Myrmecotypus mazaxoides, Perger & Dupérré, 2021

Perger, Robert & Duperre, Nadine, 2021, Myrmecotypus mazaxoides sp. nov. - a new ground-dwelling, carpenter ant-resembling sac spider species from the Bolivian orocline, with indirect evidence for species-specific mimicry (Araneae, Corinnidae, Castianeirinae), Zoosystematics and Evolution 97 (1), pp. 273-280 : 273

Myrmecotypus mazaxoides sp. nov. Figs 2 , 3 , 4 , 5 , 6 , 7A, B

Type material.

Holotype ♂ and ♀ allotype; BOLIVIA: Santa Cruz department, Santa Cruz de la Colina, Urubo; 17.760833°S, 63.24°W, 432 m. a.s.l., 21-28 Dec. 2019, R. Perger leg.; Cerrado-like grassland in urbanization (ZMH-A0014700-14701). Paratypes: 2 ♂, 5 ♀, same data as for preceding (ZMH-A0014707) • 6 ♂, 10 ♀, same data as for preceding; CBF.

Diagnosis.

Amongst species of Myrmecotypus , an elongated and constricted abdomen is only found in M. mazaxoides sp. nov. (Figs 2 , 3 , 5 ) and M. lineatus (Emerton, 1909), the latter occurring along the east coast of the United States ( Reiskind 1969). Additionally, both species share a broad carapace (carapace index ~47-52) and all eyes small and sub-equal (male of M. lineatus not described).

Females of M. mazaxoides sp. nov. can be distinguished from those of M. lineatus by the following characteristics: dorsum dark brown with an anthracite-greyish appearance in live condition (Fig. 7A, B ) (in M. lineatus , carapace yellow-orange, dorsal sclerite of abdomen yellow, posterior part of abdomen dark purple-brown with light spots), coxae II-IV translucent white, I reddish (Figs 3B , 5 ) (in M. lineatus , all coxae light), dorsal sclerite pyriform (elliptic in M. lineatus ), tibia I with 3 promarginal and 2 retromargial spines (tibia I spination 2-2 in M. lineatus ); chelicerae with two promarginal teeth with distal tooth reduced to small denticle (3 promarginal teeth in M. lineatus ); copulatory openings of epigyne anterior to spermathecae (lateral in M. lineatus ).

Remarks.

Reiskind (1969) noted the distinctness of M. lineatus while transferring this species from Castianeira to Myrmecotypus . The general habitus of M. mazaxoides sp. nov. resembles that of species of Mazax and possibly of some Apochinomma spp. Given that the generic taxonomy of Castianeirinae remains uncertain and requires detailed phylogenetic work ( Perger and Rubio 2020a), we follow Reiskind (1969) and include the newly described species tentatively in Myrmecotypus . The generic taxonomy and morphological affinities to species of other genera of Castianeirinae are addressed in the discussion.

Description of male holotype.

Body length 4.69; carapace length 2.17, width 1.11, carapace index 51; cephalic width 0.72, cephalic index 65; sternum length 0.93, width 0.67, sternum index 72; abdomen length 2.42, maximum width anterior part 0.76, maximum width posterior part 1.04, abdominal index 43; petiole length 0.10, width 0.29; dorsal sclerite length 2.32 (width agrees with abdominal width); epigastric sclerite length 0.62, width 0.74; ventral sclerite length 0.95, width 0.51; inframamillary sclerite length 0.09, width 0.15. AER 0.47; AME-AME 0.08; AME-ALE 0.02; PER 0.60; PME-PME 0.14; PME-PLE 0.11.

Carapace (Fig. 2A ). Long pyriform, truncated anteriorly, front slightly convex, cephalic area laterally somewhat narrowed, carapace widest in middle, three slight concavities in posterior half, posterior margin straight. Dorsum weakly shiny, smooth, microsculpture reticulate with evenly distributed, fine pits, dark brown; short, appressed, separate, white and brassy setae, simple on cephalic area and feathery on thoracic area (setae providing an anthracite-greyish appearance in live condition), several relatively long, forward-pointing, dark setae on front of cephalic area.

Eyes. Eight sub-equal eyes formed in two rows; PER distinctly recurved; AER slightly recurved.

Chelicerae. Orange-brown, shiny, with separated erect dark setae, area between retro- and promarginal rows of cheliceral teeth orange-white with dense white setae, two retromarginal teeth and two promarginal teeth, with distal tooth reduced to small denticle.

