Rhipidocyrtus Falin & Engel

Falin, Zachary H. & Engel, Michael S., 2014, Serendipity at the Smithsonian: The 107 - year journey of Rhipidocyrtus muiri Falin & Engel, new genus and species (Ripidiinae, Ripidiini), from jungle beast to valid taxon, ZooKeys 424, pp. 101-116 : 103-104

Taxon classification Animalia Coleoptera Ripiphoridae

Rhipidocyrtus Falin & Engel gen. n.

Type species.

Rhipidocyrtus muiri Falin & Engel, sp. n.

Diagnosis.

Closely agreeing with the generalized form of Ripidiini though larger and appearing more hump-backed than typical. Rhipidocyrtus possesses the following combination of historically diagnostic characters: unfused, two-segmented maxillary palpi; postocular ommatidia present (Fig. 4); 11 antennomeres, antennomere I simple (Figs 2, 3), antennomere II toroidal, antennomere III more robust, produced medially (Fig. 2), antennomeres IV–XI strongly uniflabellate (Figs 2, 9); mesoscutellum present but weakly developed (Fig. 2), posterior margin very weakly bisinuate with a small medial point (Fig. 5); tarsal formula 5-5-4 (Figs 10-12). Rhipidocyrtus differs from all known ripidiines in the form of the metanotum (Figs 5, 6), possessing what appears to be a reduced "metascutellar box" visible at the anterior margin of the metanotum to either side of the midline. This structure is typically either robust (most New World taxa) or absent (most Old World taxa). Likewise, Rhipidocyrtus appears unique in that the metascutellum narrows evenly to an anterior point, terminating at the anterior margin of the metanotum as a single medial sulcus (Fig. 5) (but see the following comparative comments).

Etymology.

The new genus-group name is one of several spelling variants first composed and applied to the holotype specimen and slide labels by H.S. Barber. It is a combination of the Greek words rhipido, meaning, “fanlike”, and cyrtus, meaning, “curved”. Our interpretation is that it is meant to describe the unusually convex or “hump-backed” appearance of the type species. The name is masculine.

Comments.

Rhipidocyrtus is superficially distinctive within the Ripidiini for its particularly hump-backed facies, its relative size (it is the largest ripidiine known), and possessing a pronotum that is strongly dorso-ventrally compressed laterally, resulting in an unusually abrupt lateral margin. However, despite this novel first impression it is in most regards morphologically unremarkable. It shares with most other Old World taxa a well-developed and medially-produced antennomere III as well as the presence of a mesoscutellum (albeit weakly produced), suggesting a strong relationship with that putative lineage [see Batelka et al. (2011) and Falin and Engel (in press) for discussions of supra-generic character patterns within the Ripidiini ].

That said, Rhipidocyrtus exhibits what is here tentatively described as a rudimentary "metascutellar box" sensu Falin and Engel (in press). Apart from the Old World genus described in that paper, this structure is exclusive to New World ripidiines; finding an otherwise typical Old World taxon with a rudimentary “box” may prove phylogenetically significant. However, the homologous nature of this “box” remains poorly understood and, in the case of Rhipidocyrtus , this structure may simply be an artefact of the relatively more developed flight musculature necessary for such a large individual.

While likely less phylogenetically significant than the "metascutellar box", the form of the metascutellum is considerably more obvious and also serves to differentiate this taxon from its close relatives. Typically, the metascutellum narrows anteriorly, its margins becoming more or less parallel as they terminate at either the anterior margin of the metanotum or at the metascutellar box, depending on the lineage. In the case of Rhipidocyrtus , the lateral margins converge to form a single median sulcus well before the anterior metanotal margin. A similar arrangement is illustrated for the fossil genus Paurorhipidius Kaupp and Nagel, though the authors state the metanotal structures are obscured in the type specimens (Kaupp et al. 2001) and the exact configuration is indeed uncertain. Likewise, species of the genus Blattivorus Chobaut tend to have anteriorly-narrowed, parallel-sided metascutella, in some cases terminating just before the anterior metanotal margin. However, Blattivorus appears to be a well-defined monophyletic lineage not closely related to Rhipidocyrtus ; it is unlikely the superficially similar forms of the metascutellur apex are truly homologous.