Proisotoma ramosi Arlé, 1959

Mendonça, Maria Cleide De & Abrantes, Eduardo Assis, 2010, Redescription of Proisotoma ramosi Arlé, 1959 from Brazil (Collembola: Isotomidae) with designation of the neotype, Zootaxa 2420, pp. 63-68 : 63-68

Proisotoma ramosi Arlé, 1959

( Figs 1–20 )

Material. Neotype here designated: female on slide Nº 1913 CM/ MNRJ. Brazil, Rio de Janeiro: Teresópolis (Parque Nacional da Serra dos Órgãos); 1.000 meters above sea level; 13.x.2008; Correia, M.C.R., coll.

Other material: 16 female specimens on slides Nº 1913 CM/ MNRJ. Brazil, Rio de Janeiro: Teresópolis (Parque Nacional da Serra dos Órgãos); 1.000 meters above sea level; 13.X.2008; Correia, M.C.R., coll. 5 female specimens on slides Nº 200 CM/ MNRJ Brazil, São Paulo, Parque Nacional da Serra da Bocaina ; 22.II.1988; Magnanini, C., coll. and 20 female specimens on slides Nº 266 CM/ MNRJ. Brazil, São Paulo, Parque Nacional da Serra da Bocaina ; 17.X.1988; Jesus, S., coll. The material studied is deposited in the Collembola Collection at Museu Nacional/ UFRJ.

Description. Body length: 0.77–0.86 mm (neotype: 0.81 mm). Habitus typical for the genus Proisotoma : elongated and subcylindrical. Color white with grains of black pigment under ocelli only. Integument smooth, unmodified. Abdominal segments clearly separated with a bend between last segments in lateral view.

Chaetotaxy. Common body setae smooth, acuminate and subequal; some of them a little longer laterally on body and last abdominal segments. Thorax without ventral seta. Axial setae of thorax II to abdomen IV by half tergite as 64/3336. Abdominal segment VI with unpaired setae a0: m0: p0 = 33 µm: 27 µm: 23 µm respectively ( Fig. 1 ). Macrosensilla slender and thin, with different sizes: thorax II to abdomen III (10 µm), abdomen IV (15 µm), abdomen V (17 µm); microsensilla on thorax II and abdomen III (5 µm). Macrosensillary and microsensillary set by half tergite respectively with 43/22235 and 10/001 ( Fig. 2 ).

Head. Eyes 2+2 on some black pigment grains. Postantennal organ narrow (30 µm), with weak constriction and 3–4 surrounding guard setae ( Figs 3–4 ). Ratio head diagonal: antennae = 1.17: 1. Antennal segment IV with a small rod-shaped subapical organite protected by one curved seta, 9–10 dorsal and lateral sensilla and 2–3 supplementary sensilla poorly differentiated from ordinary setae; apical lobes and basal microseta absent. Antennal segment III with about 22 setae; apical organ with two freely exposed rod sensilla, two slender guard sensilla and one small lateroventral sensillum; basal microseta absent. Antennal segment II with about 18 setae, one lateroapical sensillum and 3 basal microsetae (one ventral and 1+1 lateral). Antennal segment I with about 12 setae, one dorsal microseta and two ventral and subequal sensilla ( Fig. 5 ). Ratio of antennal segments I: II: III: IV = 1: 1.65: 1.7: 2.75. Labrum with 4/554 setae ( Fig. 6 ). Mandibles normal. Maxillary head with 3 teeth and 6 ciliated lamellae, lamella 1 clearly longer than others ( Fig. 7 ). Maxillary outer lobe with bifurcate palp, 3 sublobal hairs and one basal seta ( Fig. 8 ). Labium with 3 hypostomal setae, labial palp A with one guard, B with 4 guards, C without guard, D with 4 guards and E with 6 guards (guard e6 absent); lateral process (l. p.) smaller than E papilla ( Fig. 9 ). Head with 3+3 setae along linea ventralis.

