Animal Classification Nonchordates Chordates

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Animal Classification

Nonchordates Chordates Protozoa

Porifera

Coelenterata

Platyhelmithes

Nematohelminthes

Annelida

Mollusca

Arthropoda

Echinodermata

Hemichordata

Protochordata (Acraniata) Vertebrata (Craniata)

Urochordata

Chephalochordata

Agnatha

Ostracodermi

Cyclostomata

Gnathostomata

Placodermi

Condrichthyes

Osteichthyes

Amphibia

Reptilia

Aves

Mammalia Dr. A. S. Kolhe

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Subphylum – Protochordata (Acrania)

They lack head & cranium or skull. Notochord is confirmed to tail in larval forms of some spp. & absent in adult stage. While in some forms like Chephalochordata notochord extends along the entire body. They are small sized & exclusively marine. Vertebrae, jaws & paired appendages are absent. Ciliary mode of feeding. Sexes may be separate or united. Protochordata is divided into two classes as Urochordata & Chephalochordata

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Class -Urochordata

Exclusively marine,solitory or colonial. Body is covered with tunic or test. Notochord is confirmed to tail in larval forms only. Larva is free swimming. Coelom is absent. Pharynx has numerous stigmata formed by larval gill cleft. They are hermaphrodite. Class Urochordata is divided into Three orders.

Order I- Ascidicea (Herdmania,Ascidia,Molgula) They are sedentary marine tunicates. They may be solitary or colonial. Adult lack notochord & tail. Test is thick & permanent.

Order II- Thaliacea ( Doliolum, Salpa) They are pelagic & free-swimming. Body is barrel shaped. Test is thin, transparent & permanent. They show alternation of generation having sexual & asexual mode of reproduction. Order III- Larvacea (Oikopleura, Fritillaria) They are pelagic & transparent. Tail is present in adults & act as locomotory organ. Larval form retained through the life & shows neoteny. Sieve like ciliary feeding apertures are present.

Dr. A. S. Kolhe

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Class- Cephalochordata

Example; Amphioxus or lancelets.

Notochord extends from the head to the tail (anterior to posterior) and is present in both the

larvae and the adult.

They have a dorsal tubular neural tube without defined brain.

Motile filter feeders.

They are marine, solitary fish-like animals.

Head is absent but tail is present.

No definite coelom is present.

Sexes are separate, metamerically repeated gonads, external fertilization.

Excretory organs are protonephridia with solanocytes.

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Subphylum - Vertebrata

Characteristics:

At some stage of their life they all have:

Notochord.

Dorsal hollow nerve cord.

Pharyngeal pouches or gill slits.

Post anal tail.

Endoskeleton.

Highly cephalized highly developed sense organs and brain.

Most have paired appendages.

Closed circulatory system.

Subphylum vertebrata is divided into two infra-phyla ( super classes):

Agnatha and Gnathostomata.

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Vertebrates may be characterized by 12 general derived characteristics. Bilateral symmetry Two pairs of jointed locomotor appendages, which can include fins (pectoral and anal/dorsal

fins, as well as the forelimbs and hind limbs). Outer covering of protective cellular skin, which can be modified into special structures such as

scales, hair and feathers Metamerism found in skeletal, muscular and nervous system. This was described in a previous

lecture - structures can include ribs, vertebrae, muscles and ganglia/peripheral nerves. Well-developed coelom, or body cavity completely lined with epithelium (cellular tissue), that

may be divided into 2 to 4 compartments. Well-developed internal skeleton of cartilage and bone, separated into axial skeleton (skull,

vertebrae, ribs, sternum) and appendicular skeleton (girdles and appendages). Highly developed brain enclosed by skull, and nerve cord enclosed by vertebrae. This provides

advanced neural structures that are highly protected from damage. Well-developed sense organs (eyes, ears, nostrils) located on the head (cephalization). Respiratory system, including either gills or lungs, and located closely to the pharynx or throat. Closed circulatory system with ventral heart and median dorsal artery. Genital and excretory systems closely related, utilizing common ducts and pathways. Digestive tracts with two major digestive glands (liver and pancreas) that secrete into it.

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Superclass: Agnatha

No jaws.

No paired appendages .

A completely cartilagenous Skeleton.

A single nostril.

6 - 14 external or concealed gill slits

A persistent notochord.

