Eusirus pontomedon, Verheye & D & D & Acoz, 2021

Verheye, Marie L., D, Cédric, D, Udekem & Acoz, 2021, Integrative taxonomy of giant crested Eusirus in the Southern Ocean, including the description of a new species (Crustacea: Amphipoda: Eusiridae), Zoological Journal of the Linnean Society 193, pp. 31-77 : 58-66

EUSIRUS PONTOMEDON SP. NOV.

( FIGS 15–24)

Z o o b a n k r e g i s t r a t i o n: u r n: l s i d: z o o b a n k. org:pub: 055688C7-A2E1-4C0D-BE45-57058B3AB67A

Eusirus perdentatus – K.H. Barnard, 1932: 188 [in part],? fig. 115 (upper photograph). – Emison, 2000: 6 [in part, not figs 2–8 (= E. giganteus s.l.)]. – Andres et al., 2002: 121 [in part], figs 8B, F, H–J, not figs 7D–K, 8A, C–E (= E. perdentatus ). – d’Udekem d’Acoz & Robert, 2008: 53 [in part]. – Baird et al., 2011: 3443 [in part]. – Peña Othaitz & Sorbe, 2020: 250 [in part].

Eusirus perdentatus type tacheté – Verheye, 2011: 94, pl. 1, figs C–E, 96, pl. 2, figs B, D, F, H, J.

Eusirus cplx perdentatus spotted – d’Udekem d’Acoz & Verheye, 2013: 59, 63, fig. 3.8.3B.

Eusirus sp. aff. perdentatus Rauschert & Arntz,

2015: 64, plate 57 (unnumbered fig.).

Type material

ANT-XXIX/3, Bransfield Strait, sta. 193-8, 62°43.73′S, 57°29.04′W to 62°43.80′S, 57°29.40′W, 428–431 m, Agassiz trawl, 23 February 2013: one subadult ♀ Holotype, RBINS, INV . 150107, extr. MH17 , GenBank MT 985623 ( COI), MT 944994 (CytB) , MT 945055 ( ITS2 ) .

ANT-XIX/3–4, sta. 103-1, 61°44.88′S, 58°01.54′W to 61°45.54′S, 57°58.15′W, 107–111 m, 13 February 2002: one paratype, RBINS, INV . 132557, extr. EPE9. – ANT-XIX/3–4, sta. 106-1, 61°38.17′S, 57°32.66′W to 61°38.05′S, 57°36.39′W, 424–427 m, 14 February 2002: one paratype, RBINS, INV . 132513, extr. ED6, GenBank MT 985595 ( COI), MT 945009 (CytB) , MT 945044 ( ITS2 ) .

ANT-XXI/2, sta. 293-1, 72°51.90′S, 19°39.31′W to 72°52.07′S, 19°39.62′W, 518–542 m, 31 December 2003: one paratype, RBINS, INV . 132524, extr. EC11, GenBank MT 985574 ( COI), MT 945006 (CytB) , MT 945033 ( ITS2 ). – Same sta.: one paratype, RBINS, INV . 132527. – ANT-XXI-2, sta. 308-1, 72°50.18′S, 19°35.94′W to 72°50.09′S, 19°35.82′W, 295–309 m, 2 January 2004: one paratype, RBINS, INV . 132526, extr. EC2, GenBank MT 985578 ( COI), MT 945007 (CytB) , MT 945035 ( ITS2 ) .

