Q.1. What is an Invertebrate ? Give important features of Invertebrate.
Ans. The remaining animals which lack backbone or vertebral column are referred to as “Invertebrates”. All such animals are included in a group, “Invertebrata”. Worms butterflies, sponges, corals, snails, crabs and starfishes are included in “Invertebrata”.
There are some important featurs of Invertebrate :
Q.2. Discuss on the diversity of Invertebrates. (2005, 10)
Ans. Diversity of Invertebrates: -
The Invertebrates represent a heterogeneous assemblage which includes such diverse forms as corals, spongs, worm and butterflies. They exhibit a great diversity of form, structure, physiology, habit and habitat, etc.
1. Numerical strength: -
About one and a quarter milion species of living animals are known at present, Of these, only 5%, that is about 50,000 species belong to the chordates. The remaining 95%, that is about 1.2 milion species constitute the invertebrates. The number of extict species is around seven times the number of living species, and thus there may have been some 7 to 8 milion invertebrate species in all.
2. Size: -
The invertebrate animals range in size from the microscopic protozones to the lares-sized cephalopods.
3. Shape: -
In invertebrates, the irregular everchangingbody shape of amoeba, plant-like appearance of many sponges and coelenterates, leaf-like and ribon-shaped flatworms, elongated and vermiform annelids, nemerteans and nematods, star-shaped star-fishes, ect., display spectra of body shapes.
4. Symmetry: -
All symmetries are represented by the invertebrates. Protozones show bilateral as well as radial symmetry. Some are asymmetrical. Sponges are asymmetrical and radially symmetrical. Coelenterates are radially symmetrical. Ctenophores show biradial symmetry. The members of remaining phyla are mostly bilaterally symmetrical. Spherical sysmmetry too is represented in the invertebrates.
5. Habits and habitat (Ecology): -
The invertebrates occupy a great variety of habitats and have adapted themselves to different modules of life. They are found themselves to different modes of life. They are found in the seas, in fresh waters,in air and on all parts of land from snow-covered mountains to deserts.
6. Grades of organization: -
Invertebrates show all grades of organization. Protoplasmic grade is found in protozoa, as all activities at this level are confined within the limits of a single plasma membrane (plasmalemma). Cellular grade is characteristic of sponges because in a sponge only cells exhibit division of labour for performing specialized functions. Cell-tissue grade is seen in coelenterates as their cells are not only specialized for different functions but also certain similar cells gather together to form tissue as well.
7. Types of coelom: -
Some many-celled invertebrates, like sponges and coelenterates, are acoelomate as they have no coelom. Other invertebrates have a cavity in between the body wall and the gut. This cavity is a pseudocoelom in nematodes as it is not lined by mesoderm. In higher invertebrates, the coelom is lined by the mesoderm and hence it is the true coelom.
8. Diverified respiratory surface: -
Protozoans, sponges, coelenterats have a direct diffusion of gases between the organism and the environment. In annelids, the exchange of gases is through moist skin. Gills are common in most higher invertebrates. Echinoderms use dermal branchiae and tube feet. In insects the tracheal system is adapted for aerial respiration. Sea cucumbers have respiratory trees acting as respiratory organs.
9. Diversified excretory mechanisms: -
In protozoans, sponges and coelenterates excretion is by direct diffusion through cell membranes. Flatworms possess characteristic flame cells, while annelids and molluscs use nephridia for the purpose. The excretory devices in insects are Malpighian tubules. Echinoderms and some other invetebrates have amoeboid cells or phagocytes for storage and disposal to outside of excretory products.
10. Varied modes of reproduction: -
Invertebrates mode of reproduction varies from simple asexual binary fission to most complicated sexual reproduction. In parthenogenesis is also met with in which an unfertilized egg develops into a complete individual. It occurs in rotifers, bees some other insects and certains crustaceans. paedogenesis in which eggs produced by immature individuals develop into larvae, is seen in some invertebrates like gall fly, Miastor. In sexually reproducing invertebrates hermaphrodites or bisexual forms are met with, particularly in coelenterates, platyhelminths, annelids and crustaceans. Fertilization is either internal or external. Development is direct or indirect. In the latter case the development includes both larval stages and metamorphosis.
Q.3. Write the difference between lower higher Invertebrates.
Ans.
Q.4. Discuss about the classification of animal kingdoms.
Ans. Classification of Invertebrates: -
Kingdom Animalia: - It is divided into two subkingdom :
(i) Protozoa and (ii) Metazoa.
(i) Protozoa: -
These are Unicellular, microscopic animals. They have no tissues. Examples : - Euglena, Paramecium, Amoeba etc.
(ii) Metazoa: -
This sub kingdom includes multicellular animals. Subkingdom metazoa has been, divided into three Infra-kingdoms.
