Phylogeny of the Annelida and allies
Phylogenetic relationships of Annelids, Molluscs, and Arthropods evidenced from molecules and morphology. Article in Journal of Molecular Evolution. evolutionary relationships of the Arthropoda. 1. How are arthropods related to other major phyla of invertebrates, particularly the Annelida (segmented worms). A consensus reconstruction of arthropod relationships, based on · Progress and . features shared by arthropods and annelids have evolved convergently or.
Thus, parapodia are assumed to be part of the ground pattern of the Articulata and hence were present in the stem species of the Annelida. This is consistent with the traditional interpretation of annelid systematics, which places the errant polychaete taxa at the base of the system Hypothesis 1.
McHugh, Dahmnait Molecular evidence that echiurans and pogonophorans are derived annelids. The Annelida, which includes the polychaetes and the clitellates, has long held the taxonomic rank of phylum.
Phylogeny of the Annelida and allies
The unsegmented, mud-dwelling echiuran spoon worms and the gutless, deep-sea pogonophoran tube worms including vestimentiferans share several embryological and morphological features with annelids, but each group has also been considered as a separate metazoan phylum based on the unique characters they display.
Phylogenetic analyses of DNA sequences from the nuclear gene elongation factor-1alpha place echiurans and pogonophorans within the Annelida. This result, indicating the derived loss of segmentation in echiurans, has profound implications for our understanding of the evolution of metazoan body plans, and challenges the traditional view of the phylum-level diversity and evolutionary relationships of protostome worms.
Zoologica Scripta 26 2: In this paper, we first demonstrate the historical background for the current unsatisfactory state of systematics of the polychaetes.
We then briefly discuss our knowledge of internal and external structures. A review of the polychaete families makes up the third section; 81 families are treated in detail. Five families have been recently synonymized with others, and six families are too poorly known to be sufficiently characterized.
Fossil polychaetes are briefly mentioned, with specific attention to problems associated with incorporating them in recent systematics. The traditional separation in 'errant' and 'sedentary' polychaetes has increasingly become recognized as being unsatisfactory; however, the current trend towards grouping the polychaetes in many orders without specifying the relationships among the orders, is no more satisfactory.
The lack of consistent morphological information is a major source of uncertainty. Intensive morphological studies should remove terminological ambiguities and alleviate some of the problems. A series of cladistic analyses assess the status and membership of the taxon Polychaeta. As well as the polychaete families, non- polychaete taxa such as the Echiura, Euarthropoda, Onychophora, Pogonophora as Frenulata and VestimentiferaClitellata, Aeolosomatidae and Potamodrilidae are included in the analyses.
All trees are rooted using the Sipuncula as outgroup. Characters are based on features where present such as the prostomium, peristomium, antennae, palps, nuchal organs, parapodia, stomodaeum, segmental organ structure and distribution, circulation and chaetae. A number of analyses are performed involving different ways of coding and weighting the characters, as well as the number of taxa included.
Transformation series are provided for several of these analyses. One of the analyses is chosen to provide a new classification. The Annelida is found to be monophyletic, though weakly supported, and comprises the Clitellata and Polychaeta. The Polychaeta is monophyletic only if taxa such as the Pogonophora, Aeolosomatidae and Potamodrilidae are included and is also weakly supported.
The Pogonophora is reduced to the rank of family within the Polychaeta and reverts to the name Siboglinidae Caullery, The new classification does not use Linnaean categories and the Polychaeta comprises two clades, the Scolecida and Palpata. The Palpata has the clades Aciculata and Canalipalpata.
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The Aciculata contains the Phyllodocida and Eunicida. The Canalipalpata has three clades; the Sabellida including the Siboglinidae Spionida and Terebellida. The position of a number of families requires further investigation. In the chapter, The Annelida. Rouse presents the same higher classification, incorporates the pogonophorans as Family Siboglinidae within the polychaetes, and has Echiura retained outside annelids meantime.
Kojima,Shigeaki Paraphyletic status of Polychaeta suggested by phylogenetic analysis based on the amino acid sequences of elongation factor-1 alpha. Molecular Phylogenetics and Evolution 9 2: In order to judge whether or not Polychaeta is a paraphyletic group, I determined almost the entire amino acid sequence of elongation factor-l alpha from thirteen polychaetes, two oligochaetes, two hirudineans, two vestimentiferans, and two molluscs.
