Centromedon zoe, Horton, Tammy & Thurston, Michael, 2011

Horton, Tammy & Thurston, Michael, 2011, Centromedon zoe (Crustacea: Amphipoda: Lysianassoidea: Uristidae), a new deep-water scavenger species from the North Atlantic, with a key to the genus Centromedon, Zootaxa 2869, pp. 54-62 : 56-61

Centromedon zoe sp. nov.

( Figures 1–3 )

Type material. Holotype: female, 6.5 mm and 9 slides, NHMUK 2011.925. Allotype: male 6.3 mm (and one slide mount of antennae) NHMUK 2011.946. Paratypes: 12 mature females, average 6.5 mm (4.9–7.0 mm), NHMUK 2011.926 – 935; 12 mature males, average 6.1 mm (5.5–7.3 mm), NHMUK 2011.936 – 945; 5 mature females and 5 mature males (AM P.85244); collected at the Mid-Atlantic Ridge in the northern Atlantic Ocean, RRV James Cook, (cruise 011), station number JC011/098; freefall, acoustically-released, baited trap, deployed at 1313 hrs ( UTC) 9 August 2007, 54° 04.08' N, 34° 09.43' W at 2500 m, released at 1125 hrs, 11 September 2007; bottom time, 46 hrs.

Additional material. 678 specimens, Mid-Atlantic Ridge, JC011/079, 05–07/08/2007, 53°56.44'N, 36°11.56'W, 2564 m; 1861 specimens, Mid-Atlantic Ridge, JC011/114, 12–13/08/2007, 54°02.31'N, 34°09.60'W, 2453 m; 860 specimens, Mid-Atlantic Ridge, JC011/098, 09–11/08/2007, 54°04.08'N, 34°09.43'W, 2500 m. 879 specimens, base of Sedlo Seamount, Azores, Stn. 56319#1, 40° 11.43' N, 26° 33.99' W, 2655 m; 574 specimens, 56354#1, 39° 50.17' N, 26° 17.82' W, 2876 m. 21 specimens, Stn. 51403#1, Benthic Net 1.5/ 3m, 51° 37.7' N, 12° 59.8' W, 1292–1314 m; 6 specimens, Stn. 51403#2, Benthic Net 1.5/ 3m, 51° 37.4' N, 12° 59.2' W, 1317–1325 m; 1 specimen, Stn. 51403#3, Benthic Net 1.5/ 3m, 51° 36.8' N, 12° 59.1' W, 1319–1325 m; 11 specimens, Stn. 51403#4 Benthic Net 1.5/ 3m, 51° 36.7' N, 12° 59.6' W, 1319–1333 m; 8 specimens, Stn. 51403#5, Benthic Net 1.5/ 3m, 51° 37.8' N, 12° 58.9' W, 1289–1297 m; 11 specimens, Stn. 51420#1, Benthic Net 1.5/ 3m, 51° 37.3' N, 12° 58.6' W, 1326–1328 m; 11 specimens, Stn. 51420#3, Benthic Net 1.5/ 3m, 51° 38.3' N, 12° 58.9' W, 1293–1298 m; 6 specimens, Stn. 51420#4, Benthic Net 1.5/ 3m, 51° 37.9' N, 12° 59.5' W, 1302–1319 m – all from the ‘ Pheronema’ ground in the Porcupine Seabight.

Diagnosis. Lateral cephalic lobes subacute, not projecting; mandibular palp with 8 distolateral A2 setae; maxillipedal palp article 4 well-developed; coxa 1 weakly tapered, anterior margin concave; gnathopod 1 subchelate, propodus subrectangular; basis anterior margin fully setose; gnathopod 2 minutely subchelate; propodus rectangular; pereopods 3 and 4 dactyli long, subequal to propodus; epimeron 3 tooth acute, not upcurved; urosome 1 with distinct triangular acute carina.

Description. Holotype female 6.5 mm. Head: exposed, as long as deep; lateral cephalic lobe large, narrow, subacute; Eyes: apparently absent. Antenna 1: short; peduncular article 1 short; peduncular article 2 short, length 0.3 x article 1; peduncular article 3 short, length 0.3 x article 1; primary flagellum nine- articulate; accessory flagellum long, length 0.45 x primary flagellum, three-articulate, forming cap, partially covering callynophore; callynophore strong, two-field; calceoli absent. Antenna 2: short, length 1.17 x antenna 1; peduncle without brush setae; peduncular article 1 not greatly enlarged; weakly geniculate between peduncular articles 3–4; article 3 long, length 0.8 x article 4; flagellum well-developed, nine-articulate.

Epistome and upper lip: separate, upper lip dominant, weakly produced. Lower lip lobes: widely separated, inner lobes present. Mandible: incisor ventral margin smooth with small hook; lacinia mobilis present only on left mandible, a stemmed irregularly cusped peg; left and right accessory setal rows with simple robust setae and plumose setae; molar laminar, unridged with vestigial triturative area at tip; palp attached level with molar; article 1 short, length 0.8 x breadth; article 2 slender, length 5 x breadth, with eight distolateral A2 setae; article 3 slender, blade-like, with two long B3 setae, ten D3 setae and three E3 setae. Maxilla 1: inner plate narrow, with 2 apical pappose setae; outer plate with setal-teeth in 7/4 crown arrangement, outer row with ST1–7 large and slender, ST1 four-cuspidate, ST2 three-cuspidate, ST3 four-cuspidate, ST4 six-cuspidate, ST5 seven-cuspidate, ST6 six-cuspidate, ST7 displaced from ST6, five-cuspidate, STA-D large, slender, STA four-cuspidate, STB five-cuspidate, STC six-cuspidate, STD six-cuspidate; palp large, two-articulate, article 1, short, article 2 with seven robust terminal setae, one flag seta and one sub-terminal simple seta. Maxilla 2: inner plate narrow, tapering distally, shorter than outer plate, with two sub-parallel, medial setal rows; outer plate with short robust and plumose setae. Maxilliped: inner plate large, suboval with three robust nodular setae, setal row strong, with eight pappose setae reaching apical margin, and two marginal setae; outer plate medium, subrectangular, with six simple robust setae apically and ten robust nodular setae medially; palp large, four-articulate, article 2 slender, length 2.5 x breadth, article 3 long, slen- der, length 1.9 x breadth, article 4 well-developed, with one subterminal seta.

Gnathopod 1: subchelate; coxa large, slightly shorter than coxa 2, weakly tapered distally, anterior margin concave, anteroventral corner broadly rounded, basis slender, long, length 4.4 x breadth, strongly setose anteriorly; ischium short, length 1.0 x breadth; carpus subrectangular, lacking posterior lobe, subequal in length to propodus, length 1.9 x breadth; propodus subrectangular, margins subparallel, palm oblique. Gnathopod 2: minutely subchelate; coxa large, subequal to coxa 3; ischium long, length 2.5 x breadth; carpus length 2.4 x breadth; propodus subrectangular; dactylus inserted at anterior corner of propodus, reaching palm edge. Pereopod 3: coxa large, subrectangular; basis slender, straight, margins subparallel, dactylus long, straight. Pereopod 4: coxa deeper than wide with posteroventral lobe broadly rounded, posterior margin straight. Pereopod 5: coxa posterior lobate (no lateral ridge); basis expanded, posterior margin weakly convex, posterior lobe narrowly rounded. Pereopod 6: coxa small, posterior lobate; basis expanded, posterior margin weakly convex, posterodistal lobe narrowly rounded. Pereopod 7: coxa small; basis broadly expanded and rounded, posterodistal lobe broadly rounded; distal articles shortened, together 0.76 x length of basis.

