Zetzellia quasagistemas Hernandes & Feres

Hernandes, Fabio A. & Feres, Reinaldo J. F., 2005, Two new species of Zetzellia Oudemans (Acari: Stigmaeidae) that threaten the concept of genera: disgeneric marriage?, Zootaxa 1048, pp. 27-44 : 37-42

Zetzellia quasagistemas Hernandes & Feres sp. n. ( Figs. 23–41 )

This species resembles Z. yusti Summers in having dorsal shields smooth, two pairs of aggenital setae, tegument on venter and around dorsal shields slightly striated; prodorsal shield bearing 3 pairs of setae (vi, ve and sci), pairs c2 and d2 on small platelets, pairs h1 and h2 on the same terminal shield, tarsus IV with 7 setae. It differs from the latter in having the bases of pair c1 completely fused with hysterosomal shield; the solenidion (15) on tarsus I is relatively shorter than in Z. yusti (23); dorsal setae vi, ve, c1, c2, d1, d2, e1 and e2 also shorter; tarsus I with 13 setae (rather than 12).

Female (n=5). ( Figs. 23–28 ). Dorsum. Dorsal shields smooth; prodorsal shield bearing 3 pairs of setae (vi, ve and sci); dorsal setae as in female Z. agistzellia sp. n.; Venter. Ventral and anal setae as in female Z. agistzellia , 1 long genital pair (g1), extending to bases of ps3, ps3 is short, thick and hairy; ag1 is inserted on plate around anal opening; ag2 is inserted on the striated tegument. Gnathosoma. As in female Z. agistzellia . Legs. Chaetotaxy (I–IV): coxae 2(1)­1­2­2; trochanters 1­1­1­1; femora 5­4­2­ 2; genua 3(1)­1­0­0; tibiae 5(1)­5(1)­5(1)­5(1); tarsi 12(1)­9(1)­7(1)­7.

Developmental changes [from deutonymph female]: addition of 1 seta on trochanter IV and 1 genital seta (g1).

Male (n=5). ( Figs. 30–35 ). Dorsum. Dorsal shields smooth; prodorsal shield bearing 3 pairs of setae (vi, ve and sci); hysterosomal shield bearing 5 pairs of setae (c1, d1, e1, e2 and f1); seta d2 on small platelet; dorsal setae e1 and h1 greatly reduced, the shortest of dorsal setae. Venter. Ventral and anal setae as in Z. agistzellia sp. n.; 1 pair of aggenitals; ps1 short and thin, each inserted in a tubercle, being visible dorsally due to the curvature of this region. Gnathosoma. As in female. Legs. Chaetotaxy (I–IV): coxae 2(1)­1­2­2; trochanters 1­1­1­1; femora 5­4­2­2; genua 3(1)­1­0­0; tibiae 5(1)­5(1)­5(1)­5(1); tarsi 12(2)­9(2)­7(1)­7(1).

Developmental changes [from deutonymph male]: hysterosomal shield includes pair f1; dorsal seta e1 reduces largely at this stage; addition of 1 seta on trochanter IV, and 1 solenidion on tarsi I, II and IV; aggenital setae unchanged.

Deutonymph female. (n=2). ( Figs. 41–42 ). Dorsum. Dorsal setae as in female; Venter. Ventral and aggenital setae as in female. Gnathosoma. As in female. Legs. Chaetotaxy (I–IV): coxae 2(1)­1­2­2; trochanters 1­1­1­0; femora 5­4­2­2; genua 3(1)­1­0­ 0; tibiae 5(1)­5(1)­5(1)­5(1); tarsi 12(1)­9(1)­7(1)­7.

Developmental changes [from protonymph]: addition of 2 setae on coxa IV, 1 seta on trochanters I, II and III, 1 seta on femora I and IV and on tarsus IV; addition of 1 pair of aggenital setae.

