摘要:

Introducing a collection of six paper on segmented animals, some hot spots of current research on segmented animals are highlighted, such as criticism of the Articulata concept, the emerging notion of Ecdysozoa, the disputed presence of segmentation in basal Meta‐zoa, the doubtful existence of general macroevolutionary trends such as the so‐called Williston's law, and the possible concerted evolution of the main body axis, the proximo‐distal axis of appendages and the patterning of post‐embryonic development.

ISSN:1125-0003    

DOI:10.1080/11250009809386721

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The hydromedusan subumbrellar muscle tissues originate from a mass of endo‐ and ectoderm derived cells proliferating inwardly. This mass of cells, called entocodon, is separated by the ecto‐and endoderm through a layer of extracellular matrix, thus forming a locally triploblastic arrangement of tissues. By cavitation and differentiation, the entocodon gives rise to the striated and smooth muscle layers of the subumbrella. The structure of the striated muscle is histologically identical to that described for triploblasts, where striated muscle is mainly mesodermic. Together with the mode of development, this suggests that not all Cnidaria are diploblastic and that the subumbrellar cavity is a coelom‐like structure. The subumbreHar cavity is formed late in ontogeny, whereas the coelom in higher animals is normally formed during embryonic development. Instead of remaining closed, the subumbrella becomes open, with the muscular mesothelium in contact with the environment. This view of cnidarian structures can be pushed further while considering the regulation of modularity and metamery. The occurrence of homeotic genes in cnidarians and other ‘lower’ animals shows that the specification of body architecture has a common molecular ground throughout the animal kingdom. It is suggested that the expression of homeotic genes while specifying a given architecture might be regulated by iteration of their activity, leading to ‘low’ modular organisms and to ‘higher’ metameric ones. Replicated parts as modules and metameres might be analogous, but the affinity in their molecular specification (and possibly regulation) might indicate homology. The number of resemblances between cnidarians and ‘higher’ metazoa suggests that this phylum might be a centre of metazoan radiation, having structures which represent the living premises of the main steps of animal evolution.

ISSN:1125-0003    

DOI:10.1080/11250009809386722

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Metamerism as the serial homology is widespread among the Vendian (Late Precambrian) metazoans. Prevalence of segmented forms among the Vendian Bilateria suggests that in many phylogenetic lineages of Metazoa the evolutionary development of the bilateral symmetry and metamerism were related processes. Large number of coelenterate‐grade forms with serially homologous parts may indicate that at the earlier, pre‐Vendian stages of the metazoan history metamerism could be at great extent realised at the diploblastic level.

ISSN:1125-0003    

DOI:10.1080/11250009809386723

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The authors review the available evidence concerning the early stages of radiation of the Articulata and support the hypothesis that there was probably a range of, perhaps incompletely, metameric organisms spanning, without definite borderlines, the early ancestors of arthropods, lobopods and annelids. By the early Cambrian, the stem lineages of the living articulate phyla were well‐identified, but there still survived a number of animals whose morphology spanned, to some extent, the gaps between the living taxa. The affinities between Annelida (sensu lato) and Mollusca are briefly discussed.

ISSN:1125-0003    

DOI:10.1080/11250009809386724

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

An analysis of polychaete life‐styles and morpho‐functional adaptations, in relation to their metameric organization, is presented with the aim of summarising the main hypotheses thus far proposed as for their ancestral form, and of discussing the evolutionary implications of the metameric design. The metameric organization, which seems to have appeared early within the proto‐stome line, have reached a high diversification in marine polychaetes among the Annelida. This high diversification of ‘annelid design’ in polychaetes is probably linked to their ancient origin, their early rapid adaptive radiation, and their morphological and physiological adaptability to a great number of habitats. Primary heteronomy, i.e. the presence of larval segments in polychaetes, as an adaptation to pelagic development, as well as secondary heteronomy, i.e. the differentiation of trunk segments as adaptation to different adult life‐styles, are also discussed, stressing the necessity for a better definition of larval segments. The hypothesis of the evolution of a compartimented coelom as an adaptation to peristaltic movements in an oligochaetoid form is rejected, due to both its difficult application to vagile forms with parapodial development and complete septa, and the fact that most of the burrowing polychaetes lack complete septa. Reduction or loss of septa is accompanied by parapodia reduction in some forms, and by increased efficiency of parapodia in other. The occurrence of septa in polychaetes is probably a reflection of growth processes by which new segments are added posteriorly, it is therefore more likely that their loss, rather than their retention, requires a functional explanation. The whole body design and the occurrence of some structures seem in polychaetes strictly linked to life habit so obscuring any phylogenetic relationships. This, together with the scarcity of fossil evidence, gives rise to numerous problems in tracing a phylogenetic pattern and in hypothesising the ancestral form. Two main contrasting hypotheses have been formulated as regards the annelid ancestor: the first depicts it as errant and epibenthic, the second as burrowing or oligochaetoid form. Both hypotheses are discussed also in the light of larval morphology and reproductive biology. It is hypothesised that the ancestral form could be very close to a relatively large meiofaunal ‘polygordiid‐like’ annelid, with a biphasic cycle, in which metamerism arised for developmental constraints. From this ‘Bauplan’ an errant form may be derived, with development of parapodia to improve the efficiency of lateral contraction.