Pleonites 1 to 3: not carinate. Epimeron 2: posteroventral corner convex, broadly rounded. Epimeron 3: posteroventral corner produced acutely. Urosome: urosomite 1 with distinct carina, forming a posteriorly directed acute ‘tooth’. Uropod 1: peduncle, length 1.24 x inner ramus, with four lateral robust setae and six medial robust setae; outer ramus subequal to inner ramus; inner ramus with one medial robust seta and two lateral robust setae; outer ramus with one lateral robust seta and two medial robust setae. Uropod 2: peduncle, length 0.86 x inner ramus, with four lateral robust setae; outer ramus subequal to inner ramus; inner ramus with two medial robust setae and one lateral robust seta; outer ramus with two lateral robust setae. Uropod 3: peduncle, length 0.8 x inner ramus, with four apicolateral robust setae, four apicomedial robust setae and two medial simple slender setae; inner ramus shorter than outer ramus, length 0.84 x outer ramus, with one medial slender seta, one medial robust seta and one lateral robust seta; outer ramus two-articulate, article 2 length 0.77 x article 1, article 1 with one medial robust seta and three lateral robust setae. Telson: long, lobes tapering, length 1.56 x breadth, cleft 81%, with two dorsal robust setae per lobe; apices incised, each with apical notch and one robust seta.

Male. As for female except Antenna 1: peduncular article 2, length 0.23 x article 1; peduncular article 3, length 0.18 x article 1; primary flagellum 11-articulate; accessory flagellum, length 0.65 x primary flagellum, calceoli present. Antenna 2: long, length 2.3 x antenna 1; peduncle with brush setae; calceoli present; flagellum 22- articulate.

Distribution. North-east Atlantic Ocean, 1289–2876 m; Mid-Atlantic Ridge, Azores seamounts, Porcupine Seabight.

Etymology. The species is named in honour of the first author’s first daughter, Zoë , noun in apposition.

Remarks. This small scavenging species has been captured in great numbers in baited traps set at around 2500 m at the Mid-Atlantic Ridge. It resembles most closely the species C. typhlops , C. mediator and C. laevis . It can be distinguished from C. typhlops by the acute boss on urosome 1, the longer dactyls of the pereopods, the rectangular form of the propodus of gnathopod 2 (suboval in C. typhlops ), details of the mouthparts and antennae, and the much smaller mature female size (6 mm in C. zoe vs. 17.5 mm in C. typhlops ). It can be distinguished from C. mediator by the form of gnathopod 2 (chelate in C. mediator ), the number of articles in the antennae, the less welldeveloped molar, the number of A2 setae on the mandibular palp, and the less produced epimeron 3 tooth. It can be distinguished from C. laevis by the fully setose anterior margin of the basis of gnathopod 1 (only two setae in C. laevis ), the length of the dactyls on pereopods 3 and 4 (subequal to propodus in C. zoe , longer than propodus in C. laevis ), the anterior margin of coxa 1 (concave in C. zoe , convex in C. laevis ) and the shape of coxa 4 posterior lobe (more rounded in C. zoe ).

Tryphosella abyssi Norman, 1900 , included under Uristes by Barnard & Karaman (1991) has been recorded only once. A single 6 mm male specimen was collected at 1071 m in the ‘cold area of the Faroe Channel’ by Sir John Murray, aboard HMS Triton , in 1882 (Station 7: 60°19' N, 7°10' W). Type material of this species is not in the Norman Collection at the Natural History Museum. The description and illustrations given by Norman (1900), particularly of the sub-acute lateral cephalic lobes, the dominant upper lip, and the acute urosome boss, place it close to the new species Centromedon zoe . However, the Norman species is distinguished by the rounded posterodistal lobe of epimeron 3. Without type material, or further material that can be linked with this species it is hereby referred to nomen dubium.

Figures

FIGURE 1. Centromedon zoe sp. nov. Holotype female, 6.5 mm, habitus, antennae, uropods and telson, Y-allotype male, 6.3 mm, antennae.

FIGURE 2. Centromedon zoe sp. nov. Holotype female, 6.5 mm, gnathopods and pereopods.

FIGURE 3. Centromedon zoe sp. nov. Holotype female, 6.5 mm, mouthparts.