Evolutionary morphology of the hemolymph vascular system in hermit and king crabs (Crustacea: Decapoda: Anomala)

Abstract

The morphological transformation of hermit crabs into crab-like king crabs in the evolution of decapod crustaceans represents a remarkable case of carcinization or evolutionary shaping into a crab-like form. In this study, we focus on internal organs such as the hemolymph vascular system and adjacent anatomical structures of several Recent hermit crab (Paguridae) and king crab (Lithodidae) species. There are various correspondences in the morphology of the arterial systems in the dorsal cephalothorax of the two taxa, especially with regard to the anterior aorta, anterior lateral arteries, and hepatic arteries. In the pleon, the posterior aorta in both taxa displays a proximal bifurcation and follows an asymmetrical course. The ventral vessel system, on the other hand, which mainly supplies the limbs, differs significantly between the taxa, with pagurids displaying the plesiomorphic condition. The pattern of the ventral vessel system in Lithodidae is influenced by morphological transformations of integumental structures during carcinization. One of these transformations was the broadening of the sternites, which resulted in a widening of the space between the endosternites. In addition, changes in the morphology of the endophragmal skeleton in Lithodidae led to an increase in the potential for intraspecific variability and interspecific variation in the arterial branching pattern.

Evolutionary morphology of the hemolymph vascular system of basal araneomorph spiders (Araneae: Araneomorphae)

“…changing origins of arteries, has also been reported in crustaceans (Keiler et al, 2015(Keiler et al, , 2013. Keiler et al (2013) correlate this variability with changes in the morphology of the endophragmal skeleton.…”

“…changing origins of arteries, has also been reported in crustaceans (Keiler et al, 2015(Keiler et al, , 2013. Keiler et al (2013) correlate this variability with changes in the morphology of the endophragmal skeleton. In Lithodidae, a widening of the latter led to more space between the endosternites and is therefore interpreted as a higher freedom for growth through the removal of "guiding structures".…”

Crab or lobster? Mental principles underlying the categorization of crustaceans by biology experts and non-experts

“…However, not all members of the Brachyura are fully carcinized and do not therefore match the typological concept of a crab (Scholtz, 2014). Additionally, crabs in the typological sense are not only found within the Brachyura, but also in several other decapod crustacean groups that underwent carcinization convergently (see McLaughlin and Lemaitre, 1997;Morrison et al, 2002;Reimann et al, 2011;Tsang et al, 2011;Anker and Paulay, 2013;Bracken-Grissom et al, 2013;Guinot et al, 2013;Keiler et al, 2013). Therefore, in the case of crabs, classification based on phylogenetic relationships strongly contradicts the more intuitive grouping by external morphological similarities (see Scholtz, 2014).…”

An “ancient” complexity? Evolutionary morphology of the circulatory system in Xiphosura

“…The identity of these structures as circulatory organs, however, is doubtful for two reasons: (i) The identification was based on exclusion, in comparison to structures thought to be the digestive tract and nervous system (Ma et al, 2012(Ma et al, , 2014 rather than on convincing structural details. (ii) The reconstruction of this structure as a whole does not resemble the vasculature in any studied Recent arthropod group (Klußmann-Fricke et al, 2012;Huckstorf et al, 2013;Keiler et al, 2013Keiler et al, , 2015Wirkner et al, 2013;this study). Nevertheless, complex circulatory systems in groups of stem lineage arthropods seem likely.…”

“…The occurrence of complex circulatory systems in a broad range of arthropod taxa (Klußmann-Fricke et al, 2012;Huckstorf et al, 2013;Keiler et al, 2013Keiler et al, , 2015Wirkner et al, 2013) suggests that this complexity might be plesiomorphic and a feature of the arthropod ground pattern. As yet there is no definite answer to this question, but recent work on the fossil Fuxianhuia protensa Hou, 1987 claims to have found a complex circulatory system in this Cambrian stem lineage arthropod (Ma et al, 2014).…”