ISSN:1125-0003    

DOI:10.1080/11250009809386725

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The origin and evolution of Clitellata are discussed by inductive method, taking into account the morphological, ecological and embryonic characters of the microdriles, hirudineans and megadriles. Special attention is focused on the vascular system and on the female and copulatory apparatuses. The two marine littoral families Capilloventridae and Randiellidae, evidently primitive, contribute with their morphology and anatomy to reconstructing the physiognomy of ancestral Clitellata, but their relationships to the other microdrile families are still obscure. The Naididae and the Enchytraeidae also remain by themselves, as do the two interrelated families Tubificidae and Phreodrilidae. The primitive looking Haplotaxidae appear to be related to the Lum‐briculidae and the Alluroididae; the latter are allied to the Monili‐gastridae. Lumping together Branchiobdellae, Acanthobdellae and Euhirudinea seems to be justified, and so does suggesting the derivation of the hirudineans from the Naididae. The three orders of megadriles, i.e. Megascolecina, Lumbricina and Eudrilina, appear to be related to the Alluroididae (via the Ocnerodrilidae?), to the Haplotaxidae (via some primitively aquatic genera), and directly to the Alluroididae, respectively. The legitimacy and utility of using the comparative and inductive method in formulating and corroborating evolutionary hypotheses are stressed.

ISSN:1125-0003    

DOI:10.1080/11250009809386726

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Parergodrilus heidenReisinger, 1925 andHrabeiella periglan‐dulataPizl & Chalupský, 1984 s. 1. are the only two non‐clitellate annelids which permanently inhabit the litter and humic layers of land soils in temperate climates. Their minute body size and difficulty of extraction from the substrate account for their late discovery and subsequent scanty records. Both taxa are European. Although they widely overlap in geographic and ecological distribution, they appear only remotely related. NeitherParergodrilusnorHrabeielladisplays more than a superficial resemblance to the families formerly included in the ‘archiannelids’. Since 1960Parergodrilushas been classified with the marine interstitialStygo‐capitella subterraneaKnöllner, 1934 in the family Parergodrilidae, possibly related to some other interstitial forms or to deposit feeders of mobile bottoms. The position ofHrabeiellaappears more obscure, yet very interesting in view of the many convergences (concerning the organization of the body wall musculature, pharynx, male terminalia, spermatozoal morphology) with the oligochaetes.

ISSN:1125-0003    

DOI:10.1080/11250009809386727

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The isolated outer cornea cultured in presence of acidic Fibrob‐last Growth Factor (aFGF) can reprogramme its differentiation into lens fibres. The capacity of aFGF to promote lens differentiation is not linked to its mitogenic activity. In previous studies (Boscoet al.,1997) it was observed that the lens transdifferentiation of corneal cells occurs also when DNA replication and cell proliferation are prevented by addition of aphidicolin (a specific inhibitor of DNA polymerase in eukaryotes), to the culture medium. Experiments in which either transcription or translation have been inhibited by actinomycin D and cycloheximide, respectively, have now shown that the corneal cells are unable to transdiffer‐entiate into lens fibres. These results indicate that the multi‐step process lens‐transdifferentiation of corneal cells can be controlled also at these levels.

ISSN:1125-0003    

DOI:10.1080/11250009809386728

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A karyological study of Adriatic populations ofGobius niger, G. paganellus, G. cobitis, Pomatoschistus minutus, P. marmoratus,andZosterisessor ophiocephalus(Teleostei, Gobiidae) was conducted by fluorochrome staining lchromomycin A3(CMA3), mithramycin (MMA), C‐, AgNOR‐and Alu‐I banding methods. The NORs showed three types of location: terminal‐centromeric on one pair of medium‐small chromosomes inG. niger, G. paganellus, P. minutus,andP. marmoratus,terminal on the long arm of chromosome 23 inZ. ophiocephalus;interstitial‐pericentric on the long arm of chromosome 3 inG. cobitis.Except for the twoPomatoschistus,all species had structurally heteromorphic NOR‐bearing chromosomes. The heterochromatin was mainly cen‐tromeric and telomeric. Except forG. nigerandG. paganellus,in which only the heterochromatin of chromosome 1 was Alu‐I resistant, the endonuclease Alu‐I produced a C‐band‐like pattern. InG. niger, G. paganellus,andZ. ophiocephalus,the short arm of chromosome 1 showed variable amounts of C‐banded material. In addition, inG. nigerthe heteromorphic element of chromosome 1 presented a CMA3/MMA and Ag‐positive telomeric region on the short arm. The results obtained are discussed with respect to cytotaxonomic implications and to the features of NORs.

ISSN:1125-0003    

DOI:10.1080/11250009809386729

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Macaca sylvanushas a diploid chromosome number of 2n = 42. With the exception of chromosome 2 all chromosomes appear to have an identical banding pattern to most other macaque species. This chromosome has a clear band, localized immediately below the centromere; therefore, the karyotype ofM. sylvanusmore closely resembles that of the African Papionini, which also present a large clearly staining band on chromosome 2. C‐band‐ing intensely stained this band. Fluorescentin situhybridization (FISH) with human chromosome specific DNA probes to macaque chromosome 2 showed that human probe 7 was located on the whole q arm and on a small part of the p arm, immediately adjacent to the centromere; the remaining part of the p arm was hybridized by the DNA probe for human chromosome 21. It appears clear, from the hybridization pattern in the other primates and in the outgroups examined, that chromosome 7 was probably a syntenic region for many ancestral mammalian karyotypes and a single syntenic region in the ancestral karyotype of the primates. Human probe for chromosome 21 and 3 are found associated in New World primates and a wide range of mammalian species. Therefore, this syntenic association was probably ancestral for mammals and present in the ancestral primate karyotype. The translocation of 7 and 21 to form chromosome 2 ofMacaca sylvanusand all other Papionini is probably a recent trait linking all these species.

ISSN:1125-0003    

DOI:10.1080/11250009809386730

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor