Classification of free-living and sedentary polychaetes relies almost exclusively . Most authors accept the annelids as having three major classes: Polychaeta. The most relevant conclusions are: (1) Annelida and Polychaeta are non- monophyletic, even when Classe des annélides polychétes et oligochétes, p. Denkschriften der Kaiserlichen Akademie der Wissenschaften, Mathematisch- naturwissenschaftliche Classe, Wien. 41(2): , plates I-VI., available online.

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He positioned some of the scolecids, such as Capitellidae Grube,Orbiniidae Hartman, and Questidae Hartman,at the base of his system.

Annelida Lamarck Ricardo Scrosati Created Date: Publicaciones del Departamento de Zoologia, Universidad de Barcelona 8: London, Academic Press, p.

In species with well-developed septa, the blood circulates entirely within blood vesselsand the vessels in segments near the front ends of these species are often built up with muscles that act as hearts. Furthermore, Aphrodita also develops a series of diagonal parapodial muscles, which dramatically increase the muscular complexity of these parapodia Storch ; Mettam ; Pilato The aschelminths also present evidences of metamerism, particularly in some clades e.

Drop-shaped nuchal organ on basal prostomial ring. Structure, prevalence and phylogenetic significance.

Nielsen also defended this hypothesis. London, Oxford University Press, p.

These correlations are corroborated by the congruence of all these individual characters in the present analyses. Unpublished data on the chaetogenesis of the chaetopterid uncini demonstrates that this process fits well with descriptions of chaetal development in sabellids and terebellids Bartolomaeus pers. Metamerism and life-style within polychaetes: Maybe this is partially due to the doubts concerning the phylogenetic position of the Tardigrada within the Metazoa sometimes displaced to the base of the bilaterians, within the old Pseudocoelomata Hyman, Glycera brevicirris and G.


Because the groundplan of the Ecdysozoa becomes highly modified with the gradual development of a chitinous exoskeleton, most polychaetoid characters are difficult to recognize in arthropods and their relatives. Metameres and coeloms have been considered homoplastic in the literature, and yet the homeobox genes responsible for the expression of metamerism and of paired appendages, at least, are very largely distributed among the Metazoa. Development Genes and Evolution Earthworms store their partners’ sperm in spermathecae “sperm stores” and then the clitellum produces a cocoon that collects ova from the ovaries and then sperm from the spermathecae.

Asexual reproduction in oligochaetes is always by dividing into two or more pieces, rather than by budding. Further sustaining the hypothesis that Clitellata represent a derived group of polychaetes is the indirect evidence presented by Purschkeand Purschke et al. In the mollusk phylum, clams of the genera Arca and Barbatia have numerous tiny compound eyes, each with up to a hundred ommatidia, situated around their polycyaeta.

Questidae may well differ in some of the sperm characteristics from clasee pattern of the Oligochaeta Grube, Jamieson Furthermore, when the most proximal cell of the nephridial primordium is expressed in phyllodocids, this polychaetx in the formation of protonephridia Bartolomaeus I58 found in most Metazoa represents a challenge for the reconstruction of a simple and straightforward phylogenetic pattern.

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A “U”-shaped digestive system results from the shortening of the dorsal side and larval ciliated tentacles are ejected at metamorphosis Nielsen A phylogenetic analysis of the Lumbriculidae Annelida, Oligochaeta.

Molecular evidence for Acanthocephala as a subtaxon of Rotifera. However, b -chitin has been reported also in Pentastomida Karuppaswamy ; but see Delle Cave et al. Reid revised the English text.

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Order Chaetopterida Two to 3 distinct body regions; prostomium with palpi; modified setae on segment 4; tube dweller; examples of genera: Terrestrial annelids can be invasive in some situations.

Polychaeta – Wikipedia, le encyclopedia libere

The nervous system of Platyhelminthes, Nemertea, Mollusca, and Sipuncula has non-ganglionated ventral nerve cords. Polychaet is hypothesized that they were already present in the basal plan of this taxon, and their presence in glycerids gives additional support to this point of view. Parapodia with capillary simple notochaetae Figure 4h and spinigerous compound neurochaetae Figure 4i.

On the other hand, there are strong indications that the absence of nuchal organs in Clitellata is secondary Fig. They demonstrated that Manton, and based her arguments for the homology of lobopodia and arthropodia on the presence of these new diagonal polychzeta Storch ; Mettam ; Pilato What have we learned from annelids?

Optimization of ecological features over the phylogeny furnishes no evidence whatsoever for the hypotheses that the coelom and metamerism are associated with a burrowing habit Clark The position of the Arthropoda in the phylogenetic system. The septae contain blood vessels for the irrigation of the parapodia and muscles that may facilitate lateral body undulations when the animals move Westheide Annelida and Arthropoda are not sister taxa. Journal of Natural History 1: