Abstract
Most morphological studies focus on adult specimens, or if developmental studies are pursued, especially in Euarthropoda, they focus on embryonic development. Araneae (spiders) is one of these groups, in consequence with understudied post-embryonic development. Here we present aspects of the post-embryonic stages of different species of Mesothelae, sister group to the remaining spiders (when fossil species are not taken into account). We used different imaging methods and measured different external morphological structures to detect possible ontogenetic changes. One structure exhibiting post-embryonic changes is the chelicera. Here the significant change occurs between the last immature stage and the adult, yet only in males. For the spinnerets, we could not detect ontogenetic changes, but instead a high variability in length and width, probably due to their lack of pivot joints between the elements. The strongest morphological change during ontogeny occurred on the sternum, which begins with a rather roundish shape in the first stage and changes to being fairly elongate in shape in the last immature stages and the adult. This specific sternum shape only occurs in adults of mesothelan spiders, while opisthothelan spiders have a broader sternum also in the adult. We discuss our results in an evolutionary context, also taking into account recent finds of fossil spiders.
Highlights
The majority of zoological research focuses on adult individuals (e.g. Minelli et al 2006)
The research mainly focused on Ryuthela nishihirai, but the results were compared with data collected from Ryuthela ishigakiensis Haupt, 1983, and Heptathela kimurai and Liphistius batuensis Abraham, 1923
Major changes in the morphology of the spiderling occur before immature stage III and during the transition from the penultimate stage to the adult stage, resulting in the sexual dimorphism in the adults
Summary
The majority of zoological research focuses on adult individuals (e.g. Minelli et al 2006). The morphology of immatures and its differences from that of the conspecific adults remains largely unknown, especially (but ) concerning the post-embryonic stages. One such animal group is Araneae, spiders. Mesothelan spiders are medium to large size and live in burrows sealed with a door out of silk and soil and spend their entire life inside the burrow. Their prey is captured right in front of the burrows while close contact to the entrance is kept. The only exceptions are representatives of the group Liphistius Schiödte, 1849 which use fishing lines to catch their prey (Haupt 2003)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