Abdomen (Figs 2A , 3A ). Elongated, distinctly constricted medially, posterior part broader than anterior part; petiole only moderately developed, very narrow medially, proximal margin strongly concave; dorsal sclerite almost completely covering abdomen dorsally and laterally; ventral sclerite not reaching to level of inframamillary sclerite, latter narrow, subrectangular, broader than long. Dorsum weakly shiny, smooth, microsculpture reticulate with evenly distributed, fine pits, dark brown; covered with separate, simple, short, brassy setae, abdominal setae long, simple, not sclerotized, second pair longer than first; in constriction, distinct band of relatively long, dense feathery white setae, on anterior part of abdomen similar band, less dense in the middle, on posterior part three to four indistinct bands of similar setae.

Legs. Coxae II and III translucent white, trochanters II and III dark yellow; coxae and trochanters I and IV reddish-brown; legs mostly sparsely covered with fine, golden setae, including feathery setae, dense in some areas, femora and tibia with separated, erect, long setae; femora I and II proximal fifths reddish, distal four-fifths laterally translucent, white and dark stripes along dorsal edges, remainder of legs I and II reddish-yellow; tibia I promarginal with 3 spines, retromarginal with 2 spines; femora and tibiae III and IV reddish-brown, dark grey stripes along dorsal sides; remainder of leg III orange-light brown; leg IV tarsus yellow; legs III and IV lined with short, appressed white feathery setae.

Palp. Pedipalp tibia with two distinct, long setae and several shorter setae (Fig. 4A, B ), retrodistal margin with one small, obtuse tooth-like apophysis (Fig. 4D, E ); maximum width of tibia 96% of maximum width of bulb when viewed retrolaterally; narrow genital bulb drawn out into long neck, with long, thin, sclerotized embolus with three coils and a basal ridge (Fig. 4C ); sperm ducts with two loops, both lateral and basal to embolus tube (Fig. 4A, B ).

Female allotype.

Body length 6.23; carapace length 2.85; width 1.35; carapace index 47; cephalic width 1.00; cephalic index 74; sternum length 1.19; width 0.80; sternum index 67. Abdomen length 3.15; maximum width anterior part 1.24; maximum width posterior part 1.45; abdominal index 46; petiole length 0.16; width 0.45; dorsal sclerite length 1.04; width 0.88; epigastric sclerite length 0.74; width 0.92; inframamillary sclerite length 0.16; width 0.35. AER 0.59; AME-AME 0.10; AME-ALE 0.03. PER 0.80; PME-PME 0.18; PME-PLE 0.13.

Lateral constriction of abdomen indistinct (Fig. 5A ), length of dorsal and epigastric sclerite one-third of abdominal length, dorsal sclerite pyriform, laterally not completely covering abdomen, ventral sclerite absent; coxa II-IV translucent yellow-whitish. Remaining somatic characters as in male.

Epigyne (Fig. 6 ). Epigynal plate forming part of the epigastric sclerite. Copulatory openings situated anterior to spermathecae, pointing in anterior direction. Copulatory duct running from anterior median part of spermathecae and connecting latter at posterior margin. Spermathecae oval, dorsally convex, wall more sclerotized laterally, fertilization ducts at postero-lateral margin.

Variation.

Females (BL 6-6.5 mm) were larger than males (BL 4.8-5.2 mm). Sexual dimorphism in coxae color (coxae II-III translucent whitish in male, II-IV in female). The number of clearly distinguishable transversal bands of feathery setae on the abdomen varied between one or two in the median constriction and three or four closely before the apex. While the abdominal constriction of the male is determined by the shape of the large dorsal sclerite, it varied in females according to the nutritional or reproductive state and could be similarly constricted as in males.

Etymology.

The specific epithet, Myrmecotypus mazaxoides , is derived from the Castianeirinae genus " Mazax " and " oeidēs " (Greek) = resembling or looking like and refers to the general resemblance of the habitus of this species to species of Mazax .

Geographical and ecological distribution.

This species is only known from the type locality in the recently established urbanization of Santa Cruz de la Colina, Urubo, Santa Cruz department. This urbanization included empty plots with savanna grasslands, plant successions and bushes or houses with gardens. According to the ecoregion delineation by Navarro and Ferreira (2011), the forest in this area is considered Chiquitano forest. The urbanization was surrounded by a mosaic of forest fragments, Cerrado-like grassland and savanna. Myrmecotypus mazaxoides sp. nov. was observed foraging on the ground of open grassland during the day, under or between dense ground vegetation (Fig. 7A ). Because of its presence in open habitats, it is likely that the species also occurs in similar habitats in the Gran Chaco area in southern Bolivia, Paraguay and northern Argentina. Despite high sampling effort in several Bolivian forest ecoregions ( Perger and Perger 2017; Perger and Rubio 2018, 2020a, b), the new species was not observed in forest habitats.