Two-chambered heart .

Agnatha is divided into two classes:

Ostracodermi(extinct) and Cyclostomata (living).

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Class: Ostracodermi

Body with heavy armour of large plates on head & small bony scales. They are extinct agnathans with little resemblance superficially with cyclostomes. Lack of paired appendages. Head flat & expanded.

Example:Cephalospis

Class: Cyclostomata

The body is long, eel like. It shows trunk and compressed tail.

Paired fins are absent. Median fin is supported by cartilaginous fin-rays.

The skin Is soft and smooth. It is slimy. It as scale less.

The mouth is circular. It works like a sucker. It is surrounded by tentacles.

Notochord persists throughout life.

Skull is simple and primitive. Brain is seen.

Excretory system includes a pair of mesonephric kidneys.

Sexes are separate.

Class cyclostomata is divided into two orders: Myxinoidea( Myxine) and

Petromyzontia ( Petromyzon).

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Superclass- Gnathostomata

They have mouth with true upper & lower jaws.

They have two paired appendages.

Olfactory organs & nostrils are paired.

Well developed endoskeleton.

Three semicircular canals in each internal year.

Gnathostomata is divided into seven classes – an extinct Placodermi & six living classes.

Class- Placodermi

They had heavy armour of bony plates.

Primitive jaws, paired fins were present.

Bony endoskeleton.

Heterocercal tail.

Extinct in Permian

Ex.Climatius.

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Class- Condrichthyes - Cartilagenous fishes

Paired nostrils.

Skeleton completely cartilagenous with no endoskeletal bone.

No swim bladder.

Scales dermal placoid when present .

Gill arches internal to gills.

Freshwater and marine species.

Contains three main groups:

Subclass -Elasmobranchii

5 - 7 gill openings plus spiracle anterior to first gill.

Upper jaw not attached to braincase.

Teeth derived from placoid scales, deciduous and continually replaced.

Claspers present in males, internal fertilization, ovoviviparous.

Body is laterally compressed.

Includes two orders: Pleurotremata & Hypotremata

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Order- Pleurotremata or Squaliformes

Purely predaceous & exclusively marine.

Heterocercal tailfin - caudal fin is longer on the dorsal side than on the ventral side.

Body is spindle shaped.

Five or seven pairs of gill slits.

Ex. Scoliodon, Sphyrna & all sharks.

Order- Hypotremata or Rajiformes

Greatly flattened & bottom dwellers.

Scales not over entire body.

Pectoral fins wing like.

Crushing teeth - mollusk eaters.

Spiracles greatly enlarged.

Oviparous.

Ex. Rays, skates, sawfishes.

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Subclass - Holocephali

Upper jaw fused to braincase.

Flat, bony plates instead of teeth.

Operculum covering gill slits.

Strictly marine feeding on mollusks

Scales absent in adults.

Cloaca absent.

Have single order Chimaeriformes having similar character of subclass.

Ex. Chimaera ( Rat fish).

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Class Osteichthyes - Bony fishes

Endoskeleton made up of bone.

Jaws and paired appendages .

Gill arches internal to gills.

Gills covered by bony operculum.

Dermal scales not placoid may be cycloid,ctenoid, rhomboid or gnaoid.

Many forms have swim bladder .

Appeared in Devonian - dominant vertebrates since mid Devonian.

Arose in freshwater, moved into saltwater.

Class osteichthyes is divided into two subclasses: Actinopterigii & Sacropterigii.

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Subclass - Actinopterygii

Fin rays attach directly to girdles . Internal nostrils or nares absent . Single gas bladder. Operculum covers the gills on both side. Commonly called as ray-fined fishes. Dorsal fin is single with spine. Actinopterygii is divided into three infra-classes or super-orders.

Superorder :Chondrostei (Sturgeons and Paddlefish)

General primitive form.

Typically small. Skeleton primarily cartilage. Heterocercal tail. Gnaoid scales. Most died out by end of Mesozoic. Have two orders: Polypteryformes ( Polypterus) and Acinopenseriformes ( Acipenser).

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Superorder- Holostei

They are called intermediate ray-fined fishes & most of them are extinct.

Ganoid or Cycloid scales.

Hemiheterocircal tail.

Single air bladder. Spiracle is absent.

Divided into two orders: Semionotiformes (Gar pike) and Amiiformes (Amia).

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