SALIENT FEATURES OF NON-CHORDATA
Animals exhibit variations in the terms or their size, morphology, anatomy, physiological processes. adaptation to different environ and reproductive behaviour. The study of animal diversity is, in essence, the study of the
origin and diversification of living organisms on this planet.
DIversity can be defined as “The sum total of variations in form, functioning and behaviour that have accumulated in different lines of organisms
Attempts have been made to classify more than one million diverse animals which will reflect their similarities in structure and inter-relationships.
BROAD OUTLINE CLASSIFICATION OF ANIMAL KINGDOM
Nearly one million species of animals, have been identified in this world. For better understanding, these animals are grouped according to their similarities and differences, in
lt includes all the multicellular animals. It is divided into three branches; such as
(I) It includes minute, multicellular wormlike invertebrates.
(ii) These are marine in habitat.
(iii) The adult lives as parasites in the kidneys of many marine invertebrates.
(iv) The adult body has two layers of cells and tissues are absent.
(v) It does not contain organs and organ systems, except the presence of gonads,
(vi) The larvae are infusoriform and vermiform. Ex-Dicyema, Pseudocyema and
(i) It includes sponges
(ii) in This multicellular animal has loose organisation of cells.
(iii) It does not have distinct tissues and organs.
(iv) It includes phylum-Porifera.
- Eunetazoa or Enterozoa
(i) It includes all higher multicellular animals (except Mesozoans and Parazoans).
(ii) They contain specific body layers and nervous system.
It is divided into two divisions
(i) These multicellular animals show radial symmetry (so the name radiata).
(ii) The body contains coelenteron or gastro-vascular cavity.
(iii) They exhibit low grade of tissue organisation.
(iv) Itincludes Phylum-Coelenterata.
(i) These multicellular animals exhibit bilateral symmetry, which originates from
It is divided into two groups: (i) Protostomia; and (ii) Deuterostomia
(i) Itincludes the animals in which the mouth develops from embryonic blastopore.
(ii) The zygote shows spiral and determinate cleavage. It is classified into three sections.
(i) The coelom or body cavity is absent (so the name acoelomata).
(ii) The space between body wall and alimentary canal is filled with
(iii) It includes Phylum-Platyhelminthes.
(i) The body cavity is pseudocoel (false body cavity) type, so the name
(ii) It is not bounded by peritoneal layers.
(iii) It includes Phylum-Nemathelminthes.
(I)These animals contain true coelom.
(ii) The coelom is derived from mesoderm.
(iii) The mesoderm splits into outer somatic or parietal layer and inner splanchnic or visceral layer enclosing the coelom.
(iv) It includes three phyla i.e. Phylum-Annelida, Phylum-Arthropoda and Phylum-Mollusca.
(i) These animals contain true coelom.
(ii)The embryonic blastopore develops into anus.
(iii)It includes Phylum-Echinodermata and Phylum-Chordata.
The Kingdom Animalia is broadly divided into two sub-kingdoms: (A) Non-chordata and (B) Chordata.
(i) The non-chordates possess ventral ganglionated, solid nerve chord.
(ii) Back bone is completely absent.
(iii) Heart, if present, is usually dorsal in position.
(iv) Anus is present at the end of the tail.
(v) Respiration occurs through the body wall and also through various types of respiratory structures. These respiratory structures are not originated from pharynx.
The non-chordates can be divided into two groups.
(i)Major Phyla. Some phyla contain large number of animals. These are highly developed. It includes phyla like Porifera, Coelenterata, Platyhelminthes, Nemathelminthes, Annelida, Arthropoda, Mollusca and Echinodermata.
(ii) Minor Phyla. There are several peculiar animals which constitute separate phylum. Each minor phylum contains a few species. Such as Nemertinea (Ribbon-worms), Nematomorpha (Horse-hair worms), Rotifera (Wheel animalcule), Acanthocephala (Spiny neaded worms), Chaetognatha (Arrow-worms) etc.
(i) The body wall is three layered.
(ii) It comprises of ectoderm andendoderm
(iii) Mesogloea may be present
(iv) Ex-body wall of Hydra.
(i) The body wall is two layered.
(ii) It comprises of ectoderm, mesoderm
(iii) Mesogloea is absent
(iv) Ex-body wall of vertebrates.
(Gk. Protos-first, Zoon-animal) (The name of the Phylum was coined by Goldfuss 1820)
- These are the simplest, microscopic animalcule.
- It is unicellular or acellular orgarnism containing one or more nuclei. It does all the vital activities of one animal.
- These are solitary or colonical in habit
- Free living protozoans are mostuy aquatic, inhabiting freshwater, sea-water and damp places, but parasitic and symbionts, Iive inside the body of other plants and animals.
- Locomotary organelles may be pseudopodia, flagella or Cilia or may be absent.
- Different modes of nutrition are holozoico, holophytic, saprozoic and saprophytic.
- Osmoregulation, seen in free living protozoa, takes place with the help of contractile vacuole
- Gaseous exchange and excretion by diffusion through body surface.
- Reproduction may be asexual or sexual.
- The number of nuclei varies from one to several.
Example. Amoeba, Euglena, Trypanosoma, Vorticella and Paramoecium. This phylum includes about 30,000 species.
(L., Porous-pore; ferre-to bear) (The name of the phylum was given by Robert E. Grant, in 1836).
- It includes the sponges, containing numerous pores on the body called ostia (Sing-ostium).
- Body is multicellular with two loosely differentiated germ layers or diploblastic.
- The water circulates through ostia and canal system of the body. The canal system is the life-line of this animals. It is simple or Asconoid type, complex as syconoid type and more complex as leuconoid type. The water enters through dermal ostia into canal system and reaches the body cavity or spongocoel and leaves through osculum. This system helps in respiration, nutrition, excretion and reproduction.
- It contains special collared, flagellated cells, called choanocytes and flat, outer pinacocytes. All other cells found, are modified cells of these two.
- These are either freshwater or marine in habitat.
- The skeleton comprises of siliceous spicules (of Si02) and calcareous (of CaCO3) spicules or spongin libres. The specules or needle like structure of various shape as like monaxon triaxon, tetraxom etc.
- All sponges possess great power of regeneration.
- Asexually, it reproduces by gemmule and budding.
- Development occurs through amphiblastula and parenchymula larvae.
- These are solitary or colonial and sessile.
Example.Spongilla, Sycon, Euspongia, Leucosolenia, Grantia. The phylum includes about 5000 living species. PHYLUM-cOELENTERATA
(Gk. Koilos-hollow, enteron-intestine) (The phylum coelenterata was created by Leuckart 1847).
- A few species are freshwater but almost all are marine in habitat.
- These are solitary or colonial in nature.
- The coelenterates are radially symmetrical.
- The body wall is diploblastic with outer epidermis and inner gastrodermis.
- A jelly like mesogloea is present in between two body layers.
- The body has a single cavity, known as gastrovascular cavity or coelenteron.
- Digestion is intracellular (inside the cell) and extra cellular (inside the alimentary canal or cavity).
- Nervous system consists of diffused nervenet. There is no central nervous system.
- A single aperture, present on the hypostome, acts both as mouth and anus.
- A set of tentacles are found containing the stinging cells or nematoblasts.
- It exists in two forms i.e., Polyp (feeding state) and Medusa (Reproducing stage). But some show polymorphism.
- Asexual reproduction occurs by budding
- Some species are monoecious and other are dioecious.
- Life history shows alteration of generation or metagenesis.
Example. Hydra, Obelia, Aurelia, Sea-fan, Sea pen. (This phylum comprises of about 10,000 species).
(Gk. Platy-flat, helminthes-worm) (The term was coined by Gegenbauer 1859).
- These animals are bilaterally symmetrical and dorsoventrally flattened like a ribbon.
- Both the free living and parasitic forms are seen.
- Body is covered by cuticle.
- Organs for attachment are present.
- These are acoelomate animals.
- Except cestoda, the body is unsegmented.
- Nervous system is primitive and ladder-like
- Body wall is triploblastic (i.e., three layered).
- In parasitic forms, many organ systems are degenerated.
- Excretory system consists of protonephridia or flame cells.
- These are mostly hermaphrodites.
- Fertilization is internal. It shows self or cross-fertlization.
- Development is direct or indirect with complicated larvalforms.
- Sense organs are found in freeliving forms.
Example. Taenia, Fasciola, Planaria. (This phylum comprises of about 6,500 species)
(Gk. Nemat-Round, Helminthes-worm) (The term was created by Gegenbauer, 1859).
- These are aquatic or terrestrial animals.
- Free living or Parasitic forms are seen.
- Body is cylindrical, unsegmented and bilaterally symmetrical.
- Cilia are entirely absent.
- Pseudocoel is present.
- Digestive system is present, but circulatory, respisratory and excretory systems may be absent
- Bodywall consists of syncytial or cellular epidermis and longitudinal muscle fibres
- Body is covered with cuticle.
- Sexes are separate showing sexual dimorhism.
- Fertilization is internal and development is direct.
Example. Guinea worm (Dracunculus) filarial worm (Wuchereria) The phylum includes about 10,000 species.
(L. Annulus-Ring, eidos-form) (The term was first used by Lamarck 1809).
- These are free living and burrowing in habit, but some are commensals or parasitic.
- It comprises of aquatic (freshwater and marine) and terrestrial forms.
- Body is bilaterally symmetrical, elongated, vermiform and metamerically segmented.
- Animals are coelomate and triploblastic.
- Locomotary organs are setae or Chetae or parapodia.
- Blood vascular system is closed type.
- Blood is red due to presence of haemoglobin or erythrocruorin.
- Excretory organs are the segmentally present nephridia.
- Nervous system consists of a pair of cerebral ganglia and a double ventral nerve
- Respiration takes place by moist skin or gills or parapodia.
- These are bisexual or unisexual.
- Lar /a, when present is trochopore.
- Regenration is common.
- Some of them makes the soil porous.
Example. Earthworm (Pheretima), Leech, Nereis, Aphrodite (Sea-mouse) (This phylum has about 13,500 species).
(Gk. Arthros-Jointed, Podos-foot)
- A thick, chitinous cuticle covers the body as exoskeleton.
- Animals are bilaterally symmetrical, metamerically segmented and triploblastic.
- Lateral and jointed appendages are presented.
- Body cavity is haemocoel type.
- Circulatory system is open type, with many chambered heart.
- Respiration occurs through tracheae or booklung.
- Nervous system is annelidan type, but simple and compound eyes, chemo and tactile receptors, and balancing and auditory organs are also present.
- Excretion occurs through malpighian tubules, or green gland or coxal gland.
- Development may be direct or through larval forms.
- The body is divided into head, thorax and abdomen.
- Sexes are usually separate (dioecious) and fertilization is internal.
Example.Cockroach, Flies, Mosquito, Prawn, Crabs. (This phylum has more than 8,00,000 Species).
(L. Mollis-Soft) (The term mollusca was first used by Jonston 1650).
- Mostly aquatic forms (freshwater and marine) are seen, but some are terrestrial.
- The body is soft and unsegmented and is divided into visceral mass, head, foot and mantle,
- Shell may be external or internal.
- Respiration occurs through gill or Puimonary sac.
- Digestive system is complete with hepato-pancreas and a rasping organ (radula).
- Circulatory system is closed type. Heart is present with one or two auricles and one ventricle. Blood contains heamocyanin and amoebocyte.
- Excretion occurs by paired metanephridia.
- The olfactory organ, called osphradium is present.
- Sexes are separate or may be hermaphrodite.
- Development is direct or through free larval forms (Ex-trochophore, veliger).
Example. Pila, Unio, Nautilus, Pearl Oyster. (This phylum comprises of about 80,000 Species
(L. Echinos-Spiny or hedgehog, derma-skin) (The name of the phylum was coined by Jacobklein 1934).
- Animals are marine in habitat.
- Body is unsegmented and triploblastic.
- Coelom is enterocoelous.
- Animals are pentaradially symmetrical
- Animals are gregarious, mostly free living and pelagic.
- Water vascular system or Ambulacral system is seen.
- Locomotory organ is called tube foot or podium.
- Endoskeleton consists of calcareous plates with ossicles.
- Haemal system represents the vascular system.
- Respiration occurs through dermal branchiae, respiratory tree and bursae.
- Excretory organs are mostly absent.
- Larval forms are present (like Bipinnaria, Brachiolaria etc.)
Example. Starfish, Sea-cucumber, Sea-lily, Sea-urchin. (This phylum has about 6,000 species).
Minor Phyla. Leaving aside those major phyla, there are some minor phyla, comprising of few species. Among them some are now treated as classes, A list of minor phyla is given below for reference.
MINOR ACOELOMATE PHYLA
- Mesozoa e.g, Salinella.
- Ctenophora e.g., Beroe.
- Nemertinea or Rhynchocoela-e.g., Lineus.
- Entoprocta or Endoprocta -eg., Pedicellina.
- Acanthocephala-e.g, Moniliformis.
- Nematomorpha or Gordiacea-e.g., Gordius.
- Rotifera or Rotatoria-e.g., Epiphanes
- Gastrotricha-e.g, Chaetonotus.
- Kinorhyncha or Echinordera-e.g, Echinoderes.
- Bryozoa (Ectoprocta)-e.g, Bugula
- Brachiopoda-e.g, Lingula.
- Phoronida-e.g., Phoronis.
- Chaetognatha-e.g, Sagitta.
- Sipunculida-e.g., Sipunculus.
- Echiuroidea-e.g., Ehiurus.
- Pogonophora or Brachiata-e.g., Siboglinum.
Sub-Kingdom-Chordata. It comparises of two Phylum only.
PHYLUM-HEMICHORDATA (Gk. Hemi-Half)
- It comprises of only marine animals.
- Body is soft, fragile, triploblastic and bilaterially symmetrical.
- These are commonly called as Tongue worms.
- The worm like body is divisible into proboscis, collar and trunk.
- The notochord is called as stomochord.
- True pharyngeal gillslits are present.
- Nervous system is a network of nerve cells and fibres, embeded in the epidermis.
- Circulatory system is open type with a dorsal heart.
- Excretion occurs through single proboscis gland or glomerulus.
- Sexes are separate and fertilization is external.
- Development may be direct or through tornaria larva.
This phylum has nearly 100 species.
Example. Balanoglossus, Cephalodiscus,
THE SALIENT FEATURES OF CHORDATA
The Chordates constitute one of the two major groups of animals. Though the origin of vertebrates, is not clearly understood; yet it is presumed that, some 550 million years ago, an apparent revolution in general organisation of animal body has given rise to the emergence of vertebrate body.
The Primitive Chordates, with a notochord; and a vertebrata with a vertebral column and Cranium (so called as Craniate), are the two major subdivisions of phylum Chordata. The vertebrates can be divided into Agnatha Jawless mouth) and Gnathostomata (Mouth with Jaw). Agnatha include cyclostomes (vertebrate with circular mouth) and gnathostoma. comprises of Pisces, Amphibia, Reptiles, Aves and Mammals.
The Chordates are characterised essentially by the possession of three fundamental features. Such as
1.Notochord or Chorda Dorsalis. It is a long flexible, unsegmented, solid rod like structure, present in between
alimentary canal and central nervous system, extended from head to tail. It is composed of large, turgid,
vacuolated cells, bounded by outer chordal sheath of dense fibrous connective tissue and inner elastic sheath
or elastica internal It is a permanent, typical structure in Protochordates and is replaced by vertebral column in higher vertebrates.
- Pharyngeal Slit. These gill slits or gill clefts or branchial clefts are a series of paired perforations leading from pharynx to the outside. These are formed by evagination of endoderm and invagination of ectoderm.
These are found in all embryos and in some adult forms through notochord of vertebrates. These are respiratory in function.
- Dorsal Tubular Central Nervous System. It is a dorsal, tubular, fluid filled central nervous system, which differentiates into anterior thickened brain and posterior long spina cord. It is present dorsal to the notochord.
Other Characters of Chordates
- Cranium (Gk. Kranion-Skull). The presence of Cranium is a vertebrate character, Which may be bony or Cartilagınous in structure to accommodate brain.
- Cephalisation. The trend for the formation of a well marked head, having complete brain and sense organ, is a vertebrate character.
- Endoskeleton. The internal skeleton of the vertebrates may be bony or Cartilaginous to support the soft parts of the body.
- Exoskeleton. It consists of scales and dermal plates.
- Vertebral Column. It is a series of segmental bones or cartilages found in vereates replace notochord.
- Paired Appendages. Vertebrates possess only two pairs appendages either in torm fins or limbs.
- Post-Anal Tail. It is the posterior prolongation of the body, beyond anus, containing vertebrae, muscles, nerve cord and blood vessels.
- Ventral Heart. The muscular, pulsating, camplicated heart is ventral in position in vertebrates.
9.Closed Blood Vascular System. In the vertebrates, blood flows in closed, organis”dvessels, called arteries, veins and capillaries.
- Hepatic Portal System. This peculiar system is present in Vertebrates to store excess of carbohydrates and to eliminate ammonia, carbolic acids and bacteria.
- Red Blood Corpuscles or Erythrocytes. In vertebrates the respiratory pigment is found in erythrocytes or R.B.C.
- Pituitary Body. It produces several hormones, essential for normal growth and functioning of various systems in vertebrates. It is present in the brain.
- Endocrine Glands. The presence of ductless glands is regarded as a vertebrate characteristic.
- Pineal Body. It is a vestigial organ in higher vertebrate. But it is found to be a small clear, median third eye in lower vertebrates.
It is an incomplete list of Vertebrate Characteristics. Some more characters like sense-organs, digestive tracts, digestive glands, excretory systems and embryonic developments can be added.
Comparison Between Vertebrates & Invertebrates
The invertebrate groups differ greatly among themselves. So it is difficult to compare between these two major sub-divisions of animals. They show a few similarities.
1.A triploblastic body wall (ectoderm, mesoderm and endoderm) with a true coelom is present.
- Bilateral symmetry is seen.
- Metamerism is well marked.
Differences between Chordata and Non-Chordate (Higher groups of invertebrates)
- Notochord is present.
- A solid, ventral nervous system is
- Branchial clefts are present. present with a long, double nerve cord.
- Heart is ventral in position
- Heart is enclosed in a pericardium.
- This respiratory pigment is found in R.B.C
- The blood vascular system is always closed type.
- Blood flows backwardly in dorsal vessels| and forwardly in ventral vessels.
- The limbs are derived from single segment.
- Anus opens before the last segment or tail.
- A true metamerically segmented postanal tail is present.
- Both epidermis and dermis constitute the skin.
- The endoskeleton is made up of living tissues like bones or cartilages
- Eyes develop as outgrowths of brain. Compound eyes are never seen.
- Only sexual type of reproduction is seen.
Non-Chordate (Higher groups of invertebrates)
- Notochord is completely absent.
- Ahollow, dorsal, central nervous system is present with a single neural tube.
- The branchial clefts are absent in the pharynx
- Heart, if present, is dorsal in position.
- Pericardium is absent.
- Haemoglobin, if present, is found dissolved in plasma.
- An open type of blood vascular system is seen.
- Blood flows forwardly in dorsal vessels and backwardly in ventral vessels.
- The limbs are derived from several segments.
- Anus opens in the last segment.
- The post anal extension or true tail is absent.
- Single layered epidermis is seen in the skin.
- Endoskeleton is usually absent; but may contain a non-living exoskeleton secreted by ectoderm.
- Eyes may be simple or compund type, developing from skin.
- Reproduction is both sexual or asexual