A new species of Eusirus Krøyer, 1845 (Amphipoda, Amphilochidea, Eusiridae) from the seamount of the Caroline Plate, with redescription of Meteusiroides keyensis Pirlot, 1934 Author Wang, Yan-Rong 0000-0002-7188-4232 Department of Marine Organism Taxonomy and Phylogeny, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China & College of Biological Sciences, University of Chinese Academy of Sciences, Beijing 100049, China Author Sha, Zhong-Li 0000-0002-2192-3758 Department of Marine Organism Taxonomy and Phylogeny, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China & College of Biological Sciences, University of Chinese Academy of Sciences, Beijing 100049, China & Laoshan Laboratory, Qingdao 266237, China Author Ren, Xian-Qiu Department of Marine Organism Taxonomy and Phylogeny, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China text Zoosystematics and Evolution 2024 2024-05-23 100 2 645 662 journal article 10.3897/zse.100.114758 938B8E54-3E6F-4281-83CE-E3D32393F8F3 Eusirus carolinus sp. nov. Figs 1 , 2 , 3 , 4 , 5 Material examined. Holotype : Western Pacific • 1 brooding female (with 9 intra-marsupial individuals), 12.9 mm ; seamount on Caroline Plate ; 10 ° 30 ' N , 140 ° 9–10 ' E ; depth 520–862 m ; 26 Aug. 2017 ; MBM 286609 . Paratype : Western Pacific • 1 male ; 13 mm ; seamount on Caroline Plate ; 10 ° 30 ' N , 140 ° 9–10 ' E ; depth 520–862 m ; 26 Aug. 2017 ; MBM 286608 . Description. Body . Pleonites 1–3 carinate dorsally; pleonites 1 and 2 with acute distomiddorsal teeth; epimera 1 and 2 postero-distal corner subacute; epimeron 3 postero-distal corner rounded, without serration. Head . Lateral cephalic lobe with apically-oblique rostrum. Eyes large, reniform. Antenna 1 stout, with peduncular articles 1–3 in length ratio of 1: 0.95: 0.36; distal margin of peduncular article 1 with inner surface bearing two distal processes; article 2 distal margin produced as two triangular distal processes in outer and inner surfaces, respectively; primary flagellum 55 - articulate; first article nearly as long as the third peduncular article; accessory flagellum 1 - articulate. Antenna 2 shorter than antenna 1, with peduncular article 4 subequal in length to article 5; flagellum distinctly longer than fifth peduncular article, 29 - articulate. Eusirus carolinus sp. nov. female holotype (MBM 286609). Photographed immediately after collection by Jun-long Zhang. Mouthparts . Upper lip distally rounded, apex convex, and weakly produced, bearing fine submarginal setae. Right mandible with incisor bearing one blunt anterodistal tooth and not dentate lacinia mobilis; accessory setal row composed of 5 stout setae; molar triturative, columnar; palp 3 - articulate, much longer than mandible body; article 1 shortest; article 2 slightly shorter than article 3, with row of long simple setae; article 3 with ventral margin heavily setose; and outer margin bearing one long (about 3 / 5 length of third palp article) simple seta. Left mandible, incisor with one blunt large anterodistal tooth, lacinia mobilis 8 - dentate; accessory setal row composed of 6 setae; molar and palp similar to those of right mandible. Lower lip with weak inner lobe; outer lobe subovoid, rounded distally; both inner and outer lobes covered with marginal and submarginal setae. Maxilla 1 outer plate with 11 stout multicuspidate setae on apical margin; inner plate subovoid, apex bearing one seta; palp long far beyond outer lobe, 2 - articulate; article 2 with about 15 setae along apex and mediodistal margin. Maxilla 2 with inner plate broader than outer plate, both with fine marginal setae. Maxilliped heavily setose, inner plate short, not reaching to distal margin of first palp article, distally armed with about 10 stout setae; outer plate extending to about 1 / 2 length of article 2 of palp, laterally armed with short robust setae and distally armed with long plumose setae; palp 4 - articulate, slender, article 2 slightly longer and broader than article 3; dactylus shorter than article 3, claw-like, unguis very short, ventral margin bearing 5 long stout setae. Eusirus