Akanthophoreidae Sieg 1986

Family Akanthophoreidae Sieg, 1986

Diagnosis (modified after Sieg (1986) and Błażewicz-Paszkowycz & Bamber (2011)).

Antennule four-articled with discrete or fused terminal cap-like article (character 13, state 0/1). Mandibular molar-process tapering to thin, denticulate tip (character 26, state 0; character 27, state 3). Maxilla as large as or larger than labium (character 33, state 1), with a wide basis, tapering distally, often with setules. Labium with one pair of lobes but often with visible rudiments of outer lobes (character 24, state 1). Maxilliped palp article 2 with outer seta (character 43, state 1). Cheliped attached via elongated sclerite (character 48, state 1); carpus often with large ventral shield (character 51, state 0/1); chela flared, propodus, fixed finger and dactylus often with dorsal crenulations (character 57, state 0/1). All pereopod meri and carpi with slender bayonet-shaped spiniform setae (characters 61, 67, and 79, state 1). Pereopods 2 and 3 merus and carpus not compact, carpus longer than merus (character 24, state 1), propodus not ventrally convex and with row of small ventral spines (character 13, state 0/1). Pereopods 4–6 coxa absent (character 74, state 0), propodus with fine setules/spinules, dactylus elongate, grooved with finely setules/spinules on two edges, not fused with unguis (character 88, state 0). Uropod biramous, endopod with two elongated articles (character 94, state 2) combined longer than pleotelson, exopod biarticulated (except in Stenotanais) (character 97, state 2) and shorter than endopod article 1 (except in Stenotanais macrodactylus Larsen, 2005) (character 100, state 1). Marsupium formed from four pairs of oostegites (character 73, state 0).

Males. Preparatory male with five antennule articles. Pleopods present. Adult male probably of the swimmingtype (character 101, state 1) although this has never been conclusively demonstrated by molecular studies.

Genera included. Akanthophoreus; Chauliopleona; Mimicarhaphura; Parakanthophoreus gen. nov.; Paraleptognathia; Stenotanais; Tumidochelia.

Type genus. Akanthophoreus Sieg, 1986.

Remarks. The Akanthophoreinae, as a subfamily under Anarthruridae, was erected by Sieg (1986) who also designated Akanthophoreus as the type genus. Sieg (1986) transferred to this genus a number of leptognathiid species, including the type species of Akanthophoreus, A. gracilis (Krøyer, 1842).

The synonymisation of Akanthophoreus with Paraleptognathia by Guerrero-Kommritz (2004) is a controversial issue and is not accepted by Bird (2007) or WoRMS (accessed on 15 Feb 2014). Sticking points include the extensive surface ornamentation on the carpus, propodus, fixed finger and proximal denticulations on the fixed finger found on both P. t y p i c a Kudinova-Pasternak, 1981 (type species of Paraleptognathia) and P. bacescui Kudinova-Pasternak, 1985, and the apparent presence of three ventral setae on the cheliped fixed finger of P. t yp i ca. These characters are not found in the other species synonymized with Paraleptognathia by Guerrero- Kommritz (2004). While the cheliped ornamentation presents few problems (although also found in other unrelated genera), the fixed finger proximal denticulations, attributed much weight by Bird (2007), is not clear and the illustrations by Kudinova-Pasternak (1981) are not up to a modern standard.

While we believe that both Guerrero-Kommritz (2004) and Bird (2007) present convincing arguments for their respective (and contrary) point of views, it is not possible to verify the crucial characters (the fixed finger proximal denticulations and number of ventral setae) as the types of Kudinova-Pasternak are destroyed. We therefore here accept the validity of Paraleptognathia for those species with cheliped setulation (ornamentation) on the carpus, propodus, and fixed finger, at least until fresh material can be examined (of P. t y p i c a and P. bacescui). However, we also accept the validity of Akanthophoreus regarding the species with telson spurs (A. gracilis; A. lispopygmos Błażewicz-Paszkowycz et al., 2013; A. phillipsi (Sieg & Dojiri, 1991); A. undulatus Bird, 2007). The remaining ‘ Akanthophoreus’ species synonymized with Paraleptognathia by Guerrero-Kommritz (2004) or those described hereafter create a problem. It seems prudent here to resolve this by raising a new genus (see below) for the species that lack both the extensive surface ornamentation on the carpus, propodus, and fixed finger, and the proximal fixed finger denticulations (characters thus becoming diagnostic for Paraleptognathia), as well as those without pleotelson spurs (this character then becoming diagnostic for Akanthophoreus).

The restricted phylogenetic analysis performed during this study (Fig. 1) supports the monophyletic nature of the family with a Bremer value of 11. The new family diagnosis given here seems, by tanaidacean standards, very stable and clearly separates Akanthophoreidae from Sieg´s (1986) parent family Anarthruridae (although this was a much more inclusive taxon before or since Sieg’s revision). It is possible that some species currently assigned to the poorly defined family Leptognathiidae Sieg, 1976 in the genus Biarticulata Larsen & Shimomura, 2007 (e.g. B. elegans Kudinova-Pasternak, 1965; B. parelegans Kudinova-Pasternak, 1970; B. greveae Kudinova-Pasternak, 1976; B. parabranchiata Kudinova-Pasternak, 1977 (*); B. mironovi Kudinova-Pasternak, 1981) should be transferred to Akanthophoreidae. However, these species are too incompletely described for key characters to be assigned with confidence. Gejavis is another closely related genus but differs from the new diagnosis by: the small maxilla; the maxilliped palp having outer seta on article 1 but not on article 2; the pereopods 4–6 propodus and dactylus lacking the setule/spinules. The maxilliped palp seta on article 1 illustrated by Błażewicz-Paszkowycz & Bamber (2012: 208, fig.139H, 210) is, however, probably a mistake. This genus must be considered incertae sedis until a more comprehensive phylogenetic analysis can be performed.