They have a fixed number of segments, 33, but the segmentation is not visible externally because the cuticle is marked with annulations. Modern analysis has revealed Branchiobdella and Hirudinea are two sister groups to the lumbriculids and they are daughter groups to the tree of oligochaetes.
The animal works this cocoon forward and over its head end, whereupon the ends of the cocoon become sealed, with fertilisation and development taking place inside. They thrive in polluted waters and places with high quantities of decaying organic matter and may be very numerous.
Namely, the Acanthobdellidea, Branchiobdella and Hirudinea are monophyleticbut are embedded among the Oligochaetawhich are an evolutionary grade of Class clitellata that are outwardly similar, but not very close relatives. The mouth is on the ventral surface and is overhung by the prostomium proboscis.
The clitellum occupies segments 9 to 11 but is only noticeable during breeding periods. In particular, the leeches and earthworms appear to be very close relatives. They also lack parapodia and appendages on the prostomium, the body and the periproct terminal segment on which the anus is located.
Overall, clitellate phylogeny is not well resolved.
The front few segments or head have been modified into a sucker that usually surrounds the mouth. The gonads are Class clitellata in a few segments near the clitellum, with the testes being anterior to the ovaries.
The hindermost segments form another, larger, disc-shaped sucker located on the underside of the body. During copulation, the clitellum produces a mucus that holds worms in place whilst they mate.
This mechanism is Class clitellata to be apomorphic a newly derived characteristic rather than an evolutionarily ancestral one. They are more abundant in temperate waters in the northern hemisphere than elsewhere. The marine species are mostly tiny and live in the interstices between sand grains, from the intertidal zone to the deep sea.
The worm then creeps out backward from the coat and deposits either fertilized zygotes or both ovae and sperm into the coat, which is then packed into a cocoon.
The zygotes then develop directly in the cocoon without passing through a larval stage as opposed to other annelids, e. Historically, the group was classified into the subclasses Oligochaeta and the Hirudinea.Description of Clitellata Clitellata is a class of Annelid worms, characterized by having a clitellum - a collar that forms a reproductive cocoon during part of their.
The Clitellata are a class of annelid worms, characterized by having a clitellum - the 'collar' that forms a reproductive cocoon during part of their life cycles.
The clitellates comprise around 8, species. Unlike the class of Polychaeta, they do not have parapodia and their heads are less developed.
Comment: The arrangement of the Clitellata within the annelids remains unresolved, and various conflicting views may be found in recent resources. class Clitellata The Clitellata are a class of annelid worms, characterized by having a clitellum - the 'collar' that forms a reproductive cocoon during part of their.
Confused by a class within a class or an order within an order? Please see our brief essay. Additional Information. Encyclopedia of Life; Clitellata. Facebook. Twitter. Kingdom Animalia animals.
Animalia: information (1) Class Clitellata. Clitellata: pictures (13) Related Taxa. Species Hirudo medicinalis. The Clitellata are a class of annelid worms, characterized by having a clitellum - the 'collar' that forms a reproductive cocoon during part of their life cycles.
The clitellates comprise around 8, species.Download