Students can go through AP Inter 1st Year Zoology Notes 3rd Lesson Animal Diversity-I: Invertebrate Phyla will help students in revising the entire concepts quickly.
AP Inter 1st Year Zoology Notes 3rd Lesson Animal Diversity-I: Invertebrate Phyla
1. Phylum – Porifera :
→ Sponges are the only metazoans that lacks true embryological germ layers.
→ Highly totipotent nature of cells and presence of aquiferous system are two unique features of sponges.
→ Pinacoderm and choanoderm are the two-epitheloid layers in sponges.
→ Water current is maintained by the beating of choanocytes flagella.
→ Water (eaves spongeoceol through osculum.
→ Canal system helps in food collection, respiration and excretion.
→ Archaeocytes are totipotent cells.
→ Digestion is completely intracellular and occurs in Choanocytes and Archaeocytes.
→ Sponges have powers of regeneration and cell aggregation.
→ Sponges are the only metazoans without nerve cells.
→ Sponges are the suspension feeders.
→ Asexual reproduction is by fragmentation, budding and by gemmules.
→ Development is indirect.
→ Porifera is classified into three classes, they are, calcarea, hexactinellida and demospongia.
→ Sponges are sequential hermaphrodites, they exhibit protogyny or protandry.
→ Fertilization occurs mesophyl. Sponges show indirect development as it includes larval forms.
→ Choanocytes of sponges resemble those of Proterospongia.
2. Phylum – Cnidaria :
→ Cnidarians are diploblastic eumetazoans with tissue grade organization.
→ Cnidarians are characterized by the presence of cnidocytes, polypoid and medusoid forms.
→ Coral reefs are the large formation of calcium carbonate laid down by certain anthozoan corals in shallow tropical seas.
→ Cnidarians show radial symmetry, sea anemones exhibit biradial symmetry. Polyp is sessile while medusa is free-swimming.
→ Polyp is sessile with a mouth-up orientation. Medusa is umbrella or bell-shaped with a mouth-down orientation.
→ Mesoglea contains amoeboid cells derived from ectoderm.
→ Gastrovascular cavity helps in digestion and circulation. Digestion is first extra-cellular and then intra-cellular.
→ Medusoid forms have statocysts. Diffused conduction of nerve impulse occurs.
→ Hydrozoans medusae are craspedote whereas scyphozoan medusae are acraspedote.
→ In medusa, mesoglea is important in buoyancy.
→ In scyphozoans, scyphistoma produces ephyrae by strobilation.
→ Mesoglea is cellular in Scyphozoa and Anthozoa.
→ In anthozoans the inner free margin of mesentery is produced into aconitum that bears cnidocytes.
→ Class Scyphozoa includes jellyfish.
→ Class Anthozoa includes sea anemones, corals.
3. Phylum – Ctenophora :
→ Ctenophores are commonly known as sea walnuts or comb jellies or sea gooseberries.
→ These all are exclusively marine forms.
→ Body is radially symmetrical.
→ These are diploblastic organisms and tissue level of organisation. .
→ Locomotion by eight external rows of ciliated comb plates, hence the name ctenophora.
→ Food capture by the help of glue cells called lasso cells or colloblasts.
→ Well-marked character of ctenophores is Bioluminescence.
→ These are bisexual and reproduction is by sexual method.
→ Fertilisation is external, Development is indirect and includes a larval stage called cydippid larva.
Ex : Plourobrachia, Hormiphora.
4. Phylum – Platyhelmenthes :
→ These are triploblastic, bilaterally symmetrical Acoelomates.
→ They show cephalization and organ-system grade organization. Body cavity is absent.
→ Protonephredia are primarily osmoregulatory and secondarily excretory in function.
→ In tubellarians, body is covered by ciliated epidermis that secrets rod-shaped inclusions called rhabdoids.
→ In larger turbellarians, branched gut facilitates transport of nutrients to all parts of the body.
→ Body is covered by tegument in Trematodes and Cestodes.
