Agathidium sexstriatum, Horn, 1880

WHEELER, QUENTIN D. & MILLER, KELLY B., 2005, Slime-Mold Beetles Of The Genus Agathidium Panzer In North And Central America, Part I. Coleoptera: Leiodidae, Bulletin of the American Museum of Natural History 2005 (290), pp. 1-95 : 39-41

AGATHIDIUM SEXSTRIATUM SPECIES GROUP

DIAGNOSIS: The A. sexstriatum species group is distinguished by the following combination of characters: head narrowed behind eye, without prolonged postocular temporum (fig. 44); body not strongly convex dorsally and not contractile (figs. 49); elytron with 2– 8 serial series of punctures; aedeagus with ventral operculum divided into two plates; male tarsal formula 5–5–4, female 4–4–4; pronotum with evident posterolateral angles (fig. 52); clypeus large, separated from frons by impressed frontoclypeal suture, protruding anteriorly, from one­third to one­half of clypeus anterad of lateral margins of frons (fig. 52).

DISCUSSION: The A. sexstriatum species group includes three similar species first described by Horn (1880). Hlisnikovský (1964) proposed the subgenus Rhabdoelytrum for these species. As discussed above, it is conceivable that these species are related to Stetholiodes or other genera ( Angelini and de Marzo, 1987b; Angelini and Peck, 2000). They are conservatively maintained in Agathidium until analyses are completed. Species of the group are distributed in the western United States.

This group includes species that exhibit no observed unequivocal synapomorphies, although the rather short and broad form of the median lobe of the aedeagus, serial series of punctures, and prominently protruding clypeus make these species separable from other Agathidium included in this study. The latter character refers to forms in which the clypeus protrudes clearly beyond the anterior an­ gles of the frons located dorsad of the antennal insertions and each side of the clypeus. It is particularly useful in distinguishing the A. sexstriatum group species from most similarly small­sized Agathidium with short postocular tempora. Due to a large number of symplesiomorphic similarities, these species share a general habitus and many specific characters with the related genus Anisotoma (cf. fig. 41, see also Wheeler, 1979b) and oth­ er genera. However, the abrupt 3­segmented antennal club and distinct supraocular cari­ nae distinguish these Agathidium from all Anisotoma species and other genera.

Circumscription of these species is based on external characters, including color and punctation patterns, and male aedeagal shape. Although external characters are used extensively in the key, these features are somewhat less reliable than male aedeagal shape and, when possible, male specimens should be dissected and aedeagal shape compared with the illustrations for the most reliable identifications.

KEY TO A. SEXSTRIATUM SPECIES