Myrmecocystus perimeces

An uncommonly collected species with few details know about its biology.

Identification
A member of the subgenus Eremnocystus.

Key to Myrmecocystus subgenus Eremnocystus species.

Snelling (1976) - Worker - Recognizable by the unusually elongate, narrow head; antennal scape without erect hairs; hind tibia without erect hairs on outer face. Female - mesoscutum with entire disc with scattered coarse, setigerous punctures only; thoracic pleura with abundant long, erect hairs; clypeus only moderately shiny, densely shagreened, punctures obscure; crest of petiolar scale only slightly excised. Male: unknown.

This unique species does not appear to be closely related to other members of the subgenus Eremnocystus. The greatly elongated head is diagnostic in all sizes of the worker caste. The mesoscutal sculpturation of the female is most similar to that of Myrmecocystus yuma, but Myrmecocystus perimeces may be immediately separated from that, and all other species, by the finely and closely roughened clypeus which is not at all shiny. All other species, whose females are known, have the greater part of the clypeus shiny, very lightly shagreened, with scattered, conspicuous punctures.

Distribution
Mexico. Known only from coastal sand dunes around Bahia San Quintin, northern Baja California, Mexico.

Distribution based on Regional Taxon Lists
Neotropical Region: Mexico.

Habitat
Coastal sand dunes.

Biology
A series from San Antonio del Mar bears the notation: "circular crater 4 inches diameter in sand." Probably similar to other species of Eremnocystus, a crepuscular and/or matinal forager. A single dealate female, taken in March, indicates a mating flight following spring rains. (Snelling 1976)

Nomenclature

 *  perimeces. Myrmecocystus perimeces Snelling, R.R. 1976: 106, figs. 234-240 (w.q.) MEXICO.

Worker
Measurements. HL 0.80-1.16 (1.06); HW 0.56-0.93 (0.80); SL 0.80-1.10 (1.00); WL 1.l-1.7 (1.4); PW 0.43-0.73 (0.56).

Head: In all sizes distinctly longer than wide, CI 70-81 (75); in full face view, sides straight, only slightly narrowed toward mandibular insertions; occiput barely convex, occipital corners rounded; as long or longer than scape, SI 94-100 (94). Eye small, about as long as first flagellomere; OMD 1.67-2.14 (2.00) x EL. Mandibles septendentate.

Thorax: Slender, PW 0.38-0.47 (0.40) x WL. Mesonotum, in profile, convex, rather sharply sloping behind. Basal face of propodeum broadly rounded into posterior face.

Petiole: Scale erect; in profile, about twice higher than thick, weakly cuneate; in frontal view, crest narrow, weakly or not at all notched in middle; from above, no more than twice wider than thick.

Vestiture: Pubescence very short, scattered, on head, a minute area on vertex denser than elsewhere on head; very fine, rather sparse on pronotum, denser on meso- and metanotum, and especially on pleura and propodeum. First two gastric terga with short, fine abundant pubescence not obscuring surface, remaining segments with a few scattered appressed hairs.

Scape, inner face of fore femur, outer faces of middle and hind tibiae and sides of head without erect hairs; clypeal disc and frons with a few scattered short, erect hairs; occiput with 16-24 erect hairs, less than MOD. Pronotum and mesonotum each with a few hairs (> 10), shorter than on occiput; propodeum with a variable number (usually> 10) of very fine erect hairs. First two terga with scattered short, stiff hairs on disc; following segments with scattered longer hairs.

Integument: Clypeus polished, with sparse, coarse punctures; remainder moderately to strongly shiny, but not polished, lightly shagreened, with sparse to scattered fine punctures, denser on frontal lobes. Thorax rather strongly shiny, lightly shagreened; propodeum duller, more conspicuously shagreened. Gaster shiny, lightly shagreened.

Color: Uniformly light to dark brownish, appendages lighter; mandibles and lower part of cheeks yellowish.

Queen
Measurements. HL 1.63; HW 1.73; SL 1.53; EL 0.43; OMD 0.63; WL 3.7; PW 2.2.

