Characteristics and Classification of Cyclostomata – Imaluop

Now we are going to discuss a group of animals, Cyclostomata along with characteristics and classification of cyclostomata with their common examples. 

Basic Idea About Cyclostomata: 

The term cyclostomata represents their circular mouth without jaw and they are only members of agnatha present time and their body structure follows an eel shape. They are generally parasites and their suctorial ventral mouth and the epidermal teeth present on their tongues help them to anchor them with the body of the fish. 

Characteristics of Cyclostomata: 

• Externally their body is slender, round and eel shaped which gives them swiftness in water. 
• Paired appendages are absent, the median fin is supported by cartilaginous fin fin rays and the tail is diphycercal.  
• Their skin has no scale and their skin is covered by mucous glands but they are unicellular which makes their skin smooth and soft. 
• Their vertebrae are rudimentary present above the notochord and their notochord persist for whole life and the endoskeleton is made of fibrous cartilaginous tissue. 
• In their body muscles some special arrangements are observed and these muscles are known as myotomes.  
• On their head a single median nostril is present, mouth on ventral side and their buccal cavity have epidermal teeth on their tongues which is a special parasitic adaptation in them and their circular mouth helps them to attach with the body of the fish body. 
• Their digestive system has some special characteristics, some special fold present in their intestine and stomach is absent. 
• They respire through 5-16 pairs of gills but their gills are open externally through paired gill slits on both sides of their head and the gills present in pharyngeal pouches, due those pouches they are also known as Marsipobranchii. 
• Their circulatory system has nucleated circular erythrocytes and their heart is two chambered with one auricle and one ventricle and a special chamber conus arteriosus is present on the anterior side of heart. 
• Their excretion occurs through a pair of kidneys and their kidney is metanephric with urogenital papillary ducts. 
• Their nervous system has a nerve cord and 8-10 pairs of cranial nerves and they have semicircular canals for receiving sound waves and their olfactory sacs are responsible for perception of smell. 
• Their reproductive system has a single, large gonad without any duct system and they may be hermaphrodite, in their life cycle larva stage is present and fertilisation is external. 

Classification of Cyclostomata: 

Order Petromyzontiformes: 

• Members of this order have a ventral suctorial mouth with a rasping tongue which has horny teeth and they are known as lamps or lamp eels. 
• Their heads have a dorsal nostril and the nasal chamber is not connected with the pharynx directly because the nasohypophyseal sacs have a blind sac-like structure in them. 
• On the lateral side they have 7 pairs of gills which open outside through gill slits and the gills present inside the gill pouches which open in the respiratory pharynx. 
• They are found in both marine water and freshwater and they are sometimes known as pride in the sand. 
• In their nervous system the spinal nerves have separate dorsal and ventral roots and in sensory organs the ear have 2 semicircular canals. 
• They lay numerous eggs and development is indirect in which larval stages are a very long phase in their life cycle and metamorphosis is common in them, some common examples of this order are Lampetra and Petromyzon. 

Order Myxiniformes: 

• They are only found in marine habitat and they are popularly known as hagfish and some common examples of this order are Myxine and paramyxine. 
• Their head ends on the anterior side with a terminal mouth and the terminal circular mouth surrounded by tentacles. 
• Nostrils are present on the terminal end of the head and their nasohypophyseal sac opens into the pharynx. 
• Number of gills in this order is much more than the order of petromyzontiformes, 6-14 pairs of gills present in the gill sac. 
• In their spinal nerve the dorsal and ventral roots are fused and in their ear only one semicircular canal is present. 

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