Myoanatomy of the marine tardigrade Halobiotus crispae (Eutardigrada: Hypsibiidae)

The muscular architecture of Halobiotus crispae (Eutardigrada: Hypsibiidae) was examined by means of fluorescent‐coupled phalloidin in combination with confocal laser scanning microscopy and computer‐aided three‐dimensional reconstruction, in addition to light microscopy (Nomarski), scanning electron microscopy, and transmission electron microscopy (TEM). The somatic musculature of H. crispae is composed of structurally independent muscle fibers, which can be divided into a dorsal, ventral, dorsoventral, and a lateral musculature. Moreover, a distinct leg musculature is found. The number and arrangement of muscles differ in each leg. Noticeably, the fourth leg contains much fewer muscles when compared with the other legs. Buccopharyngeal musculature (myoepithelial muscles), intestinal musculature, and cloacal musculature comprise the animal's visceral musculature. TEM of stylet and leg musculature revealed ultrastructural similarities between these two muscle groups. Furthermore, microtubules are found in the epidermal cells of both leg and stylet muscle attachments. This would indicate that the stylet and stylet glands are homologues to the claw and claw glands, respectively. When comparing with previously published data on both heterotardigrade and eutardigrade species, it becomes obvious that eutardigrades possess very similar numbers and arrangement of muscles, yet differ in a number of significant details of their myoanatomy. This study establishes a morphological framework for the use of muscular architecture in elucidating tardigrade phylogeny. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

The first record of a rare marine tardigrade, Halobiotus crispae Kristensen, 1982 (Eutardigrada: Hypsibiidae), from the Svalbard Archipelago

A rare marine tardigrade Halobiotus crispae Kristensen, 1982 was found abundant in intertidal flats at Josephbukta, Bellsund fiord, West Spitsbergen. This is the first record of this species from the Svalbard Archipelago. So far, the species has been found only in seven other localities in the northern hemisphere (between 56° and 69°N). The present record greatly extends the known geographical range to the north and also indicates a much wider distribution of the species than formerly reported. Moreover, a potential indicative character of this species and of the study area in monitoring climatic changes is discussed.     

The morphology and ultrastructure of the Malpighian tubules and hindgut in Cenocorixa bifida (Hung.) (Hemiptera,Corixidae)

The gross morphology and ultrastructure of the Malpighian tubules and hindgut in adults of the water bug Cenocorixa bifida (Hung.) is described. These are compared with similar structures in other insects with a view to relating the observed structure with potential function.     

Head sensory organs of Halobiotus stenostomus (Eutardigrada, Hypsibiidae)

The structure and arrangement of sensory organs in the tardigrade Halobiotus stenostomus (Richters 1908) have been studied using transmission and scanning electron microscopy techniques. The sensory organs found on the head of H. stenostomus are as follows: the circumoral sensory field, cephalic papillae, anterolateral and posterolateral sensory fields, and suboral sensory region. Four types of ciliated receptor structures are described in the sensory fields. The lateral sensory fields contain two types of receptor endings, dense and lucent, which differ in the presence or absence of a collar and in the structure of the outer dendrite segment. Two more types of receptor endings, ultrastructurally differing from the lateral sensory field receptors, are located in the suboral sensory region. Receptors with an asymmetric collar have been found, and a receptor ending without a collar is described for the first time in tardigrades. Unlike in other species studied, the sensory organs of H. stenostomus lack the lymph cavity surrounding the outer receptor segment. Similarity and differences in the ultrastructure of receptors between H. stenostomus and other species of Eutardigrada and Heterotardigrada are discussed.     

