Alexandrella chione d'Acoz & Verheye 2017, sp. nov.

Alexandrella chione sp. nov.

urn:lsid:zoobank.org:act: 90F1FE7A-F36C-4411-A7A8-833B300A0862

Figs 324–335

Alexandrella australis –? Holman & Watling, 1983a: 33, in part [specimen from RV Eltanin only], not

figs 1–3. —? Klages 1988: 82, fig. 20c. —? Berge & Vader 2005a: 1330 –1332, fig. 1. Alexandrella sp. – d’Udekem d’Acoz & Verheye 2013: 62, fig. 3.8.1B (in colour).

non Acanthonotozoma australis Chilton, 1912: 205, pl. 2 fig. 19.

Etymology

From the Greek, χιων, snow. The name, which is a noun in apposition, alludes to the pure white colour of the species.

Type material

Holotype

RV Polarstern cruises

SOUTHERN OCEAN: immature ♀, cruise PS81,ANT-XXIX/3, stn 227-2, Bransfield Strait, 62°55.83ʹ S, 58°41.09ʹ W to 62°55.76ʹ S, 58°41.46ʹ W, 562–564 m, muddy bottom, Agassiz Trawl, 5 Mar. 2013, coll. C. d’Udekem d’Acoz and M. Verheye (RBINS, INV. 122887).

Description

HEAD. Rostrum tiny, extremely narrow in frontal view, reaching 0.3 of article 1 of peduncle of antenna 1 (dorsomedial tooth included); lateral head lobes triangular (forming a sharp squared angle); ventral lobe forming an extremely strong hemi-elliptic protrusion; connection between this protrusion and head forming a deep notch (shape: sharp squared angle).

EYES. Circular, small, pale, non-ommatidian, disappearing in alcohol.

PEREION–PLEOSOME TOOTH PATTERN. Pereionites 1–6 totally smooth; pereionite 7 posteriorly carinate and with medium-sized tooth projecting backwards; pleonites 1–2 carinate, with medium-sized tooth projecting backwards; pleonite 3 carinate, with distinctly sigmoid profile (distinctly convex in anterior 0.8, distinctly concave in posterior 0.2), with medium-sized tooth projecting backwards.

EPIMERAL PLATES 1–3. Posteroventral angle: very obtusely rounded in plate 1, produced into a mediumsized tooth in plates 2–3.

UROSOME ORNAMENTATION. Urosomite 1 with deep notch on proximal third, followed by elevated carina, anteriorly rounded and slightly produced forward, dorsally nearly straight (posteriorly very slightly concave), posteriorly produced into a well-developed, narrowly triangular sharp tooth overreaching urosomite 1 and forming a blunt squared angle with it (tooth 0.23 × as long as carina); urosomite 2 toothless; urosomite 3 lateral borders distally produced into a well-developed lobe, of which the tip forms a squared angle.

TELSON. Broadly rectangular, distally broad and emarginate; with very shallow broad V-shaped notch (cleft on 0.08); lobes very broad, medially forming a rounded very low projection, more laterally with shallow concavity, at their connection with lateral border forming a broad and blunt triangular tooth.

ANTENNA 1. Articles of peduncle very broad; article one with large and broad dorsomedial tooth reaching tip of article two, with strong ventral tooth reaching mid of article two; article two with broadly rounded lateral lobe; article three with broadly rounded lateral lobe; accessory flagellum distinct, uniarticulate.

ANTENNA 2. Article four with posterodistal blunt dentiform process; article five 1.3 × as long as article four.

UPPER LIP. Strongly asymmetrical, right lobe well developed, bluntly triangular and very protruding, left lobe low and very rounded.

MANDIBLES. Incisor very broad, straight and toothless (or with trace of tiny denticles near lateral corner); left lacinia mobilis very large (0.7 × as broad as incisor process); right lacinia mobilis small (0.25 × as broad as incisor process); molar absent; palp with article 1 very short, posterodistally produced into a tooth; article 2 and 3 long and narrow, posteriorly ciliate; article 2 slightly longer than article 3.

