Alexandrella martae, Berge & Vader, 2005

Berge, Jørgen & Vader, Wim, 2005, The amphipod genus Alexandrella (Amphipoda, Stilipedidae): taxonomic status, allometric growth and description of two new species, Journal of Natural History 39 (17), pp. 1327-1346 : 1340-1344

Alexandrella martae n. sp.

( Figures 7–9 )

Holotype: female 55 mm, South Georgia Isl., collected on the RV Eltanin , cruise 22, station 1585 ( USNM).

Additional material. Female, 58 ° 53–549S, 37 ° 15–199W, 2901 m, collected on the RV Eltanin, 31 August 1963, cruise 9, station 704, Blake Trawl ( USNM); female 38 mm, 68 ° 05–069S, 173 ° 38–449E, 2608–3175 m, collected on the RV Eltanin, 12 January 1967, cruise 27, station 1867, USNM ; female, 61 ° 43.089S, 60 ° 41.89W, 2830–2862 m, collected on the RV Polarstern, 19 February 2002, ANDEEP station 114-10, Agassiz Trawl.

Distribution

South Georgia Isl. (type locality), Weddell Sea and Ross Sea, 2830–3175 m .

Diagnosis

Labrum strongly asymmetrically lobed. Mandibular incisors broad, irregularly toothed, right lacinia mobilis reduced but toothed. Pereopod 1 with oostegite, pereopod 4 coxa rounded and not excavate posteriorly. Pleonites 1–3 and urosomite 1 dorsally produced.

Description

Body. Rostrum weakly developed, eyes absent. Epistome unproduced. Body dorsally with a moderate projection posteriorly on pleonites 1–3. Urosomite 1 dorsally with a strong carina posteriorly and a deep excavation anteriorly. Coxae 1 anteriorly weakly expanded, not covering the head. Pereopods 5–7 and antenna 2 elongate.

Antennae. Antenna 1 shorter than antenna 2, peduncle article 1 longer than articles 2 and 3 combined, flagellum with more than 15 segments. Accessory flagellum small, inconspicuous, uniarticulate. Callynophore absent. Antenna 2 peduncle article 4 shorter than 5, flagellum elongate with more than 30 segments.

Mouthparts. Labrum longer than broad, strongly asymmetrically lobed, right lobe much larger than left. Labium distally broad and rounded, inner lobes absent. Mandibles powerful, hinge line lateral. Incisors irregularly toothed and broad. Lacinia mobilis present on both mandibles, right lacinia mobilis smaller than left, toothed. Accessory setae-row weak, five simple setae. Molar absent. Palp short, three-articulate, article 2 longer than 3. Article 2 distally with long and short setae, article 3 laterally with one row of short setae. Maxilla 1 palp two-articulate, powerful, distally broad but not transverse, distal and distolateral margin with short robust setae. Outer plate broad, setal teeth in a 6/2 arrangement, ST not cuspidate. Inner plate large, with two distal rows of pectinate setae and one row of slender setae, medially with two groups of simple setae. Maxilla 2 outer plate not as broad as inner, both plates distally with three distinct rows of setae. Maxilliped inner plate distally with one short nodular seta, distal and medial setae-rows parallel, setae short and simple. Outer plate broad, inner margin without setae, mediodistally weakly serrate, distally with one row of short robust setae. Palp four-articulate, weakly setose, article 2 as long as articles 3 and 4 combined, article 4 pointed and powerful, distal margin cuspidate.

Pereopods and coxal plates. Coxa 1 large, weakly produced anteriorly, posterodistally with simple setae, coxae 2 and 3 long and broad, weakly longer than coxa 1, posterodistally with simple setae, coxa 4 posterior lobe rounded, posterodistal margin convex, distally rounded, coxae 5 and 6 subequal, distally with posterior lobe large, anterior lobe absent, coxa 7 distally convex and rounded. Pereopod 1 simple, basis with short simple setae on both anterior and posterior distal margins, ischium short, carpus broader than propodus, posterodistally not produced, propodus subrectangular, dactylus powerful and serrate. Pereopod 2 simple, basis with short simple setae on anterior margin, ischium short, carpus broader than propodus, posterodistally not produced, propodus subrectangular, dactylus powerful and serrate. Pereopod 3 shorter than 4, weakly setose, dactylus long and slender. Pereopods 5–7 not differentiated, elongate, progressively longer posteriorly, basis pereopod 7 concave posteriorly, posterodistally acute, dactyli long and slender.

Oostegites on pereopods 1–5, gills on pereopods 2–7.

Epimeral plate 1 small and rounded, epimeral plate 2 as large as 3, posterodistally weakly produced and acute, epimeral plate 3 posterodistally weakly produced, acute. Urosomites 1–3 free, urosomite 1 dorsally with a deep excavation medially and distally with a large acute projection, urosomites 2–3 dorsally smooth. Uropod 1 reaching beyond uropod 2, biramous, rami subequal. Uropod 3 peduncle short, biramous, rami broad, subequal. Telson longer than broad, distally weakly cleft.

Etymology

The species is named after Marte Vader Weiland, the second author’s first grandchild.

Remarks

Alexandrella martae is characterized first of all by the presence of oostegites on pereopod (or gnathopod) 1, a character unique for the two species A. martae and A. mandibulata . These two species are easily separated on the morphology of the mandibles (right lacinia mobilis and incisors) and labrum (not medially separated and with the left lobe distally convex in A. martae ).

Figures

Figure 7. Alexandrella martae n. sp. Holotype.

Figure 8. Alexandrella martae n. sp. Holotype.

Figure 9. Alexandrella martae n. sp. Holotype.