ANT-XXIII/8, sta. 603-5, 70°30.99′S, 08°48.08′W to 70°30.40′S, 08°48.13′W, 274–297 m, 7 December 2006: one paratype, RBINS, INV . 132556, extraction EPE12. – ANT-XXIII/8, sta. 604-1, 61°20.52′S, 55°09.72′W to 61°20.11′S, 55°07.26′W, 286–407 m, 19 December 2006: one paratype, RBINS, RBINS, INV . 122635. – ANT-XXIII/8, sta. 604-1, 61°20.52′S, 55°09.72′W to 61°20.11′S, 55°07.26′W, 286–407 m, 19 December 2006: one paratype, RBINS, INV . 122645 (carcass) and INV. 132380-1to 132380-5 (five microscopic slides in Euparal). – ANT-XXIII/8, sta. 605-1, 61°20.35′S, 55°29.16′W to 61°19.98′S, 55°32.67′W, 146–151 m, 19 December 2006: one paratype, RBINS, INV . 122648. – ANT-XXIII-8, sta. 608-1, 61°11.34′S, 54°43.17′W to 61°11.80′S, 54°40.05′W, 284–293 m, 20 December 2006: two paratypes, RBINS, INV . 122628. – ANT-XXIII-8, sta. 661-2, 61°39.29′S, 57°02.89′W to 61°39.20′S, 57°04.75′W, 466–467 m, 30 December 2006: two paratypes, RBINS, INV . 121704. – ANT-XXIII/8, sta. 663-1, 61°38.18′S, 57°33.17′W to 61°38.02′S, 57°37.16′W, 432–434 m, 30 December 2006: one paratype, RBINS, INV . 122638 (carcass) and INV. 132399-1 to 132399-17 (17 microscopic slides in Euparal). – ANT-XXIII/8, sta. 694-1, 63°00.10′S, 58°07.40′W to 62°59.96′S, 58°03.51′W, 220–268 m, 6 January 2007: one paratype, RBINS, INV . 122637.

ANT-XXIV-2, sta. 48-1, 70°23.94′S, 8°19.14′W to 70°23.89′S, 8°18.67′W, 595–602 m, 12 January 2008: one paratype, RBINS, INV . 132512, extr. ED5, GenBank MT 985594 ( COI), MT 945008 (CytB) , MT 945043 ( ITS2 ) .

ANT-XXIX/3, sta. 118-4, 62°25.95′S, 56°17.26′W to 62°33.71′S, 56°28.31′W, 464– 437 m, 27 January 2013: one paratype, RBINS, INV . 122803. – ANT-XXIX/3, sta. 162-7, 63°58.78′S, 56°46.24′W to 63°59.02′S, 56°46.26′W, 214–216 m, 10 February 2013: one paratype, RBINS, INV . 122854. – ANT-XXIX/3, sta. 185-3, 63°51.34′S, 55°41.11′W to 63°51.52′S, 55°41.43′W, 261–296 m, 19 February 2013: one paratype, RBINS, INV . 122833. ANT-XXIX/3, sta. 185-4, 63°51.53′S, 55°40.74′W to 63°51.53′S, 55°40.43′W, 253–255 m, 19 February 2013: one paratype, RBINS, INV . 122835. – ANT-XXIX/3, sta. 188-4, 63°50.36′S, 55°37.42′W to 63°50.53′S, 55°37.52′W, 425–427 m, 20 February 2013: one paratype, RBINS, INV . 122826. – Same sta.: one paratype, RBINS, INV . 122844. – Same sta.: one paratype, RBINS, INV . 122846. – ANT-XXIX/3, sta. 193-8, 62°43.73′S 57°29.04′W to 62°43.80′S 57°29.40′W, 428–431 m, 23 February 2013: one subadult ♀ paratype [telson illustrated], RBINS, INV . 150108, extr. MH22 , GenBank MT 985624 ( COI), MT 944991 (CytB) , MT 945056 ( ITS2 ). – Same sta.: one paratype, RBINS, INV . 122797A, extr. MH16 , GenBank MT 985622 ( COI), MT 945014 (CytB) , MT 945054 ( ITS2 ). – Same sta.: one paratype, RBINS, INV . 122797B, extr. MH27 , GenBank MT 985627 ( COI), MT 944993 (CytB) , MT 945059 ( ITS2 ). – Same sta.: one paratype, RBINS, INV . 122797C, extr. MH23 , GenBank MT 985625 ( COI), MT 944992 (CytB) , MT 945057 ( ITS2 ). – Same sta.: one paratype, RBINS, INV . 122797D, extr. MH24 , GenBank MT 985626 ( COI), MT 944995 (CytB) , MT 945058 ( ITS2 ). – Same sta.: one paratype, RBINS, INV . 122797E, extr. MH13 . – Same sta.: one paratype, RBINS, INV . 122847. – ANT-XXIX/3, sta. 193-9, 62°43.50′S, 57°27.92′W to 62°43.53′S, 57°28.28′W, 420–431 m, 23 February 2013: nineteen paratypes, RBINS, INV . 122809. – Same sta.: twelve paratypes, RBINS, INV . 122825. – ANT- XXIX/3, sta. 196-8, 62°47.80′S, 57°5.35′W to 62°47.63′S, 57°5.63′W, 542–580 m, 24 February 2013: ten paratypes, RBINS, INV . 122800. – Same sta.: one paratype, RBINS, INV . 122821. – ANT-XXIX/3, sta. 199-4, 62°57.22′S, 58°14.60′W to 62°57.33′S, 58°14.95′W, 325–339 m, 27 February 2013: two paratypes, RBINS, INV . 122810. – ANT-XXIX/3, sta. 217-6, 62°53.45′S, 58°13.06′W to 62°53.42′S, 58°13.41′W, 461–483 m, 2 March 2013: ten paratypes, RBINS, INV . 122798. – Same sta.: forty-four paratypes, RBINS, INV . 122802. – ANT-XXIX/3, sta. 217-7, 62°53.64′S, 58°12.52′W to 62°53.64′S, 58°12.37′W, 387–395 m, 2 March 2013: two paratypes, RBINS, INV . 122823.–ANT-XXIX/3,sta.227-2, 62°55.83′S, 58°41.09′W to 62°55.76′S, 58°41.46′W, 562–564 m, 5 March 2013: thirty-seven paratypes, RBINS, INV . 122811.

