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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Nevertheless, Sigalionoidea, Polynoidea, Spionida, and Paraonida remain paraphyletic. The first polychadta cirri in Nereididae, although having neither chaetae nor polyfhaeta, should not be interpreted as non-metameric.

Ch 13 Phylum Annelida The first evolutionary proposal for the group is that of Hatschek Glycera boeggemanni new species Figures Material examined Type Material: On the other hand, the large number of morphological and reproductive synapomorphies represents convincing evidence for a close relationship among these groups.

Order Spionida Sedentary; at least 2 long feeding tentacles adapted for grasping and arising from prostomium; size, 0. The body cavity in Nemertea may be considered an exaptation pre-adaptationsubsequently modified for other functions, such as providing an hydrostatic body skeleton, promoting the circulation of body fluids, producing space for the maturation of reproductive cells, etc.


Evidence for or against the homology of the head tagma of Polychaeta with that of Ecdysozoa is still lacking. The transformation of dorsal cirri into gills and the loss of ventral cirri must be the result of claswe selection for a sedentary habit.

Must all these coincidences be explained away as the result of developmental constraints see Sommer ?

The present results do not support the notion that hermaphroditism would be a strong indication of such a relationship, since this condition is found in other groups e. Allan Hancock Pacific Expedition Goniadidae, Glyceridae, and Nephtyidae.

Order Flabelligerida Sedentary; setae of anterior segments directed forward to form a cephalic head cage; prostomium and peristome retractile, with 2 palpi and retractile branchiae; size, 1 to 10 cm; examples of genera: British Chrysopetaloidea, Pisionoidea and Aphroditoidea, p.

The present results also indicate the artificiality of the traditional division of the polychaetes into Errantia and Sedentaria. I38 may be provisionally interpreted as synapomorphic for metameric animals. The present hypotheses of relationships have antecedents in the proposals of Geoffroy Saint-Hillaire and Dohrnboth of whom proposed the origin of the Vertebrata from annelid-like ancestors.

In memory of Dr. Each mesentery is similar except that the mesothelium is the lining of each of the pair of coelomata, and the blood vessels and, in polychaetes, the main nerve cords are embedded in it. Polychaete worm larva pelagic planktonic Branching nerves. In Ecdysozoa, pygidial cirri are also absent from both Cambrian lobopods and recent Onychophora.

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Annelid – Classification |

Journal of comparative Neurology Sipunculapreviously a separate phylum. From intertidal zone to m depth; in Brazil, H. Polychaete families continued to be treated as natural units without any detectable interrelationships by Hartman Interrelationships of the living phyla.

This enables these worms to withdraw rapidly from danger by shortening their polchaeta.

Mitteilungen der Zoologische Station Neapel 8: Zoologische Jahrbuch, Anatomie Neanthes ijimai Izuka, superseded cllasse of subjective synonym. A traditional definition of the prostomium Tab. Although in Phoronida and Brachiopoda the segments do not accumulate inside the larvae, there is nevertheless a rapid metamorphosis and a dramatic elongation of the metasoma. Evidence for a clade of nematodes, arthropods and other moulting animals.

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Dorsal cirrus oval and the anteriormost inserted on body wall slightly above parapodial base Figure 16a-c ; slightly shorter and rounded in posterior parapodia Figure 16d.

The issue of morphological homology.

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