ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1996.tb02328.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

We investigated a small valley of glacial origin in the northern Apennines (Italy). A multihabitat study was performed on the mosses and lichens on rocks, temporarily submersed mosses, beech litter, grass turf and sediments from pools, ponds and streams. A few species colonized more than one habitat. Several species were typical of high altitudes or latitudes, some were rare, and two,Hypsibius pradelliisp. nov. andDiphascon (Diphascon) secchiisp. nov., were new to science.

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1996.tb02329.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The presence of males in species ofEchiniscushas been reported only as recently as 1987 and is still considered to be rare. However, males have been found to be common in a disproportionately large number of species of this genus found in Australia. Evidence of sexual dimorphism is presented for five species (three of which are new to science), females and males of which are differentiated on the basis of distinctive gonopores. In all five species males are shorter with longer clavae. Males ofEchiniscus jamesisp. nov.,Echiniscus rodnaesp. nov. andEchiniscus curiosussp. nov.have significantly longer claws. InE. rodnaesp. nov. andE. curiosussp. nov. males have significantly longer lateral trunk appendages and the dorsal trunk appendage combinations of males of the latter are different from those of females. The widespread distribution of bisexual species ofEchiniscusin xeric habitats in Australia does not support the current theory that parthenogenetic species are favoured in such environments.

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1996.tb02330.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The brain ofEchiniscus viridissimus, Peterfi, 1956 is composed of a series of orthogonally arranged neuropils. The most anterior neuropils are rireumbuccal, positioned dorso‐and ventrolateral to the buccal tube and are associated with ganglia for sensory receptors of the mouth cone. Posterior to these are neuropils and ganglia for the (1) internal cirri and (2) cephalic papillae, external cirri, cirri A and clavae. They are joined by two pairs of vertical tracts to neuropils lateral to the buccal tube. A model based on the postcephalic organization of the tardigrade nervous system is used to propose a transformation of segmental ganglia that gives an arrangement congruent with the pattern of neuropils in the brain. The analysis suggests that the brain is derived from nervous elements of four segments with the fourth segment having contributed paired dorsal ganglia and their connecting vertical tracts to the first trunk ganglia of the ventral chain. The organization of the head of tardigrades is compared with that of other lobopods and arthropods and several possible key evolutionary innovations are offered. In addition homologous characters for the heads of tardigrades and other lobopods and arthropods are proposed and the nomenclature for the tardigrade cephalic nervous system is discusse

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1996.tb02331.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

A sample from the holotype population of the limno‐terrestrial eutardigradeRamazzoltius varieornatuswas 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 variatio

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1996.tb02332.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The phylogenetic position of the Tardigrada remains uncertain. This is due to the limited information available, and the uncertainty of whether some characters are homologous or analogous with other taxa. Based on some morphological characters, current discussion centres on whether the taxon branches from the annelid‐arthropod lineage, or lies within the arthropod complex. The molecular data presented here from an analysis of the 18S rRNA gene sequences are used to test the validity of these two hypotheses. Phylogenetic inference by the maximum parsimony and distance (neighbour‐joining) methods suggests that the Tardigrada is a sister group of the major protostome eucoelomate assemblage that emerged before the arthropods, annelids, molluscs, and sipunculids evolved. The tardigrade clade also appears as an independent lineage separate from the nematode clade, thus supporting the current idea that tardigrades do not have a close aschelminth relationship. The molecular data also imply that several morphological features, considered significant in determining the phylogenetic relationships of tardigrades, are not synapomorphic charact