Head: Broader than long, CI 94; in full face view, sides straight, converging slightly toward mandibular insertions; occiput slightly, evenly convex, corners well rounded; longer than scape, SI 94. Eye small, slightly longer than first flagellomere; OMD 1.46 x EL. Ocelli subequal; IOD 4.3 x OD; OOD 4.0 x OD. Mandible with seven teeth. Penultimate segment of maxillary palp broadest at base, strongly tapering toward apex; segments three and four ribbon-like, about equally broad throughout their lengths.

Thorax: Robust, PW 0.59 x WL. Apical two-thirds of mesocutum, in profile, barely convex, posterior margin below anterior margin of scutellum; scutellum barely convex, except at extreme base, strongly sloping toward rear; propodeum with broad shallow impression at summit of declivity.

Petiole: In profile elongate-cuneate, anterior and posterior faces strongly sloping toward crest; in frontal view, sides of crest rounded, middle shallowly excised; in dorsal view, about twice as wide as thick.

Vestiture: Pubescence sparse on clypeus, malar area and frons, dense on occiput, but not concealing surface; sparse and short on most of pronotum, conspicuously longer and denser along dorsal margin; long, sparse on sides of mesoscutum and pleura, absent from mesoscutal disc; sparse on scutellum and metanotum; slightly shorter, sparse on propodeum, denser above and around gland opening; abundant on discs of first four gastric terga and sterna.

Scape with about 20 fully erect hairs on outer face. In frontal view, sides of head without erect hairs; occiput with numerous stiff, erect hairs less than 0.5 x MOD, with a few longer hairs in ocellar area; frontal lobes with numerous short, fine hairs; clypeus with sparse hairs of variable length. Mesoscutum with sparse long hairs about half as long as MOD: scutellum with sparse longer hairs of variable length, some longer than MOD; metanotum and propodeum with sparse hairs about as long as those of scutum; numerous long hairs on mesopleura, many as long as or longer than, MOD. Numerous short hairs on petiolar scale: Gastric terga with numerous short, stiff hairs, shortest on first, becoming a little longer caudad, those of first segment less than 0.5 x MOD. Inner face of fore femur without conspicuous long erect hairs, though a few short, fine hairs are visible; outer faces of mid and hind tibiae with abundant erect hairs.

Integument: Face shiny, finely shagreened, but clypeus conspicuously duller, much more strongly shagreened, clypeus with scattered coarse punctures; frontal lobes finely, closely punctate; frons with fine, scattered punctures; malar area with scattered punctures, denser below, coarser than those of frontal lobes; occiput densely, finely punctate. Mesoscutal disc polished, with scattered coarse punctures; parapsis with well separated punctures about equal to those of clypeus; scutellum slightly shiny, uniformly closely punctate, punctures equal to those of lateral area of mesoscutum; pleurae and propodeum duller than scutellum, roughened, with scattered coarse, setigerous punctures and denser, finer punctures; propodeum and terga densely micropunctate.

Color: Uniformly blackish-brown; mandibles, apical middle of clypeus, lower part of cheeks, flagellum and legs lighter.

Type Material
Holotype and paratype workers (from two colonies), El Molino, 0.5 mi. S, Bahia San Quintin, 0-50', Baja Calif., MEXICO, 29 March 1970 (E. M. Fisher), in. Additional paratypes, all Baja Calif.: l queen, same data as holotype, stray; 32 workers, Bahia San Quintin, 21 May 1952 (W. S. Creighton; LACM); 25 workers, San Antonio del Mar, 0',27 May 1952 (W. S. Creighton; LACM). Paratypes in, LACM, ,.

Etymology
Mekos (Gr., length) + peri- (Gr., excessive), because of the exceptionally elongate head.

References based on Global Ant Biodiversity Informatics

 * Dattilo W. et al. 2019. MEXICO ANTS: incidence and abundance along the Nearctic-Neotropical interface. Ecology https://doi.org/10.1002/ecy.2944
 * Fernandes, P.R. XXXX. Los hormigas del suelo en Mexico: Diversidad, distribucion e importancia (Hymenoptera: Formicidae).
 * Johnson, R.A. and P.S. Ward. 2002. Biogeography and endemism of ants (Hymenoptera: Formicidae) in Baja California, Mexico: a first overview. Journal of Biogeography 29:10091026/
 * Vásquez-Bolaños M. 2011. Lista de especies de hormigas (Hymenoptera: Formicidae) para México. Dugesiana 18: 95-133