CEAMARC, Adélie Coast, sta. 47 (lot 1245), 67.0677°S, 144.66187°E to 67.036803°S, 144.67242°E, 180–205 m, 30 December 2007: one paratype, reg. no. MNHN-IU-2019–3355, extr. EE31, GenBank MT 985605 ( COI), MT 944998 (CytB) , MT 945045 ( ITS2 ). – CEAMARC, Adélie Coast, sta. 79 (lot 3678), 65.706925°S, 140.597385°E to 65.693818°S, 140.538905°E, 419–667 m, 18 January 2008: one paratype, reg. no. MNHN-IU-2019-3356, extr. EE 6, GenBank MT 985607 ( COI), MT 944999 (CytB) . – CEAMARC, Adélie Coast, sta. 79 (lot 3678), 65.706925°S, 140.597385°E to 65.693818°S, 140.538905°E, 419–667 m, 18 January 2008: one paratype, reg. no. MNHN-IU-2019-3357, extr. EE7, GenBank MT 985608 ( COI), MT 945000 (CytB) , MT 945046 ( ITS2 ). – CEAMARC, Adélie Coast, sta. 79 (lot 3678), 65.706925°S, 140.597385°E to 65.693818°S, 140.538905°E, 419–667 m, 18 January 2008: one paratype, reg. no. MNHN-IU-2019-3357, extr. EE8, GenBank MT 985608 ( COI), MT 945000 (CytB) , MT 945046 ( ITS2 ). – CEAMARC, Adélie Coast, sta. 79 (lot 3678), 65.706925°S, 140.597385°E to 65.693818°S, 140.538905°E, 420–668 m, 18 January 2008: one paratype, reg. no. MNHN-IU-2019-3358, extr. EF13, GenBank MT 985610 ( COI), MT 945002 (CytB) , MT 945047 ( ITS2 ) .

Description

( Based on female holotype RBINS, INV. 150107, except for telson: female paratype RBINS INV. 150108) .

Body dorsal armature ( Figs 15, 16, 17A): Pereionites 5–7 and pleonites 1–3 with mid-dorsal carina backwardly prolonged into strong tooth; dorsal profile of pleonite 3 sigmoid.

