Animals are metazoans that differ from plant in number of characteristics like absence of plastids, cell wall and central vacuole. There are around 1.2 million known species of animals, but scientists estimate there are closer to 8.7 million species on earth. they show great diversity in shape, size, colour, habits, habitat, structures etc.
CHARACTERISTICS OF ANIMALIA:
- They are multicellular consumers of the ecosystem.
- They are made up of eukaryotic cells and have no cell wall, plastids, central vacuole and photosynthetic pigments.
- Lower animals exhibit cellular or tissue level of organization and higher animals have organ system level of organization.
- Mostly free living and some are fixed (sponges and several coelenterates).
- They take food by ingestion i.e. holozoic in nutrition and digestion takes place in an internal cavity. Some forms have absorptive nutrition and their digestive cavity is absent. The undigested food is removed by egestion.
- They have muscle cells (for contraction and relaxation of body parts) and nerve cells (transmit nerve impulses). Poriferans lack nerve cells.
- Lower animals have asexual and sexual reproduction. Higher animals have generally sexual reproduction.
Cellular animals having the structure of a stereoblastula (embryo produced by spiral cleavage,characterized by absence of blastocoel), composed of surface layer of somatic cells and interior reproductive cells.
- PHYLUM : MESOZOA
About 50 species comes under the phylum mesozoa. They are small, worm like with bilateral symmetry. One or several of their reproductive cells are surrounded by an external layer of ciliated digestive cells. They are parasitic in cephalopods and some other invertebrates.
Examples : Dicyema, Rhopalura, etc
The animals belonging to this class show cellular grade of organisation with incipient (beginning to happen or develop) tissue formation. There are interior cells of several different kinds. There is no mouth or digestive tract and no organ systems are present. Their body shows presence of pores with one to many internal cavities. The cavities are lined with choanocytes. They are sessile, marine, a few found in fresh water. Solitary or colonial.
- PHYLUM : PORIFERA
The animal belonging to this phylum bears pore and are also known as pore bearers. About 5,000 species comes under phylum porifera. Characters of phylum porifera are same as that of branch parazoa.
Examples: Scypha or Sycon, Euplectella, Hyalonema, Euspongia, etc
The animals have tissue or organ-system grade of organisation with mouth and digestive tract. Several kinds of interior cells are also present.
- GRADE I : RADIATA
Eumetazoa with primary radial symmetry. Tissues are present. Organ system are incipient. The mesoderm is derived from the ectoderm, and it is present as an incipient tissue. The only body cavity is the digestive cavity. The digestive cavity has a mouth but no anus.
- PHYLUM : CNIDARIA (COELENTERATA)
This phylum contains about 10,000 species. The animals are with radial, biradial or radio-bilateral symmetry. The mouth is encircled by tentacles bearing nematocysts. Body cavity is known as coelenteron. Thy are sessile or free swimming, solitary or colonial, marine or freshwater.
Examples : Hydra, Aurelia, Metridium, Obelia, Corals etc
2. PHYLUM : CTENOPHORA
They are also known as comb-bearers or comb-jellies. About 90 species comes under this phylum. They show biradial symmetry. If tentacles are present, they do not encircle the mouth. They do not show presence of nematocyst. They are free swimming and marine.
Examples : Ctenoplana, Pleurobrachia, Coeloplana, etc.
2. GRADE II : BILATERIA
Eumetazoa with bilateral symmetry, or those with embryonic bilateral symmetry later modified into radial symmetry. They have organ system grade of organisation. Mostly with a well developed mesoderm of endodermal origin. Mostly with body spaces other than the digestive cavity. Mouth and anus are generally present. Bilateria is divided into two subdivision: Protostomia and Deutrostomia.
DIVISION A : PROTOSTOMIA
Mouth arises from the blastopore or from the anterior margin of blastopore. Protostomia is further subdivided into three subdivisions: Acoelomata, Pseudocoelomata and Coelomata.
SUBDIVION : ACOELOMATA
They dont show the presence of body cavity or coelom. The space present between the digestive tract and the body wall is filled with mesenchyme. The excretory system consist of protonephridia with flame bulbs.
SUPERPHYLUM : ACOELOMATA
Without coelom. Presence of mesenchyme in between the body wall and digestive tract. Excretory system consist of protonephridia with flame bulbs.The body is unsegmented. The body consist of a strobila, with the youngest segment towards the head.
- PHYLUM : PLATYHELMINTHES
They are also known as flatworms.. The phylum consist of about 12,700 species. The body is dorsoventrally flattened. Anus and circulatory system are absent. They are either free living or parasitic. They can be found in terrestrial, freshwater or marine environment.
