Development of the venom ducts in the centipede Scolopendra: an example of recapitulation

Abstract

In contrast to previous claims that (a) there is a law of recapitulation and, conversely, (b) recapitulation never happens, the evolutionary repatterning of development can take many forms, of which recapitulation is one. Here, we add another example to the list of case studies of recapitulation. This example involves the development of the venom claws (forcipules) in the centipede Scolopendra subspinipes mutilans, and in particular the development of the duct through which venom flows from the gland that produces it (proximal) to the opening called the meatus (distal) through which it is injected into prey. Most of the information we present is from early postembryonic stages--these have been neglected in previous work on centipede development. We show that the venom ducts arise from sutures that are invaginations of the cuticle. In S. s. mutilans, the invagination in each forcipule forms into a tubular structure that detaches itself from the exoskeleton and moves toward the center of the forcipule. This is in contrast to extant Scutigera, and also, probably, Scolopendra's extinct Scutigera-like ancestors, where the duct remains attached to the cuticle of throughout development. Thus, S. s. mutilans exhibits a recapitulatory repatterning of development.

The embryoid development of Strigamia maritimaand its bearing on post-embryonic segmentation of geophilomorph centipedes

“…I think the 'embryoid' terminology should be applied also to the scolopendromorphs, as they are characterized by three post-hatching stages brooded by the mother, separated by moults. In Scolopendra, the hatching instar, clearly corresponding to the last embryonic stage as in Strigamia, is called first embryonic stage by Heymons [30] and postembryonic stage I by Dugon et al [31]. The following two stages, i.e.…”

“…The following two stages, i.e. the proper post-embryonic stages, are called, respectively, second embryonic stage and foetus by Heymons [30], postembryonic stage II and fetus by Dugon et al [31], and, rather confusingly, third embryonic stage and adolescens I by Lawrence [32] and Brunhuber [33]. It is of course possible that even in this case some moults might have not been recognised, and that the situation might be more complex than it appears.…”

“…Consequently, the homology of these stages with those of Strigamia might not be straightforward, although according to their general level of development, it would seem quite plausible that Dugon's [31] postembryonic stage II in Scolopendra could match with Strigamia's peripatoid, and that the foetus in the two species would correspond. Given the extremely limited, and in general dated, literature on centipede development and considering the major differences between the epimorphic model of embryoid and the anamorphic model of 'larva', I consider it unwise at the moment to try to homologise further early post embryonic stages between Epimorpha and the more basal centipedes.…”

“…Possible evolutionary scenarios have been discussed elsewhere from both a morphological [42,43] and a palaeontological point of view [44]. A detailed analysis of development from embryo to adult has only been done, at least in part, for Scolopendra, where the foetus appears to have the same forcipular articles as the adult [31].…”

“…I don't know whether the additional article is really articulated or just a distal modification of the more basal article, but it is interesting to note that, although my material is far from clear, in the previous stage, the foetus, there could be up to 6 segments (Additional file 3: Figure S1). If this subdivision is real, the last two articles would represent the tarsus and the ungulum/claw, later fused to form the tarsungulum, as the evident transverse sulcus in the adolescens I and in Scolopendra [31] would confirm (see [43] for additional evidence and a detailed discussion). With the same argument, the additional intermediate article could be interpreted as a developmental remnant of the prefemur to be fused with the tronchanter, later in development.…”