Arthropod Structure & Development最新文献

The objective of this study is to gain a better understanding of the not well understood egg-transportation mechanisms through the female reproductive systems of crabs. For this, Carcinus maenas was chosen as a model to study the cuticular epithelium underlying the cuticle of the vagina and the ventral seminal receptacle. This cuticular epithelium is investigated by performing histochemical and ultrastructural analyses of the epithelial cells. The results show that this epithelium consists of specialized epithelial cells that show characteristic features of muscle-attachment cells or tendon cells, such as an abundance of microtubules in their cytoplasm and hemi-adherens junctions. These results improve our understanding of the mechanisms involved in the reproduction in brachyuran crabs and will have to be taken into consideration in the future, when trying to understand the functional morphology of the female reproductive system of crabs.

Claw characteristics of oribatid mites are strongly correlated with environmental factors and these characters remain constant throughout development when immatures and adults share the same ecology and lifestyle. In the present study, claw traits of oribatid mite species with constant ecology were compared with those of species showing a clear ecological shift between juvenile and adult stage. The arboreal Sellnickia caudata and the saxicolous Niphocepheus nivalis dwell in the same microhabitat during their life-cycle, whereas immatures of the terrestrial Carabodes areolatus and Mycobates carli, as well as of the aquatic Hydrozetes lemnae, are, in contrast to their adults, endophagous, meaning they feed and burrow within lichen and plant tissue. We performed a geometric morphometric investigation of their claws and could reveal significant differences in the claw shapes of immatures and adults of all species, except for N. nivalis. Claws of the endophagous juveniles of C. areolatus, M. carli and H. lemnae are generally sharper and higher than those of their adult counterparts. The burrowing lifestyle of the immatures apparently necessitates such specific claw morphologies. Despite having a constant ecology, the arboreal S. caudata also shows distinct differences between immature and adult claw traits, with juveniles possessing stronger curved and sharper claws. But immature stages also possess an additional tarsal adhesive pad which lacks in the adult stage. The presence or absence of this additional adhesive pad apparently requires changes in claw morphology to allow firm attachment on diverse plant surfaces. The present results demonstrate that claw characteristic can change during the development depending on the given ecological factors faced by each developmental stage and depending on the presence of additional attachment devices.

All major arthropod taxa possess excretory glands - a type of filtration nephridium considered ancestral for this group. Pycnogonids form a basal branch of the arthropod phylogenetic tree and are ancient aquatic chelicerates, but they were believed to lack specialised excretory organs, except for Nymphopsis spinosissimum (Ammotheidae). Whether this condition is unique or common remained unknown due to lack of anatomical data for many species. Here we examined four nymphonids: Nymphon brevirostre, Nymphon grossipes, Nymphon serratum and Pentanymphon antarcticum using scanning and transmission electron microscopy, as well as light microscopy. In adults of all four species, we found excretory organs and describe ultrastructural details of all their parts: sacculus, reabsorption channel, excretory channel and the pore. In addition to the definitive (adult) excretory organs, we also detected some larval and juvenile transitory ones and were able to trace the origin of the sacculus podocytes from the non-epithelial mesoderm of the horizontal septum. All excretory organs are located in the appendages of the first three postocular segments of the cephalosoma (although not necessarily in all of them at once) because these areas can maintain the high hemolymph pressure necessary for ultrafiltration. The ultrastructure and development of the sacculus point toward the secondary nature of this cavity, although the coelomic status of the sacculi in sea spiders and other arthropods is still unclear.

Sea spiders (Pycnogonida) are marine chelicerates. As a sister clade to Euchelicerata, Pycnogonida are an interesting group for comparative anatomy, however data on pycnogonid anatomy and biology remain scarce. This research provides a detailed account of the complete male reproductive system, gametogenesis, and sperm structure of a sea spider at the ultrastructural level. The male reproductive system of P. femoratum includes the testis, femoral, and ovigeral glands. The testis is typical of Pycnogonida: U-shaped with pedal outgrowths, opening with gonopores on legs 2-4. The testis lays within the horizontal septum, separated from it by ECM. The reproductive sinus is reduced. The ventral wall of the testis is germinative, spermatogenesis proceeds in cysts, all stages are evenly distributed throughout the whole testis. Sperm of P. femoratum is a typical sperm of animals with fertilization in mucus but without an acrosome. It lacks apomorphic euchelicerate features such as an acrosomal filament and implantation fossa. Femoral and ovigeral glands are sex-specific and likely related to reproduction. Ovigeral glands possibly secrete a fungicide substance, while the function of femoral glands remains obscure.