→ Nervous system is ladder-like. They are mostly hermaphrodites and fertilization is internal.
→ Planarians have remarkable ability of regeneration due to totipotent cells called neoblasts. Muller’s larva or Goetfs larva present in some.
→ Flukes are ectoparasites or endoparasites. Body is covered by tegument.
→ Tapeworms are endoparasites. They exhibit pseudometamerism. Strobila is divided into proglottides.
→ Trematodes and Cestoda are placed under the taxon Neodermata. In these flatworms body is covered by a non ciliated, syncytial neodermis.
5. Phylum – Nematods :
→ Nematodes are characterized by a species – specific number of cells or nuclei.
→ Tissues are cellular or syncytial.
→ Body cavity is a pseudocoelom; it is not lined by mesodermal peritoneum.
→ Digestion is extracellular and intracellular.
→ Excretory system includes excretory glands or H – shaped excretory canal system or both. Nervous system is intraepithelial.
→ Sense organs include amphids and phasmids. Nematodes are mostly unisexual and sexually dimorphic.
→ Development includes four moulds. Nematodes exhibit eutely.
→ Nematoda is classified into two classes. In Aphasmidia amphids are of various shapes. Phasmids are absent.
→ Excretory glands are present but excretory glands or excretory canals or both are present.
→ Eutely is a phenomenon in which cell divisions cease near the end of embryonic development so that number of cells of the adult is constant.
6. Phylum – Annelida :
→ Annelids are triploblastic, bilaterally symmetrical, schizocoelomates protostomes.
→ Metamerism increased the efficiency of burrowing and also resulted in independent movements of the segments.
→ In annelids cephalization is more pronounced.
→ Coelomic cavities of adjacent segments are separated by intersegmental septa whereas the two coelomic cavities of a segment are separated from each other by mesenteries.
→ Growth results from the addition of new segments from growth zone located just in front of pygidium.
→ In many polychaetes parts of Parapodia are modified into gills.
→ In all non-chordates respiratory pigment, (if present), is present dissolved in the blood plasma, unlike in chordates where it occurs in certain blood corpuscles.
→ Excretory organs are meta-nephridia that opens into coelom by a nephrostome and to the exterior by a nephridiopore.
→ During metamorphosis the larval episphere becomes the Prostomium, here as the apart posterior to the telotroch becomes the pygidium. Trunk segments arise from a growth zone anterior to the telotroch.
→ Leeches have a fixed number of segments that show superficial annuli, fill Intersegmental septa and mesenteries are absent in leeches.
→ Clitellum is conspicuous only during reproductive periods in leeches.
→ In leeches coelom is reduced due to the presence of nutrient storing botryoidal tisse.
→ Leeches are copulating hermaphrodites with a penis whereas earthworms are copulating hermaphrodites without penis.
→ Development is direct.
7. Phylum – Arthropoda :
→ Arthropoda is the largest phylum in Animalia.
→ They exhibit Heteronomous Metamerism and tagmosis.
→ They possess jointed appendages, striated muscles, and chitinous cuticle.
→ The chitinous cuticle offers protection and prevents loss of water from the body.
→ Haemocoel is the functional body cavity.
→ Alimentary canal consists of foregut, midgut and hindgut.
→ Respiratory gas exchange occurs through general body surface or gills or book gills or book lungs or tracheae.
→ Excretory organs are coxal glands, green glands and rrialpighian tubules.
→ Nervous system includes a nerve ring and double ventral nerve cord.
→ Centipedes are pisthogoneate (genital aperture at the posterior end of the trunk).
→ Millipedes are progoneates (genital aperture at the anterior end of the trunk).
→ In insects thorax bears three parts of jointed legs.
→ Urecotelic is a water conservation adaptation in insects.
→ Myriapoda and hexapoda are grouped under the infra phylum tracheata.
→ Chilopoda includes centipedes.
→ Diplopoda includes millipedes.
→ Hexapoda includes insects.
8. Phylum – Mollusca :
→ Mollusca are the second largest animal phylum.
