Myrmecotypus rubrofemoratus Perger and Rubio, 2021

Perger, Robert & Rubio, Gonzalo D., 2021, A new species of Myrmecotypus Pickard-Cambridge spider (Araneae: Corinnidae: Castianeirinae) from the Bolivian orocline, imitating one of the world’s most aggressive ants, Insecta Mundi 2021 (860), pp. 1-8 : 3-7

Myrmecotypus rubrofemoratus Perger and Rubio , new species

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( Fig. 2–4 , 5A, B )

Type material. Holotype ♂ (IBSI-Ara 1507) and ♀ allotype (IBSI-Ara 1467): BOLIVIA: Santa Cruz department, Cafetal coffee plantation (−17.469167°; −63.6925°), 3 km west of Buena Vista village, 342 m a.s.l., Pre-Andean southwest Amazon rainforest, edge of primary forest, small trees overgrown by climbing plants, beating tray sampling, 20–22 Jan 2016, leg. R. Perger . Paratypes same data as the holotype, 1 ♀ (IBSI-Ara), 3 ♀ ( CBF).

Diagnosis. Myrmecotypus rubrofemoratus new species and M. niger are the only known species of this genus with a band of black setae with the shape of an inverted “U” on the carapace ( Fig. 5A, B ), running dorsally from the level of coxae I to the carapace margin at about the level of coxae III. Additionally, both species share a similar carapace shape, translucent whitish coxa II and the remaining darker, and a globose male genital bulb with a short neck and at least one terminal projection of the tegulum basal to the embolus.

Myrmecotypus rubrofemoratus new species can be separated from M. niger by a narrower sternum (index ~44) (50–57 in M. niger ), chelicerae with one promarginal tooth (and a small distal denticle) (two teeth and a small distal denticle in M. niger ), legs with reddish areas, particularly on femora ( Fig. 4 , 5A ) (more brownish in M. niger ; cf. Fig. 5A with Perger and Rubio 2020a: 160, fig. 7F), embolus slightly curved and a tegular projection basal to embolus, consisting of two structures resembling a squid beak ( Fig. 3A ) (embolus straight and one hooked tegulum projection in M. niger ; cf. Fig. 3A with Reiskind 1969: 319, fig. 244), tibia I ventral spination 3- 3 in male and 5- 5 in female (4- 4 in both sexes of M. niger ), length of dorsal sclerite in female two-third of length of abdomen (three-fourth in M. niger ), transversal bands of white setae on abdomen absent (present in M. niger ).

Description of male holotype (IBSI-Ara 1507) ( Fig. 2 , 3A ). Body length 5.00; carapace length 2.75, width 1.24, carapace index 45.1; cephalic width 1.04, cephalic index 83.9; sternum length 1.27, width 0.57, sternum index 44.9; abdomen length 1.97, width 1.55, abdominal index 78.7; petiole length 0.15, width 0.24; dorsal sclerite length and width agrees with abdominal width; epigastric sclerite length 0.52, width 0.97; inframamillary sclerite length 0.32, width 0.52. AER 0.57; AME-AME 0.10; AME-ALE 0.03; PER 0.92; PME-PME 0.26; PME-PLE 0.20.

Carapace: Obovoid, widest in middle, truncated anteriorly, front slightly convex, cephalic area laterally somewhat narrowed, slight concavity behind cephalic region when viewed laterally, thoracic part moderately convex behind concavity when viewed laterally; three slight concavities in posterior half of carapace when viewed dorsally, posterior margin straight. Dorsal integument littered with minute granules, more separated on cephalic area, latter moderately shiny, cephalic region laterally and thoracic region finely reticulated, weakly shiny; dorsum dark brown, short, appressed, simple, separate, brassy setae, relatively dense in the middle; narrow band of short, appressed black setae with shape of inverted “U”, starting dorsally at level of coxa I and running to carapace margin at level of coxa III, black band posteriorly lined by narrow band of whitish setae (most setae broken off due to storage in ethanol).

Eyes: Eight eyes in two recurved rows; diameter AME about 20% larger than remaining, subequal eyes.

Chelicerae: 2 retromarginal teeth and 1 promarginal tooth (plus a distal denticle, hard to see).

Abdomen: Sub-globose, petiole only moderately developed, proximal margin strongly concave; dorsal scutum completely covering abdomen dorsally and laterally; inframamillary sclerite narrow, subrectangular, broader than long. Integument of dorsal sclerite littered with minute granules, finely reticulated, moderately shiny, dark brown; abdominal setae long, simple, not sclerotized, second pair longer than first; long, separate, erected, white setae on dorsum, posterior two-third densely covered with simple and feathery, short, brassy setae, sparse in anterior third.