Epimeron 1 ( Figs 16A, 24A): Narrow, tapering distally and posterodistally pointed, posteroventral margin straight.

Epimeron 2 ( Fig. 24A): Ventral margin rounded, armed with spines, posterodistal angle toothed, and posterior margin sinuous.

Epimeron 3 ( Fig. 24A): Ventral margin slightly convex, small spines present, posterior margin gently convex, postero-inferior corner rectangular, finely serrate.

Urosomite 1 ( Fig. 24B): With proximal depression followed by a mid-dorsal, sinuous carina, roundly sloping distally.

Head ( Fig. 17B): About as long as pereionites 1 and 2 combined. Rostrum short, downcurved, tip narrow but blunt, ventrally concave. Lateral lobe produced, subrectangular, unevenly rounded, apically blunt. Post-antennal sinus narrowly U-shaped. Post-antennal lobe shallow, forming a right angle. Ventral margin slightly concave. Eyes large, prominent, elongate, subreniform. Interocular space wide.

Antenna 1 ( Fig.15A,B): Whole antenna 1 conspicuously longer than whole antenna 2, shorter than body length. Peduncle of antenna 1 slightly longer than that of antenna 2. Peduncle article 1 (medial tooth included) 1.1× as long as article 2, 7× as long as article 3. Peduncle article 1 distally with ventrolateral tooth, with two medial teeth of similar size. Peduncle article 2 distally with three ventrolateral teeth (most dorsal shortest, most ventral longest) and three subequal medial teeth (two broken off on illustrated antenna). Article 3 with dorsal and ventral process. Accessory flagellum of one article, short, thin. Flagellum more than 1.8× as long as total peduncle length. Calceoli ventrally present on peduncular articles 2 and 3 and on distoventral surface of flagellar articles.

Antenna 2 ( Fig. 18C, D): Peduncular article 4 0.95× as long as article 5, 2.0× broader than article 5, flattened, 3.6× as long as wide, with seven dorsal teeth, of which one is in distal position, with six ventral protrusions (some indistinct), one subdistal tooth and distal denticle. Peduncular article 5 dorsally toothless and with short setae, ventrally with six groups of strong setae (last one in distal position) associated with weak protrusion. Calceoli ventrally present on distoventral surface of flagellar articles.

Upper lip [labrum] ( Fig. 19A): Entire, ventrally rounded, with shallow median notch, slightly more prominent than straight epistome, separated by incision.

Lower lip [paragnath or hypopharynx] ( Fig. 19B): Inner lobes small, outer lobes gaping, mandibular processes short, rounded.

Mandible ( Fig. 19C, D): Left incisor long, with cutting edge smooth except for proximolateral tooth; right incisor long, with cutting edge smooth except for proximal tooth and blunt median tooth; left lacinia mobilis much larger than right one, with four blunt teeth (most medial one largest and separated from others by shallow notch); right lacinia mobilis with margin irregular; row of normally developed raker spines present; molar process columnar, but narrowing distally, triturative surface reduced. Palp three-articulated, attached midway, much longer than mandible body; article 1 short, without setae; article 2 0.7× as long as article 3, ventral margin expanded, heavily setose (D2-setae), distally constricted; article 3 falcate, ventral margin heavily setose (D3-setae), E3-setae short, B3 (grouped in transverse rows) present.

Maxilla 1 ( Fig. 19E): Inner plate slender, oblong, subapically bearing one seta; outer plate with 11 spines, some bifid (accessory prongs short); palp twoarticulated, article 1 0.6× as long as article 2, article 2 with one row of lateral setae and two rows of medial setae on distal half.

Maxilla 2 ( Fig. 19F): Plates subequal in length, apically rounded; outer plate about half width of inner plate, with stiff setae distally; apical margin of inner plate fringed with shorter stiff setae.