Appendages. Tibiotarsi I, II and III with 21, 21 and 23 smooth and thin setae; tibiotarsi I and II with A, B and C whorls of seta complete (7 setae each) ( Figs 10–12 ); tibiotarsus III with B and C series incomplete (6 setae each) and D series with 4 setae; apical tenent setae pointed, not developed. Unguis (25 µm) of normal shape, untoothed ( Fig. 13 ). Unguiculus lanceolate, untoothed (10 µm). Ventral tube with 4+4 distal and 3 posterior setae ( Fig. 14 ). Retinaculum with 4+4 teeth and two setae on corpus; some specimens have one or 3 setae on corpus ( Figs 15–16 ). Subcoxa furcalis with 8–11 anterior and 6 posterior setae ( Fig. 17 ). Furca small, complete. Manubrium (64 µm) longer than dens, with about 12+12 posterior and 1+1 anterior setae. Dens slightly crenulated (51 µm), with 7 posterior and 11 anterior setae. Mucro long (19 µm), bidentate, with strong anteapical tooth ( Figs 18–19 ). Ratio manubrium: dens: mucro = 3.37: 2.68: 1. Female genital opening as in Figure 20 .

Remarks. Studies regarding the complicated taxonomy of Proisotoma performed by Potapov (2001), Potapov et al. (2006) and Fjellberg (2007), resulted in the redefinition, and therefore in the allocation of some species to other genera. However, these authors mostly studied the Palaeartic fauna and excluded Neotropical species which still need to be interpreted in modern terms. Palacios-Vargas and Arbea (2009) recently described two new species from Venezuela and Mexico and added a key to neotropical species of Proisotoma s.l. and related genera. However, our present study of P. r a m o s i indicates a set of characters which do not fit well into the generic diagnosis for Proisotoma s.str. proposed by Potapov et al. (2006:14). The presence of sensilla in the abdominal segments I–IV anteriorly to the p-row of setae includes this species in the Scutisoma genus, the microsensillary formula 10/001 in Proisotoma , the bifurcated maxillary palp with 3 sublobal hairs in Ballistura and the 3 and 5 sensilla in abdominal segments IV–V in the ripicola-tenella group. Therefore P. ramosi takes an intermediary position among those genera. The examination of this species from Serra da Bocaina and Serra dos Órgãos shows a general similarity with some species of Proisotoma , in particular with those of the P. minuta group: separated abdominal segments V and VI, maxillary lamella 1 longer than others, reduced number of microsensilla, furca short but complete, manubrium with 1+1 anterior seta, mucro bidentate and the B series of tibiotarsi I and II complete. However, a set of peculiar characters such as reduced pigmentation, 2+2 eyes, labrum with 4/554 setae, maxillary palp bifurcate with 3 sublobal hairs and 3+3 postlabial setae, clearly distinguish P. ramosi from other species of the genus. Furthermore both the numbers of macro- and microsensilla differ from those given by Potapov et al. (2006) from Proisotoma . Also the position of the macrosensilla on abdomen in front of the p-row does not fit with Proisotoma .

The examination of the labial palp E of P. ramosi shows 6 guard setae (e1, e2, e3, e4, e5, e7). The lost of e6 seta with the presence of e7 seta shows a unique set, until now, among the family (Fjellberg 1999).

Comparing our specimens of P. r a m o s i with the original description ( Arlé 1959), differences were observed regarding the tenaculum and dens setae. In Arlé’s description only one tenaculum seta was reported, while our specimens and those examined by Rapoport and Rubio (1963) from Chile exhibit 2 setae on the tenaculum (two of our specimens show one and 3 setae respectively). Regarding the dens chaetotaxy most adult specimens studied here show the number of anterior and posterior setae constant, 11 and 7 respectively. A few specimens exhibit 10 or fewer setae in the anterior face of dens, as recorded in the original description and in the specimens from Chile. Our study renders P. ramosi isolated in Proisotoma s. str., until a larger study, involving a phylogenetic analysis about the group, is done.

Figures

FIGURES 1 – 2. Proisotoma ramosi Arlé: 1, Body chaetotaxy; 2, distribution of body sensilla.

FIGURES 3 – 10. Proisotoma ramosi Arlé: 3, PAO and eyes; 4, head chaetotaxy; 5, left antennal segments I – V, dorsal lateral view; 6, labrum and prelabral and clypeal setae; 7, maxillary head; 8, maxillary outer lobe; 9, labial pal (l. p. –lateral process); 10, leg I, lateral view.

FIGURES 11 – 20. Proisotoma ramosi Arlé: 11, Leg II, dorsal view; 12, Leg II, lateral view; 13, Leg III, lateral view; 14, ventral tube; 15 – 16, retinaculum; 17, anterior and posterior furcal subcoxa; 18, furca, anterior view; 19, furca, posterior view; 20, female genital plate.