General Characters:

*  The term porifera (porous = pores; ferre = bearer) was proposed by Robert grant. Poriferans are characterised by numerous small pores on the body called Ostia. Poriferans are commonly called sponges.
* Sponges (= Poriferans) are, no doubt, multicellular animals, but tissue grade organisation is absent. Hence they are included in Parazoa.
* Poriferans are mainly marine animals. Few forms (of families spongilidae and potamolepidae) live in fresh water.
* All sponges are sedentary animals. Few forms are solitary and most of them are coloneal.
* Body of sponges is cylindrical, vase like or irregular in shape.
* Few sponges are radially symmetrical and others are asymmetrical.
* Poriferans are diploblastic animals. Outer layer is formed by thin cells and is called pinacoderm and inner layer is called choanoderm (formed by *choanocytes). Between these two layers, large amounts of gelatinous mesohyal is present.
* In the body of sponges, there is a spacious cavity called spongocoel or paragastric cavity. It opens out through an osculum at the free end of the body.
* The body sponges contain a peculiar system, known as canal system, through which a constant current of water is maintained. Water enters the canal system through Ostia, reaches the spongocoel and pass out through osculum.
*  The water current helps in food collection, respiration, excretion etc.
 

 Digestion is intracellular.
* Sponges have skeletal structures in the form of spicules (formed by CaCO3 or silica) and/ or spongin fibres.
* Poriferans are bisexual (hermaphrodites) animals. Fertilization is internal.
*  During development, larva is formed - such as - parrenchymula, trichimella or amphiblastula. e.g.: Sycon, Euplectella, Spongilla, Euspongia.

Classification:
Porifera is divided into three classes
 

Class - 1: Calcarea:
¤ Spicules of these sponges are formed by CaCO3 (calcareous)
¤ These sponges are marine and live in shallow waters (less depth)
¤ They may be solitary or colonial and body is simple.
e.g.: Sycon (scypha), Leucosolenia, Grantia. 

Class - 2: Hexactinellida:

¤ Spicules of these sponges are formed by silica.
¤ These sponges are marine and live in deeper water.
¤ These are solitary forms.
e.g.: Euplectella (Venus flower basket); Hyalonema (glass rope sponge)

Class - 3: Demospongiae:
¤ These sponges have silicons, spicules and spongin fibres. In some, skeleton is absent.
¤ These forms found in sea and also in fresh water.
¤ These are colonial animals.
e.g.: Spongilla - (fresh water sponge)
         Euspongia - (bath sponge)
         Chalina - (dead man's fingers)

 

 PHYLUM - CNIDARIA CNIDARIA

General Characters:
¤ Cnidarians (formerly called Coelenterates) have special cells known as Cnidoblasts /Cnidocytes/ stinging cells. They contain a poison called hypnotoxin. These cells help in offense, defence, food collection and locomotion.
¤ Except the members of genus Hydra (which live in fresh water), all other Cnidarians are marine forms.
¤ Cnidarians are diploblastic animals with outer ectoderm and inner endoderm. Between ectoderm and endoderm, gelatinous mesoglea is present.
¤ The body of cnidarians contain a cavity called coelenteron or gastro vascular cavity. It opens out through mouth. Anus is absent.
¤ Digestion is intracellular and extra cellular.
¤ Cnidarians are radially symmetrical animals.
¤ Nervous system is in the form of a diffuse net in mesoglea.
¤ Some cnidarians (e.g.: Madrepora) have calcareous (CaCO3) skeletons and are called corals. They form islands in sea called coral reefs. (e.g.: Great barrier reef near Australia)
¤ Coloneal cnidarians (especially hydrozoans) exhibit polymorphism. The main zooids are polyps (sedentary) and medusae (free swimming).
    In medusae, special sense organs are present, called statocysts. They maintain balance.
¤ Very few cnidarians are bisexual (e.g.: Hydra) and most of the cnidarians are unisexual)
¤ The life history of many cnidarians (e.g.: Obelia) exhibit alternation of generation (or metagenesis), in which polyploid stages asexually produce medusae; and medusae sexually produce polyps.

¤ Typical larva of chidarians is planula larva.
e.g.: Physalia, Adamsia, Pennatula, Gorgonia, Meandriana.