Maxilliped ( Fig. 18E, F): Inner plate short (medially extending to end of palp article 1), distally and distolaterally densely armed with spines. Outer plate oblong (medially extending one-third to onehalf length of palp article 2), laterally, apically and medially armed with long setae. Palp robust, fourarticulated, articles 1 and 2 distally dilated; article 2 longest, article 1 sparsely setose. Dorsodistal corner of palp article 2 forming a tooth-like process, bearing fringe of setae; prosterodistal corner (facial side) with four or five teeth. Palp article 3 regularly and strongly expanding distally, densely setose. Palp article 4 threequarters of overall length of article 3, claw-like, unguis short, distal half of posterior margin armed with uniform, short spines.

Gnathopod 1 ( Fig. 20A, B): Subchelate, similar to but slightly shorter than gnathopod 2. Coxal plate about as deep as maximal height of corresponding pereionite, deeper than wide (ratio of depth to width: 1.3), anteroventral angle produced into a broad rounded lobe, anterior margin concave, posterodistal angle with three serrations. Basis weakly curved, proximally narrowed, sparsely setose. Ischium subrectangular, with deep U-shaped notch on anterior border, posterodistal margin setose. Merus subtriangular, about as long as ischium, posterodistal angle rounded and setose. Carpus lobe linguiform, broad, distally tapering, posterior margin regularly convex, clearly exceeding merus, distally setose; ratio of length to width of carpus lobe: 1.57 (length of lobe measured from tip to connection with merus). Propodus subrectangular; longest (transverse) axis 1.24× length of anterior margin, posterior margin slightly concave; palm convex, longer than anterior margin, bearing shorter and longer setae, defined by a hump armed with rows of short to long spines. Dactylus falcate, reaching the hump.

Gnathopod 2 ( Fig. 20C): Subchelate. Coxal plate slightly deeper than maximal height of corresponding pereionite, subrectangular, anterior and posterior border weakly converging downwards, ventral margin weakly convex (tip of rounded lobe in posterior position), antero- and posteroventral angles with three and two serrations, respectively; ratio of depth to width of coxal plate: 1.9. Basis weakly curved, proximally narrowed, sparsely setose. Ischium subrectangular, with deep U-shaped notch on anterior border, posterodistal margin almost not setose. Merus subtriangular, about as long as ischium, posterodistal angle produced into a tooth and setose. Carpus lobe linguiform, broad, distally tapering, posterior margin regularly convex, clearly exceeding merus, distally setose; ratio of length to width of carpus lobe: 1.0 (length of lobe measured from tip to connection with merus). Propodus subrectangular; longest (transverse) axis 1.2× length of anterior margin, posterior margin slightly concave; palm convex, longer than anterior margin, bearing shorter and longer setae, defined by a hump armed with rows of short to long spines. Dactylus falcate, reaching the hump.

Pereiopod 3 ( Fig. 21A–C): Coxal plate slightly deeper than maximal height of corresponding pereionite, subrectangular, anterior and posterior border distinctly converging downwards, ventral margin nearly straight (tip of rounded lobe in posterior position), antero- and posteroventral angles with a four serrations; ratio of depth to width of coxal plate: 1.6. Merus 6.1× as long as wide, 1.7× as long as carpus, 1.23× as long as propodus, with nine anterior groups of tiny (hard to see) spines (one in distal position) and ten posterior groups of spines; carpus 3.8× as long as wide, 0.72× as long as propodus, with four (groups of) tiny anterior spines and seven groups of posterior spines; propodus 7.4× as long as wide, with eight anterior groups of spines (which are minute except for those of the distal group) and 15 posterior groups of spines; dactylus short and robust, 0.28× as long as propodus and 0.39× as long as carpus, 4.6× as long as wide.

