Phylum Mollusca - NEET-Biology

 Phylum Mollusca

Fig: Apple snail (Pila)

Characteristics:

• Mollusca is the second-largest animal phylum & includes snails, slugs, oysters, cuttlefish, octopuses, and many other familiar animals.

• Exhibit organ-system level of body organization.

• Bilaterally symmetrical, triploblastic & coelomate animals.

• The body is covered by a calcareous shell and is unsegmented with a distinct head, muscular foot & visceral hump.

• Most mollusks have a rasping tongue-like radula for feeding.

• Except for cephalopods, all mollusks have such as open circulatory system.

• Nitrogenous wastes are removed from the body by the nephridium.

• Mostly dioecious.

• Fertilization is both external & internal, oviparous with indirect development.

• Embryo developed into a free-swimming larva called a trochophore.

• Examples: Pila (Apple snail), Pinctada (Pearl oyster), Sepia (Cuttlefish), Loligo (Squid), Octopus (Devilfish), Aplysia, Dentalium (Tusk shell), Chaetopleura (Chiton)

Fig: Octopus (Devilfish)

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Phylum Hemichordata - NEET-Biology

 Phylum Hemichordata

Fig: Acorn worm (Hemichordate)

• Hemichordate = half chordate.

• It shares some (but not all) of the typical chordate characteristics.

• These are not classified as true chordates, although they are closely related.

• Some DNA-based studies evolution suggest that hemichordates are actually closer to echinoderms than to true chordates.

• It was earlier considered as a sub-phylum under the phylum Chordata. 

• But, now it is placed under a separate phylum under non-chordates.

Important characteristics:

• Exclusively marine.

• Worm-like animals with the organ-system level of organization.

• Bilaterally symmetrical, triploblastic & coelomate animals.

• The body is cylindrical & is composed of an anterior proboscis, a collar & a long trunk.

• Notochord present which allows & endodermal in origin (termed stomochord).

• Notochord occurs only in the anterior end of the body. It is called the buccal diverticulum.

• Open circulatory system.

• Perform sexual reproduction.

• Sexes are separate.

• Fertilization is external.

• Development is indirect.

• Example: Balanglossus (Tongue worm), Ptychodera & Saccoglossus.

Fig: Balanoglossus (Tongue worm)

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Class Aves - NEET-Biology

 Class Aves

Fig: Pigeon (Columba livia domestica)

Aves is the name of the class to which birds belong in taxonomy.

Important characteristics:

•  The body usually spindle-shaped, with four divisions: head, neck, trunk, and tail.

• Skin is dry without glands except the oil or preen gland at the base of the tail.

• Many of the characters of the birds are adaptations that facilitate flight.

• A bird's most obvious adaptations for flight are its wings & feathers.

• The forelimbs are modified into wings. Epidermis covered with feathers.

• The presence of feathers is the most characteristics feature of aves.

• Fully ossified endoskeleton & the long bones are hollow with air cavities (pneumatic).

• Respiration is by the lungs. The circulatory system consists of a four-chambered heart with two atria & two-ventricles; nucleated erythrocytes. Livings birds are also toothless.

• They are warm-blooded animals, i.e. they are able to maintain constant body temperature.

• The excretory system included metanephric kidneys; ureters open into cloaca; no urinary bladder; uric acid main nitrogenous waste.

• Sexes separate; females have left ovary & oviduct only; copulatory organ (penis) only in ducks, geese, paleognaths & a few others.

• Sexes are separate. Fertilization is internal.

• They are oviparous & development is direct. Amniotic eggs with much yolk & hard, calcareous shells; embryonic membranes are present in the egg during development.

• Example: Corvus (crow), Columba (pigeon), Psittacula (Parrot), Struthio (Ostrich), Pavo (Peacock), Neophron (Vulture).

• Flightless birds: Struthio camelus (African ostrich), Rhea americana (South America ostrich), Dromaius novaehollandiae (Australian emu).

Fig: Dromaius novaehollandiae 

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Phylum Echinodermata - NEET-Biology

 Phylum Echinodermata

Fig: Sea urchin (Echinodermata)

Important characteristics:

• Exclusively marine & benthic i.e. found at the bottom of the sea.

