Akanthophoreus Sieg 1986

Genus Akanthophoreus Sieg, 1986a

(Restricted synonymy and bibliography)

Akanthophoreus Sieg, 1986a: 21 –24. Guerrero-Kommritz, 2004: 8 –10. Larsen & Wilson, 2002: 2, 14.

Leptognathia G.O. Sars, 1882 (partim): Hansen, 1913 [for A. gracilis, A. inermis, A. longiremis and A. multiserratus

listed below].

Paraleptognathia Kudinova-Pasternak, 1981 (partim): Guerrero-Kommritz, 2004 [for species listed below]. Sieg,

1986a: 40–44 [synonymy of P. antarctica with A. antarctica (Vanhöffen, 1914) listed below]. Scoloura Sieg & Dojiri, 1991: 1495–1501. Dojiri & Sieg, 1997: 228–231. Larsen & Wilson, 2002: 2, 14. Type species: Tanais gracilis Krøyer, 1842, by designation (Sieg 1986a).

Species included (Japanese and Kurile-Kamchatka species in bold): A. antarctica (Vanhöffen, 1914), East Antarctica; A. australis (Beddard, 1886) Antarctica, sub-Antarctica, Kerguelen Islands; A. crassicauda n.sp. ; A. gracilis (Krøyer, 1842) [?]; A. imputatus n.sp ; A. inermis (Hansen, 1913), Arctic Ocean; A. longiremis (Lilljeborg, 1864) [?], NE Atlantic; A. multiserratus (Hansen, 1913) Iceland, Faeroe Islands; A. undulatus n.sp ; A. weddellensis Sieg, 1986 a, Antarctica, sub-Antarctica. Other species that probably belong in this genus but were transferred directly from Leptognathia to Paraleptognathia, or have Paraleptognathia as their primary generic name (Guerrero-Kommritz 2004; Dojiri & Sieg 1997) are excluded here until a formal review/decision is presented.

Diagnosis (modified after Sieg 1986a). Female. Antennule four-articled. Antenna six-articled, article 4 often with a suture line (pseudo-articulation). Molar process thick, with several terminal spines. Maxillule endite with nine terminal spiniform setae. Epignath ends with a long, thick seta. Maxilliped basis with long seta near articulation with palp; palp article 2 with two inner plumose setae and a long plain seta, and outer spiniform seta; article 3 with two inner plumose setae. Pereopods 1–3 with, pereopod 4–6 without, coxa. Merus of pereopod 1 with one spiniform seta, carpus with two. Carpus of pereopod 3 with three spiniform setae. Dactylus of pereopods 4–6 long and grooved, with double row of small spines; carpus of pereopods 4– 6 with three spiniform setae and smaller seta. Pleopod biramous, exopod inner row with strong proximal setae. Uropod biramous, endopod and exopod two-articled. Marsupium of four pairs of oostegites.

Preparatory male. Generally as above but antennule thicker, four or five-articled. Pleon and pleopods proportionately larger.

Natatory male (when present). Habitus quite distinct from female, with enlarged pleon and shorter pereon (pereonites much broader than long). Antennule seven-articled, with numerous aesthetascs. Mouthparts reduced, with remnants of maxilliped, maxillule palp, maxilla and epignath.

Remarks. Considerable confusion and generic transfers have accompanied this genus, the establishment of which was originally a much-needed initiative by Sieg (1986a) in separating the taxon from the ‘dustbin’ that Leptognathia had become. This had been exacerbated by Lang (1968) with the synonymising of several genera with Leptognathia. Three separate issues have conspired to create a near-intractable taxonomic and nomenclatural status, overlaying the already complex morphological character-state distributions. First, it was unfortunate that Sieg selected Leptognathia gracilis (Krøyer, 1842) as the type species for Akanthophoreus, since this is itself an apparently complex taxon, the original description was poor (but of its time), and the type specimen is damaged, incomplete and barely recognizable.

Secondly, it is clear that Krøyer’s original species (type locality ‘Spitsbergen’), is identical to Leptognathia longiremis sensu Sars (1896), itself synonymous with Leptognathia sarsi Hansen, 1909. This is a large and robust species characterized primarily by lateral pleotelson spurs as well as crenulated margins on the cheliped propodus and dactylus. Because Sieg’s view of Akanthophoreus gracilis (e.g. Sieg 1986a) did not match the longiremis sensu Sars / sarsi taxon, a new genus, Scoloura Sieg & Dojiri, 1991, was established for a Californian species with pleotelson spurs. Rather than mention the obvious similarity with Leptognathia longiremis sensu Sars / sarsi, comparisons were made with Mimicaraphura Sieg, 1986a and Paraleptognathia Kudinova-Pasternak, 1981. It is possible that Sieg was also influenced by the perceived discrepancy in the number of maxillule endite spines – up to eleven in the known species of Akanthophoreus but only nine in Scoloura.

Thirdly, scarce mention was made of the genus Scoloura by Guerrero-Kommritz (2004) in his revision of Paraleptognathia, with which Akanthophoreus was synonymized – only to remark that the resemblance was “very intriguing”. This revision, and probably for the same motive that Sieg had earlier (and without published reasons) switched generic names from Akanthophoreus to Paraleptognathia, was based on the five-articled antennule expressed in preparatory (sub-adult) males in some species of Akanthophoreus that appeared to be directly homologous with that of the species Paraleptognathia typica Kudinova-Pasternak, 1981. That (i), this character also appears in other genera, including the very close sibling taxon Chauliopleona, (ii) not all species of Akanthophoreus have five-articled antennules in preparatory males and (iii) Paraleptognathia was inadequately described by Kudinova-Pasternak and appears to have highly modified chelipeds, with dentition on the proximal part of the fixed finger, a highly expanded carpal shield and with extensive surface ornamentation/armament, makes this synonymy untenable.

It is also becoming apparent that the genus Akanthophoreus itself may be masking several genus-level species groups and the overlap of characters within these and the closely related genera Chauliopleona and Paraleptognathia sensu Guerrero-Kommritz needs further investigation. However, while it is not the intention to fully revise either Akanthophoreus or Paraleptognathia here, it is unavoidable that synonymies are briefly mentioned; a new look at the A. gracilis-A. longiremis complex from Icelandic/Faroese/west European waters is also in preparation (Bird ined.)