LOWER LIP. Lower lip without inner lobes, outer lobes broad with small acute projection at outer corners.

MAXILLA 1. Inner plate setose along medial margin and along a row on inner face, notched at the level of this row to allow imbrication of outer plate; palp biarticulate, expanded distally with 1 marginal row of spines + row of short setae.

MAXILLA 2. Inner plate distinctly larger than outer, rounded, posterior setae conspicuously longer than those more anterior but not strongly plumose, also sparse setae on surface of plate; outer plate triangular.

MAXILLIPED. Outer plate exceeding palp, setose medially; inner plate extending beyond distal margin of palp article 1, setae on distal margin of moderate length; palp 4-articulate, article 2 longest, article 4 less than 0.5 length of article 3.

GILLS. From gnathopod 2 to pereiopod 7.

OOSTEGITES. From gnathopod 2 to pereiopod 5.

GNATHOPOD 1. Coxa very broad, expanding distally, anteroventral corner very broadly rounded, ventral margin straight; leg achelate; carpus very broad, 1.8 × as long as propodus; propodus strongly tapering.

GNATHOPOD 2. Coxa broad, anteriorly rounded, posterodistally angulate; leg achelate; carpus very broad, 1.5 × as long as propodus; propodus weakly tapering.

PEREIOPOD 3. Coxa broad, with anterior border rounded, distally produced into a large blunt tooth, posterior margin very slightly concave; leg robust: propodus 4.8 × as long as wide; dactylus short: 3.6 × as long as broad, 0.4 × as long as propodus, with row of small spines on posterior border.

PEREIOPOD 4. Coxa anteriorly forming a strong regular curve, with ventral corner angulate (forming a distinct acute angle), with posteroventral border strongly concave; leg robust very similar to that of pereiopod 3.

PEREIOPOD 5. Coxa posteriorly produced into a triangular tooth (forming a squared angle), posteroventrally also produced into a triangular tooth (forming a blunt acute, nearly squared angle); basis fairly narrow, posterior border very weakly concave, posterodistal corner broadly rounded, posteromedial carina distally produced into a small rounded lobe; carpus, propodus and dactylus missing.

PEREIOPOD 6. Coxa posteriorly forming a rounded obtuse angle, posteroventrally produced into a triangular tooth (forming a blunt acute angle); basis of medium width; posterior border very weakly concave, posterodistal corner forming a blunt squared angle (not rounded); carpus, propodus and dactylus missing.

PEREIOPOD 7. Coxa posteriorly straight, posteroventrally forming an obtuse (nearly squared) angle; basis extremely broad, with posteroproximal strong rounded process, posterodistally produced into a sharp triangular tooth forming an acute angle projecting forward (that tooth is 0.17 × as long as basis, tooth included).

Colour pattern

White, except for mouthparts, gnathopods (red) and carpus, propodus and dactylus of pereiopods 3–4 (pale pink); eyes pale yellow.

Body length

30 mm.

Distribution

Bransfield Strait, 562–564 m (present data).

Remarks

Alexandrella chione sp. nov. (Bransfield Strait shelf) is similar to Alexandrella australis (eastern Weddell Sea abyss) and Alexandrella sp. 3 (South Sandwich Islands abyss). The most visible difference concerns the ventral lobe of head, which is much stronger and proximally narrower in Alexandrella chione sp. nov. than in other species. In addition to the characters given in the key, it must be mentioned that the lacinia mobilis of the right mandible is more developed and the posterodistal tooth of the basis of pereiopod 7 is longer in Alexandrella chione sp. nov. than in Alexandrella sp. 3 as illustrated by Holman & Watling (1983). Very little information is given on the adult specimens of ‘ Alexandrella australis ’ recorded at 935 m in the Bransfield Strait by Holman & Watling (1983) and Berge & Vader (2005a), but they may be A. chione sp. nov., which is described herein from a specimen collected at similar depths in the same area.