Leptohyphes mandibulus Baumgardner, 2007

Baumgardner, D. E. & Mccafferty, W. P., 2010, Revision of the genus Leptohyphes Eaton (Ephemeroptera: Leptohyphidae) in North and Central America, Zootaxa 2360 (1), pp. 1-33 : 16-19

Leptohyphes mandibulus Baumgardner

Leptohyphes mandibulus Baumgardner, 2007:417 .

Diagnosis: The reduced number of outer incisor denticles on both the left and right mandibles will distinguish this species from others in the genus Leptohyphes in Central America. While the vast majority of species within the genus Leptohyphes have four denticles on the outer incisor of the left mandible and three on the right mandible, L. mandibulus has only two outer incisor denticles on each mandible. In addition, the coloration of the operculate gills (basal half dark, apical half pale), and the contrasting coloration of the body and legs is also distinct for this species.

Description: Male Adult: Unknown. Larva: Length. Body, 3.0–3.5 mm; caudal filaments, 2.0–2.5 mm. General coloration gray and black. Head: Dark reddish brown to black; small genal projections present; tubercles absent; antenna light brown. Left mandible ( Fig. 37 ): outer incisor two lobed, teeth fused almost their entire distance; inner incisor two lobed; prostheca arising at base of inner incisor, with highly branched setae projecting towards molar region. Right mandible ( Fig. 38 ): outer and inner incisors two lobed, fused almost their entire distance; prostheca arising at base of inner incisor with highly branched, elongate setae projecting towards molar region; molar region mostly fused. Thorax: dark reddish brown to black; without anterolateral projections or median tubercles; hind wing pads present in males, absent in females. Legs. Proleg ( Fig. 39 ): femur with transverse row of elongate setae on dorsal surface; anterior and posterior margins with few, scattered filiform and acuminate setae; tibia with evenly spaced, elongate setae along anterior margin; posterior margin with few, scattered filiform setae; tarsus without setae on anterior or posterior margin; ventral surface with row of four to six robust setae. Meso- and metalegs ( Fig. 40 ): femora without setae present on dorsal surface; anterior margin with few setae of none; posterior margin with elongate stage along distal half of margin; tibiae with sparce elongate setae along anterior margin; posterior margin with few, scattered filiform and elongate setae; tarsus with elongate setae along anterior margin, and few filiform setae along distal half of posterior margin. Claws ( Fig. 41 ) with one submarginal denticle, and a single row of four to six marginal denticles, similar in shape and size with equal spacing. Abdomen: Dark reddish brown to black; terga 5-9 each with a pair of elongate setae located medially on posterior margin; tubercles absent; operculate gill with basal portion black, apical portion pale ( Fig. 16 ); scattered acuminate setae present along inner and apical margins; gill formula 2/6/6/6/2.

Distribution: This species is currently known only from the type locality in northwestern Costa Rica.

Discussion: Of interest for L. mandibulus are the changes associated with the mandibles on mature and pre-emergent larvae. Mandibular description in the above species description is based upon relatively mature larvae, but not pre-emergent larvae. In pre-emergent larvae, the outer incisors of the right mandible are reduced to a single, rounded structure, while the inner incisor is reduced to a single denticle ( Fig. 42 ). For the left mandible, the outer incisors are fused into a single, large incisor, while the inner incisor is reduced to a single denticle ( Fig. 43 ). Reduction and fusion of incisors is very rare among leptohyphid mayflies and is usually a result of wear associated with feeding. However, numerous larval paratypes associated with L. mandibulus also displayed this condition, indicating it is probably a naturally occurring condition resulting from maturation, and not necessarly a result of feeding.

Type material examined: HOLOTYPE: Mature Male Larva – COSTA RICA: Alajuela Province; NE of Bijagua, nr. Las Flores, Río Areuo (N10º21'06", W85º21'05"), 07.vi.2000, WDS Shepard [ TAMU] . PARATYPES: Same data as holotype, 6 larvae [ FAMU], 25 larvae [ TAMU] .

Figures

FIGURES 37–43. Characteristics of larval structures of Leptohyphes mandibulus. 37, left mandible (dorsal) [scale bar C]. 38, right mandible (dorsal) [C]. 39, foreleg (dorsal) [A]. 40, hindleg (dorsal) [B]. 41, mesoclaw (ventrolateral) [D]. 42, right mandible, pre-emergent larva (dorsal) [C]. 43, left mandible, per-emergent larva (dorsal) [C]. Scale bars (mm): A = 0.40; B = 0.50; C, D = 0.20.

FIGURES 13–17. Characteristics of Leptohyphes spp. larval legs and abdominal structures. 13, hindleg (dorsal) [scale bar E]. 14, posterior margin abdominal terga 6 (dorsal) [A]. 15, abdominal tergites 7-9 (ventral) [E]. 16, gill 2 (dorsal) [B]. 17, gill 2 (ventral) [D].