→ Gastropods are the secondarily asymmetrical.
→ Body is covered by a calcareous shell secreted by the mantle epithelium.
→ The space between mantle and visceral mass is called mantle cavity or pallial cavity.
→ Buccal cavity contains a rasping structure called Radula, except in the bivalves.
→ A crystalline style composed of digestive enzymes is present in the stomach of bivalves and some gastropods.
→ Second gills are formed by the folding of mantle epithelium.
→ Atria receives oxygenated blood from the gills.
→ Osphradium is a chemoreceptor, which helps in detection of the quality of water.
→ In most species, TrochOphore develops into a veligar larva.
→ Foot in aplacophorans, if present, is a fold that lies in the pedal groove.
→ Nervous system is ladder-like in aplacophorans and polyplacophorans.
→ In Chiton shell is divided into eight shell valves.
→ Neopilina is considered as a living fossil.
→ Heart of monoplacophorans is unique with two pairs of atria opening into a pair of ventricles.
→ Serial repetition of internal organs in several systems is one of the most striking features of monoplacophorans.
→ Gastropoda is the largest and the most diverse molluscan class.
→ Only left nephridium, atrium and gills are present in most living gastropods.
→ Gills of bivalves are plate like and help in filter feeding or suspension feeding.
→ Development of fresh water bivalves includes a specialized veligar called glochidium larva which is ectoparasitic on the gills of fish.
→ Gills, atria and nephridia are one pair each in dibranchiates and two pairs each in tetrabranchiates.
→ Eyes of cephalopods are superficially similar to those of vertebrates.
→ Mollusca classified into seven classess. They are
- Aplacophora.
- Polyplacophora,
- Monoplacophora,
- Gastropoda,
- Scaphopoda,
- Pelecypoda and
- Cephalopoda.
→ It develops into a veligar larva.
9. Phylum – Echinodermata :
→ These are free-living animals. They are primarily bilaterally symmetrical.
→ Endoskeleton consists of calcareous ossicles located in the dermis.
→ Pedicellariae are compound ossicles useful for defense and cleaning the body.
→ Body cavity is enterocoelom. Water vascular system is derived from coelom.
→ Tube feet are useful in locomotion, food capture, gas exchange and excretion.
→ Blood vascular system is of open type and is poorly developed.
→ Excretory wastes diffuse out through respiratory surface.
→ Nervous system lacks ganglia.
→ A hypothetical larva called Dipleurula is considered as the ancestor for all echinoderm.
→ In feather stars, free-swimming doliolaria and sessile pentacrinoid larva occur in life history.
→ Auricularia larva, doliolaria larvae occur in life history of sea cucumbers.
→ Bipinnaria and brachilaria larvae occur in life history of starfish.
→ Oral surface is upward in Pelmatozoa but downward in Eleutherozoa.
→ Anus is present on oral surface in Crinoidea, absent in Ophiuroidea.
→ Madreporite is absent in Crinoidea, oral in Ophiuroidea and is internal in Holothuroidea.
→ Sea lilies are stalked arid sessile.
10. Phylum – Hemichordata :
→ These are a small group of worm-like marine animals.
→ These are bilaterally symmetrical, triploblastic and Coelomate animals.
→ The body is cylindrical and composed of an anterior proboscis, a collar and a long trunk.
→ The stomochord is present (once believed to be the notochord).
→ Circulatory system is of open type with a dorsal heart.
→ Respiration takes place by paired gill slits.
→ Development is indirect and includes a tornaria larve.
Ex : Balanoglossus (acron worm), Saccoglossus.
→ Amphids : They are the cuticular depressions present on the lips surrounding the mouth in the nematodes. They are well developed in free living nematodes and serve as chemoreceptors.
→ Autotorpy : It is the process of voluntary breaking of the injured part of the body (self mutilation or amputation). It is a device developed to protect the body from the enemies and parasites as seen in the echinoderms .
→ Bothridia : The leaf like organs present on the scolex of certain cestodes. They act as the . organs of attachment to the body parts of the host.
