New amphipods of hydrothermal vent environments on the Mid‐Atlantic Ridge, Azores Triple junction zone

This work is the third publication on the new amphipod species collected from the Azores Triple junction zone by the cruises ATOS, DIVA 2, MARVEL, PICO and SEAHMA 1. Seven new species and a new genus are described belonging to six families, Eusiridae, Leucothoidae, Oedicerotidae, Phoxocephalidae, Pleustidae, and Podoceridae. They were sampled in four sites, Menez Gwen, Lucky Strike, Saldanha and Rainbow.


Introduction
While we possess a lot of data on Atlantic bathyal amphipods, this is not true for amphipods that live on the Mid-Atlantic Ridge. Amphipods are not especially abundant at most locales on the Mid-Atlantic Ridge and sampling is difficult; we thus have had little material to study from each cruise. It was necessary to wait for the development of multiple programmes to obtain sufficient specimens for proper study.
During the diving cruises of IFREMER (Brest, France), sometimes in collaboration with English or Portuguese teams, on the Mid-Atlantic Ridge in the Azores Triple junction zone, some specimens of Amphipods were sampled: Stenothoidae (Bellan-Santini 2005) from DIVA 1 and 2, PICO, MARVEL and ATOS cruises, Rhachotropis (Bellan-Santini 2006) from DIVA 2, MARVEL and FLAME 2 cruises. Seven new species belonging to six families from ATOS, DIVA 2, MARVEL, PICO and SEAHMA 1 cruises come from the same zone. The seven new species belong to six families, Eusiridae, Leucothoidae, Oedicerotidae, Phoxocephalidae, Pleustidae, and Podoceridae.
This new genus with an urosomite 1 elongate, a basis of P3-5 rectilinear, resembles a Podoceridae, but with an accessory flagellum absent, mouthparts basic, coxae medium, gnathopods subchelate, rami of uropod 3 broadly lanceolate, telson entire, will be attributed to the family Eusiridae.
Etymology. Podosirus in reference to the two families Podoceridae and Eusiridae.
Relationship. The Eusiridae family is a complex family with more than 60 genera more or less well defined. Podosirus which possesses the various characters of the family differs from the other genera by: -eyes absent, -the presence of a distal process on the first article of antenna 1, -accessory flagellum absent, -gnathopods diverse, subchelate, not eusirid, -the shape of pereopods 3-7, with basis rectilinear, merus longer than propodus, propodus curved in claw-shaped and proximally humped.  Diagnosis. Rostrum short and rounded, eyes absent. Gnathopod 1 narrow, propodus twothirds length of carpus, dactylus short, one-quarter length of propodus. Pereopods 3 and 4 similar, linear. Pereopods 5-7 basis narrow. Telson triangular elongate, more than two times long as broad.
Etymology. Named for the cruise ATOS.
Relationship. Thomas and Klebba (2006) give 84 species for the ''leucothoid clade'', after the revision of the family in Lowry et al. (2000). In the Atlantic genus Leucothoe only two species are blind, L. rostrata Chevreux, 1908 andL. uschakovi Gurjanova, 1951. Leucothoe rostrata was sampled from Azores near Menez Gwen site, at 1360 m deep. It has a rostrum very long and pointed, as long as three-quarters of the first article of antenna 1; telson heart-shaped, a little longer than broad. Leucothoe ushakovi, sampled from Greenland at 3000 m, is a very large species (34 mm) with a rostrum well developed, inner lobe of maxilla 2 with many small setae, coxa 1 hardly directed anteriorly, epimeral plate 2 with a posterodistal point. Elsewhere two other species are blind or with eyes very poorly developed, Leucothoe pacifica Nagata, 1963, with an epimeral plate sinuate at lower posterior corner and pereopods 5-7 with lobed basis and Leucothoe panpulco Barnard, 1961, with ''epimeral   Diagnosis. Rostrum shorter than article 1 of antenna 1 peduncle. Eyes absent. Antennae equal and short. Gnathopods 1 and 2 similar, subchelate, without long lobate carpus.
