On the ontogeny of Leptodora kindtii (Crustacea, Branchiopoda, Cladocera), with notes on the phylogeny of the Cladocera

Abstract

Leptodora kindtii, a large predaceous cladoceran, is among the most deviant species of the Cladocera. Therefore, its phylogenetic position has traditionally proven difficult to determine. Its many peculiar features include, among others, long, stenopodous, forwardly directed trunk limbs, a posteriorly placed dorsal brood pouch, a tri-lobed lower lip, and a long, segmented abdomen. This study describes the ontogeny of L. kindtii (Haplopoda), including general body proportions, appendages, the carapace, and other external structures in an attempt to facilitate the comparison of its aberrant morphology to that of other branchiopods. In general, the early embryos are similar to the early embryos of other cladoceran taxa with respect to body shape and size and position and orientation of the early limb buds. Many of the unusual features of L. kindtii appear late in ontogeny. The carapace appears at an early stage as a pair of dorsolateral swellings in a position corresponding to the gap between the mandibles and the first pair of trunk limbs; it later becomes posteriorly transposed by a gradual fusion of its more anterior parts to the dorsal side of the thorax. The tri-lobed "lower lip," under the labrum of the late embryo and the adult, develops as a fusion of the first maxillae (lateral lobes) to an elevated sternal region behind the mouth (median lobe). The stenopodous, segmented trunk limbs in the adult develop from embryonic, elongate, subdivided limb buds, similar to those seen in early stages of other branchiopods. Two conflicting possibilities for the phylogeny of the Cladocera, involving two different positions of L. kindtii (Haplopoda), are discussed. Several characters support a sister-group relationship between the Haplopoda and Onychopoda. However, some characters support the Anomopoda and Onychopoda as sister groups, leaving the Haplopoda outside this clade. In contrast to recent suggestions, we prefer to retain the term "Cladocera" in its original sense as comprising the Haplopoda, Ctenopoda, Anomopoda, and Onychopoda.

Cell lineage analysis of the mandibular segment of the amphipod Orchestia cavimana reveals that the crustacean paragnaths are sternal outgrowths and not limbs

“…2, 7). Even the median lobe of the so-called lower lip of the raptorial cladoceran Leptodora kindtii might represent fused paragnaths [55]. Accordingly, we tentatively conclude that the paragnaths lobes are homologous throughout Crustacea.…”

Unraveling the origin of Cladocera by identifying heterochrony in the developmental sequences of Branchiopoda

“…[40,68] and Haplopoda e.g. [49,71,72,85-87]. This developmental study into Penilia avirostris constitutes the first attempt to describe both external and internal morphology in parallel in a cladoceran species.…”

“…The parthenogenetically produced subitaneous eggs of cyclestheridans and cladocerans develop within the dorsal brood pouch under the carapace of the mother animal (Cyclestherida [60-62]; Cladocera [1,4]). Within them, various embryonic stages develop which are morphologically clearly distinguishable and separated by embryonic molting cycles (Cyclestherida [60-62]; Cladocera [49,50,63-65]). The non-swimming embryo-like larvae [49] which hatch are carried under the dorsal part of the carapace (Cyclestherida: [60-62]; Cladocera: e.g.…”

Stages and other aspects of the embryology of the parthenogenetic Marmorkrebs (Decapoda, Reptantia, Astacida)

“…This is not a far-fetched assumption as demonstrated by other crustaceans. For instance, the raptorial cladoceran Leptodora kindtii shows a direct development in its parthenogenetic phase (Gerberding 1997;Olesen et al 2003) whereas the bisexually produced embryos hatch as a specialized nauplius larva (Sars 1873).…”