Myrmecotypus mazaxoides sp. nov. co-occurred with four different species of Castianeira (not determined) in the same habitat, three of which were commonly observed and had a dark body (blackish or black with grey) and red legs. A single male of Mazax cf. ramirezi Rubio & Danişman, 2014, was collected as well, among individuals of M. mazaxoides sp. nov.

Ant mimicry.

Eleven ant species with a similar or larger body length than adults of M. mazaxoides sp. nov. (BL 4.8-6.5 mm) were found in the investigated plots. However, all individuals of the new species were collected close to the entrance of subterranean formicaries of Camponotus cf. melanoticus Emery, 1894. Myrmecotypus mazaxoides sp. nov. and C. cf. melanoticus shared an elongated, sub-oval abdomen, a weakly shiny, dark brown integument with anthracite tinge, fine brassy pubescence and sparse white setae on the posterior abdomen, and completely red legs (Fig. 7 ). The reddish pedipalps of the spider resembled the reddish mandibles of the ants. Major workers of C. cf. melanoticus were unlikely models, as they were larger and had proportionally larger heads. The body length of adults of M. mazaxoides sp. nov. (BL 4.8-6.5 mm) was similar to the range of minor workers (BL 5.8-6.2 mm) of C. cf. melanoticus .

No other ant species with a weakly shiny, greyish body, short brassy pubescence or completely red legs was observed in the studied area. Two additional ant species had an oval abdomen, but one of those species had a brown pronotum and a black, shiny abdomen ( Camponotus cf. fastigatus Roger, 1863), and the other species a reddish forebody and abdomen with golden pubescence ( Camponotus cf. blandus Smith, F., 1858).

When the first author approached the individuals of M. mazaxoides sp. nov., they were hiding under ground vegetation (e.g., Fig. 7A ). In contrast, individuals of C. cf. melanoticus started to run fast and erratically after coming into contact with the hand of the main author, and many approached and some successfully administered a bite. The ants also behaved aggressively towards individuals of M. mazaxoides sp. nov. that came to close to the entrance of the formicaries, attacking and biting the spiders. The spiders rapidly retreated after such agonistic behavior.

For about six months, the colony of C. cf. melanoticus was expelled by a colony of the larger Camponotus renggeri Emery, 1894, which was attracted by mealybugs on a nearby stand of introduced Croton plants. During the absence of C. cf. melanoticus , no individuals of M. mazaxoides sp. nov. were observed, despite a similar sampling effort. After the removal of the mealybugs by the main author, C. renggeri stayed away and the site was re-colonized by C. cf. melanoticus and M. mazaxoides sp. nov., indicating a strong mimetic relationship between these ants and spiders.

Figures

Figure 2. Myrmecotypus mazaxoides sp. nov., holotype male (ZMH-A 0014700): A. Dorsal; B. Ventral. Scale bars: 0.5 mm. Please note that most setae are broken off due to storage in ethanol.

Figure 3. Lateral views of Myrmecotypus mazaxoides sp. nov.: A. Holotype male (ZMH-A 0014700); B. Female allotype (ZMH-A 0014701). Scale bars: 0.5 mm. Please note that most setae are broken off due to storage in ethanol.

Figure 4. Myrmecotypus mazaxoides sp. nov., palp male holotype (ZMH-A 0014700), A, B. Ventral view; C. Tip embolus; D, E. Lateral view. (Em = embolus; RTA = retrolateral tibial apophysis).

Figure 5. Myrmecotypus mazaxoides sp. nov., allotype female (ZMH-A 0014701): A. Dorsal; B. Ventral. Scale bars: 0.5 mm. Please note that most setae are broken off due to storage in ethanol.

Figure 6. Myrmecotypus mazaxoides sp. nov., epigyne female allotype (ZMH-A 0014701), A. Ventral view; B. Internal genitalia cleared, dorsal view. (CO = copulatory opening; CD = copulatory duct; ST = spermatheca; FD = fertilization duct).

Figure 7. Life habitus and morphological resemblance between spider and possible ant model: Myrmecotypus mazaxoides sp. nov., males: A. In natural habitat; B. On white background. Camponotus cf. melanoticus Emery, 1894 (minor workers): C. In natural habitat; D. On white background.