carolinus sp. nov. female holotype (MBM 286609). G 1 R. Right gnathopod 1; G 2 R. Right gnathopod 2 (also showing the medial side of the distal margin of the carpus). Coxal gills present on pereopods 2–7. Oostegites present on pereopods 2–5. Gnathopods and pereopods . Gnathopods similar in shape: gnathopod 1 subchelate, eusirid form; coxa 1 broadened distally, slightly expanded anteroventrally; basis steady in width, not distinctly broadened distally; anterior margin flat, bearing several setae; posterior margin with a group of setae distally; ischium short, with rounded lobe anterodistally; carpus lobe linguiform, narrow, covered with long setae anterior margin; outer face with acute pointed process distally and inner face rounded distally; propodus wider than long, subrectangular, shorter than carpus in length of anterior margin, with one group of defining setae; palm lined with numerous crooked setae submarginally; dactylus falcate, fitting palm. Gnathopod 2 similar to gnathopod 1, stout, eusirid form, coxa rectangular, ventral margin convex; basis slightly longer than that of gnathopod 1; ischium, merus, carpus propodus, and dactylus similar in appearance to gnathopod 1. Pereopod 3 slender, coxa rectangular; basis linear; anterior margin with simple setae; merus about twice as long as carpus, distinctly longer than propodus; propodus with posterior margin bearing several small stout setae; dactylus elongate, slightly curved; posterior margin dentate. Pereopod 4 broken, coxa subequal in length to coxa 3, posteriorly emarginated, postero-distal corner subacute, basis linear, anterior margin with simple setae. Pereopod 5 shorter than pereopods 6 and 7; coxa equilobate, both expanded posteroventrally; basis increasing in length from pereopods 5 to 7, with posteroventral lobe, posterior margins lateral border moderately expanded, serrate, anterior margin with short robust setae; merus increasing in length from pereopods 5 to 7, posterodistally strongly produced, margins with stout setae; carpus subequal in length to merus, margins with stout setae; length ratios of merus to propodus 1: 0.77: 1.20; dactylus nearly straight, anterior margin with about distal 1 / 3 length dentate. Pereopods 6 and 7 subequal in length; coxa 6 bilobate; merus longer than that of pereopod 5; carpus distinct shorter than merus; propodus slender; margins with stout setae; length ratios of merus to propodus 1: 0.77: 1.31. Pereopod 7 with posterior margins of basis lateral border moderately expanded and distinctly concave, posterodistal corner subacute; length ratios of merus to propodus 1: 0.68: 1.25. Eusirus carolinus sp. nov. female holotype (MBM 286609). UL. Upper lip; LL . Lower lip; Md L. Left mandible (not showing molar and palp); Md R. Right mandible; Mx 1 R. Right maxilla 1; Mx 2 R. Right maxilla 2; Mxp. Maxillipeds. Uropods and telson . Uropod 1 with peduncle subequal in length to outer ramus, bearing numerous short laterals and long medial robust setae dorsally, with one enlarged stout seta at mesiodistal corner; inner ramus 1.3 times as long as outer ramus, both rami bearing robust setae and lateral and medial margins. Uropod 2 with rami lanceolate; peduncle slightly shorter than outer ramus; lateral margin with two subdistal robust setae dorsally; medial margin with seven robust setae; inner ramus nearly twice as long as outer ramus; both rami with inner and medial margins bearing dense robust setae; outer ramus narrower than inner ramus. Uropod 3 shortest, rami lanceolate, subequal in length; peduncle 0.5 times as long as rami; lateral margin bearing one long distal robust sate dorsally; medial margin bearing three small robust setae dorsally; both rami with lateral and medial margin setose dorsally. Telson long, slightly tapering distally, reaching about half of the length of uropod 3 rami, length about twice its breadth at base, cleft 15 % of length. Eusirus carolinus sp. nov. female holotype (MBM 286609). P 3 R. Right pereopod 3; P 4 R. Right pereopod 4; P 5 R. Right pereopod 5; P 6 R. Right pereopod 6; P 7 R. Right pereopod 7; E 