Deutonymph male. (n=2). ( Fig. 43 ). Dorsum. Dorsal setae as in female; Venter. Ventral setae as in female; 1 pair of aggenitals. Gnathosoma. As in female. Legs. Chaetotaxy (I–IV): coxae 2(1)­12­2; trochanters 1­1­1­0; femora 5­4­2­2; genua 3(1)­1­0­ 0; tibiae 5(1)­5(1)­5(1)­5(1); tarsi 12(1)­9(1)­7(1)­7.

Developmental changes [from protonymph]: same leg chaetotaxy as in deutonymph female; there is no addition in aggenital setae, that distinguishes this stage from deutonymph female; this condition remains in the adult male.

Protonymph (n=2). ( Figs. 39–40 ). Dorsum. Dorsal setae as in female. Venter. Ventral setae as in female; 1 pair of aggenitals. Gnathosoma. As in protonymph of Z. agistzellia . Legs. Chaetotaxy (I–IV): coxae 2(1)­1­2­0; trochanters 0­0­0­0; femora 4­4­2­ 1; genua 3(1)­1­0­0; tibiae 5(1)­5(1)­5(1)­5(1); tarsi 12(1)­9(1)­7(1)­6.

Developmental changes [from larva]: addition of leg IV; addition of one ventral seta on coxae I and II, and two ventral setae on coxa III; addition of 1 pair of aggenital setae.

Larva (n=3). ( Figs. 37­38 ). Dorsum. Prodorsal shield smooth, partly invaded by tegumental striae along median line; dorsal setae setting on isolated platelets, no hysterosomal shield formed; platelets bearing setae e1 and e2 fused; median transversal suture dividing prodorsum and hysterosoma. Venter. 2 pairs of ventral setae (1a and 3a) between coxae II and III, respectively; 3 pairs of anal setae, ps3 shortest of anals, ps1 a little slender than other anals. Gnathosoma. As in larva Z. agistzellia . Legs. Chaetotaxy (I–IV): coxae 1(1)­0­0; trochanters 0­0­0; femora 4­4­2; genua 2(1)­1­0; tibiae 5(1)­5(1)­ 5(1); tarsi 12(1)­9(1)­7(1).

Remarks: This species inhabits mostly the base of rubber tree leaflets, in association with the mites Lorryia formosa Cooreman, 1958 (Tydeidae) , preying on their eggs and immatures, and with Tenuipalpus heveae Baker, 1945 (Tenuipalpidae) (Hernandes & Feres, submitted). It was found associated with Z. agistzellia sp. n.

Etymology: From Latin quasi, meaning almost, suchlike, and Latin mas, meaning male. The specific designation refers to the similarities of males of Agistemus concerning some dorsal aspects: pair f1 born on the main shield, and pair e1 reduced; the pair d2, however, is set on small platelets aside the main shield in males as much as in females.

Type material: Holotype female (n. 5.832) collected from Hevea brasiliensis Muell. Arg. (Euphorbiaceae) , February 6, 2002, Cedral, São Paulo, Brazil. Paratypes: 4 females, 5 males, 2 deutonymph females, 2 deutonymph males, 2 protonymphs, 3 larvae from the same host and type locality, collected from May 2001 to January 2003.

Both species herein described appear to present some difficulties for their placement among stigmaeids. Females of Zetzellia agistzellia sp. n, undoubtedly fit in Zetzellia , whereas males clearly fit under Agistemus . If only females or males had been found, they would certainly have been classified as Zetzellia or Agistemus , respectively. However, all stages were found together, and no females of Agistemus nor any “traditional” males of Zetzellia were found, and that fact allows us to conclude that they belong to the same species. Analysis of immature stages also adds more strength to this hypothesis, as we have found two kinds of deutonymphs: female, with dorsal arrangement of shields and genital setae as in the adult female (except seta g1, present only in adult females), and male, with dorsal shields and genital setae as in the adult male. In Z. quasagistemas sp. n, females expressly fit under this genus, whereas males have the setae f1 unusually inserted on the main plate, resulting in an additional pair on this shield. This latter character is often found in males of Agistemus . In this species, there are also two kinds of deutonymphs, which resemble females and males, respectively ( Figs. 41–43 ).