Infra-kingdom 1. Mesozoa: -
These are parasitic, worm like animals and lack tissues. They have been included in phylum mesozoa. Example- Dicyema.
Infra-kingdom 2. Parazoa: -
They are marine as well as fresh water forms and have cellular grade of body organization. They lack-tissues, choanocyte cells are found. They have been included in phylum Porifera. Example - All sponges.
Infra-kingdom 3. Eumetazoa: -
Tissues and organs are found. They include all the remaining metazoans. Infra-kindom Eumetzoa has been divided into two divisions.
Division A. Radiata: -
These are radially symmetrical animals which do not have organs i.e. their body organization is of tissue grade. Two phyla are included in this division.
Phylum (a). Cnidaria: -
Nematoblast cells are found, tantacles present and comb plates are absent. Example- Obelia and Hydra.
Phylum (b). Tenophora: -
They possess comb plate which helps in locomotion. Nematoblasts and tentacles absent. Example- Beroe. Division B. Bilateria- Bilaterally symmetrical animals, triploblastic and have organ grade of body organization. Bilateria has been divided into 3 sections.
Section 1. Acoelomata: -
Body cavity or coelom absent. Space between body wall and visceral organs is occupied by mesoderm formed of parenchyma. It includes two phyla.
Phylum (a). Platyhelminthes: -
They are parasitic and flat worms. Example- Tapeworm or Taenia, Liver fluke or Fasciola.
Phylum (b). Nemertinea (Rhynchocela): -
Thin, elongated, ribbon like aquatic animals. Example- Stichostemma.
Section 2. Pseudocoelomata: -
Pseudocoel found in the adult stage, parenchyma fills the spaces between body wall and visceral organs in young stage. This section includes three phyla.
Phylum (a). Aschelminthes: -
Slender, elongated and round body mouth and anus at two different ends of the body. Example- Ascaris.
Phylum (b). Entoprocta: -
Fixed and stalked animals, mouth and anus located at one end close to each other. Example- Lonosoma.
Phylum (c) Acanthocephala: -
These are flat bodies parasites, no alimentary canal, thorny proboscis at anterior end. Example- Acanthocephala.
Section 3. Eucoelomata: -
They have true coelom lined with mesoderm. Section Eucoelomata includes 13 phyla.
Phylum (a) Ectoprocta or Bryozoa: -
Aquatic, minute, colonial moss like animals. The digestive tract U-shaped. Example-Bugula.
Phylum (b) Brachiopoda: -
Body covered with shell formed of calcium carbonate, interior with two spiral arms called lophophore. Commonly called lampshells. Example- Lingula.
Phylum (c). Phoronida: -
Worm. like cylindrical, unsegmented, live in self secreted membranous tube, lophophore is horse shoe-shaped and the digestive tract U-shaped. Example Phoronis.
Phylum (d). Mollusca: -
Soft bodies animals having a membranous covering called mantle which secrete calcarious shell. Mostly aquatic forms respiring by gills and possess a muscular foot for locomotion. Example- Unio, Pila.
Phylum (e). Annelida: -
Segmented worms underground or aquatic having setae for locomotion. Body cavity is true coelom. Example- Earthworm, Nereis.
Phylum (f). Sipunculoidea: -
Unsegmented body without setal. Example- Sipunculus or peanut worm.
Phylum (g). Echiuroidea: -
Anterior end of the body projected a proboscis infront of the mouth. Anus at the posterior end. A pair of ventral setae. Example - Echiurus.
Phylum (h). Arthopoda: -
Body covered with exoskeleton formed of chitin, jointed and paired appendages. Body divided into three parts head, thorax and abdomen. Compound eyes. Example - Cockroach, Scorpion Prawan.
Phylum (i). Chaetognatha: -
Marine animals,, slender and transparent body. Mouth surrounded by spicules, bristles or hooks. Example- Arrow worm or sagitta.
Phylum (j). Echinodermata: -
Marine animals with pentamerous body provided with spines in skin, water-vascular system and tube feet for locomotion are present. Example- starfish and sea cucumber.
Phylum (k). Pogonophora: -
Slender body shaped like a long tube. No digestive tract, beared like ciliated tentacles. Example- Beard worm or Spirbrachia.
Phylum (1). Hemichordata: -
Unsegmented body, respiration by gills, rudimentary notochord. Example- Tongue worm or Balanoglossus.
Phylum (m). Chordata: -
Natochord present at some stage of life. Hollow nerve cord on the dorsal side and heart on the ventral side of the body. They are aquatic, terrestrial or aerial. Example- fish, frog, snake, bird, dog, man.
In this way Storer and Usinger divided the animal kingdom into 23 phyla. Out of these 10 are major phyla and the remaining ones are minor phyla.