Examples: Fasciola, Taenia, Planaria etc
2 . PHYLUM : NEMERTINEA OR RHYNCHOCOELA
They are also known as ribbon worms. The phylum consist of about 750 species. The body is slender, elastic, soft and covered with cilia. They don't show show segmentation. The mouth is anterior with a long eversible proboscis. Their digestive tracts are complete with anus. Circulatory system is present. They are free living, mostly marine, few are terrestrial and freshwater dwellers.
Examples : Stichostemma, Cerebratulus etc
SUBDIVISION : PSEUDOCOELOMATA
Space is present between digestive tract and body wall. This space is known as a pseudocoel, it is not a true coelom but it is the remnant of the blastocoel. Anus is present with or without protonephridia. Flame bulbs are present or absent.
- PHYLUM ; ACANTHOCEPHALA
They are also known as spiny headed worms. The phylum consist of about 500 species. They are parasitic and minute worms with protrusible (eversible) proboscis. The proboscis contains recurved spines. Digestive tract is absent.
Examples : Gigantorhynchus, Echinorhynchus etc.
2.PHYLUM : ENTOPROCTA
The phylum consist of about 60 species. The digestive tube is U-shaped. Mouth and anus are close together surrounded by ciliated tentacles. They are sessile, solitary or colonial. Most of them are marine and a few are freshwater forms.
Examples : Loxosoma, Pedicellina etc.
SUPERPHYLUM : ASCHELMINTHES
An assemblage of pseudocoelomates. All have the anterior mouth, posterior anus and a straight digestive tube.
- PHYLUM : ROTIFERA
They are microscopic. About 1500 species are present. Anterior end is with a ciliated corona. Pharynx with internal jaws known as trophi. Protonephridial system is present with terminal flame buds. They are mostly freshwater and some are marine.
Examples : Brachionus, Philodina, Rotatoria, etc.
2. PHYLUM : GASTROTRICHA
They are also known as hairy stomach worms. About 150 species are present. They are microscopic. Ventral surface is flattened and ciliated. Cuticle is with spines, plates or scales and is unsegmented. Pharynx is tubular and devoid of trophi. They are mostly freshwater and marine.
Examples : Chaetonotus, Macrodasys, etc.
3. PHYLUM : KINORHYNCHA
About 60 species are present. They are small. More or less spiny without superficial cilia. Body is unsegmented with the anterior end an introvert. They are marine.
Examples : Echinoderes, Pycnophyses, etc.
4. PHYLUM : NEMATODA
They are also known as round worms. About 10,000 species are present. Body is rounded, slender, covered by a continuous cuticle, often tapered at ends. Cilia is absent. Epidermis is divided into four or more chords. Only longitudinal muscles are present in the body wall. Long muscular pharynx having triradiate lumen. They are either free living or parsitic. They are found in either fresh water or marine water or in the soil.
Examples : Ascaris, Rhabditis, Enterobius, Ancylostoma, Wuchereria, etc.
5. PHYLUM : NEMATOMORPHA
They are also known as horse-hair worm. About 230 species are present. Body is long slender, cylindrical, slender with dorsal and ventral epidermal chords. Gonoducts joining the intestine. Lrval stages are parasitic and adults are free living.
Examples : ordius, Nectonema, etc.
SUBDIVISION : COELOMATA
Animals with a true coelom and usually well developed ectomesoderm. Excretory organs are protonephridia with or without nephrostome. Anus is present.
SUPERPHYLUM : INARTICULATA
Unsegmented, coelomate protostomes.
- PHYLUM : PRIAPULIDA
About 8 species are present. body surface is covered with spines and tubercles. Proboscis is anterior
Urinogenital pores are separate from the digestive tube in both sexes. Protonephridia is terminating in solenocytes joining the gonoducts. They are marine.
Example : Priapulus.
2. PHYLUM : SIPUNCULIDA
They are also known as peanut worms. About 275 species are found. Body is elongated and cylindrical with retractile anterior introvert. Short hollow tentacles around the mouth. No segmentation or setae. Anus is dorsal. They are marine.
Examples : Sipunculus, Phascolosoma, etc
3. PHYLUM : MOLLUSCA
They are soft-bodied animals. About 1,28,000 species are present. Body is soft covered by mantle usually with an anterior head and a ventral muscular foot. Mantle secrets the shell. Shell sometimes is vestigial and sometimes in several pieces. Coelom is reduced. They are terrestrial, Freshwater and marine.
Examples : Pila, Unio, Chiton, Sepia, Nautilus, etc.
