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The annelids (/ ˈ æ n ə l ɪ d z /), also known as the segmented worms, are animals that comprise the phylum Annelida (/ ə ˈ n ɛ l ɪ d ə /; from Latin anellus ' little ring '). [ 3 ] [ a ] The phylum contains over 22,000 extant species , including ragworms , earthworms , and leeches .
Clitellate annelids are segmented worms characterised by the clitellum or girdle which is located near the head end of mature individuals. The mouth is on the ventral surface and is overhung by the prostomium (proboscis). The brain is not located in the head but in one of the body segments.
Limnatis nilotica grows to a length of about 10 cm (4 in). It has powerful jaws and a sucker at both the anterior and the posterior end. The general colour is dark green and there are green spots in rows on the dorsal surface and bands of yellowish-orange and green on the sides.
Pleistoannelida is a group of annelid worms that comprises the vast majority of the diversity in phylum Annelida.Discovered through phylogenetic analyses, it is the largest clade of annelids, comprised by the last common ancestor of the highly diverse sister groups Errantia and Sedentaria (Clitellata and related polychaetes) and all the descendants of that ancestor.
The annelids, collectively called Annelida, are a large phylum of animals, comprising the segmented worms, with about 15 000 modern species including the well-known earthworms and leeches The main article for this category is Annelid .
Nereis are osmoconformers.They are dioecious (individuals are male or female) and they release their haploid gametes into the water, a process called spawning.Moreover, upon fertilization and mitotic divisions of the zygote, Nereids form a larval stage which is similar to that of molluscs – i.e. a trochophore larva.
Errantia is a diverse group of marine polychaete worms in the phylum Annelida. Traditionally a subclass of the paraphyletic class Polychaeta, [4] it is currently regarded as a monophyletic group within the larger Pleistoannelida, composed of Errantia and Sedentaria. [2] These worms are found worldwide in marine environments and brackish water.
Trochophores exist as a larval form within the trochozoan clade, which include the entoprocts, molluscs, annelids (including echiurans and sipunculans) and nemerteans. Together, these phyla make up part of the Lophotrochozoa ; it is possible that trochophore larvae were present in the life cycle of the group's common ancestor.