Pereiopod 4 ( Fig. 21D, E): Coxal plate slightly deeper than maximal height of corresponding pereionite, 1.3× as deep as wide, pentagonal; anterodorsal margin nearly straight; anteroventral margin straight; anterodorsal and anteroventral margin connecting with low curve ornate with five serrations; connection between anterodorsal and anteroventral border (ventral tip of coxa) forming a blunt right angle; posteroventral border weakly concave and serrate; posterodorsal border distinctly concave; connection between posteroventral and posterodorsal border forming a right angle. Leg similar to P3, but merus, carpus and propodus a bit longer. Merus 6.7× as long as wide, 1.7× as long as carpus, 1.25× as long as propodus, with ten anterior groups of tiny (hard to see) spines (one in distal position) and 13 posterior groups of spines; carpus 4.3× as long as wide, 0.73× as long as propodus, with six (groups of) minute anterior spines and nine groups of posterior spines; propodus 7.6× as long as wide, with 11 anterior groups of spines (which are minute except for those of the distal group) and 15 posterior groups of spines; dactylus short and robust, 0.26× as long as propodus and 0.36× as long as carpus, 4.4× as long as wide.

Pereiopod 5 – 7 relationships ( Fig. 22 A, C, E): Pereiopods 5–7 similar, long, slender; pereiopod 5 shortest, pereiopod 6 and pereiopod 7 subequal. Basis increasing in length from pereiopod 5 to pereiopod 7 [carpus, propodus and dactylus of pereiopod 6 illustrated abnormally short and probably regenerated].

Pereiopod 5 ( Figs 22A, B, 23A, B): Coxal plate less deep than maximal height of corresponding pereionite, bilobed, posterior lobe longest. Basis 1.6× as long as wide, 0.73× as long as carpus, anterior margin nearly straight for most of its length, setose on proximal 0.3, spinose on distal 0.7, with two small distal teeth, posterior border expanded, distinctly serrate (13 serrations), proximal 0.3 convex, distal 0.7 nearly straight (weakly concave), posterodistal corner forming a right angle; ischium short, with strong anterodistal tooth and strong posterodistal tooth, with two anterior (groups of) spines; merus 4.4× as long as wide, spinose on both sides; carpus 6.7× as long as wide, 1.3× as long as merus, spinose on both sides; propodus 14.2× as long as wide, 1.7× as long as merus, spinose on both sides; dactylus 5.6× as long as wide, 0.13× as long as propodus; dactylus with spinose posterior border.

Pereiopod 6 ( Figs 22C, D, 23C, D): Coxal plate less deep than maximal height of corresponding pereionite, bilobed, posterior lobe longest. Basis 1.5× as long as wide, anterior margin convex, setose on proximal 0.3, spinose on distal 0.7, with two small distal teeth, posterior border expanded, distinctly serrate (14 serrations), proximal 0.3 convex, distal 0.7 nearly straight (weakly concave), posterodistal corner produced into a tooth; ischium short with strong anterodistal tooth and strong posterodistal tooth, with one anterior spine; carpus, propodus and dactylus of pereiopod 6 illustrated abnormally short and probably regenerated.

Pereiopod 7 ( Figs 22E, F, 23E, F): Coxal plate less deep than maximal height of corresponding pereionite, unilobed. Basis 1.4× as long as wide, 0.81× as long as carpus, anterior margin with angular discontinuity on proximal 0.5, weakly convex and setose on proximal 0.5, straight and spinose on distal 0.5, with two small distal teeth, posterior border expanded, distinctly serrate (13 serrations), proximal 0.3 convex, distal 0.7 concave, posterodistal corner produced into a tooth; ischium short, with strong anterodistal tooth and strong posterodistal tooth, with one anterior spine; merus 5.5× as long as wide, spinose on both sides; carpus 7.4× as long as wide, 1.2× as long as merus, spinose on both sides; propodus 15.2× as long as wide, 1.5× as long as merus, spinose on both sides; dactylus 6.6× as long as wide, 0.18× as long as propodus.

Coxal gills: From gnathopod 2 to pereiopod 7, proximally voluminous, sack-like (partly pleated), distally lamellate; with oblong accessory gill.

Oostegites: From gnathopod 2 to pereiopod 5, narrowly elliptic.