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1996.tb02333.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Differential interference contrast micrographs from stretched animals, serially sectioned semi‐thin and ultrathin sections revealed that the cerebral ganglia (supraoesophageal mass) of the eulardigradeMilnesium tardigradumlie above the buccal tube and adjacent tissue like a saddle. It has an anterior indentation which is penetrated by two muscles that arise from the cuticle of the forehead. The cerebral ganglia consist of lateral outer lobes bearing an eye on each side, and two inner lobes which extend caudally. Between the inner lobes a cone‐like projection tapers into a nerve bundle. Each outer lobe is joined with the first ventral ganglion. From the outer lobe near the eye the ganglion for a posterolateral sensory field extends to the epidermis. Anterior to the supraoesophageal mass are three dorsal ganglia for the upper three peribuccal papillae. Two additional ganglia attached to the cerebral mass supply the lateral cephalic papillae. The cerebral ganglia are covered by a thin neural lamella. The pericarya which surround the neuropil have large nuclei. Near the axons in the centre of the supraoesophageal mass the cytoplasm is crowded with vesicles of different size and appearance. Some of them resemble synaptic vesicles while others resemble dense core bodies. Structurally different types of synapses and axons can be distinguished within the neuro

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1996.tb02334.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The excretory and osmoregulatory system ofHalobiotus crispaeconsists of two lateral and one smaller dorsal Malpighian tubules, which empty into the digestive tract in the transition zone of the midgut and rectum. The tubules are identical at the ultrastructural level, and consist of an initial segment with three large cells, a thin transitional distal part lacking a nucleus, and a proximal part with 9–12 nuclei. The initial segment possesses deep basal infoldings and interdigitating, finger‐shaped processes of the plasma membrane, large mitochondria and giant nuclei. The distal part is a short section which supports the initial segment. Cellular offshoots from the succeeding proximal part constitute the distal part. The distal and proximal parts contain intercellular canals with concretions of variable size. The exit of the proximal part into the digestive tract is characterized by the presence of microvilli. Correlated with the different stages in the cyclomorphosis ofH. crispae, we observed size variation of the Malpighian tubules; thus, pseudosimplex stages have the largest tubules. We present suggestions concerning the physiology of the tubules and compare the Malpighian tubules of Tardigrada with the Malpighian papillae of Prot

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1996.tb02335.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The male gamete, a cell widely used for evaluating phylogeny in different animal groups, remains relatively unknown in tardigrades. In this paper the spermatozoa of thirteen species of eutardigrades among four genera and three families is evaluated in order to determine whether sperm morphology can be used as a taxonomic character. Spermatozoa ofAmphibolus volubilisandA. weglarskaeare very similar and this resemblance is congruent with the remarkable similarity of sclerified parts of the species. In addition, the spermatozoa of eight species of the genusMacrobiotuswere examined yielding two groups showing strong intragroup similarities. The first group includesM. pseudohufelandi, M. sandrae, M. macrocalix, M. terminalsandM.joannae, and the secondM. richtersi, M. areolatusandM. harmsworthi.Again, these groupings were congruent with those determined by analysis of sclerified structures. In contrast, a marked similarity was found between the spermatozoa otDiphascon (Adropion) scoticumandPlaticrista angustata, whereasDiphascon (Diphascon) humicuswas appreciably different from both species. Resemblances found in this study between spermatozoa and sclerified body parts suggests that the spermatozoa are suitable characters for use in systematic studies.

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1996.tb02336.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The genome size of tardigrades has been documented to date in seven species of eutardigrades, and it is among the lowest in invertebrates. In this paper the evaluation of genome size is extended to eight other speeies of eutardigrades and to one species of heterolardigradcs, in order to obtain a more comprehensive picture of minimum DNA content evolution in this phylum. The genome size of the heterotardigradePseudechiniscus juanitae(0.6 pg), measured using le cells, is found to resemble that of some eutardigrades. Thus, it is not possible to discriminate between the two classes of tardigrades on this basis. Literature and new data on eutardigrades also suggest that families or subfamilies cannot be discriminated on the basis of genome size. Nevertheless, genome size and sperm cell shape are correlated. A lower DNA content always corresponds to a more specialized male gamete. In general, in tardigrades, the low genome size and its low variation could be related to the high specialization of the phylum. Preliminary data on nuclear AT contents suggest that the variations in those values are correlated with genome size variations.

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1996.tb02337.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY