Oediceropsis bicornuta, Bellan-Santini, 2007

Bellan-Santini, Denise, 2007, New amphipods of hydrothermal vent environments on the Mid-Atlantic Ridge, Azores Triple junction zone, Journal of Natural History 41 (9 - 12), pp. 567-596 : 579-584

Oediceropsis bicornuta n. sp.

( Figures 9–12 )

Type locality. Mid-Atlantic Ridge, Lucky Strike (Tour Eiffel), 37 ° 17.32 9 N, 32 ° 16.51 9 W, 1686 m.

Material examined. DIVA 2 cruise (particle trap triple 4 June 1994 – 1 July 1994, 1.5 m of the bottom), foot of black smoker. Tour Eiffel, 1686 m, 1 female holotype MNHN-Am 7469 .

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 67- articulate 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.

Gnathopods subchelate. Gnathopod 1 basis fringed on both edges, ischium and merus short; carpus lobate, as long as wide, lobe not extending along the propodus; propodus enlarged length/breadth ratio 7:5, palm rounded, fringed with numerous short setae, delimited by a spine; dactylus curved, as long as palm. Gnathopod 2 basis fringed on the anterior edge; ischium and merus short; carpus lobate, lobe setose; propodus ovate, palm rounded, delimited by a spine, dactylus curved, long as palm. Pereopods 3 and 4 basis setose on both edges, merus distally enlarged, dactylus long. Pereopod 5 basis slightly lobate, strongly setose on both edges, merus ovate, fringed by long plumose setae on posterior edge and distal anterior one, dactylus long and blade shaped. Pereopod 6 basis proximally lobate, fringed on both edges by long setae; merus ovate, fringed with long setose seta on the posterior edge and simple setae on the anterior edge; dactylus seveneighths length of propodus and blade-shaped. Pereopod 7 elongate, basis slightly lobate, fringed on both edges by long setae, plumose setae on the lobe; ischium short, merus/ carpus/propodus/dactylus ratio 10:12:9.5:10, all articles fringed on both edges by robust setae.

Epimeral plate 3 rounded, fringed with short setae. Uropod 1 peduncle long and spinose, equal rami spinose, peduncle/rami ratio 13:8. Uropod 2 peduncle long and spinose, peduncle/rami ratio 9:8. Uropod 3 lost. Telson entire, as long as wide, distally excaved, fringed with small setae on the sides, two pairs of little distal setae.

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 and O. proxima Chevreux, 1908 . Oediceropsis bicornuta is distinguished from O. brevicornis by absence of eyes, size of antenna 1 reaching the end of article 4 of antenna 2, absence of hump in the coxa 4 and the telson distally excaved; from O. elsula by size of rostrum, shape of gnathopod 1 carpus and propodus, absence of posterior hump in the coxa 4, shape of telson. Oediceropsis proxima considered as very near to O. brevicornis has a short description, but coxa 4 is expanded posteriorly with a sharp upturned point; in Oediceropsis bicornuta the posterior edge of coxa 4 has only a small distal hump without point; the propodus of gnathopod 1 in O. proxima is longer than wide as gnathopod 2, in O. bicornuta the propodus of gnathopod 1 is as long as wide; the first two pereopods of O. proxima have the dactylus longer than propodus, in O. bicornuta dactylus/propodus have a ratio 2: 2.6 in pereopod 3 and 2: 2.3 in pereopod 4. The telson of Oediceropsis proxima has a crenulated distal margin not excavated as in O. bicornuta ; O. proxima has no calceoli on antenna 2.

Distribution and habitat. Mid-Atlantic Ridge, central Atlantic Ocean.

Etymology. The name is suggested by the special shape of the membrane enveloping the proximal element of the calceoli.

Figures

Figure 9. Oediceropsis bicornuta, Diva 2. Holotype female. (1) habitus; (2) antenna 1; (3) antenna 2; (4) mandible; (5) labium; (6)maxilla 1; (7) maxilla 2; (8) maxilliped; (9) coxa 1; (10) gnathopod 1; (11) gnathopod 2. Scale bar 100 Mm.

Figure 10 Oediceropsis bicornuta, Diva 2. Holotype female. (1) pereopod 3; (2) pereopod 4; (3) pereopod 6; (4) pereopod 7. Scale bar 1000 Mm.

Figure 11. Oediceropsis bicornuta, Diva 2. Holotype female. (1) head; (2) pereopod 5, (3) epimeral plate 3; (4) uropod 1; (5) uropod 2; (6) telson. Scale bar 6 100 Mm; 2, 3, 4, 5: 1000 Mm.

Figure 12. Oediceropsis bicornuta, Diva 2. Holotype female. (1) antenna 2 flagellum with calceoli et setose seta; (2) Antenna 2, calceolus. Scale bar 1: 100 Mm; 2: 10 Mm.