4. PHYLUM : ECHIURIDA
They are also known as adder-tailed worm. About 150 species are present. Body is cylindrical with trough-shaped elastic proboscis. Mouth is ventral. Trunk with setae. Coelom is spacious. They are marine.
Examples : Echiurus, Urechis, etc.
SUPERPHYLUM : ARTICULATA
Segmented coelomate animals. Characterised by segmentation of embryonic stages, even though the adult may have secondarily lost its metameric organisation.
1. PHYLUM : ANNELIDA
Also known as ring or segmented worms. About 8,700 species. Body elongated and metamerically segmented. Coelom spacious, typically divided into metameric compartments. They are mostly terrestrial, freshwater and marine.
Examples : Nereis, Hirudinaria, etc.
2. PHYLUM : TARDIGRADA
Also known as water bears or bear animalcules. Minute. Body is cylindrical and segmented with four pairs of unsegmented legs terminating in claws. Coelom transitory replaced by a haemocoel. No appendages associated with mouth.
Examples : Echiniscus, Hypsibius, etc.
3. PHYLUM : ONYCHOPHORA
Also known as claw bearers. About 73 species. Body is worm like. elongated and unsegmented. Thin unsegmented cuticle covers the body. Many pairs of short unsegmented legs. Head with three pairs of appendages, two of which are associated with mouth. Tracheal system for respiration. Moist terrestrial.
Example : Peripatus.
4. PHYLUM : PENTASTOMAIDA
Also known as tongue worms. About 70 species. Worm like body with two pairs of claws or short appendages at the sides of the mouth. Respiratory system absent. Parasitic in vertebrates.
Examples : Porocephalus, Cephalobaena, etc.
5. PHYLUM : ARTHROPODA
Also known as joint footed animals. About 9,00,000 species. Body is segmented with jointed appendages usually terminating in claws. Exoskeleton chitinous. Coelom greatly reduced and replaced by a haemocoel. Terrestrial, freshwater and marine.
Examples : Prawns, Scorpions, Centipedes etc.
SUBDIVISION : DEUTEROSTOMIA
Bilateria in which the mouth does not arise from the blastopore or near its anterior margin. Coelom arise from the primitive gut.
SUPERPHYLUM : TENTACULATA
Animals with a circular, crescentic or double spirally coiled edge bearing ciliated tentacles are known as lophophore. Mouth and anus near together. Intestine forming a loop.
- PHYLUM : PHORONIDA
This phylum consist about 15 species. Solitary worm like animals. Body enclosed in a chitinous tube,
Closed circulatory system. One pair of metanephridia. Marine.
Examples: Phoronis, Phoronopsis, etc.
2. PHYLUM : ECTOPROCTA OR BRYOZOA
They are also known as moss animals. About 4000 species. Sessile or colonial animals with a lophophore. Body enclosed in a gelatinous, chitinous or calcareous covering. Anus outside of the lophophore region. Mostly marine, few freshwater.
Examples: Bugula, Plumatella, etc
3. PHYLUM : BRACHIOPODA
Consist of about 260 species. Solitary animals with a lophophore. Body enclosed in a bivalve shell. one or two pairs of metanephridia. Marine
Examples: Lingula, Crania, Hemithyris, etc
4. PHYLUM : ECHINODERMATA
About 6,000 species. Animals with secondary radial symmetry. Water vascular system present. Locomotion by tube feet.
Examples: Starfish, Brittle star, Sea urchins, Sea lillies, etc
5. PHYLUM : CHAETOGNATHA
Also known as arrow worms. Consist of about 50 species. Small, slender, elongated, transparent animals, body divided into head, trunk and tail. Hooks or bristles near mouth, paired fins on trunk and a terminal tail fin. Digestive tube complete. Planktonic and marine. Free-living.
Examples: Sagitta, Spadella, etc
6. PHYLUM : POGONOPHORA
About 43 species. Body elongated in a chitinous tube. Anterior end with one to many tentacles. Endoskeleton, gill-slits, and digestive tube absent. Deep water and marine.
Examples: Siboglinum, Polybrachia, Spirobrachia, etc
7. PHYLUM : HEMICHORDATA
About 80 species. Also known as acorn worms. Animals permanently bilateral with gill slits. Endoskeleton poor. Embryo lacking a typical notochord. Marine.
Examples: Balanoglossus, Cephalodiscus, etc
8. PHYLUM : CHORDATA
Consist of about 45.000 species. Animals permanently bilateral. A dorsal tubular nerve cord, a notochord and paired pharyngeal gill-slits present at some stage in life-history. Terrestrial, freshwater, marine.
Examples: Ascidians, Fishes, Frogs and Toads, Lizards and Snakes. Birds and Mammals, etc
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