→ Cercaria : It is a free swimming larva consisting of an ovoid body and a tail. It occurs in the life history of liver flukes.
→ Choanopyte : It is a specialized flagellated cell with a cup shaped collar around the base of the flagellum. It maintains the current of water through the body.
→ Clitellum : It is a belt or girdle shaped thickening of the skin, in a specific region of the body (14 to 16 segments in Pheretima). It secretes the cocoon and albumen (food for the developing young one), during the breeding season.
→ Cocoon : It is a bag like structure secreted by the clitellum. Eggs and sperms are deposited into it. Fertilization and development occurs within the cocoon.
→ Comb plates : They are ciliated plates helping in locomotion in the ctenophores.
→ Ctenidia : They are the respiratory organs of molluscs. Each ctenidium (gill) consists of a central axis and one or two rows of filaments.
→ Flame cell : It is a hollow cell containing a tuft of cilia in the inner space. It is excretory and osmoregulatory in function. Flame cell is a primitive type of excretory organ (protonephridium).
→ Gemmules : They are the ‘internal buds’ of some sponges aiding in asexual reproduction. They also help tide over unfavourable conditions.
→ Juvenile : It is an immature young form resembling the adult in all aspects.
→ Madreporite : It is a circular porous plate, present in the body of most echinoderms. Through its pores sea water enters the water vascular system.
→ Mesenteries : They are vertical partitions dividing the coelenteron of sea anemones. They are developed as inward folds of the endoderm. They bear cnidoblasts.
→ Miracidium : It is a free swimming larva of liver fluke. It contains ciliated epidermis, penetration glands, etc. It transforms into the sporocyst stage in the body of freshwater snail, which is the invertebrate host of liver fluke.
→ Moulting or Ecdysis : It is the process of casting off the outer body wall. During development of nematode larvae, the cuticle is cast off 4 times.
→ Mullers larva : It is the characteristic larva of turbellarians. It bears an apical tuft of cilia. Nephridia : They are highly coiled excretory organs derived from the ectoderm.
→ Osculum : It is a large opening present at the free end of a sponge body. Water from the spongocoel flows out through the osculum.
→ Ostia : They are numerous openings present on the body of a sponge. Water is drawn in through the ostia and sent out through the osculum (choanocytes play an important role in drawing in water).
→ Parapodia : They are hollow biramous appendages of polychaetes. They bear tufts of many setae and help in locomotion.
→ Parenchymula : It is the larva of sponges such as Clathrina. It is similar to the planula of cnidarians. It is covered with cilia all over.
→ Pedicellariae : They are ‘forceps like structures’ (modified spines) in the body of sea stars and sea urchins . They remove foreign particles that may settle on the body surface and thus help in keeping the body surface clean.
→ Phasmids : They occur in some nematodes. They are well developed in parasitic nematodes and are glandulosensory in function.
→ Planula : It is a ciliated, double walled, free swimming larva characteristic of a cnidarian.
→ Polyembryony : Formation of several young ones from a single zygote. It occurs during the formation of redia and cercaria larvae in the life history of a liver fluke.
→ Poyp or Hydranth : It is a flower shaped or hydra shaped zooid of the colonial cnidarians such as Obelia. It bears several tentacles around the mouth. It is a nutritive zooid.
→ Radula : It is a thin ribbon shaped body lying in the buccal cavity of molluscs. It consists of a median stalk and two lateral lobes. Each lobe bears many rows of chitinous teeth. Radula works like a ‘file’ and rasps the vegetable food.
→ Redia : It is an elongated larva of liver fluke produced by the sporocyst asexually/ partheno- genetically. It gives rise to the second generation of rediae or the cercaria larvae.
→ Rhabdites : They are rod shaped bodies present in the epidermal cells of turbellarians. On discharge they form a slimy (mucus) substance helping in locomotion by smoothening the path of gliding movement and also in defence.
