Animal Kingdom Part 5

(Chordates - General account, Pisces and Amphibians)

The phylum chordata has three most important characteristics:

1. They have a notochord either throughout life or during early embryonic development
2. Dorsal hollow nerve chord
3. Paired gill slits on either sides of pharynx at some stage; may or may not be functional

 

 

 

Body plan of Chordates

Source:http://staff.tuhsd.k12.az.us/gfoster/standard/chordate.gif

Other important characters are as follows-

1. Bilaterally symmetrical and metamerically segmented, triploblastic, coelomate animals having a true coelom, enterocoelic or schizocoelic in origin.
2. A post anal tail usually projects beyond the anus at some stage and may or may not persist in the adult.
3. A cartilaginous or bony, living and jointed endoskeleton present in majority of members (vertebrates).
4. Pharyngeal gill slits present at some stage; may or may not be functional.
5. Digestive system complete with digestive glands.
6. Blood vascular system closed. Heart ventral with dorsal and ventral blood vessels. Hepatic portal system well developed.

(7) Excretory system consists of proto-or meso- or meta-nephric kidneys.

8. Sexes separate with rare exceptions.

Outline Classification of Phylum Chordata

 

 

 

 

 

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Group A. Acrania (Protochordata) or Lower Chordata

Exclusively marine, small-sized chordates

No appendages, cephalization and exoskeleton

 

Coelom enterocoelic, formed by fusion of pouches budded off from embryonic archenteron.

Notochord may persist throughout life and is not replaced by vertebral column. No skull, cranium and verterbral column

Phyrynx with permanent gill clefts.

 

Endostyle present

Heart chamber less when present. No. red blood corpuscles in blood

Group B. Craniata (Euchordata) or Higher Chordata

Aquatic or terrestrial, mostly large sized vertebrates

Usually two pairs of appendages, well-developed head and exoskeleton present

Coelom schizocoelic, formed by splitting up of mesoderm

 

Notochord replaced by a vertebral column. Skull and cranium present

 

 

Phraryngeal gill clefts persist or disappear

Endostyle absent

Heart made of 2, 3 or 4 chambers. Blood has R.B.Cs

Kidneys protonephridia                           Kidneys meso– or metanephric

Sexes separate or united. Reproduction asexual as well as sexual.

Gonoducts usually absent

Sexes separate.

Only sexual reproduction, Gonoducts always present

 

Division I. Agnatha

2     Division II. Gnathostomata

Without true jaws                                    True jaws present

Paired appendages absent                      Appendages paired (pectoral &

pelvic) present

Inner ear with 2 semi-circular canals.    Inner ear with 3 semi-circular canals Notochord persistent in adults               Notochord persists or replaced by

vertebrae

 

Classification of chordata :

Phylum chordata can be divided into two groups: Acrania (Protochordata) and Craniata (Euchordata).

Group A. Acrania (Protochordata) : (Gr. a, absent; kranion, head, or, Gr. protos, first; chorde, cord). All marine, small, Primitive or lower chordates. Lacking a head, a skull or cranium, a vertebral column, jaws and brain. About 2,000 species known. The Acrania is divided into three subphyla: Hemichordata, Urochordata and Cephalochordata

Subphylum I. Hemichordata : (Gr. hemi, half; chorde, cord). Body divided into 3 regions: Proboscis, collar and trunk. Hemichordates are now studied as a separate invertebrate phylum

 

Class 1. Enteropneusta : (Gr. enteron, gut; pneustos, breathed). Body large and worm-like. Gill slits numerous. Intstine straight. Acorn or togue worms. 70 species. Balanoglossus, Saccoglossus.

Class 2. Pterobranchia : (Gr. pteron, feather; branchion, gill). Body small and compact. Gill-slits one pair or none. Intstine U–shaped. Pterobranchs. 20 species. Cephalodiscus, Rhabdopleura.

 

 

Subphylum II. Urochordata or Tunicata : (Gr. oura, a tail; L. chorda, cord). Notochord and nerve cord only in tadpole-like larva. Adult sac-like, often sessile and encased in a protective tunic.

 

Class 1. Ascidacea : Sessile tunicat3es.  Gill-clefts numerous. eg. Ascidians or sea squirts. About 1,200 species. Herdmania, Molgula.                 Herdmania shows

retrogressive metamorphosis.

Class 2. Thaliacea : Free-swimming or pelagic tunicates. Sometimes colonial. Salps or chain tunicates. 30 species. Salpa, Doliolum, Pyrosoma.

