Megalolaelaps Berlese, 1892 (Megalolaelapidae)

MAŠÁN, PETER & HALLIDAY, BRUCE, 2014, Review of the mite family Pachylaelapidae (Acari: Mesostigmata), Zootaxa 3776 (1), pp. 1-66 : 50-51

Genus Megalolaelaps Berlese, 1892 (Megalolaelapidae)

Pachylaelaps (Megalolaelaps) Berlese, 1892c: 72 . Type species Pachylaelaps haeros Berlese, 1888 .

Notes. When Berlese (1892c) described Megalolaelaps , as a subgenus of Pachylaelaps , he included two species, Pachylaelaps heros Berlese, 1888 (sic, should be haeros ) and Pachylaelaps athleticus Berlese, 1888 , but did not designate a type species. He also doubtfully included Pachylaelaps tetragonoides (Dugès) , P. gigas (Dugès) and P. savignyi (Audouin) in this subgenus. Vitzthum (1942, page 761) designated M. haeros as the type species.

The original descriptions of M. haeros and Megalolaelaps are of limited value for species and genus recognition. Fonseca (1946) provided a more useful re-description of Megalolaelaps immanis Berlese, 1910 , and also proposed the new monotypic family Megalolaelapidae (as Megalolaelaptidae) to accommodate this genus. We consider this action to be reasonable because M. immanis exhibits a combination of characters not observed in Pachylaelapidae . These species are 3–4 mm long and up to 2 mm wide, so they are among the biggest known Mesostigmata . More valuable information about Megalolaelaps can be found in Gorirossi-Bourdeau (1956) and Hennessey & Farrier (1988).

Fonseca (1946), Gorirossi-Bourdeau (1956) and Hennessey & Farrier (1988) redescribed and illustrated two species of Megalolaelaps , from which we derived the brief differential comparison between Megalolaelapidae and Pachylaelapidae (see below). Fonseca (1946) described the female and male of Megalolaelaps immanis , and Gorirossi-Bourdeau (1956) and Hennessey & Farrier (1988) redescribed the female of Megalolaelaps ornatus ( Keegan, 1946) (Gorirossi-Bourdeau only gnathosomal structures of the species). Females of these species can be easily separated based especially on the position of the metasternal lyrifissures, the form of the epigynal shield, and the form and size of the metapodal platelets. In M. ornatus , (1) the metasternal gland openings are unusually situated on the sternal shield; (2) the epigynal shield is pyriform, constricted between coxae IV and widened posteriorly, with the genital setae almost medially positioned on the shield; (3) the metapodal platelets are bacillate and inconspicuous in size. In M. immanis , (1) the metasternal gland openings are not placed on the sternal shield and the shield has the normal two pairs of lyrifissures; (2) the epigynal shield is irregular, subpentagonal, with the anterior portion more expanded than the narrow posterior part, concave on its posterior margin, with genital setae inserted closer to the lateral margins; (3) metapodal platelets are suboval and conspicuously enlarged.

Both species possess the following specific character states that are not found in Pachylaelapidae , and which could be considered as the main diagnostic characters for the family Megalolaelapidae : (1) ventral shield absent (in Pachylaelapidae , the ventral shield bears at least one pair of ventral setae and is always developed, either as a part of the genitiventral or ventri-anal shield in females, or as a part of the holoventral or ventri-anal shield of males); (2) exopodal platelets are absent, so the inner margin of the peritremes is adjacent to the soft integument of the circum-coxal surface (in Pachylaelapidae , exopodals are present, usually well developed and covering the soft integument of the intercoxal areas, closely abutting or fused to the peritrematal shield to form a well developed endopodal-exopodal-peritrematal shield complex); (3) the anal shield in the male is free (in Pachylaelapidae , the anal shield of males is always fused and incorporated into the holoventral or ventri-anal shield); (4) the spermatodactyl is long, tightly coiled, and inserted medially in the outer lateral surface of the movable digit (in Pachylaelapidae , the spermatodactyl is never tightly coiled); (5) the size of the three cheliceral segments exhibits sexual dimorphism, in which the cheliceral segments of the male are larger and more robust than those of the female (in Pachylaelapidae , the chelicerae of both sexes are similar in size); (6) the palp trochanter has a large, horn-like projection on the anteroventral surface, which does not occur in Pachylaelapidae .

In addition, there may be other characters in Megalolaelapidae which are considered as unusual or rarely developed in Pachylaelapidae , for example: (1) metasternal setae inserted on soft integument, (2) hypertrichy of lateral and ventral soft integument, (3) epistome with anterior apex bifid, (4) palp apotele 2-tined. Unfortunately no information on the sperm access system or dorsal shield and leg setation in Megalolaelaps is available in the published literature. It is not clear why some authors ( Vitzthum, 1931; Baker & Wharton, 1952; Krantz, 1965; Hennessey & Farrier, 1988) classified Megalolaelaps in the Pachylaelapidae , except spur-like setae pl1 and al1 on the tarsus II (in female of M. ornatus ), which can also be found in some Macrochelidae ( Krantz, 1965) .