Classification of animals in the animal kingdom
There are about 31 phyla, 68 classes and 350 orders of living animals, recognized in the animal kingdom.
The following classification is based on the work of Hyman, Barnes and Storer with slight modification.
Kingdom animalia :
It includes the entire fauna (animal population) of the world.
Unicellular, microscopic animals.
Protozoa (First animals)
(i) About 50,000 species, solitory or colonial
(ii) Single celled body with single or many nuclei.
(iii) Nutrition holozoic, holophytic or saprozoic
(iv) Free living, commensal, symbiotic or parasitic.
Euglena, Paramaecium etc.
Subkingdom 2-Metazoa :
Multicellular animals. Cells are arranged in layers or tissues. Metazoans are divided into 3 branches.
Branch 1- Mesozoa :
Digestive cells few, external ciliated. No tissue or organs.
Phylum 2- Mesozoa:
(I) About 50 species
(ii) Worm like, small endo-parasites of marine invertebrates.
(iii) Body with an outer single layer of ciliated digestive cells, enclosing one or several reproductive cells.
Dicyema, Rhopalura etc.
Branch 2- Parazoa :
Digestive cells many, internal, flagellated. Tissues poorly defined. Organs are absent.
Phylum 3 Porifera (sponges):
(i) About 5,000 species.
(ii) Pore bearing body.
(iii) Different kinds of water canal system are found.
(iv) Flagellated collar cells or choanocytes are found.
(v) Skeleton of minute calcareous spicules or spongin fibers.
(VI) Sessile, solitary or colonial
Leucosolenia, Sycon, Euspongia etc.
Branch 3 – Eumetazoa :
Multicelled animals with defined organs, mouth and digestive cavity, Subdivided into two grades- Radiata and Bilateria.
Grade (A) Radiata:
1. Body radially symmetrical sometimes bilateral symmetrical which is a secondary adaptation.
2. Organ system incipient i.e., not well developed.
4. Coelomic cavity invariably absent.
5. Tentacles with nematocysts, comb plates in some.
6. Main opening of digestive cavity is mouth.
Grade (B) Bilateria:
1. Body bilaterally symmetrical. Sometimes radial symmetrical which is a secondary adaptation.
2. Organ systems well marked.
4. Pseudocoelom or true coelom or coelom is present.
5. Tentacles, if present without nematocyst. No comb plates
6. Digestive cavity opens externally through mouth and anus.
Grade (a) radiata :
Radially symmetrical body, diploblastic animal. External opening is mouth. Phylum 4 Coelentrata (with hollow intestine)
(i) About 10,000 species, cnidoblast cells are found (cnidaria)
(ii) Radial symmetry. Two or three layers of cells.
(iii) Sac like gastrovascular cavity.
(iv) Sessile or free swimming
(v) Solitary or colonial.
Hydra, Obelia, Aurelia etc.
Phylum 5-Ctenophora (comb-bearer):
(i) Comb-jellies, about 90 species.
(ii) Biradial symmetry.
(iii) 2 tentacles and 8 longitudinal rows of ciliated comb plates for locomotion.
(iv) Free swimming, marine.
Pleurobranchia, Cestum, Beroe etc.
Grade (b) bilateria:
Bilaterally symmetrical, triploblastic animals with organ-system. Digestive tract complete with anus. It is subdivided into two divisions.
Division 1- Protostomia:
1. Mouth arises from blastopore or from the anterior margin of blastopore.
2. Coelom either absent or Pseudo coelom is present. In few schizocoelic coelom is found.
3. Cleavage spiral and determinate.
4. Trochophore larva is found.
Division 2- Deuterostomia:
1. Mouth arises anteriorly some distance away from blastopore.
2. Enterocoelic coelom (true coelom) is found.
3. Cleavage radial and indeterminate.
4. Tornaria or bipinnaria larva is found.
Barnes had divided this division into 4 subdivisions-
Subdivision I Acoelomata:
No body cavity or coelom. Body cavity is filled by mesenchymal parenchyma.
Phylum 6- Platyhelminthes (flatworms):
(i) About 15,000 species.
(ii) Body dorso-ventrally flattened.
(iii) Digestive tract branched or absent.
(iv) No anus and circulatory system.
(v) Free living or parasitic.
Planaria, Fasciola, Taenia etc.
Phylum 7- Rhynchocoela or Nimertinea (Ribbon Worms):
(i) About 750 species.
(ii) Body dorsoventrally flattened and ciliated.
(ii)Mouth and anus are present. Proboscis reversible.
Cerebratulus, Lineus etc.
Subdivision II – Pseudocoelomata
Body cavity is a pseudocoelom. It is a persistent blastocoel, not lined by mesoderm.
Phylum 8- Acanthocephala ( spiny headed worms):
(i) About 500 species.
(ii) Minute worm like endoparasites.
(iii) No digestive cavity.
(iv) Protrusible proboscis with recurved spines.
Acanthocephalus, Gigantorhynchus etc.
Phylum 9- Entoprocta:
(i) About 60 species. All are sessile.
(ii) Body of calyx and slender stalk.
(iii) Digestive tube U-shaped.
(iv) Mouth and anus close together and surrounded by a tentacular crown.
Pedicellina, Loxosoma etc. Superphylum Aschelminthes (Sac worms)
An assemblage of pseudocoelomates with anterior mouth, posterior anus and straight digestive tube. Predominantly aquatic. Free living, epizoic or parasitic. It includes 5 phyla.
Phylum 10- Rotifera (wheel animalcules):
(i) About 1,500 species.
(ii) Microscopic animalcules.
(iii) Anterior end with ciliated crown.
(iv) Pharynx with internal jaws.
Philodina, Rotatoria etc.
Phylum 11- Gastrotricha (Hairy stomach worms):
(i) About 175 species. Microscopic animalcules
(ii) Ventral surface flattened and ciliated.
(iii) Cuticle with spines, plates or scales.
Chaetonotus, Macrodasys etc.
Phylum 12- Kinorhyncha (Jaw moving animals):
(i) About 100 species, Small in size.
(ii) Cuticle segmented and with recurved spines.
(iii) Spiny anterior end or proboscis retractile.
Echinoderes, Pycnophyes etc.
Phylum 13- Nematoda (Round worms):
(i) About 12,000 species.
(ii) Body slender and Cylindrical.
(iii) Cuticle tough often ornamented.
(iv) Radial or biradial arrangement of structures around mouth.
(v) Free living or parasitic.
Ascaris, Trichinella, Wuchereria etc.
Phylum 14- Nematomorpha (Horsehair Worms):
(i) About 100 species.
(ii) Body long, thread-like.
(iii) Larval stage are parasitic in insects.
(iv) Adult free-living in water or dump soil.
Nectonema, Gordius etc,
Subdivision iii- lophophorate coelomata:
Coelom develops as schizocoel or enterocoel. They are with a crown of hollow tentacles (lophophore) surrounding mouth.
Phylum 15- Phoronida:
(i) About 15 species.
(ii) Worm-like unsegmerited body enclosed in chitinous tube.
(iii) Lophophore horseshoe-shaped.
Phylum 16- Bryozoa or Ectoprocta (moss animals):
(i) About 4,000 species, sessile.
(ii) Body enclosed in a gelatinous chitinous or calcareous covering
(iii) Lophophore V-shaped or circular.
Plumatella, Bugula etc.
Phylum 17- Brachiopoda (lamp shells):
(i) About 260 species.
(ii) Body enclosed in two unequal calcareous shell valves.
(iii) Lophophore W-shaped.
Lingula, Crania etc.
Subdivision IV Schizocoelous Coelomata
Coelom is a schizocoel which originates as a space by the splitting of the embryonic mesoderm.
Phylum 18- Priapulida:
(i) 8 species.
(ii) Sausage or cucumber-shaped marine animals with a swollen proboscis.
(iii) Body surface covered with spines and tubercles.
Priapulus, Halicryptus etc.
Phylum 19- Sipunculida (peanut worms):
(i) About 275 species.
(ii) Body elongated and cylindrical with retractile anterior end.
(iii) Lobes or tentacles around mouth.
(iv) Anus dorsal.
Sipunculus, Aspidosiphon etc.
Phylum 20- Mollusca (soft bodied animals):
(i) About 80,000 species.
(ii) Body soft unsegmented, with ventral muscular foot.
(iii) Mantle with shell glands.
(iv) External limy shell of 1, 2, or 8 plates.
Chitons, Pila, Unio etc. Phylum 21-Echiurida (Adder-tailed worms)
(i) About 60 species.
(ii) Body cylindrical unsegmented with anterior retractile proboscis.
(iii) One pair of large ventral setae below mouth.
Echiurus, Urechis etc.
Phylum 22- Annelida (Ringed worms):
(i) About 8,700 species.
(ii) Body elongated, metamerically segmented.
(iii) Setae for locomotion.
Pheretima, Nereis, Leech etc.
Phylum 23- Tardigrada (Water bearers):
(i) About 180 species.
(ii) Body segmented with 4 pairs of unsegmented legs terminating in claws
Echiniscus, Hypsibius etc.
Phylum 24- Onychophora (Claw bearers):
(i) About 73 species.
(ii) Worm like unsegmented body covered by thin cuticle.
(iii) Many pairs of short stumpy legs ending in claws.
Phylum 25- Arthropoda (Joint legged animals):
(i) About one million species.
(ii) Body segmented with jointed appendages.
(iii) Exoskeleton chitinous.
(v) Body cavity haemocoel.
Prawns, Insects, Flies etc.
Phylum 26- Pentastomida (Tongue worms):
(i) About 70 species.
(ii) Worm like unsegmented body with two anterior appendages terminating in claws.
(iii) Blood sucking endoparasites of vertebrates
Cephalobaena, Porocephalus etc.
Cleavage radial and indeterminate. Mouth arises some distance away from blastopore. Coelom is an enterocoel which originates as pouches of embryonic gut (archenteron).
Phylum 27- Chaetognatha (Arrow worms):
(i) About 50 species.
(ii) Small elongated transparent body bearing postanal tail and lateral fins.
(iii) Anterior end with grasping spines.
Sagitta, Spadella etc.
Phylum 28- Echinodermata (Spiny skinned animals):
(i) About 6,000 species.
(ii) Secondarily pentamerous radial symmetry.
(iii) Calcareous endoskeleton of plates bearing external spines.
(iv) A part of coelom is as water vascular canals.
(v) Locomotion by tube feet.
Starfish, Brittle stars etc.
Phylum 29- Pogonophora (beard worms):
(i) About 80 species.
(ii) Body long, enclosed in a chitinous tube.
(iii) Anterior end with one too many tentacles.
(iv) No digestive tract.
Siboglinum, Spirobrachina, Polybrachia etc.
Phylum 30- Hemichordata (acorn worms):
(i) About 80 species.
(ii) Body worm like, divided into proboscis, collar and trunk.
(iii) With gill slits.
Balanoglossus, Cephalodiscus etc.
Phylum 31- Chordata:
(i) About 49,000 species.
(ii) Dorsal tubular nerve cord, notochord, and pharyngeal gill slits at some stage in life history.
(iii) Tail postanal.
Ascidians, Amphioxus, Fishes, Birds, Man etc.