1–3. Epimeral plates 1–3; U 1 R. Right uropod 1; U 2 R. Right uropod 2; U 3 R. Right uropod 3; T. Telson; H. Head; A 1. Antenna 1 (also showing ventral side of distal margin of peduncular article 1 and accessory flagellum); A 2. Antenna 2. Description of intra-marsupial individual . Based on one of the intra-marsupial individuals of the holotype . Rostrum present. Antenna 1 with peduncle articles less setose; primary flagellum only slightly longer than peduncle, 5 - articulate; each article slightly longer than the third peduncular article, less setose; accessory flagellum 1 - articulate. Antenna 2 much shorter than antenna 1, peduncle less setose; articulations of flagellum inconspicuous and less setose. Gnathopods 1–2 similar in shape and size, subchelate, eusirid form; carpus lobe linguiform broader than that of adult, only covered with several setae mediodistally; propodus similar in form to that of the adult, but without setae; anterior margin subequal in length to carpus; palm not bearing crooked setae submarginally; dactylus stout, slightly curved. Pereopods 3 and 4 subequal in length and similar in form, less setose; dactylus nearly straight, slightly shorter than propodus, with posterior margin not dentate. Pereopod 5 shorter than pereopods 6 and 7. Pereopod 6 basis with posterior margin smooth, not serrate, anterior margin without setae; merus with large posterodistal pointed process bearing one seta; length ratios of merus to propodus 1: 0.83: 1.33; dactylus elongate, about half length of propodus, nearly straight, anterior margin not dentate. Pleonites 1–3 not carinate; pleonites 1–2 with small acute mid-dorsal tooth. Uropods 1–3 similar to those of adults but without robust setae on peduncles and rami. Telson long, length 1.6 times its breadth at base, cleft 15 % of length, narrower than that of adult, slightly tapering distally. Eusirus carolinus sp. nov. , one of the intra-marsupial individuals of female holotype (MBM 286609, 2.5 mm). G 1 R. Right gnathopod 1; P 6 R. Right pereopod 6; T. Telson; A 1. Antenna 1 (showing accessory flagellum); A 2. Antenna 2; E 1–3. Dorsolateral parts of epimeral plates 1–3. Coloration. Anterior part of body is red with yellow eyes; gnathopods 1–2 are deep red; and antennae 1–2 and posterior part of body are pale red. Etymology. The new species is named after its type locality, the Caroline Plate. Distribution. Presently known only from a seamount of the Caroline Plate at a depth of 520–862 meters. Remarks. Table 1 shows the distribution, depth information, and important characters of Eusirus species. Nine species have been reported from the Pacific, including Eusirus antarcticus Thomson, 1880 ; E. bathybius Schellenberg, 1955 ; and E. bulbodigitus Jung, Kim, Soh & Yoon, 2016 ; E. columbianus Bousfield & Hendrycks, 1995 ; E. cuspidatus Krøyer, 1845 ; E. fragilis Birstein & M. Vinogradov, 1960 ; E. hirayamai Bousfield & Hendrycks, 1995 ; E. liui Wang, Sha & Ren, 2021 ; and E. parvus Pirlot, 1934 . Eusirus carolinus sp. nov. can be distinguished from E. bathybius , E. fragilis , and E. liui by having large, well-pigmented eyes ( Schellenberg 1955 ; Birstein and Vinogradov 1960 ; Wang et al. 2021 ). The new species differs from the remaining six Pacific Eusirus species by presenting the posterior margin of epimeron 3 as smooth, while epimeron 3 presents a serrate posterior margin in the mentioned six species ( Krøyer 1845 ; Stebbing 1906 ; Pirlot 1934 ; Gurjanova 1951 ; Bousfield and Hendrycks 1995 ; Jung et al. 2016 ; Othaitz and Sorbe 2020 ). The body of Eusirus carolinus sp. nov. only has distomiddorsal teeth on pleonites 1–2, while the pereonite 7 of three species, E. cuspidatus , E. hirayamai , and E. parvus , also has a distomiddorsal tooth other than the teeth on pleonites 1–2 ( Krøyer 1845 ; Pirlot 1934 ; Hirayama 1985 ). The new species also differs from E. hirayamai by the rami of uropod 3 subequal in length and from E. parvus by having a unilobed coxa 7 ( Pirlot 1934 ; Hirayama 1985 ; Bousfield and Hendrycks 1995 ). Distribution, depth, and important characters of Eusirus species.
Species Distribution Important characters Depth References
E. abyssi N Atlantic 60 ° 37 ' N, 27 ° 52 ' W eyes absent, pereonite 7 unknown, pleonites 1–3 with distomiddorsal teeth, epimeron 3 unknown, coxa 7 unilobed, uropod 3 unknown, telson unknown. 1505 m Stephensen 1944
E. antarcticus S Pacific (New Zealand), S Indian Ocean, Antarctica eyes present, pereonite 7 (with distomiddorsal tooth described by Stebbing (1906) , while in the key of Andres et al. (2002) without that tooth, pleonites 1–2 with distomiddorsal teeth, epimeron 3 with posterior margin serrate, coxa 7 unknown, uropod 3 unknown, telson cleft 40 % of length. 0–1800 m Stebbing 1906 ; Andres et al. 2002 ; Othaitz and Sorbe 2020
E. bathybius NW Pacific, off Japan eyes absent, pereonite 7 and pleonites unknown, epimeron 3 smooth, coxa 7 unilobed, uropod 3 with outer ramus shorter than inner one, telson only apex notched. 0–7900 m Schellenberg 1955 ; Bousfield and Hendrycks 1995 ; Othaitz and Sorbe 2020
E. biscayensis N Atlantic, Bay of Biscay, off Iceland eyes present, pereonite 7 with distomiddorsal tooth, pleonites 1–3 with distomiddorsal teeth, epimeron 3 with posterolateral margin serrate, coxa 7 unilobed, uropod 3 with outer ramus slightly shorter than inner one, telson only apex notched. 358–4330 m Bonnier 1896 ; Stebbing 1906
E. bonnieri NE Atlantic Ocean eyes absent, pereonite 7 with small distomiddorsal tooth, pleonites 1–3 with small distomiddorsal teeth, epimeron 3 serrate, coxa 7 unilobed, uropod 3 with outer ramus shorter than inner one, telson cleft 20 % of length. 370–1099 m Othaitz and Sorbe 2020
E. bouvieri Southern Ocean eyes present, pereonite 7 without distomiddorsal tooth, pleonites 1–2 with distomiddorsal teeth, Pleonite 3 with dorsal longitudinal carina, epimeron 3 serrate, coxa 7 and uropod 3 unknown, telson cleft less than 20 % of length. 0–400 m Chevreux 1911 ; Andres et al. 2002
E. bulbodigitus NW Pacific, off Korea eyes present, pereonite 7 without distomiddorsal tooth, pleonites 1–2 with distomiddorsal teeth, pleonite 3 without dorsal carina, epimeron 3 serrate, coxa 7 unilobed, uropod 3 with outer ramus slightly shorter than inner one, telson cleft less than 20 % of length. 33 m Jung et al. 2016
E. carolinus sp. nov. Pacific eyes present, pereonite 7 without distomiddorsal tooth, pleonites 1–2 with distomiddorsal teeth, epimeron 3 smooth, coxa 7 unilobed, uropod 3 with rami subequal in length, telson cleft about 15 % of length. 520–862 m the present study
E. columbianus NE Pacific, 52 ° – 55 ° 19 ' N, 128 ° 30 ' – 130 ° 27 ' W eyes present, pereonite 7 without distomiddorsal tooth, pleonites 1–2 with distomiddorsal teeth, epimeron 3 serrate, coxa 7 bilobed, uropod 3 with outer ramus shorter than inner one, telson cleft about 30 % of length. 12–150 m Bousfield and Hendrycks 1995
E. crosnieri Indian Ocean, NW Madagascar, 12 ° 43 ' S, 48 ° 15 ' E eyes present but not pigmented, pereonite 7 with distomiddorsal tooth, pleonites 1–3 with distomiddorsal teeth, epimeron 3 serrate, coxa 7 unknown, uropod 3 with rami subequal in length, telson cleft about 30 % of length. 245–255 m Ledoyer 1982; Andres 1996 ; Othaitz and Sorbe 2020
E. cuspidatus N Pacific; Arctic Basin eyes present, pereonite 7 with distomiddorsal tooth, pleonites 1–2 with distomiddorsal teeth, epimeron 3 with posterior margin serrate, coxa 7 unilobed, uropod 3 with outer ramus shorter than inner one, and telson cleft 50 % of length. 37–400 m Krøyer 1845 ; Stebbing 1906 ; Gurjanova 1951 ; Bousfield and Hendrycks 1995 ; Jung et al. 2016 ; Othaitz and Sorbe 2020
E. fragilis * N Pacific eyes absent, pereonite 7 without distomiddorsal tooth, pleonites 1–2 with distomiddorsal teeth, epimeron 3 smooth, coxa 7 unilobed, uropod 3 unknown, and telson cleft less than 15 % of length. abyssal Birstein and M. Vinogradov 1960; Bousfield and Hendrycks 1995
E. giganteus Antarctica, 63 ° 09 ' S, 59 ° 10 ' W eyes present, pereonite 7 with distomiddorsal tooth, pleonites 1–3 with distomiddorsal teeth, epimeron 3 serrate, coxa 7 unilobed, uropod 3 with outer ramus slightly shorter than inner one, telson cleft 18 % of length. 221–690 m Andres et al. 2002
E. hirayamai NW Pacific, off Japan eyes present, pereonite 7 with distomiddorsal tooth, pleonites 1–2 with distomiddorsal teeth, epimeron 3 with posterior margin fully serrate, coxa 7 unilobed, uropod 3 with rami subequal in length, telson cleft less than 30 % of length. <50 m Hirayama 1985 ; Bousfield and Hendrycks 1995
E. holmii Arctic Ocean, N Atlantic eyes present, pereonite 7 with distomiddorsal tooth, pleonites 1–2 with distomiddorsal teeth, epimeron 3 with posterior margin fully serrate, coxa 7 unilobed, uropod 3 with rami subequal in length, telson cleft about 10 % of length. 172–1900 m Stebbing 1906 ; Stephensen 1912 ; 1944 ; Macnaughton et al. 2007
E. laevis Antarctica eyes present, pereonite 7 without distomiddorsal tooth, pleonites without distomiddorsal tooth, epimeron 3 smooth, coxa 7 unilobed, uropod 3 and telson unknown. <48 m, epipelagic Walker 1903 ; Andres et al. 2002
E. laticarpus Antarctica eyes present, pereonite 7 without distomiddorsal tooth, pleonites 1–2 with distomiddorsal teeth, epimeron 3 only with 3 serrations at distomiddorsal corner, coxa 7 unilobed, uropod 3 with rami subequal in length, telson cleft 40 % of length. 0–400 m Chevreux 1906 ; Andres et al. 2002 ; Othaitz and Sorbe 2020
E. latirostris Indian Ocean eyes absent, pereonite 7 without distomiddorsal tooth, pleonite 3 with distomiddorsal tooth, epimeron 3 with posterior margin smooth, coxa 7, uropod 3 and telson unknown. 2500 m Ledoyer 1982
E. leptocarpus NE Atlantic eyes present, pereonite 7 without distomiddorsal tooth, pleonites 1–3 with distomiddorsal teeth, epimeron 3 with posterior margin fully serrate, coxa 7 unilobed, uropod 3 with rami subequal in length, telson cleft about 20 % of length. 346–1098 m Krøyer 1845 ; G. O. Sars 1893 ; Stebbing 1906 ; Othaitz and Sorbe 2020
E. liui NW Pacific, Okinawa Trough, 27 ° 32 ' N, 126 ° 58 ' E eyes absent, pereonite 7 without distomiddorsal tooth, pleonites 1–2 with distomiddorsal teeth, epimeron 3 with posterior margin and posteroventral corner serrate, coxa 7 unilobed, uropod 3 with outer ramus slightly shorter than inner one, telson unknown. 1243 m Wang et al. 2021
E. longipes Arctic Ocean, NE Atlantic eyes present, pereonite 7 without distomiddorsal tooth, pleonites 1–2 with distomiddorsal teeth, epimeron 3 with posterior margin serrate, coxa 7 unilobed, uropod 3 with rami subequal in length, telson cleft about 20 % of length. 6–1098 m Krøyer 1845 ; Stebbing 1906 ; Lincoln 1979 ; Bousfield and Hendrycks 1995 ; Othaitz and Sorbe 2020
E. meteorae NE Atlantic eyes present, pereonite 7 with distomiddorsal tooth, pleonites 1–3 with distomiddorsal teeth, epimeron 3 with only distal part of posterior margin serrate, coxa 7 unilobed, uropod 3 with rami subequal in length, telson cleft about 30 % of length. 50–150 m Andres 1996
E. microps Antarctica eyes present, pereonite 7 with distomiddorsal tooth, pleonites 1–2 with distomiddorsal teeth, epimeron 3 with posterior margin fully serrate, coxa 7 and uropod 3 unknown, telson less than 30 % of length. epi- and mesopelagic Walker 1906 ; Andres et al. 2002
E. minutus Off Norway, off South Africa eyes present, pereonite 7 with distomiddorsal tooth, pleonites 1–2 with distomiddorsal teeth, epimeron 3 with lower 1 / 3 length of posterior margin serrate, coxa 7 unilobed, uropod 3 with outer ramus much shorter than inner one, telson cleft about 15 % of length. 200 m, 752 m Krøyer 1845 ; G. O. Sars 1893 ; Stebbing 1906
E. nevandis Indian Ocean, off Kenya, 4 ° 00 ' S, 41 ° 27 ' E eyes present, pereonite 7 with small distomiddorsal tooth, pleonites 1–2 with small distomiddorsal teeth, epimeron 3 with posterior margin smooth, coxa 7 and uropod 3 unknown, telson less than 20 % of length. 1510–2500 m Barnard 1961 ; Ledoyer 1982
E. parvus Western Pacific, Indonesia eyes present, pereonite 7 with distomiddorsal tooth, pleonites 1–2 with distomiddorsal teeth, epimeron 3 with half-length of posterior margin serrate, coxa 7 bilobed, uropod 3 and telson unknown. 315 m Pirlot 1934 ; Jung et al. 2016
E. perdentatus Antarctica eyes present, pereonite 7 carinate, with large distomiddorsal tooth, pleonites 1–3 carinate, with large distomiddorsal teeth, epimeron 3 only posteroventral corner serrate, coxa 7 unilobed, uropod 3 with rami subequal in length, telson cleft less than 20 % of length. 0–928 m Emison 2000 ; Andres et al. 2002 ; Verheye and d’Udekem d’Acoz 2020
E. pontomedon Antarctica eyes present, pereonite 7 carinate, with large distomiddorsal tooth, pleonites 1–3 carinate, with large distomiddorsal teeth, epimeron 3 only posteroventral corner serrate, coxa 7 unilobed, uropod 3 with rami subequal in length, telson less than 20 % of length. 107–668 m Verheye and d’Udekem d’Acoz 2020
E. propeperdentatus Antarctica, 61 ° 30 ' S, 55 ° 00 ' W eyes present, pereonite 7 carinate, with large distomiddorsal tooth, pleonites 1–3 carinate, with large distomiddorsal teeth, pleonites, epimeron 3 smooth, only with small spines, coxa 7 unilobed, uropod 3 with outer ramus slightly longer than inner one, telson less than 20 % of length. epi-and mesopelagic Andres 1979 ; Othaitz and Sorbe 2020
E. propinquus N Atlantic eyes present, pereonite 7 without distomiddorsal tooth, pleonites 1–2 with distomiddorsal teeth, epimeron 3 with posterior margin serrate, coxa 7 unilobed, uropod 3 with rami subequal in length, telson cleft about 47 % of length. 183–1141 m Krøyer 1845 ; G. O. Sars 1893 ; Stebbing 1906 ; Othaitz and Sorbe 2020
E. tjalfiensis Davis Strait, 70 ° 41 ' N, 52 ° 07 ' W eyes present but not pigmented, pereonite 7 without distomiddorsal tooth, pleonites 1–2 with distomiddorsal teeth, epimeron 3 with posterior margin serrate, coxa 7 unilobed, uropod 3 with outer ramus much shorter than inner one, telson cleft less than 20 % of length. 750–800 m Stephensen 1912 ; 1944
E. tridentatus Antarctica eyes present but not pigmented, pereonite 7 with distomiddorsal tooth, pleonites 1–2 with distomiddorsal teeth, epimeron 3 with posterior margin smooth, distoventral margin lightly serrate, coxa 7, uropod 3 and telson unknown. unknown Bellan-Santini and Ledoyer 1974 ; Andres et al. 2002
* Translation of the original description: eyes absent; pereonites and pleonite 1 with weak longitudinal carina, pleonites 1 and 2 with small distomiddorsal teeth, pleonite 3 and segment 1 of without tooth, posteroventral angle of epimeron 1 produced into small acute tooth; head with anterolateral angle acute, rostrum extending 1 / 3 length of basal article of antenna 1, antennae 1 broken off at peduncular article 1; antenna 2 article 3 four times shorter than article 4 and three times shorter than article 5; upper lip rounded, mandible with stout cylindrical molar process, serrated incisor process, large lacinia mobilis and spine row, palp article 1 much longer than article 2, maxilla 1 inner lobe with 2 very short distal setae, outer lobe with 11 multi-cusped spine-teeth, palp thin, bearing row of fine setae on its end, palp article 1 two times shorter than article 2, maxilla 2 inner lobe rounded, as long as, but two times broader than outer lobe, both lobes equipped with setae distally; maxilliped similar with those of Е. bathybius , but outer lobes slightly broader than inner lobes; coxa 1 strongly expanding distally, with rounded anterior margin; coxa 2 smaller than coxa 1; plate 4 small, with convex anterior and concave posterior margins; plates 5–7 oval, gnathopods 1 and 2 typical for Eusirus , gnathopod 1 significantly shorter than gnathopod 2, carpus with posterior margin bearing a tuft of setae on acute projection distally, propodus of gnathopods 1 and 2 similar in shape and size, width less than 1.5 times exceeding their length, Pereopods 3, 4, and 6 broken off; Pereopod 5 with basis slightly expanding distally; basis of pereopod 7 strongly expanding distally; width almost equal to the length, epimera 1 and 3 rounded, with smooth posterior margin, epimeron 2 with acute posteroventral angle, uropod 1 rami equal in length, uropod 2 exopod slightly shorter than endopod, uropod 3 broken off, telson triangular, width slightly less than length; distal end with an acute-angled notch. Remarks. The species described herein sharply differs from all other species of the genus by the smooth epimer III posterior margin and short triangular telson (Birstein and M. Vinogradov 1960, translated by Dr. Olga A. Golovan).