• Spiny skinned free swimming, triploblastic & coelomate animals.

• Adult echinoderms are radially symmetrical but larvae are bilaterally symmetrical.

• Lack of head and do not show segmentation.

• The digestive system is complete with the mouth on the ventral side & anus on the dorsal side.

• The most characteristic feature in Echinodermata is the presence of the water vascular (or ambulacral) system. Tube feet are contractile appendages of the water vascular system; serve for locomotion, food capture, respiration & attachment of the body to the substratum. They constitute glands & filtering devices.

• Respiratory organs are skin gills or papulae (starfish), peristomial gills (sea-urchins), genital bursae (brittle stars), cloacal respiratory tree (holothurians).

• Perform sexual reproduction. Sexes are separate. Fertilization is usually external. Development is indirect with free-swimming larva.

The phylum Echinodermata is divided into two subphyla:

• Pelmatozoa: It has a single living class Crinoidea represented by sea lilies or feather stars like Antedon, Rhizocrinus, etc.

• Eleutherozoa: It has four living classes: Asteroidea (Asterias), Ophiothrix, Echinoidea (sea urchin), Holothuroidea (sea cucumbers).

Fig: Sea cucumber (Holothuroidea)

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Class Osteichthyes - NEET-Biology

Class Osteichthyes

Fig: Catla fish 

• The vast majority of vertebrates belong to a superclass of gnathostomes called Osteichthyes.

• Unlike chondrichthyans, nearly all living osteichthyans have an ossified (bony) endoskeleton with a hard matrix of calcium phosphate [Ca3(PO4)2].

Important characteristics:

• It includes both marine & freshwater fishes with a bony endoskeleton.

• They have four pairs of gills that are covered by an operculum on each side.

• The heart is two-chambered (one auricle & one ventricle).

• Most fishes can control their buoyancy with an air bladder known as the swim bladder. 

• Movement of gases from the blood to the swim/air bladder (fish maw) increases buoyancy, making the animal rise; transfer of gas back to the blood causes the animal to sink.

• Adult kidneys are mesonephric. Excretion is chiefly ammonetelic.

• They are cold-blooded animals.

• Sexes are separate. Fertilization is usually external.

• Mostly oviparous, rarely ovoviviparous or viviparous.

• Development direct, rarely with metamorphosis.

• Examples: Latimeria (Lobe-finned fish), Dipnoi (Lung-fish), Hippocampus (Sea-horse), Exocoetus (Flying fish), Echeneis or Remoro (Suckerfish), Anguilla (eel), Anabas (Climbing perch), Catla-Catla (Catla), Pterophyllum (Angelfish), Betta (Fighting fish).

Fig: Dipnoi (Lung-fish)

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Class Amphibia- NEET-Biology

 Class Amphibia

Class: Amphibia

• Amphibians are vertebrates, that can live in both aquatic (water) as well as terrestrial (land) environments.

• The name amphibian is derived from the Greek word "amphibious" meaning living a dual life.

• The first amphibian came into existence in the Devonian period.

Important characteristics:

• Soft, moist (without scales) & glandular skin.

• Endoskeleton mostly bony.

• Notochord does not persist.

• The eyes have eyelids.

• A tympanum represents the ear.

• Respiration is by gills, lungs, and through the skin.

• Larvae with external gills which may persist in some aquatic adults (like salamanders).

• The heart is three-chambered (two auricles & one ventricle).

• The alimentary canal, urinary & reproduction tracts open into a common chamber called cloaca which opens to the exterior.

• Kidneys are mesonephric.

• Excretion is ureotelic.

• They are cold-blooded animals.

• Sexes are separate. Fertilization is external.

• They are oviparous & development is direct or indirect.

• Example: Ichthyophis (blind-worm), Ambystoma (American salamander), Hyla (tree frog), Necturus (Mudpuppy), Alytes (Midwife toad), Bufo (Toad), Rana tigrina (Indian Bullfrog)

Fig: Rana tigrina

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