Classification
Phylum cnidaria is divided into three classes.

Class - 1: Hydrozoa
Phylum platyhelminthes is divided into 3 classes.
¤ Except Hydra (live in fresh water), all others are marine
¤ Both polyoid and medusoid stages are present.
¤ Cnidoblasts are present in ectoderm only.
¤ Coelenteron is spacious.
¤ Germ cells are developed from ectoderm. 
 e.g.: Hydra (fresh water polyp)
          Obelia: (seafur)
          Physalia: (Portuguese man of war) 

Class - 2: Scyphozoa
¤ All are marine forms. They are commonly called Jelly fishes
¤ Only medusoid stages are present (free swimming)
¤ Mouth is surrounded by four oral arms.
¤ Cnidoblasts are present in ectoderm and endoderm.
¤ Large amount of mesoglea is present and hence the name Jelly fishes.
¤ Germs cells are developed from endoderm.
e.g.: Aurelia (Jelly fish)
         Rhizostoma
 

Class - 3: Anthozoa or Actinozoa
¤ All are marine forms. They are commonly called sea anemones, corals etc.
¤ Only polyploid stages are present (sedentary = fixed).
¤ Coelenteron is divided into chambers by mesenteries.
¤ Cnidoblasts are present in Ectoderm and endoderm.
¤ Reef (Island) building true stony corals belong to this class.
¤ Germ cells are developed from endoderm
e.g.: Adamsia (Sea anemone)
         Corallium (precious coral)
         Gorgonia (Sea fan)
         Pennatula (Sea Pen)

 

PHYLUM PLATYHELMINTHES 

General Characters:

¤ Animals of platyhelminthes (Platus-Flat, helminth-worm) have thin, dorsoventrally flattened and leaf like bodies. Hence, they are commonly known as Flat worms.
¤ Most of the flatworms are parasites. Some are freeliving (e.g.: Planaria)
¤ These are triploblastic and bilaterally symmetrical animals.
¤ Parasitic flat worms have hooks and/ or suckers for attachment to host tissues.
¤ In tapeworm digestive system is absent (because they live in digested food).
In others digestive system is present with mouth and branched intestine. Anus is absent.
¤ Nervous system consists of cephalic ganglia (brain) and nerve cords forming a ladder like system.
¤ Body of flat worms contain flame cells (protonephridia) which acts as excretory organs. But their primary function is osmoregulation.
¤ These are bisexual animals. Fertilisation is internal.
¤ Development contains many larval stages (miracidium, sporocyst, redia, carcaria etc) some larvae exhibit polyembryony.
¤ Few forms like Planaria have great power of regeneration
e.g.: Planaria, Fasciola, Taenia.

Classification:
    Phylum platyhelminthes is divided into 3 classes.
 

Class - 1: Turbellaria
¤ Turbellarians are free living animals found in fresh water, sea water or in moist soil.
¤ Body is covered by cilia. Epidermal cells contain mucus forming rhabdites.
¤ They have a distinct head.
¤ Turbellarians reproduce asexually and sexually. In the life history of some turbellarians, a free swimming mulleis larva is formed.
e.g.: Dugesia (Planaria); Convoluta 

 
Class 2. Trematoda:
¤ Trematodes are commonly called flukes and are parasitic.
¤ Body is covered by a thick cuticle (tegument).
¤ They have two suckers (oral sucker and ventral sucker/ acetabulum) for attachment to host tissues.
¤ Intestine is divided into two main branches.
¤ These are mainly bisexual animals (Schistosoma/ blood fluke is unisexual)
¤ Life cycle is complicated with many larvae (Miracidium - Sporocyst - Redia - Cercaria - Metacercaria)
e.g.: Fasciola (Liver fluke of sheep)
Schistosoma (Blood Fluke of man) 

 
Class 3. Cestoda:
¤ Cestodes are commonly known as tapeworms and are parasitic.
¤ Body is divided into scolex, neck and strobila.
¤ Scolex has hooks, suckers, leaf like bothria (for attachment to host tissues).
¤ Strobila is divided into a number segments called proglottids (pseudometamerism)
¤ Digestive system is absent.
¤ These are bisexual animals and life history is complicated.
e.g.: Taenia solium (pork tapeworm)
Echinococcus granulosus (dog tapeworm) 
 

