Macrelmis moesta ( Horn, 1870 )

Barr, Cheryl B., 2021, Revision of Macrelmis Motschulsky, 1860 in the Southwestern United States and Northern Mexico with Description of Four New Species (Coleoptera: Elmidae: Elminae), The Coleopterists Bulletin 75 (1), pp. 93-120 : 111-112

Macrelmis moesta ( Horn, 1870)

( Figs. 1, 15–16)

Macrelmis moesta was described as Elsianus moestus by Horn (1870) from a unique female specimen (H. P. Brown, unpublished data) from the San Pedro River, Cochise County, Arizona. The male genitalia of the species are described and illustrated ( Figs. 16a–b) herein for the first time. For the past 150 years M. moesta has been the only species recorded for Arizona, and the more widespread, formerly undescribed species M. shepardi has been confused with it (H. P. Brown, unpublished data). Arizona records from Gila and Yavapai counties attributed to M. moesta by Brown (1971) are actually of M. shepardi . Macrelmis moesta is known only from a few localities in far southeastern Arizona

16) Male genitalia, a) Dorsal view, b) Lateral view.

(Gila/Graham counties, San Carlos River; Greenlee County, Blue River and tributary Pigeon Creek; Pinal County, Aravaipa Canyon; Pima County, Sabino Canyon; Cochise County, Cave Creek), but it likely also occurs in the adjacent state of Sonora, Mexico. Macrelmis moesta has not been found to occur in the same streams as M. shepardi , but one specimen has been examined from the type locality of M. harleyi in Cochise County ( Fig. 5).

Diagnosis. Macrelmis moesta ( Figs. 15a–b) is rather small, 3.4–4.16 mm long and 1.4–1.6 mm wide. It externally resembles and is close in size to M. shoemakei ( Figs. 17a–b), but M. moesta is more densely granulate and the male genitalia are very different: in M. moesta ( Figs. 16a–b) the penis is a little bit longer than the parameres and abruptly narrowed at the apical 1/3; in M. shoemakei ( Figs. 18a–b) the penis is much longer than the parameres and narrowly spatulate. Macrelmis mexicana ( Figs. 12a–b) is also of similar size, but the pronotal sublateral carinae are obscure or lacking (prominent in M. moesta ), and in the males, the penis ( Figs. 13a–b) is nearly parallel-sided and not abruptly narrowed towards the apex. Macrelmis harleyi ( Figs. 3a–b) and M. shepardi ( Figs. 6a–c), which like M. moesta also occur in Arizona, are both much larger, over 4.2 mm long and 1.8 mm wide, and the males have different genitalia ( Figs. 4a–b, 7a–b). The male genitalia of M. moesta ( Figs. 16a–b) somewhat resemble those of M. texangusta ( Figs. 10a–b), but the parameres are narrower and the penis is wider at the tip.

Description. Male genitalia: Elongate, about 3× as long as wide; well sclerotized. Phallobase much longer than parameres; parameres a little shorter than penis ( Figs. 16a–b). In dorsal view ( Fig. 16a), parameres with lateral margins nearly parallel at basal 2/3, inner margins sinuate, apices rounded and weakly curved inward; penis wide at basal 2/3, abruptly narrowed at apical 1/3 with lateral margins nearly parallel, apex rounded to broadly rounded; penis at base much wider than paramere base, at apical 1/3 wider than paramere apical 1/3. In lateral view ( Fig. 16b), phallobase ventral margin strongly arcuate; paramere with ventral margin moderately arcuate, variably narrowed at apical 1/4, apex bluntly rounded; penis with apex narrowly rounded and slightly curved ventrally.