Hirondellea sindhusagar, Horton & Thurston, 2009

Horton, Tammy & Thurston, Michael, 2009, Hirondellea sindhusagar (Crustacea: Amphipoda: Lysianassoidea), a new deepwater scavenger species from the Indian Ocean, with a key to the genus Hirondellea *, Zootaxa 2096 (1), pp. 433-441 : 435-440

Hirondellea sindhusagar sp. nov.

Figures 1–3

Holotype: female, 5.8 mm, ( NHM Reg. N o. 2008.3468) . Paratypes: 3 males ( NHM Reg. N o ’s. 2008. 3469–3471) , 11 females ( NHM Reg. N o’s. 2008.3471–3481), collected off the coast of Pakistan in the northern Arabian Sea , RRV Charles Darwin, (cruise 151), station number 56137#5, baited trap attached to Profilur autonomous lander; deployed at 1322 ( UTC) 13/10/03, 22º 51.067' N, 65º 59.916' E at 1864m, recovered at 0448 hrs, 14/10/03; bottom time, 14.2 hrs; bottom temperatures max = 3.55ºC, min = 3.52ºC, mean = 3.53ºC . 107 females ( NHM Reg. N o’s. 2008.3482–3491) , 53 males ( NHM Reg. N o’s. 2008.3492–3501), 56141 # 01, site A1200, trap attached to Profilur autonomous lander, 16/10/03, deployed at 0108 ( UTC) 22º 59.784' N, 66º 24.786' E at 1182m, recovered 16/10/03 @1240 hrs; bottom time, 10.5 hrs. Bottom temperatures max = 7.34ºC, min = 7.28ºC, mean = 7.31ºC .

Description. Based on adult female, 5.8 mm. Head: exposed, deeper than long; lateral cephalic lobe large, broad, subacute; eyes present, subtriangular, grey, non-ocellate. Antenna 1: short, 0.17 x body; peduncular article 1 short, length 1.2 x breadth; peduncular article 2 short, 0.1 x article 1; peduncular article 3 short, 0.175 x article 1; primary flagellum 5-articulate; accessory flagellum long, 0.7 x primary flagellum, 3-articulate, forming cap partially covering callynophore; callynophore weak, 2-field; calceoli absent. Antenna 2: length 1.1 x antenna 1; peduncle without brush setae; peduncular article 1 not greatly enlarged; article 3 short, 0.9 x article 4; flagellum well-developed, 6-articulate.

Mouthpart bundle: subquadrate. Epistome and upper lip separate, upper lip dominant. Epistome slightly rounded. Upper lip: produced, rounded apically. Interantennal carina: notched proximally. Mandible: incisor ventral margin smooth; lacinia mobilis present only on left mandible, a small stemmed robust seta (difficult to make out on slides and not visible in illustration); left and right accessory setal rows with simple robust setae; molar subconical, setose; palp attached proximally; article 1 short, 1.3 x breadth; article 2 slender, 5.2 x breadth, with 10 distolateral A2 setae; article 3 slender, blade-like, with 8 D3 setae, 1 A3 seta and 3 E3 setae. Maxilla 1: (described from paratype female since the holotype maxilla 1 was in poor orientation for interpretation) inner plate narrow, with 2 apical setae; outer plate with setal teeth in unusual 7/4 arrangement (almost 8/3?), row with ST1–7 large and slender, ST1 3-cuspidate, ST2 3-cuspidate, ST3 4-cuspidate, ST4 4- cuspidate, ST5 4-cuspidate, ST6 6-cuspidate, ST7 7-cuspidate, STA–D large, broad, STA 2-cuspidate, STB 3- cuspidate, STC 3-cuspidate, STD 4-cuspidate; palp large, 2-articulate, article 1, short with 3 or 4 inner notches. Maxilla 2: inner plate broad, truncate distally, shorter than outer plate. Maxilliped: inner plate large, subovate, apical margin concave, with 3 teeth bearing robust nodular setae and 4 simple robust setae across apical margin; 2–3 setae in medial setal row; outer plate medium, subovate, with medial margin weakly crenulate and slightly concave distomedially; palp large, 4-articulate, article 2 slender, length 2.6 x breadth, article 3 long, slender, length 3 x breadth, article 4 well-developed, with 2 subterminal setae.

