Two new cave-dwelling species of the short-tailed Whipscorpion genus Rowlandius (Arachnida: Schizomida: Hubbardiidae) from northeastern Brazil, with comments on male dimorphism

Abstract

Two new species of the arachnid order Schizomida, Rowlandius ubajara sp.nov. and Rowlandius potiguar sp.nov., are described based on both male and female specimens collected in caves from northeastern Brazil. Rowlandius ubajara is known only from the Ubajara Cave, in the state of Ceará; R. potiguar is recorded from 20 caves of the Apodi Limestone Group, in the state of Rio Grande do Norte. A remarkable dimorphism in male pedipalp length is described and analyzed in R. potiguar. The distribution of male pedipalp length is clearly bimodal in the species, but the two male morphs (homeomorphic and heteromorphic) present some overlap in the sizes of this structure. Moreover, males show a steeper allometry in pedipalp length than females, indicating that this trait is under a different selective regime in males and in females.

Figure 1. Geographic distribution records of Rowlandius ubajara sp.nov. (star) and R. potiguar sp.nov. (triangles) in northeastern Brazil.

The black area represents the range of limestone outcrops from the Apodi Group in the state of Rio Grande do Norte.

Figure 2. New species of Rowlandius from northeastern Brazil.

(A) Rowlandius ubajara sp.nov., female from Ubajara, Ceará, Brazil. (B, C) Rowlandius potiguar sp.nov., male from Felipe Guerra, Rio Grande do Norte, Brazil. Note the extremely elongated pedipalp (arrow). (D) R. potiguar, female from Felipe Guerra, Rio Grande do Norte, Brazil (arrow indicates the pedipalp).

Figure 3. Rowlandius ubajara sp.nov.

(A) Male (holotype UFMG 3895), flagellum, dorsal view; (B) ventral, (C) lateral, (D) pedipalp, retrolateral view. (E) Female (paratype, IBSP 44), pedipalp, retrolateral view; (F) female internal genitalia, dorsal view (LL lateral lobes of the spermathecae, ML median lobes). Scale bars: 6–8 0.1 mm; 9–10 0.2 mm; 11 0.04 mm.

Figure 4. Rowlandius potiguar sp.nov.

(A) Male (holotype, UFMG 3897), flagellum, dorsal view; (B) ventral, (C) lateral, (D) pedipalp, retrolateral view. (E) Male (paratype UFMG 3899), pedipalp, retrolateral view. (F) Female (paratype, IBSP 45), pedipalp, retrolateral view; (G) female internal genitalia, dorsal view (G gonopod, LL lateral lobes of the spermathecae, ML median lobes). Scale bars: 12–14 0.1 mm; 15–17 0.2 mm; 18 0.04 mm.

Figure 5. Rowlandius potiguar sp.nov.

(A) Male (UFMG 3901), flagellum and posterior tip of opisthosoma, posterior-dorsal view, (B) apex of male flagellum, lateral view (arrows indicate uropygid pores), (C) male pedipalp, trochanter, prolateral view (arrow indicates prolateral spur), (D) male pedipalp, tarsus, prolateral view (arrows indicate tarsal spurs).

Figure 6. Rowlandius potiguar sp.nov.

(A) Male (UFMG 3901), pedipalp, tarsus, prolateral view (arrows indicate uropygid pores), (B) chelicerae, apex, prolateral view (S serrula; numbers indicate setae types, according to [28]). (C) Female (UFMG 3902), flagellum and posterior tip of abdomen, dorsal view; (D) internal genitalia, dorsal view (arrows indicate chitinized arch); (E) lateral lobe of spermathecae, bulb; (F) gonopod (arrow), dorsal view.

Figure 7. The allometry of pedipalp length in Rowlandius potiguar sp.nov., indicating male dimorphism.

(A) Histogram of male pedipalpal patella length overlaid by the two ‘facing gamma distributions’ (θ = 0.163, λ = 1.91, lower bound = 0.48 mm for homeomorphic males; θ = 0.201, λ = 2.88, upper bound = 2.25 mm for heteromorphic males) estimated by a finite mixture model (as proposed by Rowland & Qualls [33]). The bars represent the frequency (scale on the left) of males in each pedipalpal patella length bin, and the curves represent the distributions of predicted probabilities (scale on the right, in %) of each pedipalpal patella length for both male morphs, as estimated by the model. (B) The relationship between the length of pedipalpal patella and the length of prosoma. Filled black dots and black line indicate males with a probability of being heteromorphic higher than 95%, empty dots and dashed line indicate males with a probability of being homeomorphic higher than 95%, filled gray dots indicate males with probabilities lower than 95% of being either morph, and crosses and dotted line indicate females. Axes are isometric to show male morphs in the most objective fashion.