 

Subphylum III. Cephalochordata : (Gr. kephale, head; L. chorda, cord). Notochord and nerve cord present throughout life along entire length of body. Class Leptocardii : Body fish-like, segmented with myotomes and numerous gill-slits. Free swimming and burrowing. Lancelets. About 30 species.

 

Branchiostoma (= Amphioxus), Asymmetron.

 

Group B. Craniata (Euchordata): They are higher chordates or vertebrates with distinct head, a vertebral column, jaws and brain protected by a skull or cranium. The Craniata includes a single subphylum, the vertebrata.

 

Subphylum IV. Vertebrata : (L. vertebratus, backbone). Notochord supplemented or replaced by a vertebral column or backbone formed of overlapping vertebrae. Usually dioecious. Vertebrates are largest chordate subphylum including about 46,500 species. The vertebrata is divided into two divisions: Agnatha and Gnathostomata as follows;

Division I. Agnatha : (Gr. a, not; gnathos, jaw). Jaw less primitive fish-like vertebrates without true jaws and paired limbs.

Class 1. Ostracodermi. (Gr. ostrakon, shell; derma, skin). It includes extinct orders of ancient primitive heavily armoured, Palaeozoic, world's first vertebrates, collectively called the ostracoderms. Caphalaspis, Drepanaspis. Class 2. Cyclostomata. (Gr. cyklos, circular; stoma, mouth). Body eel-shaped, without scales, jaws and lateral fins. Mouth rounded and suctorial. Gills 5–16 pairs. Parasites and scavengers. 45 species. Lampreys (Petromyzon) and hagfishes (Myxine).

 

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vertebrates with true jaws and paired limbs. Gnathostomata is divided into two super classes. All fishes like aquatic gnathostomes are placed in the superclass Pisces, whereas all the four legged terrestrial gnathostomes in the superclass Tetrapoda.

Superclass 1. Pisces                                 Superclass 2. Tetrapoda

Exclusively aquatic                                   Aquatic or terrestrial.

Paired limbs, if present, as fins.              Paired pentadactyle limbs present Median fins present                                 Median fins absent

Skin usually moist and scaly                   Skin usually dry and cornified Respiration aquatic, by gills                    Respiration aerial, by lungs Sense organs functional in water                      Sense organs functional in air.

It includes fishes only.                             It includes the classes- Amphibia, Reptilia, Aves and Mammals

Superclass Pisces

Class 1 Placodermi (Extinct)

• Primitive earliest jawed fishes of Palaeozoic era. Examples : Placoderms. Climatius, Dinichthys. Class 2 Chondrichthyes
• Mostly marine with Cartilaginous endoskeleton. Examples : Scoliodon (dogfish), Chimaera (ratfish). Class 3 Osteichthyes
• Freshwater as well as marine with bony endoskeleton.

Examples : Labeo (rohu), Protopterus (lungfish), Hippocampus (sea horse)

 

 

 

Chondrichthyes (Cartilaginous Fishes/Elasmobranchs

General characters-

1. Mostly marine and predaceous.
2. Body spindle shaped.
3. Fins both median and paired, all supported by fin rays. Pelvic fins bear claspers in male. Tail heterocercal.
4. Skin tough with minute placoid scales and mucous glands.
5. Endoskeleton entirely cartilaginous, without true bones (Gr. chondros, cartilage + ichthys, fish). Notochord persistent. Vertebrae complete and separate. Pectoral and pelvic girdles present.
6. Mouth ventral. Jaws present. Teeth are modified placoid scales. Stomach J-shaped. Intestine with spiral valve.
7. Respiration by 5 to 7 pairs of gills. Gill-slits separate and not covered by Operculum. No air bladder and lungs.
8. Heart 2–chambered (1 auricle and 1 ventricle). Sinus venosus and conus arteriosus present. Both renal and portal systems present. Temperature variable (poikilothermous).
9. Kidneys opisthonephric. Excretion ureotelic. Cloaca present.
10. Brain with large olfactory lobes and cerebellum. Cranial nerves 10 pairs.
11. Olfactory sacs do not open into pharynx. Membranous labyrinth with 3 semicircular canals. Lateral line canal system present.
12. Sexes separate. Gonads paired. Fertilization internal. Oviparous or ovoviviparous.