PHYLUM - NEMATODA 

General Characters:
¤ Nematodes are commonly called round worms.
    (Circular in cross section)
¤ Most of the nematodes are parasitic and very few are free living (in water or on land).
¤ These are triploblastic, bilaterally symmetrical and Pseudocoelomates.
¤ Body is elongated and unsegmented.
¤ Body is covered by cuticle (formed by a protein-collages) and epidermis is in syncitial state.
¤ Alimentary canal is in the form of a straight tube with mouth and anus.
¤ Excretion is done by a rosette gland and its ducts.
¤ Nervous system consists of a nerve ring and nerves with ganglia.
¤ Anteriorly, all nematodes have chemoreceptors called amphids. some nematodes posteriorly have glandulo sensory structures called Phasmids.
¤ Nematodes are unisexual and exhibit sexual dimorphism (male and female are in two different shapes/ forms). Female is longer than male. Generally posterior end of male is curved. Males have cloaca at the posterior end.
¤ Most of the nematodes are oviparous (lay eggs). Some are ovoviviparous.
[e.g.: Wuchereria (Development of young one with the egg within mother without getting any nourishment from mother is known as ovoviviparity)].
¤ During development, larvae undergo four moultings.
e.g.: Ascaris, Wuchereria, Ancylostoma
 

Classification:
Phylum Nematoda is divided into two classes.
Class - 1: Aphasmidia
¤ In these nematodes, phasmids are absent.
¤ Excretory system is poorly developed.
e.g: Trichinella (trichina worm)
Trichiuris (whip worm). 
 

Class - 2: Phasmidia
¤ In these nematodes, phasmids are present.
¤ Excretory system is well developed.
e.g.: Ascaris (round worm), Ancylostoma (hook worm)
Enterobius (pin worm), Wuchereria (filarial worm).

     
PHYLUM - ANNELIDA 

General characters:
1. The term Annelida (annulus-little ring = segment) was proposed by Lamarck.
2. Most of the annelids are marine (e.g.: Nereis). some live in fresh water and few are terrestrial (live on land)
3. These are triploblastic animal and are coelomates (Schizocoelic coelom)
4. Body of annelids is divided into a number of segments or metameres. The segmentation is known as metamerism or metameric segmentation.
5. Coelom is filled with coelomic fluid, which gets as hydraulic skeleton, that support the body during locomotion or in burrowing.
6. Annelids move with the help of parapodia (e.g.: Nereis), suckers (e.g.: Leech) or with the help of setae (eg: Earthworm)
7. Annelids respire through general body surface by diffusion.
8. Circulatory system is of closed type. Heart is absent. Blood contains pigments like haemoglobin or chlorocruarin (They are found dissolved in plasma)
9. Excretory organs are nephridia.
10. Nervous system consists of a nerve ring around pharynx and a double ventral nerve cord.
11. Polychaetes are unisexual and others are bisexual.
12. In unisexual annelids (Polychaetes), during development, a free swimming larva is formed, known as trochophore.
e.g.: Nereis
         Pheretima
         Megascolex
         Hirudinaria
 

Classification:
Phylum Annelida is divided into three classes
Class - 1: Polychaetes: (Poly = many), chaete = setae
¤ Polychaetes are marine forms and are commonly called bristle worms.
¤ Some of the polychaetes move among the weeds and rocks; some live in tubes and few live in burrows.
¤ Adistinct head is present with eyes, palps and cirri.
¤ Locomotory structures are parapodia, which contains numerous setae.
¤ Parapodia also help in respiration. 
¤ Clitellum is absent
¤ These are unisexual animals. During development trochophore larva is formed.
   e.g.: Nereis (Sandworm and ragworm)
             Aphrodite (Sea mouse)
             Arenicola (Lug worm)
 

Class - 2: Oligochaeta: (Oligos = few; Chaetae = Setae)
¤ Oligochaets are terrestrial animals, that live in burrows in moist soil. But few forms live in fresh water (e.g.: Tubifex)
¤ Head is absent.
¤ Locomotion is effected by setae present in body wall.
¤ Clitellum is present, which secretes the cocoon (egg case)
¤ These are bisexual animals
¤ Development is direct (larva is absent)
    e.g.: Pheretima, Megascolex, Tubifex 