Epimeral plate 3 rounded, fringed distally by long setae. Uropod 1, rami equal, longer than peduncle. Uropods 2 and 3 rami equal and longer than peduncle. Telson entire longer than wide, discreetly excavated with two terminal setae and one subterminale.
Etymology. Name refers to the fact that species is blind.
Relationship. The genus Monoculodes has been defined in the Oedicerotidae with antenna 2 short, subchelate gnathopods with the carpal lobes more or less enlarged. Jo (1990) has given a good diagnosis of the genus; Bousfield and Chevrier (1996) considered Monoculodes to be a complex and gave a ''formal rediagnosis''. They consider that in this large group a subgeneric division is required.
Only four Monoculodes are blind with gnathopods 1 and 2 similar, without long lobate carpus and with a rostrum longer than lateral cephalic lobes: M. abacus Barnard, 1961, M. latissimanus Stephensen, 1931, M. rostratus Stephensen, 1931 and M. sudor Barnard, 1967. Monoculodes abacus has the rostrum reaching the end of the first peduncular article of antenna 1, propodus of gnathopods 1 and 2 are triangular. Monoculodes latissimanus has the propodus of the gnathopod 1 ''extremely broad, nearly as broad as long'', pereopods 3-7 have the dactyli long ''nearly as long as the two preceding joints together''; the lateral lobe is quadrate. Monoculodes rostratus has a rostrum ''as long as the head behind the process''; gnathopods 1 and 2 have the carpus with a long process. Monoculodes sudor has the rostrum ''reaching to apex of article 1 of antenna 1''; lateral cephalic lobe with subacute apex; dactyli of pereiopods 3 and 4 slightly longer than propodus; telson rounded apically. With Monoculodes anophthalma, only M. latissimanus has been found in the Atlantic, in Greenland.     Diagnosis. Antenna 1 short, accessory flagellum absent. Antenna 2 shorter than half of body length, peduncle article 5 with a long antero-distal curved spine, each article of the flagellum with a plumose seta and a calceolus. Eyes absent. Telson normal.
Description. Holotype female with oostegites, 16 mm. Head is equal to the two first segments of the mesosome. Body smooth. Eyes absent. Rostrum short, as long as lateral cephalic lobe. Lateral cephalic lobe quadrate. Antenna 1 reaching the end of article 4 of the peduncle of antenna 2; article 1 robust with single setae on the superior edge and plumose setae at the inferior edge; article 2 equal to 0.6 of article 1, setose; article 3 equal to half of article 2; accessory flagellum absent, flagellum 13-articulate. Antenna 2 shorter than half of body length, peduncle article 5 with a long curved antero-distal spine, as long as the eight first articles of the flagellum, and a posterior spine less long and straight; flagellum 67articulate bearing at the inferior edge of each article a plumose seta and a calceolus. Mandible with incisor process denticulate, molar columnar, palp triarticulate, first article short and smooth; article 2 slightly curved and fringed with many short setae, one long subterminal seta; article 3 fringed with a single row of short setae, three long distal setae. Maxilla 1 inner plate rounded, fringed on the inner edge by five plumose setae, outer plate with seven bidentate spines, palp biarticulate, article 1 setose on the external edge, article 2 setose on the external edge and at the distal part of the inner edge. Maxilla 2 both plates equal and hardly setose. Maxilliped inner and outer plates setose on the inner edge, palp four-articulate, article 2 enlarged in the medial part, article 3 wide distally, article 4 falcate. Coxa 1 enlarged distally, distal edge fringed with numerous setae. Coxa 2, subrectangular, distal edge slightly shorter, rounded and fringed with numerous setae. Coxa 3 rectangular, distal edge setose, coxa 4 not excavate posteriorly, only concave, distal edge and half posterior edge setose.