 

Examples : True sharks- Dogfishes (Scoliodon), spiny dogfish (squalus) seven gilled shark (Heptanchus), Zebra shark (stegostoma), hammer- headed (Sphyrna), whale shark (Rhineodon).

Skates and rays-skate (Raja), stingray (Trygon), electric ray (Tropedo), eagle ray (Myliobatis), guitar fish (Rhinobatus), sawfish (Pristis). Electric organ are found in Torpedo

Rat fishes or chimaeras- Hydrolagus (= Chimaera).

Scoliodon (Dog fish)

Scoliodon is carnivorous, feeding on other fishes, crabs, etc. It is surface feeder. Both upper and lower jaws have homodont teeth. The teeth are not meant for masticating the food, but for catching and preventing the escape of the prey. Some pores called ampullary pores are present on the upper and lower surface of the head; each pores lead into an ampulla (plural. ampullae), called Ampulla of Lorenzini through which the fish gets information about temperature variations in the surrounding water. Behind the head on each side, are present

five oblique openings, known as gill slits, which communicate internally with the pharynx. The gill slits expel the water out from the pharynx.

The caudal fins surrounds the tail, exhibiting asymmetry (upper epicaudal lobe and lower hypo caudal lobe). Such a type of tail, in which two different kinds of lobes are present, is known as heterocercal tail. Numerous dermal placoid scales are embedded in the skin for protection. The male has a pair of claspers attached to the pelvic fins. The claspers help in the copulation. It is also eaten as food and yields liver oil. Shark is viviparous. Mermaid purse is egg case of shark.

 

 

 

 

Torpedo (Electric Ray)

Torpedo is bottom dwelling, carnivorous fish which stuns or kills the prey and enemies with electric shock from its electric organs. The electric organs are modified muscles. Large openings called spiracles are present behind the eyes and are used for talking water inside for breathing.

 

 

Osteichthyes (Bony fishes)

General Characters:

1. Inhabit all sorts of water-fresh, brackish or salt.
2. Body spindle-shaped and streamlined.
3. Fins both median and paired, supported with fin rays of cartilage or bone. Tail usually homocercal.
4. Skin with dermal scales of 3 types; ganoid, cycloid or ctenoid. No placoid scales.
5. Endoskeleton chiefly of bone (Gr., osteon, bone + ichthyes, fish). Cartilagenous in sturgeons. Notochord replaced by distinct vertebrae Claspers absent.
6. Mouth terminal or sub terminal. Jaws usually with teeth. Cloaca absent, anus present.
7. Respiration by 4 pairs of gill covered by an operculum.
8. An air (swim) bladder often present. Lung-like in some (Dipnoi.
9. Ventral heart 2-chambered (1 auricle + 1 ventricle). Sinus venosus and conus arteriosus present. Aortic arches 4 pairs. Erythrocytes oval, nucleated. Temperature variable (poikilothermous).
10. Adult kidneys mesonephric. Ammonotelic.

11. Brain with very small olfactory lobes, cranial nerves 10 pairs.
12. Well developed lateral line system. Internal ear with 3 semicircular canals.
13. Sexes separate. Gonads paired. Fertilization usually external. Mostly oviparous, rarely ovoviviparous or viviparous.

 

Classification of Osteichthyes

Subclass I. Sarcopterygii : (Gr., sarcos, fleshy + pterygium, fin)

1. Paired fins leg-like or lobed.
2. Olfactory sacs usually connected to mouth cavity by internal nostrils or choanae, hence also called as choanichthyes (Gr., choana, funnel + ichthyes, fish).
3. Popularly called fleshy or lobe-finned, or air breathing fish. Divided into 2 orders: Crossopterygii and Dipnoi.

Order 1. Crossopterygii – (Gr., crossoi, a fringe + pteryx, fin)

1. Paired fins lobe like.
2. Internal nares present or absent. Spiracles present.
3. Air bladder vestigial.

Example– Primitive fleshy-finned extinct fishes. Single living genus Latimeria.

Order 2. Dipnoi – (Gr., di, double + pnoe, breathing)

1. Internal nares present and spiracles absent.
2. Air bladder single or paired, lung-like

Examples – Lung fishes. Only 3 living genera of lung fishes: Neoceratodus(Australian lung fish), Protopterus(African lung fish) and Lepidosiren(South American lung fish)

 

Subclass II. Actinopterygii – (Gr., actis, ray + pteryx, fin)

1. Paired fins thin, broad, without fleshy lobes.
2. Olfactory sacs not connected to mouth cavity.
3. Popularly called ray-finned fishes.

