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GENERAL CHARACTERISTICS , AFFINITIES , AND BIOLOGY OF CYCLOSTOMES.

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  GENERAL CHARACTERISTICS AND CLASSIFICATION OF CYCLOSTOMES UPTO CLASSES .  Cyclostomata is a group of chordates that comprises the living jawless fishes: the lampreys and hagfishes. Both groups have round mouths that lack jaws but have retractable horny teeth. The name Cyclostomata means "round mouths". Their mouths cannot close due to the lack of a jaw, so they have to constantly cycle water through the mouth.     GENERAL CHARACTERS OF CYCLOSTOMATA: - Cyclostomes are jawless primitive vertebrates. They may be marine or fresh water. They include hag fishes and lampreys. Ø The body is long, eel like. It has a trunk and a compressed tail. Ø Paired fins are absent. Median fin is supported by cartilaginous fin-rays. Ø The skin i.e soft and smooth. It is slimy. It is scale less.   Ø Z-shaped myomeres are present in the trunk and tail. Protractor and retractor muscles move the tongue.   Ø In this group a true coelom is seen.   Ø These vertebrates do ...
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CHARACTERS AND AFFINITIES OF HEMICHORDATES.

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                        Definition and Introduction Hemichordates is an independent phylum of marine invertebrates closely related to Echinodermata. They were previously classified as a subphylum of Chordata. Members exhibit the following key features:   - Enterocoelous coelom : Coelom develops through enterocoely in three compartments (protocoel, mesocoel, metacoel).   - Pharyngeal gill slits : Used for filter feeding.   - Stomochord: A buccal diverticulum, initially mistaken for a notochord.   - Body division: Vermiform structure with three regions – proboscis, collar, trunk.     Examples include Balanoglossus, Saccoglossus, and Glossobalanus, classified under Class Enteropneusta . Affinities with Chordata Similarities to chordates include:   - Pharyngeal gill slits - Dorsal hollow nerve cord in some species     Objections to Inclusion in Chordata: ...
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