Pterostillichus caecus Straneo, 1949

Allegro, Gianni & Giachino, Pier Mauro, 2020, Abacaecus n. gen. walterrossii n. sp., a notable hypogean carabid species from Sierra Leone, Western Africa (Coleoptera, Carabidae, Pterostichinae), Zootaxa 4766 (3), pp. 435-446 : 443-445

Pterostillichus caecus Straneo, 1949

( Figs. 5 , 6 )

Additional description. In the original description given by Straneo (1949) some characters were ignored or, in our opinion, erroneously interpreted. Moreover, only a schematic drawing of habitus was provided by this author and therefore many important features were insufficiently illustrated, such as male genitalia. For this reason we consider as important to provide an integrative description of a few characters and their illustrations.

Second antennomere almost centrically inserted on first (fig. 6a).

Prosternal intercoxal process widely rounded (fig. 6e).

Mentum glabrous, distincly broader than long, medial tooth with bifid apex; paramedial mental setae present; paramedial pits distinct, large (fig. 6b).

Elytra with obsolete striae; lacking of a parascutellar pore at base (fig. 6c). Epipleura almost indistincly ‘crossed’ before apex.

Tarsomeres dorsally glabrous and delicately rugulose, without medial carina (fig. 6d).

Aedeagus with median lobe distally subrectilinear in lateral view (fig. 5b); median lobe in dorsal view with a triangular apical lamella, moderately bent to right and blunt at apex (fig. 5c). Ostium long, in dorsal position, not reaching basal bulb.

Remarks. The taxonomic position of P. caecus is unclear and its tribal affiliation remains problematic. It seems to belong to a phyletic lineage long separated from that of A. walterrossii n. sp. With the exception of some common characters that can be interpreted as adaptation to hypogean life and as a result of convergent evolution (microphthalmy, reduced pigmentation, markedly protruding fore angles of pronotum, presence of a single supraorbital seta, lack of seta at hind angles of pronotum), which are recurrent also in Pterostichini adapted to the subterranean environment, there are very few other characters shared between these two species.

Straneo (1949) attributed P. caecus to Pterostichini sensu stricto (sensu Jeannel, 1942b) which are, as far as we know, absent in Africa ( Jeannel, 1948). More probably it belongs, in our opinion, to a separated phyletic lineage within Pterostichinae , maybe related to Abacetini . The strongly transverse mentum, the angular base of stria 1 (‘‘scutellar stria’’ auct.) absent, and the morphology of aedeagus (incl. dorsal position of ostium) support the hypothesis of a relation with Abacetini ; on the contrary, the second antennomere not eccentrically inserted (although some genera of Abacetini sensu lato possess the second antennomere more or less centrally inserted) and the lack of a parascutellar pore at base of elytra (even if this character is common to other pterostichine-grade taxa) contrast this hypothesis. Probably only molecular analysis will help to shed light on its taxonomic position and phylogenetic relationships.

Figures

FIGURE 5. Optical microscope images of Pterostillichus caecus Straneo: a) habitus of holotype (scale bar = 1 mm), b) aedeagus in left lateral view, c) aedeagus in dorsal view, d) labels of holotype.

FIGURE 6. SEM images of body parts of Pterostillichus caecus Straneo: a) head in right lateral view, b) mentum, c) base of pronotum and elytra, d) metatarsum, e) prosternal intercoxal process.