Alexandrella Chevreux 1911

Genus Alexandrella Chevreux, 1911

Alexandrella Chevreux, 1911: 1167 (genus described without referring to any species).

Epimeriopsis K.H. Barnard, 1931: 428; type species: Acanthonotozoma australis Chilton, 1912.

Iphimediopsis Schellenberg, 1931: 126, invalid junior homonym of Iphimediopsis Della Valle, 1893; type-species, by original designation and monotypy: Acanthonotozoma australis Chilton, 1912.

Bathypanoploea Schellenberg, 1939: 137 (footnote), replacement name for Iphimediopsis Schellenberg, 1931, non Della Valle, 1893; type species: Bathypanoploea schellenbergi Holman & Watling, 1983, designated by Berge & Vader (2005b).

Parandaniexis Nicholls, 1938: 42; type-species, by original designation and monotypy: Parandaniexis mixtus, an invalid junior homonym of Parandaniexis Schellenberg, 1929.

Pseudandaniexis Nicholls, 1938: corrigendum, replacement name for Parandaniexis Nicholls, 1938, non Schellenberg, 1929.

Pseudiphimediopsis Ruffo, 1949: 18, replacement name for Iphimediopsis Schellenberg, 1931, non Della Valle, 1893.

Astyroides Birstein & Vinogradova, 1960: 152; type species: Astyroides carinatus Birstein & Vinogradova, 1960.

Alexandrella – Chevreux 1912: 213 (Alexandrella dentata designated as type species, by monotypy). — Chevreux 1913: 134. — K.H. Barnard 1932: 153. — J.L. Barnard 1969: 161, 263, 453 –454. — Holman & Watling 1983: 32. — Andres & Lott 1986: 132. — J.L. Barnard & Karaman 1991: 703, 704. — Berge 2003b: 2 (discussion). — Berge & Vader 2005a: 1329 (discussion). — Serejo 2014: 135 (discussion).

Acanthonotozoma – Chilton 1912: 487.

Bathypanoploea – J.L. Barnard 1969: 122. — Holman & Watling 1983: 46–47. — J.L. Barnard & Karaman 1991: 380, 391 –392, 702, 706. — Berge & Vader 2005b: 81–83. — Berge & Vader 2005c: 3–4.

Astyroides – Holman & Watling 1983: 46.

Bathypanoplea – d’Udekem d’Acoz & Robert 2008: 55. — Serejo 2014: 133, 135 (misspelling for Bathypanoploea).

non Acanthonotozoma Boeck, 1876: 237; type species: Acanthonotus cristatus Ross, 1835.

Etymology

The name Alexandrella presumably refers to Alexander Island, where the type species of the genus was collected.

Remarks

We decided to include the description of a new Alexandrella species herein because this genus belong to the same large clade as Epimeria (Verheye et al. 2016b, 2017) and because the new species is large, very characteristic and was already mentioned and illustrated in the cruise report of ANT-XXIX/3 (d’Udekem d’Acoz & Verheye 2013). Moreover, we felt that a quick overview of Alexandrella taxonomy would be a good test for checking whether the underestimated biodiversity found in Epimeria was unique for large Antarctic amphipods or representative of a general situation. This led us to draw a dire conclusion, that the taxonomy of Antarctic Alexandrella is even messier than for Epimeria before our present revision, and a significant number of undescribed species obviously occur in the Southern Ocean. The uniform morphology of Alexandrella species simply contributed to mask its true taxonomic diversity and to promote the convenient but spurious concept of ‘variable widespread species’. The morphological differences between the genera Alexandrella and Bathypanoploea as proposed by Holman & Watling (1983) are ill-defined (Berge & Vader 2005b, 2005c) and genetic data (Verheye et al. 2016b) confirm that Bathypanoploea pulchra (as A. schellenbergi) and Alexandrella cf. mixta (as A. aff. dentata) are very close relatives. The two genera are therefore considered herein as synonyms. Besides the species from the temperate and polar parts of the southern hemisphere treated herein, Alexandrella includes an Atlantic abyssal species: A. setosa Serejo, 2014 (see Serejo 2014) and two abyssal species from the North Pacific: Alexandrella carinata (Birstein & Vinogradova, 1960) and a second, undescribed species examined by the first author. The species described and illustrated as Astyroides carinatus by Birstein & Vinogradova (1960) exhibits almost all the characters of Alexandrella. J.L. Barnard (1969) considered Astyroides as a junior synonym of Alexandrella, and it is only reluctantly that Holman & Watling (1983) accepted Astyroides as valid. In the reprint of Birstein & Vinogradova (1960) available to us, there is a handwritten comment by Vinogradova relegating Astyroides into the synonymy of Alexandrella. This synonymization is formally adopted herein.