They are divided into 3 orders: Chondrostei, Holostei and Teleostei.

Chondrostei – (Gr., chondros, cartilage + osteon, bone)

(1) Primitive ray-finned cartilaginous ganoids.

Examples – Acepenser (Sturgeon), Polyodon (paddlefish)

Holostei – (Gr., holos, entire + osteon, bone)

1. Ganoid or cycloid scales. Intermediate ray-finned fish, transitional between Chondrostei and Teleostei Examples –Lepisosteus (garpike) Teleostei – (Gr., teleos, complete + osteon, bone) (1) Scales cycloid, ctenoid or absent.
2. A hydrostatic swim bladder usually present.
3. Advanced or modern ray-finned fishes

 

Examples – Harpodon (Bombay duck) Cyprinus (carp), Labeo rohita (rohu), Catla, Carassius (Goldfish), Clarius (Magur), Heteropneustes (singhi), Wallago (lachi), Mystus (tengra), Electrophorus (electric eel) Anguilla (freshwater eel), Muraena (moray) Hemirhamphus (half beak), Belone (garfish), Hippocampus (sea horse), Syngnathus (pipe fish), Fistularia (flute fish) Ophiocephalus or channa (snake head), Symbranchus (eels),Pterois (scorpion fish), Pleuronectes, Synaptura, Solea, Echeneis or Remora (sucker fish), Tetrodon (globe fish).

 

Scales:

1. Cosmoid: These are not found in living fishes and are composed of four distinct layers - outermost ganoine, followed by cosmine, spongy bone and innermost compact bone.

 

2. Placoid: They have a backwardly directed spine arising from a basal plate.

 

3. Ganoid or rhomboid scales are thick, diamond or rhomboid plates.

 

4. Cycloid: These are thin, flexible, circular in outline, marked with concentric lines of growth which can be used for determining age.

 

5. Ctenoid: They have numerous small comb likes spines.

 

 

Amphibia

General characters

1. The amphibians can live only in fresh water and on moist land, and are carnivorous, cold blooded, oviparous, tetrapod vertebrates.
2. Head distinct, trunk elongated. Neck and tail may be present or absent.
3. Usually 2 pairs of pentadactyle limbs (tetrapod), some limb less. Paired fins absent. Median fins, if present, without fin rays.
4. Skin soft, moist and glandular. Pigment cells (chromatophores) present.
5. Exoskeleton absent. Digits claw less. Some with hidden dermal scales.
6. Endoskeleton mostly bony. Notochord replaced by vertebral column. Skull dicondylic with 2 occipital condyles.
7. Upper or both jaws with small homodont teeth. Tongue often protrusible. Alimentary canal opens into cloaca.
8. Respiration by lungs, skin and mouth lining. Larvae with external gills which may persist in some aquatic adults.
9. Heart 3–chambered (2 auricles + 1 ventricle). Sinus venosus present. Aortic arches 1-3 pairs. Renal and hepatic portal systems well developed Erythrocytes large, oval and nucleated. Body temperature variable (poikilothermous).
10. Kidneys mesonephric. Urinary bladder large. Excretion ureotelic.
11. Brain poorly developed. Cranial nerves 10 pairs.
12. Nostrils open into buccal cavity. Middle ear with a single rod-like ear ossicle, called columella. Larval forms and some aquatic adults with lateral line system.
13. Sexes separate. Male without copulatory organ. Gonoducts open into cloaca. Fertilization mostly external. Females mostly oviparous.
14. Development indirect. Cleavage holoblastic but unequal. No extra– embryonic membranes. Larva a tadpole which metamorphoses into adult

Classification:

The living amphibians have 2,500 species. They dominated the World during carboniferous period.

Subclass I. Stegocephalia (Extinct) – Limbs pentadactyle. Skin with scales and bony plates.

Order 1. Labyrinthodontia – Oldest known tetrapods called stem Amphibia. Example – Eryops.

Order 2. Phyllospondyli – Small salamander-like. Example – Branchiosaurs (Ichthyostega).

Order 3. Lepospondyli – Small salamander or eel-like. Examples – Diplocaulus, Lysorophus.

 

Subclass II. Lissamphibia (living) –

Modern Amphibia without dermal bony skeleton.