 
Class - 3: Hirudinea
¤ Hirudinea includes the Leeches. They live in fresh water. Few forms live in sea and very few in moist soil.
¤ The body is dorsoventrally flattened.
¤ Number of segments is limited. Each true segment is divided into sub segments by annuli.
¤ There are two suckers, one is anterior (in which mouth is present) and the other is posterior
¤ Setae, parapodia etc. are absent.
¤ Clitellum is formed only during breeding season.
¤ The body cavity contains an elastic tissue called botryoidal tissue. 
¤ These are bisexual animals. Development is direct (Larva is absent). In male reproductive system, a copulatory penis is present.
    e.g.: Hirudinaria (fresh water leech)
             Pentobdella (marine leech)
            Haemodispa (leech in moist soil)
 

EARTHWORM 

Introduction
¤ There are many genera of earthworms in the world. The most common earthworms in our area are Pheretima and Megascolex.
¤ Earthworms are burrowing animals, that live in burrows in moist soil. They are nocturnal animals.
¤ The longest/ largest earthworm in the world is Megascolides australis. The smallest earthworm is Chaetogaster annandalei. The longest/ largest earthworm in India is Drawida grandis.
¤ Earthworms are commonly called friends of farmers because
    a. They make the field porous (with their burrows) and thus it is aerated
    b. They bring the fertile sub-soil to surface as worm castings.
 

Morphology/ External features (Pheretima posthuma)
Shape: Body of pheretima (earthworm) is long, round and cylindrical.
Size: It grows to a length of 10-15 cm and measures 3-5 mm in diameter
Colour: Earthworms are brown in colour. Dorsal side is dark brown and ventral side is light brown.
Segmentation: The body of pheretima is metamerically segmented. It contains 100- 120 segments.
Peristomium: I segment of pheretima is known as peristomium because it encircles the mouth.
Prostomium: Attached to the anterior surface of peristomium, there is a small fleshy bulb like structure called prostomium. It bears some sensory cells.
Pygidium/ anal segment: Last segment of the body of earthworm contains anus. Hence last segment is called anal-segment or pygidium.
Clitellum (or cingulum): The body wall of pheretima around 14-16 segments
becomes thick and girdle like. It is called clitellum. It forms the cocoon.
Due to clitellum, body of earthworm can be divided into three parts:
   a. Pre clitellar region -- 1 to 13 segments
   b. Clitellar region -- 14 to 16 segments
   c. Post clitellar region -- 17 to last segment

Setae or chaetae
a. Setae are minute, chitinous, spine, like S shaped characters.
b. They live in setigerous sacs in body wall.
c. They help in locomotion.
d. Setae are absent in peristomium, pygidium and in clitellar segments.

Body wall, wall of intestine and coelom
¤ Bodywall: Bodywall of earthworm in dermomuscular
a. Body of earthworm is covered by a non cellular, brown semitransparent cuticle.
b. Below the cuticle, is a layer of cells known as epidermis. It also contain gland cells and sensory cells.
c. Below the epidermis, is a thin layer called dermis.
d. Dermis is followed by a layer of circular muscles and then a layer of longitudinal muscles.
e. The inner most layer of body wall is the outer coelomic epithelium (Parietal layer)
¤ Wall of intestine
a. The outer most layer of wall of intestine is the inner coelomic epithelium (Visceral layer)
b. Below the inner coelomic epithelium are the layers of longitudinal muscles and then circular muscles.
c. Inner most layer of wall of intestine is endoderm.
¤ Coelom: The space between outer and inner coelomic epithelia is the coelom.
It is filled with coelomic fluid. It acts as hydraulic skeleton during locomotion and in burrowing.
Digestive system
     The digestive system of earthworm consists of an alimentary canal and its associated digestive glands.
¤ Alimentary canal: It is a straight tube extending between mouth and anus. Mouth lies on the ventral side of the first segment (peristomium). It opens into a thin walled buccal cavity, lies in 1-3 segment, which is continued as a muscular pharynx (3rd to 4th segments) Pharynx opens into a narrow oesophagus (5th to 7th) which is enlarged into a muscular bulb like chamber called gizzard in 8th segment. Gizzard grinds the food into fine particles (hence, it is also called grinding mill). Gizzard opens into tube like stomach (9th to 14th). Stomach opens into the intestine (15th to last). Intestine is divided into three parts.
a. Pretyphlosolar part: 15th to 26th - Typhlosole is absent. Digestion of food is completed in it.
b. Typhlosolar part: 27th to last but 23rd to 28th segment typhlosole is present. Digested food is absorbed here.
c. Post Typhlosolar part: Last 23rd to 28th segments. Typhlosole is absent. Undigested matter is temporarily stored.
    In Last segment, rectum (that is post typhlosolar part of intestine) opens out through anus.
¤ Digestive glands: In the dorsal wall of pharynx, there are pharyngeal glands (secrete mucin and proteolytic enzyme). In the wall of stomach, calciferous glands are present. Their secretions neutralise the humic acid. In the wall of  intestine, intestinal glands are present. They secrete amylase, cellulose, trypsin, lipase etc. In 26th segment, intestine has a pair of caecae, that extend upto 22nd segment. They help in digestion and absorption
¤ Digestion: Earthworm eats soil and utilises the decomposing organic matter resent in it. Enzymes digest the food and undigested soil reaches the rectum and pass out through anus as small, round ball called worm castina.

