Mixturopoda, Baker, Anne S. & Monson, Frank D., 2007

Baker, Anne S. & Monson, Frank D., 2007, Mixturopoda Baker and Monson, a new genus of the uropodine family Metagynuridae (Acari: Mesostigmata) from the British Isles, Zootaxa 1665, pp. 1-17 : 2-4

Mixturopoda gen. nov. ( Figs. 1–27 )

Diagnosis

The deutonymph and adults can be distinguished from those of Metagynella , the only other metagynurid genus, by the absence of pedofossae and the presence of a large, rounded triangular–pentagonal tritosternal base (versus small and approximately rounded rectangular). Also, the genital shield of the adult female of Mixturopoda bears setae st5 (versus devoid of setae) and is not incorporated into the ventral plate, while internal genitalic structures between coxae IV are absent in both sexes.

Description

Adult idiosoma approximately parallel-sided, with foveate integument; undivided dorsal shield covers dorsum, bears c. 46 pairs setae; posteroventral marginal shield present, not subdivided into platelets; tritosternum uniramous, base rounded triangular–pentagonal, wider than long; jugular plates absent; margins of hypognathal groove not fused; peritremes straight, not convoluted; exo- and endopodal shields not fused between coxae I and II; palp setal complement (trochanter–tarsus) 2-5-4-10 -13, missing seta on genu hypothesized to be d3, apotele bifid; chelicera with dorsal seta and distal bulbous sensilla-like structure on fixed digit, pilus dentilis, lateral lyrifissure and sclerotized node absent; gnathotectum with roughly triangular base and long slender central prong; scabellum and pedofossae absent; coxae I approximately cylindrical, located in gnathopodal cavity, not covering base of tritosternum (in uncleared specimens, almost abutting base); femur I with 1 anterolateral and 4 dorsal setae, II with 9 setae, III and IV with 6; genu II with 8 setae; tibiae I– IV with 7 setae, comprising 3 dorsals, 2 laterals and 2 ventrals; tarsus I without ambulacrum, terminating in enlarged hollow receptors; tarsi II–IV with dorsal lyrifissure near peripodomeric fissure, 17 setae present, posterolateral seta pd3 absent from basitarsi, dorsal setae ad1 and pd1 fine and noticeably longer than other tarsal setae. Female genital shield located posterior to coxae IV, not incorporated into ventral shield, bearing genital setae st5, paragynial shields absent; internal genitalic structures between coxae IV not visible; anus located on ventrianal shield. Male genital aperture circular, located between coxae IV; femur II with greatly enlarged anteroventral seta, tarsus II curved, terminating in large claw-like structure interpreted as seta av1, posteroventral seta pv1 of tarsi III–IV enlarged. Deutonymph with 30 pairs setae on undivided dorsal shield, outer setal row borne on separate platelets (some may be contiguous); marginal shield represented by platelets, each bearing 1 seta; opisthogastric region with small shield just posterior to coxae IV and larger ventrianal shield.

Phoretic deutonymph, protonymph and larva Unknown.

Type species

Mixturopoda evansi sp. nov., by monotypy.

Remarks

The family Metagynuridae was proposed by Balogh (1943) for his monotypic genus Metagynura . Unaware of Balogh’s publication, Camin (1953) erected the new family Metagynellidae to accommodate the genus Metagynella . Subsequently, Metagynura and Metagynellidae were found to be junior synonyms of Metagynella and Metagynuridae respectively ( Ryke 1958). Until now, the only additions to the family have been new species of Metagynella .

Metagynurids are diagnosed by the position of the female genital shield posterior to coxae IV; in other uropodines it is between coxae II–IV. The new taxon is assigned to the family on the basis of possessing this unique character state. Comparison of M. evansi with specimens and/or morphological accounts of the 15 nominate species of Metagynella shows that it shares with them other morphological features originally attributed to the family, namely: ambulacra absent from tarsi I ( Balogh 1943; Camin 1953); markedly long sternal shield ( Balogh 1943), and small male genital aperture located between coxae IV, non-contiguous coxae I inserted in the gnathopodal cavity, dorsal shield covering the idiodorsum, marginal shield comprising a narrow posteroventral border, dorsal marginal shields absent and cheliceral shaft very long ( Camin 1953). Also, M. evansi and Metagynella species have subcylindrical coxae I that do not cover the tritosternal base. The familial characteristic of presence of pedofossae ( Balogh 1943; Camin 1953) is lacking in Mixturopoda , as are oval internal genitalic structures between coxae IV ( Balogh 1943) and an oval-shaped idiosoma with smooth integument ( Camin 1953). Furthermore, the form of the tritosternal base, which is regarded as constant within uropodine genera ( Hirschmann & Zirngiebl-Nicol 1969), clearly differs between the new taxon and species of Metagynella (large and rounded triangular–pentagonal versus small and approximately rounded rectangular). All species of Metagynella for which the female is known have the genital shield devoid of setae and enclosed by the ventral shield. Neither the free female genital shield nor the location of setae st5 on this shield seen in M. evansi has previously been recorded in the Uropodina . These unique character states, together with the lack of pedofossae and the form of the tritosternal base, clearly distinguish the new taxon from Metagynella and, therefore, the establishment of a new genus is warranted.

The placing of Mixturopoda in the Metagynuridae necessitates the following amendments to the familial diagnosis: female genital shield posterior to coxae IV, free or enclosed in the ventral shield, with or without setae st5; coxae I subcylindrical, not covering the tritosternal base; idiosoma oval or parallel-sided, with smooth or foveate integument; oval internal genitalic structures between coxae IV present or absent; pedofossae present or absent; tritosternal base small and approximately rounded rectangular or large and rounded triangular–pentagonal. The diagnosis of Metagynella should also be qualified as follows: female genital shield enclosed in the ventral shield, without setae; idiosoma oval, with smooth integument; oval internal genitalic structures between coxae IV present or absent; pedofossae present; tritosternal base small, approximately rounded rectangular.

Figures

FIGURES 1 – 2. Mixturopoda evansi gen. nov., sp. nov. (female). 1, idiosoma, dorsal view, with detail of j 1 to right, right-hand member of two posteriormost setal pairs arrowed; 2, idiosoma, ventral view. DSH = dorsal shield, ESH = exopodal shield, GSH = genital shield, i = poroid, MpSH = metapodal shield, MSH = marginal shield, pas = postanal seta, SSH = sternal shield, VSH = ventrianal shield.