→ Setae : They are small, /‘-shaped, chitinous structures present in the pits (setal sacs) of the body wall of earthworms. They aid in locomotion. In some, setae are modified into ‘penial setae’ and help in copulation.
→ Spicules of a sponge : They are the supporting structures of the body secreted by scleroblasts. They are of different shapes and sizes. They are made up of calcium carbonate or silica.
→ Spongocoel: It is the large central cavity of a sponge body.
→ Statocyst: Statocyst is a sense organ concerned with the maintenance of equilibrium of the body.
→ Syncytium : It is a multinucleate mass of protoplasm without any division into cells. The tegument of flatworms is syncytial.
→ Trichemella : It is a larval form characteristic of the hexactinellid sponges.
→ Trochophore : It is the characteristic larva of annelids. It is ‘top’ shaped and bears one or more bands of cilia, an epical tuft, an eye etc. It contains coelom and nephridia. It is believed to be the forerunner of higher invertebrates.
→ Zooid : It is a individual member of a ‘coelenterate’ colony. They serve different functions (division of labour).
→ Invertebrate Phyla includes the animals which are without back bone.
→ The invertebrates constitute about 90% of the known animals.
→ Invertebrates are characterised by
- a segmented body
- Jointed appendages
- Exoskeleton
- Brain
→ Invertebrate Phyla (Etymological meaning) – Examples:
- Porifera (Pore bearing)- Sponges
- Cnidaria (stinging nettle) – Hydra, Jellyfish, coral
- Ctenophora (Comb bearing)-Comb Jellies
- Platyhelminthes(Flat Worm) – Flat Worms
- Nematoda (Thread like)-Round Worms
- Annelida (Ringed) – Leeches
- Arthropoda (Jointed Legs) – Spiders, Insects
- Mollusca (Soft) – Octopus, Squid, Pila
- Echinodermata (Spiny skinned) – Star Fish
- Hemichordata (Half cord) – Acorn Worms
→ Anthozoans are commonly called as sea anemones. [IPE]
They are sedentary marine animals.
→ Polychaetes are marine annelids. They are commonly bristle worms or clam worms. [IPE]
→ LimulUs(king crab) is the living fossil arthropod. The respiratory organs are book gills. [IPE]
→ Crustaceans are aquatic mandibulate arthropods. [IPE]
→ Aristotle’s lantern is a complex 5 jawed masticatory apparatus present in buccal cavity of sea urchins. Ex: Echinus (Sea urchin) [IPE]
→ Echinoidea is a class of phylum echinodermata. [IPE]
→ In case of poriferans, the spongocoel is lined with flagellated cells called choanocytes. [NEET-2017]
→ Important characteristic that hemichordates share with chordates is pharynx with gill slits. [NEET-2017]
→ Metagenesis refers to alternation of generation between asexual and sexual phases of an organism. [NEET-2015]
→ Exoskeleton is mainly responsible for diversification of insects on land. [NEET-2015]
→ Trichinella spiralis endoparasites of humans does show viviparity. [NEET-2015]
→ Planaria possesses high capacity of regeneration. [NEET-2014]
→ Cnidaria represents both marine and fresh water species. [NEET-2014]
→ One of the representatives of phylum arthropoda is silver fish. [NEET-2013]
→ Pheretima and its close relatives derive nourishment from decaying fallen leaves and soil organic matter. [2012 PMT]
→ One very special feature in the earth worm Pheretima is that the typhlosole greatly increases the effective absorption area of the digested food in the intestine. [2011 PMT]
→ Flatworms are triploblastic. [2010 PMT]
→ An example of animal having a single opening to the outside that serves both as mouth as well as anus is Fasciola. [2010 PMT]
→ If a live earthworm is pricked with a needle on its outer surface without damaging its gut, the fluid that comes out is coclomic fluid. [2009 PMT]
→ A group of animals Aschelminthes (round worms) is bilaterally symmetrical and triploblastic. [2009 PMT]
→ Ascaris is characterised by presence of neither true coelom nor metamerism. [2008 PMT]