Photokinesis of Macrobiotus hufelandi (Tardigrada, Eutardigrada)

Macrobiotus hufelandi Schultze, 1834 was tested for response to light. Size groups of less than 120 m and of 120 m or more were used. It was found that the smaller, younger size group exhibited a statistically significant negative response to light. This is hypothesized to function in conservation of body moisture and be more important to the smaller individuals because of the greater surface area-to-volume ratio. An experiment on response to gravity was done in an effort to determine if the negative photokinesis was the total result of a more complex type of behavior but this experiment did not detect any significant response to gravity in either of the size groups. Observation of the bacterial trails left by the tardigrades indicates that this behavior is not negative phototaxis, but rather negative photokinesis which is a non-directed, random movement in which the animal either increases its speed or changes its direction when exposed to light.     

Light and electron microscopic studies on the excretory system of Macrobiotus richtersi Murray, 1911 (Eutardigrada)

Summary The excretory system of Macrobiotus richtersi consists of one dorsal and two lateral components and shows a high degree of structural complexity. In each of these a tricellular external lobe and a column can be distinguished, the two parts being connected distally. The surface of the lobe cells is increased by deep basal infoldings and fingerlike processes which form a labyrinth next to the basal lamina. Their cytoplasm contains numerous mitochondria, a well developed rough endoplasmic reticulum, dictyosomes, and granules in amounts depending on the physiological state of the animal. Excretory crystals occur in caveolae located in the lobe: between the fingershaped processes of the cell and in the space enclosed by the basal lamina on one side and the column on the other.The column faces an extracellular channel meandering along its whole length which is surrounded on the outside by a basal lamina. Morphologically the column is similar to the protonephridial channel of Rotifera. At the ultrastructural level, the cytoplasm of the column shows numerous mitochondria, rough endoplasmic reticulum, lysosomes, and a well developed Golgi apparatus. The lumen of the channel is coated by glycocalyx. At the base of the column several small cells form the proximal part of a duct that communicates with the gut.The morphology and ultrastructure of the excretory system of M. richtersi have been compared with similar a system in Isohypsibius megalonyx (Greven, 1979), and on these grounds a proposal is put forward to call the excretory organs of Tardigrada nephridia instead of Malpighian tubules.     

Morphometric analysis of Ramazzottius varieornatus (Hypsibiidae: Eutardigrada)

A sample from the holotype population of the limno-terrestrial eutardigrade Ramazzoltius varieornatus was examined in order to elucidate the variation occurring in the size of the sclerified structures of the pharyngeal apparatus. A frequency plot of body lengths was also produced to deduce the effectiveness of this technique in estimating the number of moults exhibited by this species. Problems associated with collecting and using morphometric data in this way are discussed. Additional ultrastructural information associated with moulting is also presented. New species within the genus may be difficult to recognize in the absence of adequate data related to intraspecific variation.     

The ovary structure, previtellogenic and vitellogenic stages in parthenogenetic species Dactylobiotus dispar (Murray, 1907) (Tardigrada: Eutardigrada)

The reproductive system of Dactylobiotus dispar consists of the ovary and the oviduct that opens into the rectum. The sack-like ovary is filled with the developing oocytes, which are assisted by the trophocytes. In D. dispar, the mixed vitellogenesis takes place. One part of the yolk material is produced inside the oocyte (autosynthesis), the second part is absorbed by micropinocytosis while the third part is synthesized in the trophocytes and is transported to the oocytes through the cytoplasmatic bridges. Moreover, rRNA, lipids and mitochondria are transfered from the trophocytes to the oocytes. The histochemical researches show that the reserve material accumulated in the oocytes contains proteins, polysaccharides and lipids.     

The ultrastructure of Malpighian tubules and hindgut of Frankliniella occidentalis (Pergande) (Thysanoptera : Thripidae)

The ultrastructure of the western flower thrips, Frankliniella occidentalis (Pergande) (Order : Thysanoptera), has 4 Malpighian tubules that are free of the intestine as they leave their junction at the pyloric region. The tubules consist of an epithelium with a single type of microvillated cells; proximally, the cells are lined by a thin cuticle. Numerous mitochondria, basal infoldings of the plasma membrane and vesicles with varying densities suggest active transit of fluid in the cell for osmoregulation. Two of the Malpighian tubules are bent posteriorly and closely adhere to the hindgut in the region of the rectal pads where the 2 epithelia are separated only by a basal lamina. The ultrastructure of this region suggests possible fluid reabsorption from the gut lumen.     

