Axiidea de Saint Laurent, 1979

Poore, Gary C. B., Dworschak, Peter C., Robles, Rafael, Mantelatto, Fernando L. & Felder, Darryl L., 2019, A new classification of Callianassidae and related families (Crustacea: Decapoda: Axiidea) derived from a molecular phylogeny with morphological support, Memoirs of Museum Victoria (Mem. Mus. Vic.) 78, pp. 73-146 : 76-77

Infraorder Axiidea de Saint Laurent, 1979

Axiidea de Saint Laurent, 1979b: 19 , 28.— Robles et al., 2009: 310–314.— Dworschak et al., 2012: 187.

Callianassoidea .— Sakai, 2005a: 1125.

Callianassidea .— Sakai and Sawada, 2006: 1357–1358.

Callianassida.— Sakai, 2011: 3.

Remarks. The Axiidea have been diagnosed simply as decapods having pereopods 1 and 2 chelate. The name Axiidea , rather than others suggested by Sakai (2005a, 2011) and Sakai and Sawada (2006), has become almost universally adopted ( Poore et al., 2014).

Poore’s (1994) Callianassoidea included Laomediidae Borradaile, 1903 ; Upogebiidae Borradaile, 1903 ; Callianideidae Kossmann, 1880 ; Thomassiniidae de Saint Laurent, 1979a ; Ctenochelidae Manning and Felder, 1991 ; and Callianassidae Dana, 1852 . This concept was first doubted by a reappraisal of morphology ( Sakai, 2005a; Sakai and Sawada, 2006) and later by molecular data ( Robles et al., 2009; Tsang et al., 2008). Sakai (2005a) included in Callianassoidea , families Callianassidae ; Axiidae Huxley, 1879 ; Callianideidae ; Ctenochelidae and Gourretiidae Sakai, 1999 , in fact, all Axiidea . But in a later synthesis, Sakai (2005b) omitted Axiidae and Callianideidae from Callianassoidea . Sakai and Sawada (2006) expanded Callianassoidea to five families. Sakai (2011) included ten families in Callianassoidea , four with two subfamilies each, and included nine families in Axioidea. This dichotomy does not reflect the two clades discovered by investigation of molecular relationships ( Robles et al., 2009), where Axiidae are sister to a clade with all other families. This history was summarised by Robles et al. (2009) and Dworschak et al. (2012). The relationships in the phylograms of both Tsang et al. (2008) and Robles et al. (2009) led to our expanded study (Robles et al., in press).

We do not recognise Callianassoidea at the formal superfamily level within Axiidea because, firstly, it has such a convoluted history (outlined above), secondly, doing so leaves other axiidean families hanging, and thirdly, it is impossible to diagnose unambiguously with a unique synapomorphy. Axiidae have been shown to belong to one of two axiidean clades ( Robles et al., 2009; Tsang et al., 2008), while the “callianassoid” subclade plus Strahlaxiidae , Micheleidae and Callianideidae belong to the other in a paraphyletic relationship ( Robles et al., 2009; Tsang et al., 2008). All callianassoids have a lobster-like form with a flaccid pleon longer than the carapace (but so do most callianideids); all lack a long seta on the triangular posterior lobe of the scaphognathite (but so do some Strahlaxiidae ); all have a complete linea thalassinica, a hinge separating the dorsal regions of the carapace from the branchiostegite (but this is partially evident in some Callianideidae ); all except one species have flat contiguous eyestalks (but so do callianideids). Pleopods 3–5 of callianassoids have triangular or subtriangular endopods with straight mesial margins that are closely connected to their pairs by short or moderately long appendices internae and exopods that are usually longer than and enclosing the endopods. This condition is less pronounced in some ctenochelids and callianopsids, which approach axiids, strahlaxiids and micheleids in having the endopods of pleopods 3–5 linear or oval, weakly connected to their pairs by long appendices internae, and the exopods shorter than or as long as the endopods, but not enclosing the endopods. Species of Callianidea have pleopods 3–5 as in most callianassoids. The uropodal exopod of most callianassoids has an elevated dorsal plate, a region at the end of the anterior margin defined by a transverse row of setae but, again, it is not true of all because a dorsal plate is absent in Callianopsidae , Ctenochelidae and Paracalliax .

The number of well-defined clades with consistent molecular support prompted us to recognise seven “callianassoid” families. All had been previously recognised at least as subfamilies. Four other families of Axiidea are Axiidae , Callianideidae , Micheleidae and Strahlaxiidae . The following family diagnoses use 21 characters adequate to distinguish all 11 families. The bold italic parts in diagnoses are character states, generated with the aid of Intkey ( Dallwitz, 2010), that distinguish each family from every other family in at least one respect.