Mejicanotrichia tridentata (Bueno-Soria & Hamilton, 1986)

Figures 4A-C, 5A-D

Material examined.

15 larvae (IN-TR-00222). Mexico, Chiapas, Ixhuatán, 95 km 2.8 N Ixhuatán, tributary of the Teapa River (409 m a.s.l., 17°18'41.06"N, 93°0'17.78"W), 18 April 2019; leg. M. Ramírez-Carmona, O. Lagunas-Calvo and G. Rivas-Lechuga.

Diagnosis.

Body mostly membranous ventrally. Thorax reddish-brown with dark spots dorsally. Abdominal tergites with dark and irregular spots (Fig. 4A). Conspicuous, dark, subtriangular sclerites on pleural area (Fig. 4B). A subtriangular and curved propleural sclerite is notoriously distinct from that of other species of the genus (Figs 1B, 4B; Bowles et al. 1999: figs 4-7). Abdominal dorsal tergites are long and narrow, with a larger number of setae than in M. harrisi . In addition, these tergites have a pigmentation pattern that is evenly distributed.

Description.

Body dorsoventrally depressed, range length 2.0-2.3 mm, widely covered with thick, long, and colorless setae (Fig. 4A). Body mostly covered dorsally with fine pigments spots, appearing as “sandpaper” (Fig. 4C). Larval case absent until before pupation.

Head. Ocherous-brown, prognathous, without visible ecdysial sutures.

Thorax. Pro-, meso-, and metanotum divided longitudinally by a medial ecdysial line. Three thoracic nota each with two lateral processes, which have two thick and opaque setae. Pronotum widening posteriorly. Anterior margin of pronotum with a ridge of thick setae, anterolateral corners folding ventrally. Anterior portion of pronotum slightly covering back of the head (Figs 4A, 5A). First pair of legs slightly smaller, tibiae and tarsi of all legs each with two rows of fine setae on dorsal region (Fig. 5B). Two oval sclerites behind the insertion of the legs on each sternite. Anterior margin of meso- and metanotum with row of thick setae, separated at least twice the basal diameter of setae. Lateral margins short and darkened, appearing as longitudinal bars. Mesonotum covered extensively with thick and short setae.

Abdomen. Long and widened, narrowing posteriorly. Ventral region with irregularly distributed, thick, short setae. Segments I-VIII with dorsal tergites, largely covering dorsum of each segment; first sclerite divided longitudinally. Tergites II-VII with lacunae in middle and beyond posterior margin (Fig. 5C); with two fine and dark setae on posterolateral margins, and well-developed thick setae on anterior and posterior margins (Fig. 4C). Anterior margins of tergites II-VI each with a slight notch in the middle; fine pigment spots linearly grouped beyond posterior margin of tergites (Fig. 5D). Abdominal projections without tergites; lateral margins with row of thick and prominent setae, one of which noticeably longer than rest. Segment IX short and shield-shaped, with setae on posterior margin, as well as six setae medially on segment. Anal prolegs projected caudally, cylindrical, with well-developed claws.

Comments.

The specimens were collected at a water temperature of 25 °C; with pH between 7.8-8.4; water presented a hardness of 136.8 mg CaCO3/l; the dissolved oxygen was 4.5 mg/l and 57% of oxygen saturation.