Morphology and ultrastructure of the Malpighian tubules of the Chilean common tarantula (Araneae: Theraphosidae).

Relatively little is known about the morphology and ultrastructure of the Malpighian tubules of spiders (Arachnida: Araneae). Our study represents the first investigation of the Malpighian tubules of a theraphosid spider and is the only study to examine the living Malpighian tubules using confocal laser scanning microscopy. In theraphosid spiders, the Malpighian tubules originate from the stercoral pocket in the posterior portion of the opisthosoma and extend forward toward the prosoma in a dendritic pattern. There are three distinct segments (initial, main, and terminal), all dark brown in appearance. Each segment has distinctive ultrastructural features. Both the terminal and the main segment appear to be composed of at least two cell types with finger-like cytoplasmic protrusions associated with one of these types. The terminal segment, which is most proximal to the stercoral pocket, is the largest in diameter. It is composed of large, cuboidal cells containing many mitochondria and lipid inclusions. The main segment is intermediate in diameter with many mitochondria and secretory vesicles present. The initial segment is relatively thin in comparison to the other segments and is intimately associated with the digestive gland. The cells of the initial segment contain very little cytoplasm, fewer mitochondria, secretory vesicles, and prominent inclusions.     

Phenotypic Variations in the Life History of Two Clones of Macrobiotus richtersi (Eutardigrada, Macrobiotidae)

A comparative study of life history traits of two clones (CDMr01 and CDMr02) of a triploid thelytokous apomictic population of the eutardigrade Macrobiotus richtersi has been carried out. Both clones were reared under the same lab conditions: temperature of 14 °C, photoperiod of 12 h/12 h (L/D), and nematodes ad libitum as food. Statistical analysis of the life history traits considered has indicated interclonal variability. The two clones were significantly different in the number of eggs per clutch (fertility), number of eggs laid per female per life span (fecundity), hatching percentage of eggs and hatching time. Similarities between clones have been observed with regard to life span, total number of ovipositions per life span, and age at first oviposition. In addition, significant differences in hatching time, with eggs hatched over a long period, were found within each clone. Interclonal variability in life history traits indicated the effects of genetic factors, whereas intraclonal variability reflected the effects of environmental factors. The evolutionary and adaptive significance of the life history phenotypic variations is discussed.     

Development of the Malpighian tubules in Cloeon dipterum (Ephemeroptera)

The development of the Malpighian tubules is studied in Cloeon dipterum through all stages from the youngest larva to the adult. The Malpighian tubules are found to be outgrowths of the posterior part of the endodermal midgut and not of the ectodermal hindgut. In the adult the part of the intestine with the tubule openings becomes separated by an ingrowing fold of the epithelium from the anterior main part of the midgut that forms a large thin-walled and air-filled bladder. The characteristics of the developmental stages, which served to determine the age of the animals, are given.     

Studies on water and ion transport in homopteran insects: ultrastructure and cytochemistry of the cicadoid and cercopoid Malpighian tubules and filter chamber

The filter chamber is a complex junction of anterior and posterior extremities of the midgut and Malpighian tubules. The sac-like anterior extremity, or filter chamber proper, comprises two cell types. These are large cuboidal cells which secrete a mucoprotein, and extremely thin cells which have regular tubular invaginations of the basal plasma membrane. The posterior extremity of the midgut and the internal Malpighian tubules coil round the filter chamber proper. They consist of thin epithelial cells identical in ultrastructure. The basal plasma membrane in these cells is formed into leaflets. A thin cellular sheath and thick muscle layers surround the filter chamber. The filter chamber proper is lined by the mucoprotein secretion of the cuboidal cells. This secretion appears to bind potassium ions. ATPase and alkaline phosphatase cannot be detected in the filter chamber epithelia. The structure and cytochemistry of the filter chamber suggests that water flows from filter chamber proper to midgut and Malpighian tubules by passive osmosis. This may be facilitated by ion binding in the filter chamber proper and by hydrostatic pressure engendered by contraction of the muscular coat. The Malpighian tubules appear to be structurally and chemically adapted for ion secretion by active transport and possibly for reabsorption in the Malpighian duct segment.     