 

Order 1. Gymnophiona or Apoda – (Gr., gymnos, naked + ophioneos, serpet-like) or (Gr., a, without + podos, foot)

1. Limb less, blind, elongated worm like, burrowing tropical forms known as caecilians.
2. Tail short or absent, cloaca terminal.
3. In some dermal scales embedded in skin.
4. Skull compact, roofed with bone.
5. Limb girdle absent.
6. Males have protrusible copulatory organs, Examples - Ichthyophis, Uroaeoryphlus. Ichthyophis is a Limb less amphibian.

 

Order 2. Urodela or Caudata – (Gr., Ura, tail + delos, visible) or (L., cauda, tail)

1. Lizard-like amphibians with a distinct tail and with 2 pairs of limbs.
2. Skin devoid of scales.
3. Gills permanent or lost in adult.
4. Males without copulatory organs.
5. Larvae aquatic, adult-like, with teeth.

Examples – Ambystoma (Tiger salamander), Salamandra (salamander),

Amphiuma (congo eel), Plethodon. Siren (mud eel).

 

Order 3. Salientia or Anura – (L., saliens, leaping ) or (Gr., an, without + nura, tail)

1. Amphibia without tail in adults.
2. Hind limbs usually adapted for leaping and swimming.
3. Adults without gills or gill openings.
4. Tympanum present.
5. Skin loosely-fitting without scales. (6)Fertilization always external.

Examples – Alytes (midwife toad), Pipa(Surinam toad), Xenopus(African toad), Bufo (common toad), Hyla (tree toad), Gastrotheca (marsupial frog), Rana (common frog), Polypedates or Rhacophorus (tree frog) .

 

 

Five representatives of classes of Amphibia: A.Salamander; B. Leopard frog; C. Ichthyophis; D. A tropical tree toad; E. Mudpuppy

 

Practice Test Papers

1. In which of the following the notochord is present in embryonic stage

 

(a) Vertebrates (b) Some chordates (c) All chordates (d) Non-chordates

 

2. In Urochordata notochord is found in

 

(a) Head of adult (b) Tail of adult (c) Tail of larva (d) Test of adult

 

3. The animal who possesses notochord throughout life is

 

(a) Fish (b) Amphioxus (c) Bird (d) Snake

 

4. Sea horse is an example of

 

(a) Mammalia (b) Pisces (c) Aves (d) Reptilia

 

5. Which of the following has a cartilagenous endoskeleton

 

(a) Elasmobranch (b) Dipnoi (c) Mollusca (d) Bony fishes

 

6. Torpedo is commonly known as

 

(a) Sea horse (b) Electric ray (c) Globe fish (d) Sucker fish

 

7. Salamander belongs to the class

 

(a) Reptilia (b) Amphibia (c) Aves (d) Mammalia

 

8. Limbless amphibians belong to the order

 

(a) Anura (b) Urodela (c) Gymnophiana (d) Squamata

 

9. Midwife toad is another name for

(a) Alytes (b) Hyla (c) Rhacophorus (d) Pipa 10.Tailless amphibians are the members of the group

(a) Salientia (Anura) (b) Gymnophiona (Apoda) (c) Urodela (Caudata) (d) Cyclostomata

 

11. Elasmobranchs have............ scales.
12. Ctenoid scales are found in…….
13. Middle ear of amphibians has a single rod-like ear ossicle, called ……
14. Tetrapods includes three classes namely…..
15. The structure through which the fish gets information about temperature variations in the surrounding water is known as …….
16. The male of chondrichthyes has a pair of claspers attached to the pelvic fins. The claspers help in ……...
17. What does Agnatha refer to?
18. Enlist scientific and common names of lung fishes. Neoceratodus(Australian lung fish), Protopterus(African lung fish) and Lepidosiren(South American lung fish)
19. Write down three most important characteristics of phylum chordata:

1. They have a notochord either throughout life or during early embryonic      development
2. Dorsal hollow nerve chord
3. Paired gill slits on either sides of pharynx at some stage; may or may not be functional

20. Give an outline classification of phylum chordata

Answers and Solutions

1.c

2. b
3. b
4. b
5. a
6. b
7. b
8. a
9. a
10. a
11. Elasmobranchs have placoid scales.
12. Ctenoid scales are found in osteichthyes
13. Middle ear of amphibians has a single rod-like ear ossicle, called collumella
14. Tetrapods includes three classes namely amphibians, reptiles, mammals
15. The structure through which the fish gets information about temperature variations in the surrounding water is known as Ampulla of lorrenzini