NEMATOCARCINOIDEA IS NOT A

Baeza, J. Antonio, Bauer, Raymond T., Okuno, Junji & Thiel, Martin, 2014, Molecular phylogeny of hinge-beak shrimps (Decapoda: Caridea: Rhynchocinetes and Cinetorhynchus) and allies: a formal test of familiar and generic monophyly using a multilocus phylogeny, Zoological Journal of the Linnean Society 172 (2), pp. 426-450 : 443-444

THE SUPERFAMILY NEMATOCARCINOIDEA IS NOT A

NATURAL ENTITY

In the species-rich and diverse infraorder Caridea , the systematic relationships amongst genera, families, and superfamilies are unsettled ( Chace, 1992, 1997; Martin & Davis, 2001; Bracken et al., 2009; De Grave et al., 2009; De Grave & Fransen, 2011; Li et al., 2011; Baeza, 2013; see also Table 1). In particular, the superfamily Nematocarcinoidea has historically been considered a monophyletic clade including a total of four families (i.e. the marine Eugonatonotidae , Nematocarcinidae , Rhynchocinetidae , and the freshwater Xiphocarididae ) and nine genera ( Chace, 1992; Holthuis, 1993; Martin & Davis, 2001; De Grave et al., 2009; De Grave & Fransen, 2011). Traits that define the Nematocarcinoidea include, amongst others, (1) the mandible with a subtruncate molar process that also has a transversely ridged grinding surface; (2) the first maxilla with the distal endite not usually large; (3) the second maxilla with the distal endite mesially bilobate bearing a palp that is not vestigial; (4) the first maxilliped with an endite not unusually large bearing an exopod with a lash and distinct caridean lobe; (5) the slender, pereopod-like third maxilliped, neither broad nor operculate, that bears an exopod; (6) the first pereopod stouter than the second pereopod; (7) chelate first and second pereopods; (8) the second pereopod with an entire carpus; and (9) pereopods one to three with strap-like epipods ( Chace, 1992).

Specimens from three families and five currently recognized genera were included in the present study. Based on cladistic analysis of morphological characters, Christoffersen (1990) concluded that the Nematocarcinoidea was polyphyletic and resurrected various superfamilies to contain the different families and genera within the group. One of these superfamilies, the Eugonatonotoidea , included the monotypic family Eugonatonotoidae and the genus Eugonatonotus . The Nematocarcinoidea was redefined to include two genera in the family Nematocarcinidae : Nematocarcinus and Lipkius (see Christoffersen, 1990). The genus Lipkius , originally placed in the family Rhynchocinetidae by Yaldwyn (1960), was transferred to this family Nematocarcinidae by Christoffersen (1990). Lastly, the family Rhynchocinetidae was grouped with the family Palaemonidae into the superfamily Palaemonoidea . Christoffersen’s proposal was rejected by most taxonomists during recent decades, including the most recent taxonomic arrangements of the Palaemonoidea used by De Grave et al. (2009) and De Grave & Fransen (2011).

The results from this study partially support Christoffersen’s (1990) phylogenetic hypothesis based on morphological traits. In disagreement with Chace (1992), Holthuis (1993), De Grave et al. (2009), and De Grave & Fransen (2011), the one-phase SATé-II and two-phase phylogenetic analyses using two nuclear genes showed that the specimens from the families Eugonatonotidae , Nematocarcinidae , and Rhynchocinetidae did not cluster together and did not form a single, well-supported monophyletic clade. Furthermore, the Bayes factor analyses (conducted in MrBayes and using the two-phase Bayesian inference phylogenetic analysis as a framework) revealed no support for the monophyly of the superfamily Nematocarcinoidea . These Bayes factor analyses are considered robust herein given that all molecular phylogenetic trees obtained with the one-phase SATé-II method and the two-phase approaches that used different inference methods (ML and BI) resulted in the same general topology. Altogether, the above information implies that the Nematocarcinoidea [sensu Holthuis, (1993), Chace (1992), and Martin & Davis (2001)] is polyphyletic as suggested by Christoffersen (1990).

Also in agreement with Christoffersen’s (1990) ideas, the specimen of Eugonatonotus did not form a wellsupported monophyletic clade with members of the Nematocarcinidae and Rhynchocinetidae in any of the reconstructions. Thus, shrimps from the genus Eugonatonotus represent a natural entity deserving elevation to the superfamily and family level, namely the Eugonatonotoidea and Eugonatonotidae , respectively, as suggested by Christoffersen (1990) (see proposed taxonomic rearrangement below). Importantly, the topologies of the different one- and two-phase phylogenetic trees further suggest that the genera Lipkius and Nematocarcinus do pertain to the Nematocarcinidae sensu Christoffersen (1990) , in disagreement with the currently accepted taxonomic arrangement in the Caridea ( Holthuis, 1993; Chace, 1997; Burukovsky, 2005; De Grave et al., 2009; De Grave & Fransen, 2011). The two specimens of Lipkius and the three species of Nematocarcinus segregated according to genus and formed a monophyletic clade. Nonetheless, their monophyletic status and sister relationship was poorly supported by ML and BI analyses. Certainly, future studies including additional representatives from the different families above and molecular markers will help to decipher the systematics of nematocarcinid shrimps.

Overall, the present phylogenetic findings are in line with those of Bracken et al. (2009), Li et al. (2011), and Baeza (2013), who questioned the validity of the superfamily arrangement within the Caridea and monophyly of several families. The results from this study and those of Bracken et al. (2009) and Li et al. (2011) point to the notion that the Nematocarcinoidea is not a natural clade within the Caridea .