Key to the species of Antarctic and sub-Antarctic Alexandrella

This key to Antarctic and sub-Antarctic Alexandrella is tentative and has not the pretention to be a rigorous identification tool. Characters visible without dissection have been used whenever possible.

1. Pereionite 7 with strong posterodorsal tooth ………………………………………………………2

– Pereionite 7 without posterodorsal tooth …………………………………………………………..6

2. Article 1 of peduncle of antenna 1 with short dorsomedial tooth; dactylus of pereiopods 3–4 long; posteroventral border of coxa 4 straight or nearly so ……………………………………………3

– Article 1 of peduncle of antenna 1 with long dorsomedial tooth; dactylus of pereiopods 3–4 short; posteroventral border of coxa 4 strongly concave ……………………………………………5

3. First posterodorsal tooth on pereionite 7 …………………………………………………………4

– First posterodorsal tooth on pereionite 6 ………………….. Alexandrella sp. 1 [High Antarctic]

– First posterodorsal tooth on pereionite 5 or more anterior pereionite(s)………………………… …………………………………………………………………… Alexandrella sp. 2 [Shag Rocks]

4. Telson cleft on 0.37 ………………………………………………………………………………… Alexandrella schellenbergi (Holman & Watling, 1983) [north-east of Falkland Islands, 2675 m]

– Telson cleft on 0.2 or less ………………… Alexandrella pulchra Ren in Ren & Huang, 1991 [South Shetland Islands, tip of Antarctic Peninsula, eastern Weddell Sea, at about 300–700 m]

5. Anteroventral lobe of head moderately developed, triangular or bluntly triangular; dorsal carina of pleonite 3 with straight profile; posterodistal corner of basis of pereiopod 6 broadly rounded ……6

– Anteroventral lobe of head very strong, hemi-elliptic; dorsal carina of pleonite 3 with distinctly sigmoid profile; posterodistal corner of basis of pereiopod 6 forming a blunt squared angle [pereionite 6 without posterodorsal tooth; posterior tooth of carina of first urosomite 0.23 × as long as whole carina and forming a fairly deep notch with carina] ……… Alexandrella chione sp. nov.

6. Pereionite 6 with small posterodorsal tooth; crest of urosomite 1 with long posterior tooth and deep posterior notch ……………………………………… Alexandrella australis (Chilton, 1912)

– Pereionite 6 without posterodorsal tooth; crest of urosomite 1 with small posterior tooth and no posterior notch …………………………………………………………………… Alexandrella sp. 3

7. Telson truncate, notched or cleft but not convex ………………………………………………8

– Telson convex and entire [carina of urosomite 1 compact, not elongate] ……………….…………… ……………………………………………………. Alexandrella polarsterni (Berge & Vader, 2005)

8. Pleonites 1–3 strongly toothed; gnathopod 1 with oostegite [deepsea species recorded below 2500 m] ………………………………………………………………………………………… 9

– Pleonites 1–3 weakly toothed (or not toothed); gnathopod 1 without oostegite [shelf species] …10

9. Right mandible with lacinia mobilis reduced to simple tooth…………………………………… …………………………………………………… Alexandrella mandibulata Berge & Vader, 2005

– Right mandible with lacinia mobilis smaller than left, but broad, with two teeth, of which one is bicuspid ……………………………………………… Alexandrella martae Berge & Vader, 2005

10. Gnathopods 1–2 simple; body dorsally weakly or not carinate …………………………………11

– Gnathopods 1–2 subchelate, body dorsally strongly carinate [telson scarcely emarginate]……… ……………………………………… Alexandrella subchelata Holman & Watling, 1983 s. lat.

11. Telson emarginate; mandibular incisors not toothed along entire margin; antennae subequal [Antarctic species] …………………………………………………………………………………12

– Telson truncate with tiny median notch; mandibular incisors toothed along the entire margin; antenna 1 shorter than antenna 2 …………………………………………………………………… ………………… Alexandrella inermis Bellan-Santini & Ledoyer, 1987 [Prince Edward Island]

12. Pereionites 1–7 with a pair of lateral triangular teeth ……………………………………………… ……………………………………… Alexandrella dentata Chevreux, 1912 [Bellingshausen Sea]

– pereionites 1–7 smooth ……………………………………………………………………………… ………………… Alexandrella mixta Nichols, 1938 s. lat. [circum-Antarctic complex of species]