Hydraena Micromadraena

Hydraena (Micromadraena), new subgenus

Type Species: Hydraena (Micromadraena) parvipalpis new species

This unusual group comprises six species: H. parvipalpis, H. fortipes, H. genuvela, H. serripennis, H. rubridentata, and H. breviceps.

All of the specimens in this group have been collected from "sifted litter (leaf mold, rotten wood)", are nonaquatic, and have a distinctive habitus related to the microhabitat. The maxillary palpi and legs are short, and can consequently be hidden beneath the laterally widened head and the very wide elytral explanate margin. The labrum is small, directed ventrad, and hidden in dorsal view. Despite these modifications, the derived characters of Hydraena are still present (see Perkins 1989, 1997): 1) the labrum, although reduced in size, still forms an interlocking device with the mandibles; 2) the procoxal cavities are closed behind by the widened apex of the intercoxal process; 3) the mentum is produced in the midline; 4) the hypomeron has the characteristic Hydraena morphology; 5) females have a pair of sensory clusters on the gonocoxite; and 6) the spermatheca does not have unusual morphology (Figs. 231, 232).

The unusual reduced appendage morphology is matched by the unusual aedeagal morphology: the aedeagus has very short parameres, which originate from the base; each paramere has two short setae. Very short parameres with reduced number of setae and having the origination basally appear in a few other groups (Fig. 345): Hydraena monikae group (Perkins 2014; four species in South Africa), and some Parhydraenini including Parhydraenopsis species in northeast Africa, and Protozantaena species in Madagascar and southern Africa (Perkins 2009). The shape of the basal orifice in Parhydraenini is characteristic and differs distinctively from the shape in Micromadraena, which is more like that present in other Hydraena. The similarity in the short parameres is discussed in the Hydraena subgenera section. In short, it is possible that Micromadraena is more closely related to the Hydraena monikae group than to the other Madagascar Hydraena. The aedeagi in both of these groups are similar in having a main piece that is tubular in cross section, a distal piece that is a rather simple, a rigid flagellum, a similarly shaped basal orifice, and the very short parameres. In habitus the two groups are quite dissimilar.

Both sexes of H. (Micromadraena) have very wide explanate elytral margins, males having the edges more strongly serrate than those of females. The femoral-tibial articulations are shielded by the wide explanate margin.

The morphology of concealed appendages and thick cuticle of species in this group could possibly be termed an anti-ant defense system; the collector of most of these hydraenids, Brian L. Fisher, was targeting litter dwelling ants. There are other groups of terrestrial Hydraena that have shortened appendages, for example undescribed species in New Caledonia (Perkins, in prep.), but these species have a very different aedeagus, indicating relationship with H. (Hydraenopsis). Unfortunately, no specimens collected in absolute alcohol were available; DNA sequence data must await more collections.

Etymology. Named in reference to the short appendages, the short parameres, the geographical distribution (Madagascar), and relationship to Hydraena.