Remarks. The calceoli of antenna 2 of this species have an original shape. Lincoln and Hurley (1981) have given good descriptions of the different types of calceoli. They describe nine structural types for different families. They consider that for eusirid, gammarellid and oedicerotid types, the calceoli are ''immediately distinguished … from other calceoli'' by ''the distinct separation of the proximal and distal elements and the remarkable cup-shaped configuration of the former''. In Oediceropsis bicornuta, a membrane with two acute tips envelops the fluted proximal parabolic element, the distal element is saucer shaped with a ridged plate interiorly.
Relationship. In the Oedicerotidae, the genus Oediceropsis is characterized by the buccal structure; rostrum small or absent; gnathopods similar to one another, subchelate; articles 4 and 5 of antenna 2 with several very large or elongated and curved spines. Three species of Oediceropsis have been described; O. brevicornis Lilljeborg, 1865; O. elsula Barnard, 1966 andO. proxima Chevreux, 1908   Description. Holotype female with oostegites, 9 mm. Pleon segments 1-3 each without setae. Head relatively short. Antenna 1 flagellum nine-articulate, accessory flagellum eightarticulate. Antenna 2 peduncle without ensiform process, flagellum nine-articulate. Maxilla 1 inner plate with two plumose setae, palp with two distal spine-like setae, one subterminal and three lateral setae, and numerous small hair-like setae on the surface. Maxilla 2 inner plate shorter than outer, with ten plumose setae, outer plate with 12 setae. Maxilliped inner plate short with five plumose setae, palp article 4 long with a nail as long as article 4. Coxae 1-3 with distal margin entire, without tooth, the distal margin fringed with long setae. Gnathopods similar. Gnathopod 2 propodus narrower than gnathopod 1, palm more excavate, defined by a prominence with a spine. Pereopods 3 and 4 carpus with two strong and long spine-like setae on postero-distal corner; propodus with two setae on posterior margin and two or three distal setae; dactylus half length of propodus. Pereopod 6 with long dactylus, dactylus/propodus ratio 5:6. Pereopod 7, basis serrate posteriorly, lobe reaching end of merus.
Epimeral plate 2 with postero-distal corner angular bearing five setae on the proximal part of the distal margin. Epimeral plate 3 with a postero-distal corner in hook shape. Uropod 1 peduncle with four marginal setae and a stout distal spine, rami equal with respectively three and four setae. Uropod 2 rami subequal with three spines each. Uropod 3 peduncle short with six distal setae, inner ramus exceeding first article of outer ramus, without distal seta, outer ramus biarticulate, article 1 with two terminal setae, article 2 with a long distal seta. Telson as broad as long, each lobe with two short subdistal and two lateral setae.
Etymology. The name of the species is derived from the name of the PICO cruise.
Relationship. Barnard and Karaman (1991) list 17 species in the genus Harpinia, three new species were described subsequently, Harpinia agna Karaman, 1987, H. ala Karaman, 1987and H. zavodniki Karaman, 1987. Only two species also have an epimera 3 with a hooked corner: H. agna and H. crenulata. Harpinia pico differs from H. agna by the shape of epimera 3, the size of the antennae, the shape of article 4 of the maxilliped palp, the shape of pereopod 7 basis and by the pilosity. Harpinia pico differs from H. crenulata by the shape of epimera 3, size of flagellum of antennae, article 4 of maxilliped palp, basipodite of pereopod 7 and uropod 1.   Description. Holotype female, 8 mm. Body strongly built, last segment of mesosome and segments of metasome dorsally gibbous. Head as long as the two first segments of the mesosome, rostrum short. Eyes not visible. Antenna 1 half length of body, article 1/2/3 ratio 8:5:2, accessory flagellum as a scale, flagellum 54-articulate. Antenna 2 half as long as antenna 1, flagellum 24-articulate. Mandible with incisor process denticulate, molar large, palp triarticulate, article 1 short, 2 and 3 long and setose. Maxilla 1 inner plate rounded with two terminal setae, outer plate with five distal spines and a row of fine setae on the inner margin. Maxilla 2 ordinary, inner plate shorter than outer. Maxilliped palp fourarticulate, article 3 produced distally, article 4 well developed.
