The external morphology of the pseudoscorpion Roncus andreinii

Abstract

The external morphology of the four postembryonic instars of Roncus andreinii (di Caporiacco, 1925) is described and compared with one of the related R. lubricus L. Koch, 1873 (Gabbutt & Vachon, 1967), with particular emphasis on disposition of the chelal trichobothria in relation to growth. From the evaluation of characters it is concluded that a few morphometric and chaetotaxic characters (i.e. the length, ratio and shape of pedipalpal articles, the ratio of fingers/pedipalpal hand, the chaetotaxy of sternites II and III) represent good specific discriminants, while the relative position of trichobothria along the chelal axis is nearly the same in both species. The localization of the growing and non‐growing regions along the pedipalpal fingers may be of practical use in the search for new taxonomic characters.

Postembryonic development in pseudoscorpions: allometry in Geogarypus italicus (Pseudoscorpiones: Geogarypidae)

“…In observing the extent of the non-growing distal region, the situation is completely inverted with a narrower distal non growing region in the tritonymph to female stage. The calculated extent of the growing portion (expressed as %) is different when compared to values reported for the families Chernetidae, Cheliferidae and Neobisiidae (Gabbutt 1969, 1972; Gardini & Benelli 1991). However, the absolute length of the distal non-growing region (DNGR) of G. italicus are comparable with those derived from studies on other species.…”

“…It appears also that elements proximal to the tip of the chela move independently from the trichobothria placed in the basal portion. In comparing the relative positions of G. italicus with other species like Roncus lubricus L. Koch, 1873 and R. andreiini (di Caporiacco, 1925) the most relevant feature is the ratio value of est that in G. italicus is closer to trichobothria placed in the basal portions such as eb, esb and isb while in both species of Roncus L. Koch, 1873, the value of the est ratio is comparable to the relative position of those trichobothria located in the apical portion of the chelal axis (Gabbutt & Vachon 1967; Gardini & Benelli 1991). The calculated ratios and increments clearly prove that the growth of the chelal axis does not occur evenly during the post embryonic process; for instance, in G. italicus differently from what was observed in other species (Gabbutt 1969), the basal and apical portions seem to undergo limited growth.…”

“…The terminology adopted follows Chamberlin (1931), Gabbutt (1972) and Gardini & Benelli (1991). In this work the term instar has been applied in its usual definition to identify the developmental phase between two molts (Canard & Stockman 1993), while stage is used when a pair of successive instars are considered.…”

“…Testing trichobothria positions.-Since trichobothria appear sequentially, it is possible to quantify the ''movement of each of them'' during the post embryonic process by simply subtracting their distance from the tip of the chela from that measured in the previous instar: negative values will describe a movement toward the tip in contrast with positive values that will outline a shift to a more basal position along the chela (following Gabbutt (1969), Gardini and Benelli (1991)).…”

“…Gabbutt and Vachon were the first who explored chelal allometry (Gabbutt & Vachon 1965, 1967Gabbutt 1969Gabbutt , 1972, followed by only two studies by Sivaraman (1982) and Gardini & Benelli (1991). Studies related to other body parts are even more rare and mostly focused on addressing sexual dimorphism (Zeh 1987;Palen-Pietri et al 2019), despite the fact that many body features could potentially yield interesting information (Harvey 1987(Harvey , 1988.…”