This is not the first time these two genera have been the subject of discussion. Wood (1967) argued that the dorsal organization of platelets in Zetzellia has four different patterns, which exhibit a gradual change from 3 pairs of small median plates to a large median plate (= the hysterosomal shield). In that context, the genus Agistemus , which has a far more uniform arrangement, appears to represent a next step towards the integration of hysterosomal shield. Since both genera share many features and can only be distinguished by the location of seta d2 ( Wood 1967), Wood considered that the distinction was not enough to support a new genus, Agistemus . He solved this by suggesting the definition of Zetzellia to be enlarged to include all species of Agistemus . However, his suggestion was not accepted by most acarologists (e.g. Meyer 1969, Khanjani & Ueckermann 2002), who continued to use the previous definition of Summers (1960) and Gonzalez (1965).

Based on ontogenetic data, Gonzalez (1965) believed that Agistemus evolved from the Z. maori group of species. Meyer (1969), however, suggested ontogenetic data could merely support that “ Zetzellia is ancestral to Agistemus ” (p. 256). The present authors believe that Agistemus probably originated from a Zetzellia ­like ancestor, which evolved a large median shield comprising 5 pairs of setae, including d2. Since Zetzellia spp. present heterogenous arrangements of dorsal shields, and if Gonzalez (1965) is right, that genus might be paraphyletic, with a group of species giving birth to a new genus, Agistemus .

The discovery of such species raises some problems concerning the genus concept among Stigmaeidae . Since we found two species which have features of both Agistemus and Zetzellia present in different sexes, maybe those features do not reflect a real degree of difference enough to split two genera, and should be under review. Wood (1967) mentioned another two species of Zetzellia , Z. maori Gonzalez (1965) and Z. oudemansi Wood (1967) , which have different organization of dorsal shields for females and males. Males of the two latter species resembles Z. australis in the aspect of dorsal shields. Zetzellia malvinae Matioli, Ueckermann & Oliveira (2002) and Z. graeciana ( Gonzalez 1965) also have different dorsal organization for females and males.

It is an intriguing fact that, concerning two species that closely resemble Z. agistzellia sp. n, namely Z. gonzalezi and Z. silvicola , only females were found, and it would be worthwhile to speculate on whether the males of those species also resemble the Agistemus ­like males of Z. agistzellia . Males of Zetzellia quasagistemas sp. n, are unusual in having 5 pairs of setae on the hysterosomal shield. The presence of at most 4 pairs of setae was thought to be the rule in Zetzellia ( Summers 1966) . A remarkable feature of males of Agistemus is that the dorsal seta f1 is borne on the hind margin of hysterosomal shield, and seta e1 seems to be frequently reduced. Zetzellia quasagistemas also has those features. Unusually, Agistemus tarsilobus Flechtmann (1995) appears to have that setae f1 directly inserted on the tegument.

It is an unfortunate fact that only a few descriptions of Zetzellia spp. include details of males, e.g. Z. mali (Ewing, 1917) , Z. graeciana , Z. maori , Z. oudemansi and Z. malvinae . Most species have been described based only on females, which is problematic given that a single species can show sex differences enough to possibly mislead taxonomists to erect new taxa. The discovery of more species with such sexually dimorphic features shall help to solve this puzzle, and a complete cladistic analysis of stigmaeid genera using molecular, morphological and ontogenetic characters should provide a clearer picture of the evolution of this family. Descriptions of immatures should also throw more light on this matter.

Figures

FIGURES 23 – 29: Zetzellia quasagistemas sp. n. (female) 23. dorsum, 24. anogenital region, ventral, 25. palp, 26 – 29. legs I – IV.

FIGURES 30 – 36: Zetzellia quasagistemas sp. n. (male) 30. dorsum, 31. anogenital region, ventral, 32. palp, 33 – 36. legs I – IV.

FIGURES 37 – 43: Zetzellia quasagistemas sp. n. (immatures) 37 – 38. Larva. 37. dorsum, 38. anogenital region. 39 – 40. Protonymph. 39. dorsum, 40. anogenital region. 41 – 42. Deutonymph female. 41. dorsum, 42. anogenital region. 42. Anogenital region of deutonymph male.