Phylogeny of the Annelida and allies
Phylogenetic relationships of annelids, molluscs, and arthropods evidenced from molecules Annelids and arthropods have long been considered each other's closest Arthropods/genetics*; DNA, Ribosomal/genetics*; Evolution, Molecular . The annelids also known as the ringed worms or segmented worms, are a large phylum, with .. As in arthropods, each muscle fiber (cell) is controlled by more than one neuron, . Feeding structures in the mouth region vary widely, and have little correlation with Annual Review of Ecology, Evolution, and Systematics. Nov 2, Can it be defined? Molecular Biology and Evolution 12(4): Phylogenetic relationships of annelids, molluscs, and arthropods.
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This pattern is called teloblastic growth. These are secreted by the one-cell deep epidermis outermost skin layer. A few marine annelids that live in tubes lack cuticles, but their tubes have a similar structure, and mucus -secreting glands in the epidermis protect their skins.
Below this are two layers of muscles, which develop from the lining of the coelom body cavity: The simplest are unjointed and form paired bundles near the top and bottom of each side of each segment. The chetoblasts produce chetae by forming microvillifine hair-like extensions that increase the area available for secreting the cheta.The Arthropods - Educational Video for Kids.
When the cheta is complete, the microvilli withdraw into the chetoblast, leaving parallel tunnels that run almost the full length of the cheta. Parapodia are unjointed paired extensions of the body wall, and their muscles are derived from the circular muscles of the body.
They are often supported internally by one or more large, thick chetae. The parapodia of burrowing and tube-dwelling polychaetes are often just ridges whose tips bear hooked chetae. In active crawlers and swimmers the parapodia are often divided into large upper and lower paddles on a very short trunk, and the paddles are generally fringed with chetae and sometimes with cirri fused bundles of cilia and gills.
From each segmental ganglion a branching system of local nerves runs into the body wall and then encircles the body. Vertebrates have a different system, in which one neuron controls a group of muscle fibers.
Their large diameter decreases their resistance, which allows them to transmit signals exceptionally fast. This enables these worms to withdraw rapidly from danger by shortening their bodies. Experiments have shown that cutting the giant axons prevents this escape response but does not affect normal movement. Intensive morphological studies should remove terminological ambiguities and alleviate some of the problems.
Phylogeny of the Annelida and allies
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. 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.
How Are the Annelid & the Arthropod Different?
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. 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.
The first two classes consist of worms differentiated primarily by the use of parapodia for movement; the third includes leeches. The Arthropoda phylum contains five classes: Crustacea shrimp and lobsterArachnida spiders and scorpionsChilopoda centipedesDiplopoda millipedes and Insecta roaches and beetles. According to the University of California's Museum of Paleontology website, the Annelida phylum contains about 9, species.
The Arthropida phylum comprises an estimated 6 million to 9 million species of arthropods. Body Structures Members of the Annelida and Arthropoda phyla differ in their body formations.
Annelid species typically have tubelike bodies consisting of numerous segments, known as somites, covered in stiff hairlike structures called setae that help the annelid move forward. Leeches have somites but not setae; instead, they have suckers on both ends of their flatter bodies. On the other hand, arthropods have more complex segmented bodies covered in an exoskeleton that protects their organs and muscles.
Most arthropods also have visible distinctions between their heads, bodies and legs; this is not the case for annelids.