#biology class 11

Animal Classification

Class Actinopterygii includes

Class Actinopterygii comprises ray-finned fishes, largest vertebrate radiation with over 30,000 species including minnows, perches, cods and seahorses. Median and paired fins supported by slender bony lepidotrichia or ceratotrichia derived from dermal bone, permitting fine control, folding and versatile locomotion, lacking fleshy muscular lobe of Sarcopterygii. Lungfishes belong to Dipnoi, coelacanths to Actinistia within lobe-finned group, cartilaginous fishes to Chondrichthyes. Whole-genome duplications including teleost-specific duplication fueled diversification, ecological dominance in fr

Ref: Campbell Biology, 12th ed., Chapter 34: Actinopterygii; NCBI Bookshelf, Osteichthyes Classification

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Animal Classification

Respiratory organs in fishes are

Fish respiration primarily involves branchial gills supported by pharyngeal arches. Each gill arch bears filaments further divided into lamellae containing dense capillary networks. Water flows unidirectionally, driven by buccal-opercular pumping in osteichthyans or ram ventilation, counter to blood flow within lamellae, maximizing oxygen extraction via countercurrent exchange with efficiency exceeding 80%. Lungs are present only in dipnoan lungfishes for air breathing, skin respiration minor, tracheae characteristic of insects. Such branchial adaptation supports active swimming, reflecting aq

Ref: NCERT Class 11 Biology, Chapter 4: Pisces – Gills; Campbell Biology, 12th ed., Chapter 42, Gills

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Animal Classification

Pisces are characterized by

True fishes or Pisces display circulatory architecture comprising two cardiac chambers, single thin-walled atrium receiving deoxygenated blood from sinus venosus and single thick-walled ventricle pumping to ventral aorta and gills via bulbus arteriosus. Oxygenated blood proceeds via dorsal aorta to systemic tissues in single circuit, no pulmonary bypass, resulting in low systemic blood pressure. This two-chambered heart contrasts with three-chambered design in amphibians and reptiles with double circulation partially mixing, and four-chambered separation in birds, mammals and crocodilians enab

Ref: Campbell Biology, 12th ed., Chapter 42: Fish Circulation; NCERT Class 11, Chapter 4, Pisces Heart

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Animal Classification

Jawless fishes lack

Jawless fishes retain ancestral craniate morphology lacking innovations of gnathostomes. Most conspicuously they lack paired pectoral and pelvic fins that provide stabilization, braking and maneuvering in cartilaginous and bony fishes. Instead, locomotion depends on median dorsal and caudal fins plus body undulation creating anguilliform waves. Additional primitive characters include absence of true scales in hagfishes, cartilaginous cranium, single nostril and persistence of notochord. Gill basket supports branchial structures. Absence of paired fins reflects evolutionary stage predating appe

Ref: NCERT Class 11 Biology, Chapter 4: Cyclostomata; Brusca & Brusca, Chapter 24, Agnatha Paired Fins

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Animal Classification

Lampreys feed mainly by

Lampreys exhibit parasitic feeding in adult phase. Using sucker-like buccal funnel armed with keratinized horny teeth and rasping tongue-like piston, they attach to teleost fishes, abrading skin, secreting anticoagulant lamphredin from buccal glands to prevent clotting, then ingesting blood, lymph and macerated tissue. Unlike active predation capturing whole prey or filter feeding of larval ammocoetes feeding on detritus, adult trophic mode depends on host, sometimes leading to host mortality but typically non-lethal. Suctorial parasitism compensates for jawlessness and correlates with anadrom

Ref: Hickman et al., Integrated Principles of Zoology, Chapter 24: Lamprey Feeding; Campbell Biology, 12th

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Animal Classification

Jawless fishes belong to class

Class Agnatha includes extant jawless craniates, representing earliest diverging vertebrate lineage lacking jaws derived from mandibular branchial arch, also lacking true paired appendages, dentine and bone in many forms. Characteristics include persistent notochord surrounded by arcualia, single median nostril in lampreys, multiple gill pouches opening separately, keratinized tooth-like structures and cartilaginous skeleton. Modern examples are Petromyzon lamprey and Myxine hagfish. Chondrichthyes, Osteichthyes and extinct Placodermi are jawed gnathostomes. Agnatha thus serves as stem group c

Ref: NCERT Class 11 Biology, Chapter 4: Cyclostomata Agnatha; Campbell Biology, 12th ed., Chapter 34

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