Legs: Coxa II translucent whitish, the remaining coxae reddish-brown; femora and tibia I+II reddishbrown, with longitudinal dark areas along edges, dark areas become broader distally; tibia III+IV and metatarsus III+IV blackish with a reddish tinge, metatarsus I and tarsus IV blackish, metatarsus and tarsus II reddish; tarsus I proximally reddish, distally blackish; legs mostly sparsely covered with fine, golden hairs, including feathery hairs, dense in some areas.

Palp ( Fig. 3A ): Margin of tibia continuous; tarsus with globose genital bulb drawn out into short neck, terminating in a slightly curved embolus and and a tegular projection basal to embolus, consisting of two structures resembling a squid beak, the basal smaller than the distal one; palpal ducts with several basal and one lateral loop.

Female allotype (IBSI-Ara 1467) ( Fig. 3B, C ). Body length 5.31; carapace length 2.75, width 1.35, carapace index 49.1; cephalic width 1.15, cephalic index 85.2; sternum length 1.30, width 1.75, sternum index 43.9; abdomen length 2.25, width 1.75, abdominal index 77.8; petiole length 0.20, width 0.30; dorsal sclerite length 1.40 (width agrees with abdominal width); epigastric sclerite length 0.62, width 0.71; inframamillary sclerite length 0.25, width 0.45. AER 0.63; AME-AME 0.10; AME-ALE 0.05; PER 0.97; PME-PME 0.26; PME-PLE 0.22.

Thoracic part dorsally more convex than in male, larger abdomen, smaller dorsal sclerite, ventral sclerite absent, tibia I ventral spination 5-5. Remaining somatic characters as in male.

Epigyne ( Fig. 3B, C ): With two widely separated, small rounded genital openings, posterolateral to spermathecae; two pouches (or furrows) slightly posterior and towards the middle of each opening (presumably for fitting of male tegular projections); conspicuous, eggplant-shaped spermathecae, copulatory ducts short, entering the spermathecae basally.

Etymology. The specific epithet, rubrofemoratus , refers to the reddish femora of this species.

Geographical and ecoregion distribution. This species is only known from the type locality in Buena Vista, Santa Cruz department, Bolivia. Specimens of M. rubrofemoratus new species were collected along an edge of a primary forest fragment, on small trees overgrown by climbing plants. According to the ecoregion delineation by Navarro and Ferreira (2011), the forest in this area is considered the Pre-Andean southwest Amazon rainforest ( Fig. 1 ). Along the same forest edge, individuals of M. niger , M. tahyinandu and two species of Castianeira Keyserling were collected. However, individuals of all these species were obtained from different trees, co-occurring with different potential ant models (see below).

Ant mimicry. Adults of M. rubrofemoratus new species were obtained close to aggregations of the carpenter ant Camponotus femoratus . Both shared a similar body length (~ 5 mm), a dark brown body with appressed, short, brassy and erected, long, white setae and legs with reddish areas, forebody obovoid, truncate anteriorly and sub-globose abdomen ( Fig. 5 ). During the beating tray collecting in branches with nests of C. femoratus , these ants immediately launched annoying mass attacks with several ants administering painful bites and spraying formic acid. The spiders appeared to avoid direct contact with the ants, as they were only collected in branches several meters away from the ants. In more distant areas of the sampled forest edge without Camponotus femoratus , no specimen of M. rubrofemoratus new species was found.

Figures

Figure 1. Ecoregion distribution of Myrmecotypus rubrofemoratus new species, according to the regionalization by Navarro and Ferreira (2011). Collection location indicated by red circle, map produced with QGIS (version 2.14.3, http:// www.qgis.org/en/site).

Figure 2. Myrmecotypus rubrofemoratus new species: Holotype male (IBSI-Ara 1507), dorsal.

Figure 3. Myrmecotypus rubrofemoratus new species, genitalia. A) Palp male holotype (IBSI-Ara 1507), ventral view. B–C) Epigyne female allotype (IBSI-Ara 1467). B) Ventral. C) Same, cleared.

Figure 4. Myrmecotypus rubrofemoratus new species: Paratype female (CBF). A) Dorsal. B) Lateral (Please note that most hairs are broken off due to storage in ethanol). Scale bar 1 mm.

Figure 5. Comparison of ant-mimicking Myrmecotypus spider and potential ant model. A–B) Myrmecotypus rubrofemoratus new species female, habitus in life. A) Dorsal. B) Lateral. C–D) Potential ant model Camponotus femoratus (Fabricius, 1804). C) Dorsal. D) Lateral.