Observations on the life history ofEukoenenia chilangaMontaño (Arachnida: Palpigradi)

Abstract

The life history of a palpigrade is reconstructed through morphological and morphometric multivariate analyses applied to a series of 37 individuals collected in a single locality in Tlalnepantla, Estado de Mexico, during different seasons. Those analyses reveal the presence of three life stages: protonymph, deutonymph and adult. Morphologically, males and females can be distinguished as deutonymphs and adults. Morphometrically the sexes can be recognized in all of the life stages, unprecedented for the family Eukoeniidae. Our current knowledge of the life history of palpigrades is quite limited and slightly confusing because of the terminology chosen by former authors. Living members of the order Palpigradi are classified into two different families: Prokoe- neniidae Condeand Eukoeneniidae Petrunkevitch, which differ in their life histories. Rucker (1903) presented the first life history of a palpigrade, specifically that of Prokoeninia wheeleri (Rucker) from Texas, USA. This species has four life stages, which she named: ''First Known Stage'', ''Second Stage'', ''Last Stage'', and ''Adult''. Subsequently, Van der Hammen (1982), reviewing Rucker's findings, indicated that the first known instar had no opisthosomatic papillae, two pairs in the second known, and three pairs in the third known instar and in adults. Van der Hammen then speculated that because ''There is an important gap between the sizes of Rucker's first and second known instars, and the occurrence of an instar of intermediate size, with one pair of papillae, seems highly probable.'' Finally, he proposed the existence of a prelarva (without any supporting evidence), a larva (Rucker's first known instar, without papillae), a protonymph (speculative, with one pair of papillae), a deutonymph (Rucker's second instar), a tritonymph (Rucker's third instar) and the adult; thus, from Rucker's four observed instars, Van der Hammen stretched Prokoenenia life history to include six stages! Conde ´ (1984) working with Eukoenenia proposed that these palpigrades have one instar less than prokoeneniids, but named them as follows: Immature A (sexes not recognizable), Immature B (female subadult), Immature C (male subadult), and adults (male and female); that is, three instars but with different terms between female (B) and male (C) subadults. He further proposed that in prokoeneniids, the Immature A stage is divided into two subsets A1 and A2 (Conde ´ 1984, 1996, 1998), which is rather confusing: B and C represent the same instar, whereas A1 and A2 represent two consecutive instars. A preliminary morphological analysis of a series of 12 specimens of Eukoenenia chilanga Montano 2012 collected on 13 June 2003 north of Mexico City suggested the presence of three distinct instars in the field (Table 1; also, see Montano 2006). Therefore, extra collecting efforts were carried out in 2006-2007, and a comprehensive morphometric analysis was undertaken. METHODS