Phylogenetic analysis by the neighbor-joining NJ method and the maximum likelihood ML method indicated the monophyly of Clitellata the oligochaetes and hirudineans.Shape of Life: Marine Arthropods - A Successful Design
In both the NJ and ML trees, vestimentiferans and clitellates were derived from polychaetes independently. The present results strongly suggest that Polychaeta is a paraphyletic group. Fauchald Recent views on the status, delineation and classification of the Annelida. The Clitellata have also been proposed to be a member of the Polychaeta, potentially making this latter taxon synonymous with the Annelida.
The relationships within the traditionally formulated Polychaeta have never been investigated using cladistic methodology. Recent classifications of polychaetes show a large number of "orders" with no real attempts to relate the groups in a phylogenetic sense.
In this paper a number of recent studies on annelid systematics and classification are reviewed. Special emphasis is placed on the cladistic parsimony analyses of Rouse and Fauchaldwhere a comprehensive assessment of the relationships among the various polychaete and annelid groups was attempted.
A contrasting result by Westheide using a different methodology, is also outlined and discussed. Rouse Life history evolution of marine invertebrates: New views from phylogenetic systematics. Established theories on the evolution of the diverse life histories of marine metazoans, specifically invertebrates, were developed in the absence of rigorous phylogenetic methods. With improved estimates of evolutionary relationships for various marine invertebrate groups, based on phylogenetic systematics, we can now critically evaluate the assumptions upon which these theories are based.
Several studies emphasizing a phylogenetic systematics approach have recently examined the evolutionary transitions among reproductive traits and challenge us to reconsider the generality of the assumptions made about life history evolution.
The results point towards exciting possibilities for a better understanding of the great diversity of reproductive and developmental modes we observe in marine invertebrates today. Cahiers de Biologie Marine, Vestimentiferan tube-worms are one of the dominant groups of organisms present at deep-sea hydrothermal vent habitats in the eastern Pacific Ocean.
Understanding how they have evolved to thrive in such harsh environments is a subject of great interest to marine biologists. In order to assess the degree and polarity of this evolutionary change, we have used a molecular phylogenetic approach to examine the age and history of the vestimentiferans.
Considerable debate persists concerning the taxonomic status and evolutionary origins of vestimentiferans. Jones argued that the vestimentiferan body plan was sufficiently distinct to warrant placement in a unique phylum, the Vestimentifera. On the other hand, Southwardamong others, challenged the erection of a separate phylum for these worms. During the course of recent taxonomic debates, various authors have also referred to these worms as the Order Vestimentifera Class Afrenulata: Although the rationale behind such changes in taxonomic rank may be legitimate, higher taxonomic categories are manmade constructs that are not meaningful for describing the diversity or the age of a monophyletic clade of organisms.
To avoid assigning rank to taxonomic names throughout this manuscript, we use the terms "vestimentiferan" and "perviate pogonophoran" i. To date, our work has focused on partial sequences from the mitochondrial cytochrome c oxidase subunit 1 CO1 gene Black et al. The present molecular data provide support for the inclusion of perviate pogonophorans and vestimentiferans as a clade within a paraphyletic grade of traditional annelid taxa. Furthermore, extant vestimentiferans appear to be a relatively young group that radiated during the Cenozoic.
A great deal of controversy surrounds the evolution of arthropod legs and wings. The Polyphyletic Hypothesis If we embrace the idea of polyphyletic origins, then arthropods are represented by as many as four major phyla -- each of which is presumed to have evolved separately from primitive annelid ancestors: Chelicerata -- 70, species -- including spiders, scorpions, mites, ticks, horseshoe crabs, and sea spiders. Crustacea -- 30, species -- including shrimp, crabs, lobsters, woodlice, barnacles, amphipods, branchiopods, and copepods.
Generalized Biramous Appendage of an Arthropod Evidence to support the polyphyletic hypothesis can be found in the comparative anatomy of appendages and in the embryonic development of the head and mouthparts.
Anderson whose studies of arthropod eggs has revealed that initial cell division in crustacean embryos is holoblastic spiral cleavagewhereas the eggs of all other arthropods are meroblastic superficial cleavage. Embryological development of the head and mouthparts has also been offered as evidence to support the polyphyletic hypothesis. Symphyla The Myriapods Regardless of whether we adopt a monophyletic or a polyphyletic classification scheme, it is apparent that the insects have more in common with the myriapods than with any other taxon of the Arthropoda.
The myriapods include both Chilopoda centipedes and Diplopoda millipedes as well as two other classes that are not as well-known: All myriapods exhibit ametabolous development there is no significant change in body form as they mature.