Although molecular analyses have contributed to a better resolution of the animal tree of life, the phylogenetic position of tardigrades (water bears) is still controversial, as they have been united alternatively with nematodes, arthropods, onychophorans (velvet worms), or onychophorans plus arthropods. Depending on the hypothesis favoured, segmental ganglia in tardigrades and arthropods might either have evolved independently, or they might well be homologous, suggesting that they were either lost in onychophorans or are a synapomorphy of tardigrades and arthropods. To evaluate these alternatives, we analysed the organisation of the nervous system in three tardigrade species using antisera directed against tyrosinated and acetylated tubulin, the amine transmitter serotonin, and the invertebrate neuropeptides FMRFamide, allatostatin and perisulfakinin. In addition, we performed retrograde staining of nerves in the onychophoran Euperipatoides rowelli in order to compare the serial locations of motor neurons within the nervous system relative to the appendages they serve in arthropods, tardigrades and onychophorans.

Although gradual deterioration of life functions with age is not a fundamental rule, it is pervasive among living organisms, regardless of their mode of reproduction and the number of constituent cells. However, deterioration can be temporarily arrested or slowed down due to the process of anhydrobiosis. Two modes of anhydrobiosis can be distinguished for the developmental and adult stages of animals. Developmental resting stages are reported for different animals, including sponges (Porifera), stingers (Cnidaria), flatworms (Platyhelminthes), insects (Insecta), copepods (Copepoda) and branchiopods (Branchiopoda). However, anhydrobiosis occurring at any stage of animal life, including adults, is found only in a few invertebrate phyla, namely roundworms (Nematoda), wheel animals (Rotifera) and water bears (Tardigrada). Notably, in the second group anhydrobiosis has been proposed to eliminate or slow‐down aging symptoms. This, in turn, may correlate with higher fitness and fecundity, and increased offspring longevity. We present available data concerning anhydrobiosis of tardigrades, bdelloid rotifers and nematodes, the only animals known to be capable of anhydrobiosis as adult individuals. The impact of anhydrobiosis on animal aging is illustrated by two models based on experimental data, namely the “Sleeping Beauty” and “Picture of Dorian Grey” models. According to the “Sleeping Beauty” model, anhydrobiotic organisms do not age during anhydrobiosis, whereas the “Picture of Dorian Grey” model predicts that the anhydrobiotic organism ages, at least during the initial stage of anhydrobiosis. Finally, we discuss possible implications of these models for individual longevity and survival as well as phenotypic diversity of taxa and their evolution. A better understanding of life strategies of anhydrobiotic animals both at the ontogenetic and phylogenetic levels can provide answers to many fundamental questions and useful practical outputs in branches of applied sciences.

The freshwater shrimp Neocaridina heteropoda (Crustacea, Malacostraca, Decapoda) originates from Asia and is one of the species that is widely available all over the world because it is the most popular shrimp that is bred in aquaria. The structure and the ultrastructure of the midgut have been described using X-ray microtomography, transmission electron microscopy, light and fluorescence microscopes. The endodermal region of the alimentary system in N. heteropoda consists of an intestine and a hepatopancreas. No differences were observed in the structure and ultrastructure of males and females of the shrimp that were examined. The intestine is a tube-shaped organ and the hepatopancreas is composed of two large diverticles that are divided into the blind-end tubules. Hepatopancreatic tubules have three distinct zones – proximal, medial and distal. Among the epithelial cells of the intestine, two types of cells were distinguished – D and E-cells, while three types of cells were observed in the epithelium of the hepatopancreas – F, B and E-cells. Our studies showed that the regionalization in the activity of cells occurs along the length of the hepatopancreatic tubules. The role and ultrastructure of all types of epithelial cells are discussed, with the special emphasis on the function of the E-cells, which are the midgut regenerative cells. Additionally, we present the first report on the existence of an intercellular junction that is connected with the E-cells of Crustacea.

This study investigates mechanisms of adaptation to metal toxicity peculiar to the midgut epithelium of Epilachna cf. nylanderi (Mulsant, 1850) (Coccinellidae). This species of beetle has currently been identified in only one locality in South Africa and is known to feed on the nickel hyperaccumulator Berkheya coddii Roessl. (Asteraceae), an endemic plant species of the South African ultramafic ecosystem. Our focus involves an analysis of the morphological features of cells forming the midgut epithelium, which is the first organ exposed to toxic levels of metals ingested by the insect. Through the three key processes of apoptosis, necrosis, and autophagy, excess metals are eliminated from the organism and homeostatic conditions are maintained. Apoptosis and necrosis are both known to be involved in the degradation of midgut epithelial cells, while the role of autophagy is mainly implicated in the disintegration of the organelles of cells. This study reports on the participation of these three key degenerative processes in the removal of excess metals based on targeted observations of the insect midgut epithelium by light and electron microscopies. Additionally, the TUNEL reaction was specifically used to detect apoptosis.