Ultrastructural changes in the gut and the Malpighian tubules of Epilachna varivestis after application of the new antibiotic Nikkomycin involve an osmoregulatory defect

The effect of the antibiotic Nikkomycin was investigated on the Malpighian tubules and the gut of fourth-instar larvae of the Mexican bean beetle, Epilachna varivestis. Within the Malpighian tubules, three different stages in cell alterations can be recognized. A stage of increased activity (Stage A), and two stages of dedifferentiation (Stages B and C) which are distinguishible by characteristic mitochondrial morphology. In Stage C individuals, when Malpighian tubule function stops entirely, alterations in the midgut take place, that are signs of increased activity. Measurements of hemolymph osmotic pressure showed that there is a considerable increase to a higher level which is maintained. Compared with the ultrastructural data, the regulation of osmotic pressure on a higher level may, in part, be the result of compensation for the failure of Malpighian tubule function by the midgut.     

Autophagy as the cell survival in response to a microsporidian infection of the midgut epithelium of Isohypsibius granulifer granulifer (Eutardigrada: Hypsibiidae)

The midgut epithelial cells of many invertebrates may possess microorganisms which act as symbionts or pathogens (bacteria, microsporidia, viruses). During our previous studies on Isohypsibius granulifer granulifer Thulin, 1928 (Tardigrada, Eutardigrada), which examined alterations of the midgut epithelium during oogenesis, we found that some of the specimens were infected with microsporidia. All stages of pathogens occurred in the cytoplasm of the digestive cells in the midgut epithelium of I. g. granulifer that were infected with microsporidia: meronts, sporonts, sporoblasts, and spores. The cytoplasm of the digestive cells was rich in mitochondria, cisterns of rough endoplasmic reticulum (RER), and Golgi complexes. Autophagy in the digestive cells of the dorsal midgut was much more intensive in comparison with noninfected specimens. Membranes of phagophores surrounded the pathogens forming autophagosomes. These latter structures fused with lysosomes forming autolysosomes and residual bodies appeared. Neither glycogen granules nor droplets of varying electron density, which accumulated in digestive cells during vitellogenesis and choriogenesis, appeared in individuals with microsporidia. While the midgut epithelium in noninfected specimens takes part in vitellogenesis and choriogenesis, in infected specimens, midgut cells are involved in the process of autophagy as a survival strategy.     

Milnesium berladnicorum sp. n. (Eutardigrada,Apochela, Milnesiidae), a new species of water bear from Romania

In a lichen sample collected from a tree in Bârlad town (Vaslui County, Romania), a new tardigrade species belonging to the genus Milnesium (granulatum group) was found. Milnesium berladnicorumsp. n. is most similar (in the type of dorsal sculpture) to Milnesium beasleyi Kaczmarek et al., 2012 but differs from it mainly by having a different claw configuration and some morphometric characters. Additionally, the new species differs from other congeners of the granulatum group by the different type of dorsal sculpture, claw configuration and some morphometric characters.     

A new species of Tardigrada (Eutardigrada: Milnesiidae): Milnesium krzysztofi from Costa Rica (Central America)

Abstract

A new eutardigrade species Milnesium krzysztofi sp. nov. is described from Costa Rica. M. krzysztofi sp. nov. differs from the most similar Milnesium katarzynae Kaczmarek et al., 2004 mainly by the presence of spurs on internal claws I–III and on external claw IV.