Moribaetis brachiostrinus Romero & Esquivel, 2018

Romero, David & Esquivel, Carlos, 2018, Moribaetis brachiostrinus (Ephemeroptera: Baetidae), a new species of mayfly from Costa Rica, Zootaxa 4433 (3), pp. 531-541 : 533-539

Moribaetis brachiostrinus Romero & Esquivel , sp. nov.

Known from male and female nymph in last instar, adult unknown.

Material examined: Holotype, mature ♀ nymph; Costa Rica, Puntarenas prov., Península de Nicoya, Reserva Biológica Karen Mogensen , Quebrada Negra , 9°52'7.84"N / 85° 3'33.89"W, 300 m. elev., 22 September 2016, F. Sibaja-Araya coll., deposited at the MNCR . Paratypes, 1 mature ♂ nymph, same data as holotype, deposited at MZUCR ; 2 immature nymphs, same data as holotype, deposited at the MZUCR ; 1 ♀ nymph, same data as holotype, deposited at PERC ; 1 immature nymph, same data as holotype, deposited at PERC ; 1 mature nymph ♂ and 3 immature nymphs, same data as holotype, deposited in the collection of LEUNA .

Diagnosis. Mature nymph. The following combination of characters can be used to recognize M. brachiostrinus as follows: 1) light-violet colored gills ( Fig. 3 ); 2) short antennae ( Fig. 4 a, b ), deflected downward reaching gill 1 to 2; 3) lateral branches of epicranial suture with two pronounced curves ( Fig. 4 a, b ); 4) mandibles with incisive area very long, projected beyond labrum margin, and two tufts of short setae between prostheca and mola ( Fig. 5 b, c ); 5) segment 1 of labial palp near 1,5 length of segment 2, and segment 2 with 7 dorsal setae ( Fig. 6 c ); 6) paraglossa with two rows of apical setae; 7) maxillary palp longer than galea-lacinia ( Fig.6 a ); 8) paraproct with a distinctive triangular projection (arrow in Fig. 7 d )

Size: male larva: body length 7,5 mm; antennae 3,0 mm; cerci 8,5 mm, terminal filament 3,0 mm; female larva: body length 9,5 mm; antennae 3,0 mm; cerci 10,5 mm, terminal filament 3,5 mm.

Coloration pattern: the same in both sexes ( Fig. 2 ): dorsally yellow-brown, ventrally brown-pale; pronotum and mesonotum with dark midline; abdominal terga yellow-brown, terga 5 and 9 pale, terga 2–8 with two middle dark markings and dark lateral marginal spots, lighter on 5. Head grayish brown, vertex darker with irregular pattern of spots; scape and pedicel grayish brown with shading on fringes, pedicel with dark spot. Legs graybrown; anterior face of femora with pale patch at base and apex, posterior face pale with dark brown median spot; tibia and tarsus uniformly colored. Gills membrane violet with dark tracheae ( Fig. 3 ) Cerci yellow-brown, paler ventrally, with a dense row of dark setae on inner margins and with a short, lighter segment on the base and near the middle; terminal filament with a dense row of dark setae on the margins, clearer on the base.

Body morphology. Head: Epicranial suture with two pronounced curves on the lateral branches; frons extended but not forming a keel ( Fig. 4 a ). Antennae ( Fig 4 b ) ventrally deflected reaching gill I or II; scape and pedicel with scales, clumped setae and fine setae; scape with brown shading on margins, pedicel with dark spot on inner side. Labrum ( Fig. 5 a ) narrowed basally with anterior margin rounded, prominent basomedial area, dorsal surface covered with short setae and 18–20 submarginal setae; ventrally with long plumose setae on anterior margin, and a row of 8–9 spines in sublateral margin. Mandibles with two tufts of short setae between prostheca and molar area; incisors projected beyond labrum margin (generally truncate in mature nymphs). Right mandible ( Fig. 5 b ): innermost incisors tridentate, arranged in descending order, free from outermost incisor and with basal row of short setae at the base; slender, comb-shaped apex prostheca extending beyond the level of innermost incisors. Left mandible ( Fig. 5 c ): innermost incisors fused apically with outermost incisors; prostheca well developed; subtriangular process on the base of mola (thumb) elongate and curved, mola with reduced denticles. Hypopharynx ( Fig. 6 a ): lingua apically trilobate and covered with fine, short setae, which are longer at apex; superlinguae bilobate with fine, long setae on dorsal and ventral surfaces, outer lobe larger, with triangular shape towards the apex; base of superlinguae acute, with inner margin comb-shaped. Maxilla ( Fig. 6 b ): Segment II of the maxillary palp similar in size to segment I and exceeding the length of the galea-lacinia; lacinia with a strong apical seta; galea with a line of long setae at the base, and two rows of setae of different lengths on the outer margin of the apex, two of which are pectinate and robust. Labium ( Fig. 6 c ): labial palps not exceeding the length of paraglossa; segment I of labial palp near 1,5 the length of segment II, segment II with weak inner apical lobe and 7 dorsal setae, segment III broader than long and heavily covered of fine setae and a few spines; paraglossae with three apical rows of bristles and long setae on outermost margin; glossae with long setae on inner margin and without fine setae on dorsal surface.

Thorax: Procoxal osmobranchiae present and curved, appressed against the coxae ( Fig. 7 a ). Legs ( Fig. 7 c ): dorsal edge of femora fringed with fine setae and with short spine-like setae spaced regularly, clustered on apex above insertion of tibiae; ventral edge with short and stout scattered setae; tibiae with fine setae and spine like-setae spaced irregularly on dorsal edge, and scattered on ventral edge; dorsal margin of tarsi with short setae, 4 rows of dense setae on distal section, and 3 ventral stout setae; claws with 8-9 denticles and a long, curved seta inserted above second denticle.

Abdomen: Gills of segment 1 smaller than those of following segments, with sclerotized margins, anterior margin serrate with 4-6 fine denticles and short setae among serrations, posterior margin covered with long, fine setae ( Fig. 7 b ). Terga ( Fig. 8 ): posterior margin with sharp denticles, irregular in length, and some fine setae between denticles; dorsal surface densely covered with trapezoid protuberances. Paraprocts with short spines on posterior margin, increasing in size towards apex on the large lobe and of similar size on the small lobe, with a distinctive triangular projection on the middle of posterior margin, surface with some dispersed trapezoid protuberances, setae absent ( Fig. 7 d ). Cerci with dense row of setae on inner margins; terminal filament with dense row on lateral setae.

Etymology: brachia, L. meaning gill; ostrinus, L. meaning purple, in reference to the distinctive gill color of this species.

Figures

FIGURE 2. Coloration pattern of Moribaetis brachiostrinus sp. nov. for male and female mature nymph.

FIGURE 3. Gill coloration for mature nymph of Moribaetis brachiostrinus sp. nov.

FIGURE 4. Moribaetis brachiostrinus sp. nov., a) mature nymph head (male left; female right). b) Antennal scape and pedicel detail.

FIGURE 5. Moribaetis brachiostrinus sp. nov., mature nymph mouthparts. a) labrum (left v. v., right d. v.), b) right mandible, c) left mandible.

FIGURE 6. Moribaetis brachiostrinus sp. nov., mature nymph mouthparts. a) maxilla, b) hypopharynx (left v. v., right d. v.), c) labium (left d. v., right v. v.).

FIGURE 7. Moribaetis brachiostrinus sp. nov., mature nymph. a) procoxal osmobranchia detail, b) gill, c) leg, d) paraproct.

FIGURE 8. IV tergum detail of Moribaetis brachiostrinus sp. nov., mature nymph.