Coxae increasing in size, coxa 1 anteriorly rounded, coxa 4 not projecting at the inferoposterior corner. Gnathopods subchelate. Gnathopod 1 small, merus not produced more than one-third length of carpus; carpus as long as propodus, propodus pyriform with the palm setose and spinose, defined by an angle and a spine. Gnathopod 2 large, carpus less than half length of propodus, with a small lobe; propodus very large, distally expanded, palm transverse, delimited by a spine, armed with setae and two rows of strong spines; dactylus as long as palm. Pereopods 3 and 4 basis posteriorly setose, ischium short, merus, carpus and propodus bearing marginal spines, dactylus smooth. Pereopods 5-7 basis posteriorly lobate, anteriorly armed with spines, merus, carpus, propodus spinose, dactylus smooth. Epimeral plate 3 with posterior and distal edges rounded with a very small process in the distal corner. Uropod 1, rami unequal, inner as long as peduncle, outer shorter. Uropod 2 outer ramus as long as half of inner, armed by spines on both sides. Uropod 3 outer ramus slightly longer than half of inner. Telson entire, oval.
The mature female without head has a gnathopod 2 with the palm of the propodus bearing on each side of the central edge five and seven spines. The holotype of 8 mm has four spines on each side.
Etymology. This species is named after the Rainbow site.
Relationship. This species is referable to the Stenopleutes. In the eight species cited in Barnard and Karaman (1991), none is blind and only two, Stenopleustes eldingi Gurjanova, 1930 andS. latipes (Sars, 1858), have a large gnathopod 2. Stenopleustes eldingi has three setae on the inner plate of maxilla 1, and gnathopod 2 has an oval propodus, not expanded distally. Stenopleustes latipes, according to the description of Sars (1893) and redraw by Hendrycks and Bousfield (2004), differs from S. rainbowi by the presence of eyes ''rather large, oblong, reniform'' and ''dark red'', a coxa 1 ''with the anterior corner angularly produced'', the propodus of gnathopod 1 with edge ''smooth bearing a few small spinules besides fine hairs''. Gnathopod 2 propodus is variable with maturity, according to Sexton (1909) Sars (1893) reported a ''small projection above the middle, and having below on the outer side a somewhat projecting, broadly-truncated lobe armed with five strong spines within the latter there is a groove, defined above by a ridge bearing a similar row of spines'', ''the telson is very small and distinctly navicular in form, tip evenly rounded''. Diagnosis. Body cylindrical, smooth. Eyes not visible. Antennae long, equal in length. Gnathopod 2 slightly shorter than gnathopod 1. Pereopods 3-7 long and with slender basis. Uropods 1 and 2 biramus, rami shorter than peduncle. Telson entire triangular.
Mandible normal, palp article 2 longest, articles 2 and 3 setose. Labium with welldeveloped inner lobes. Maxilla 1 inner plate with three distal setae, and four small medial setae, outer plate with seven spines, palp biarticulate, distal article long with five distal spines and 13 setae. Maxilla 2 normal, inner plate slightly shorter than outer. Maxilliped inner plate with distal part straight, with four spines and numerous setae; outer plate normal, not reaching apex of palp article 2, with strong spines on medial margin; palp with four articles, second long, article 3 not lobate.
Etymology. This species is dedicated to the Portuguese teams, which have continued to work in the Mid-Atlantic Ridge, after the death of our friend Professor Luiz Vieira Caldas Saldanha.
Distribution and habitat. Xenodice frauenfeldti was collected in the Arctic ocean, North Atlantic and North sea between 150 and 565 m. Xenodice portuguesi was collected at the Saldanha site from 2223 m depth where an evolutive hydrothermal field of low activity was described.