Key to Myrmelachista males of Costa Rica

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This key is based on: Longino, J.T. 2006. A taxonomic review of the genus Myrmelachista in Costa Rica. Zootaxa. 1141:1-54.

Longino stated the following about Male characters:

Males vary somewhat in the relative size of the ocelli, but the primary differences are in the genitalia. Terminology follows Snodgrass (1941). The pygostyles are small setose papillae projecting from beneath the posterior margin of the 8th abdominal tergite. These may be present and easily visible or variously reduced to near invisibility or absence. The basiparamere is always present and large. It usually has a pronounced dorsal lobe that is similar to but shorter than the paramere. It varies from broadly triangular and blunt to long, thin, and needle-like. In the smallest males the lobe may be very short or absent. The paramere is articulated to the basiparamere and is always present and elongate, sometimes broad at the base and tapering to a blunt point, or broad and parallel at the base and then tapering to a blunt point (looking like a seal head in profile), or long and thin with somewhat parallel sides, tapering to a point at the end. Internal to the paramere is the volsella, comprising two parts, the cuspis and the digitus. The cuspis is external to the digitus and closely applied to the inner wall of the paramere. The relationship of cuspis to digitus is somewhat like human thumb to clasped fingers. The cuspis is always shorter than the digitus and may be widely separated from it or with the apex converging on the dorsal margin of the digitus. The cuspis may be large, heavily sclerotized, and paddle shaped. From this state it shows reduction to a thin rectangular strip, to a small pointed needle-like structure, to a tiny triangular remnant fused to the inner margin of the paramere, and finally to completely absent. The digitus varies a great deal in shape, from a short, sharply down-turned triangle, to a long tapering blade, to a scimitar-shaped blade that becomes broader toward the apex before narrowing, to a blunt paddle-shaped structure. Internal to the volsella is the aedeagus, comprising two penial valves. The penial valve has an anterodorsal apodeme, a broad and elongate blade, and a posterior upturned tooth. The apodeme may meet the dorsal margin of the blade at nearly a right angle, resulting in a strongly upturned aedeagus relative to the main axis of the abdomen, or the apodeme may gently curve into the dorsal margin and project back at an obtuse angle, such that the aedeagus is not as strongly upturned in side view.

Within species there is variation in degree of sclerotization of males, accompanied by variation in the size and robustness of genitalic elements. Less heavily sclerotized males also seem to have narrower and shorter basiparamere lobes, parameres, and volsellae. The variation is primarily among colonies and variation within colonies is low. The cause of high inter-colony variation is unknown. It could be due to ontogenetic changes in synchronous batches of males, intraspecific variation that is either genotypic or phenotypic, or evidence of cryptic species.

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1

  • Antenna with 11 segments; apodeme of penial valve meeting dorsal margin of blade at nearly right angle . . . . . 2
  • Antenna with 10 segments; apodeme of penial valve rounding into dorsal margin at obtuse angle . . . . . 4

2

return to couplet #1

3

return to couplet #2

4

return to couplet #1

  • Basiparamere lobe absent or reduced to short triangular tooth, much shorter than paramere; cuspis absent . . . . . 5
  • Basiparamere lobe well developed; cuspis present or absent . . . . . 6

5

return to couplet #4

  • Ocelli small, width of median ocellus less than distance between median and lateral ocellus; petiolar dorsum with few to no erect setae . . . . . Myrmelachista plebecula
  • Ocelli large, width of median ocellus greater than distance between median and lateral ocellus; petiolar dorsum with conspicuous tuft of erect setae . . . . . Myrmelachista lauropacifica

6

return to couplet #4

  • Pygostyles present; basiparamere lobes and parameres very long and thin . . . . . 7
  • Pygostyles absent or reduced to tiny unsclerotized remnants; basiparamere lobes and parameres thin or broad . . . . . 8

7

return to couplet #6

8

return to couplet #6

  • Digitus greatly expanded distally and with thickened posterodorsal and posterior margins, forming a bulla at apex . . . . . Myrmelachista longiceps
  • Digitus evenly tapered or scimitar-shaped, never forming a bulla at apex . . . . . 9

9

return to couplet #8

  • Cuspis absent or reduced to sharply triangular or spine-like process, closely appressed to inner surface of paramere and distant from digitus . . . . . 10
  • Cuspis present and subrectangular, separated from inner surface of paramere, apex sometimes approaching or touching dorsal margin of digitus . . . . . 12

10

return to couplet #9

  • Digitus scimitar-shaped; cuspis present as a spiniform tooth; maxillary palpus always 6-segmented . . . . . Myrmelachista joycei
  • Digitus more evenly tapered from base to apex; cuspis as above or absent; maxillary palpus 5 or 6-segmented . . . . . 11

11

return to couplet #10

  • Maxillary palpus 5-segmented; cuspis present as a small triangular or spiniform tooth . . . . . Myrmelachista haberi

12

return to couplet #9

13

return to couplet #12

  • Basiparamere lobe and paramere broad at the base, shorter; digitus tapering to a point at apex . . . . . 14

14

return to couplet #13

  • Ocelli relatively large, width of median ocellus usually greater than distance between median and lateral ocellus; distance between lateral ocelli about equal to distance from lateral ocellus to compound eye . . . . . Myrmelachista flavocotea
  • Ocelli relatively small, width of median ocellus usually less than distance between median and lateral ocellus; distance between lateral ocelli less than distance from lateral ocellus to compound eye . . . . . Myrmelachista nigrocotea
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