Gnathopod 1: subchelate; coxa reduced, shorter than coxa 2, straight, tapered, anteroventral corner subtriangular; basis moderately setose anteriorly, long, length 4.2 x breadth; ischium short, length 1 x breadth; carpus subtriangular, subequal in length to propodus, length 1.4 x breadth; propodus margins subparallel; palmar angle acute, palm straight, dactyl greatly overreaching palm edge. Gnathopod 2: minutely subchelate, coxa large, shorter than coxa 3; ischium long, length 2.7 x breadth; carpus length 2.6 x breadth; propodus subrectangular, palmar angle obtuse, palm straight, weakly pectinate distally; dactylus inserted at anterior corner of propodus, reaching palm edge. Pereopod 3: coxa large, subrectangular; basis slender, straight, margins subparallel, propodus posterior margin with simple setae, dactylus long, weakly curved. Pereopod 4: coxa deeper than wide, with posteroventral lobe broadly rounded, posterior margin sloping anteriorly; propodus posterior margin with simple setae. Pereopod 5: coxa lobate posteriorly (no lateral ridge); basis weakly expanded, posterior margin straight, posterior lobe rounded. Pereopod 6: coxa small, strongly lobate posteriorly; basis weakly expanded, proximal posterior margin concave, posterodistal lobe broadly rounded. Pereopod 7: coxa small, weakly lobate posteriorly; basis expanded and rounded, proximal posterior margin convex, posterodistal lobe broadly rounded.

Pleonites 1 to 3: smooth dorsally. Pleonite 3: extended over urus. Epimeron 1: anterior margin slightly concave, anteroventral corner without tooth. Epimeron 2: posteroventral corner rounded, posterior margin convex. Epimeron 3: posteroventral corner subquadrate, ventral margin without short robust setae. Urosomite 1: anterior sinus present, boss a rounded hump. Uropod 1: peduncle 1.4 x inner ramus, without apicolateral robust setae, 1 apicomedial robust setae, and 7 dorsomedial setae; outer ramus slightly longer than inner ramus; inner ramus with 3 medial robust setae, without lateral robust setae and neither margin microsetose; outer ramus with 1 lateral robust setae, without medial robust setae. Uropod 2: peduncle 0.96 x inner ramus, without apicolateral robust setae, 1 apicomedial robust seta, without dorsomedial setae, and with 3 dorsolateral robust setae; outer ramus subequal to inner ramus. Inner ramus not constricted, with 4 medial robust setae, without lateral robust setae, and with neither margin microsetose; outer ramus without medial robust setae, 2 lateral robust setae, and with neither margin microsetose. Uropod 3: peduncle 0.84 x inner ramus, 2 apicolateral robust setae, 4 apicomedial robust setae and simple setae, and without medial simple slender setae; inner ramus slightly shorter than outer ramus, 0.9 x outer ramus, without medial robust setae or medial slender plumose setae; outer ramus 2-articulate, article 2 1.2 x article 1, with neither margin microsetose, article 1 without medial robust setae and slender plumose setae, and with 1 lateral robust seta. Telson: broad, slightly tapering, length 1.2 x breadth, weakly cleft 15 %; apices not incised, apices with 1 robust seta and 1 subapical robust seta per lobe.

Male. 3 male paratypes: As for female except with a greater number of aesthetascs on antenna 1; calceoli present on antenna 1 articles 5 and 6; longer antenna 2.

Remarks. This small species was collected in large numbers from the bathyal Arabian Sea (~ 1200–1800 m). It is a scavenging species attracted to the baited traps along with a number of other lysianassoid species. The species belongs to the group without a constriction on the inner ramus of uropod 2 and most closely resembles Hirondellea brevicaudata . It can be distinguished from that species by the very weakly cleft telson (15% in H. sindhusagar , 35% in H. brevicaudata ); the finer and more elongate rami of uropod 3 (in particular the unusually elongate article 2 of the outer ramus), the more acutely produced posteroventral corner of epimeron 3 and the subacute lateral lobes of the head. In addition, the two species can be separated by the finer characters of the mouthparts, particularly the maxilliped inner plate which in H. sindhusagar , has three unusual nodular ‘teeth’.

H. sindhusagar can be separated from the other species with an unconstricted uropod 2 inner ramus ( H. gigas , H. dubia ) by the absence of a multi-toothed dactyl on gnathopod 1 (as in H. gigas ) and the short, broad propodus of gnathopod 1 (c.f. elongate and strongly tapering gnathopod 1 in H. dubia ).

Distribution. Off the coast of Pakistan in the northern Arabian Sea, Indian Ocean at depths between 1182 and 1864 m.

Etymology. This species is named after the collecting locality of the Arabian Sea, which was known as the Sindhu Sagar to Indians in the Vedic period of their history.

Figures

FIGURE 1. Hirondellea sindhusagar sp. nov. Holotype female, 5.8 mm, habitus, antennae, and gnathopods.

FIGURE 2. Hirondellea sindhusagar sp. nov. Holotype female, 5.8 mm, mouthparts.

FIGURE 3. Hirondellea sindhusagar sp. nov. Holotype female, 5.8 mm, pereopods, uropods and telson.