pointing upwards; urosomite 3 with dorsolateral borders nearly straight.
TELSON. Cleft on 0.2; tips of lobes very broad and very rounded, notch narrowly V-shaped.
GNATHOPODS 1–2. Carpus and propodus broad; propodus expanding distally, palm distinct.
PEREIOPODS 5–7. Merus, carpus and propodus of pereiopods 5–7 of medium width; dactylus long; basis of pereiopods 5–6 of normal width, with posteroproximal process present, sword-like, parallel to axis of basis, with posterodistal corner bluntly angular and pointing in posterior direction; basis of pereiopod 7 broad with posterior border very convex, with deep notch on distal 0.8, forming a blunt-tipped acute angle, with posterodistal corner very bluntly angular and pointing backwards.
Body and appendages with a homogeneous and diffuse orange dotted/mottled pattern; legs with colour more intense; eyes reddish.
Up to 55 mm.
Eastern shelf of Weddell Sea, 457– 574 m.
Dauby et al. (2001a, as E. georgiana) state that “this weakly mobile large amphipod (up to 40 mm) can be found, sometimes in abundance, on coarse sediment bottoms or at the base of animal colonies”. According to them, “digestive tract analyses of 31 specimens revealed a wide variety of food items identifiable by hard remnants: crustaceans (mysids and amphipods), polychaetes (setae of terebellids), holothurioid ossicles and hydrozoan perisarcs; planktonic items (diatoms, radiolarians, foraminifers) also form a significant part of the diet; finally, as for the other deposit-feeders, sponge spicules (which form a major component of bottom mats) and mineral particles complete the food, the latter providing evidence of feeding on the sediment; both these items, albeit ‘inorganic’, are likely to be of considerable nutritional value, since they may be densely coated with bacteria, the importance of which has been shown in the Weddell Sea.” Dauby et al. (2001b) concluded that E. xesta (as E. georgiana) is a deposit feeder.
Epimeria xesta is sympatric with E. angelikae, though they have different bathymetric ranges, with E. angelikae being found at greater depths: 781–1194 m vs 457– 574 m. The morphologically most similar species to E. xesta is E. cyphorachis from the South Shetland Islands and from the tip of the Antarctic Peninsula. In E. xesta, the rostrum is narrower in frontal view than in E. cyphorachis, the ventral corner of coxa 4 bluntly angulate instead of being sharply angulate, and the posterior notch of pereiopods 5–7 is narrower.