Blood vascular system/ or/ circulatory system:
¤ As the blood flows in blood vessels, the circulatory system of pheretima is described as closed type.
¤ Among the main blood vessels, Dorsal Blood Vessels (DBV) and Ventral Blood Vessels (VBV) are prominent.
¤ Connecting the DBV and VBV, there are (4 pairs of lateral hearts). Blood flows DBV to VBV through them.
¤ On the pharynx and oesophagus (in 4th, 5th and 6th segments), there are blood glands. They produce blood cells and haemoglobin. Blood cells are phagocytic.
¤ In earthworm, haemoglobin is found dissolved in plasma of blood.
 

Respiration:
¤ In earthworm, moist skin (Body surface) acts as respiratory organ.
¤ To keep skin moist, coelomic fluid flows out through dorsal pores.
 

Excretory system
     Separation and elimination of nitrogenous wastes from the body known as excretion. In earthworm, excretory organs are nephridia.
 

Types of nephridia:
¤ If the nephridium has nephrostome, it is described as open type.
e.g.: septal nephridia.
¤ If the nephridium lacks nephrostome, it is described as closed type.
e.g.: pharyngeal nephridia and integumentary nephridia.
¤ If the nephridium opens into the alimentary canal (Buccal cavity) pharynx or intestine etc), it is called Enteronephric nephridium.
e.g.: pharyngeal nephridia and septal nephridia.
¤ If the nephridium opens out, it is called exonephric nephridium
e.g.:  Integumentary nephridia.
 

Nephridia in pheretima
    Pheretima has three types of nephridia. They are pharyngeal nephridia, Integumentary nephridia and septal nephridia.
¤ Pharyngeal nephridia: These are present in groups. Two such groups are present in each of the segments: 4th, 5th and 6th. These are closed type and enteronephric type.
¤ Integumentary nephridia: These are minute nephridia present in segments from 3rd to last. They are closed type and exonephric type (In clitellar segments, the number of these nephrida is more. Hence, these segments are called forests of nephridia).
¤ Septal nephridia: These are present in segments from 15th to last (attached to septa - The septum separating 15th and 16th segments has septal nephrida on both sides). These are open type and enteronephric type.

Nervous system
          Nervous system of earthworm contains a nerve ring, a ventral nerve cord and nervous formed from them.
¤ Nerve ring is present around pharynx in 3rd and 4th segments. It is formed by cerebral ganglia (brain), sub pharyngeal ganglia and circum pharyngeal connectives.

¤ Ventral nerve cord arises from subpharyngeal ganglia and extends upto last segments along mid ventral line in each segment. From 5th, VNC possess a segmental ganglion.
¤ Cerebral ganglia supply nerves to prostomium and peristomium circum pharyngeal connectives supply nerves to 1st and 2nd segments. Subpharyngeal ganglia supply nerves to 3rd & 4th segments. From 5th segment onwards, nerves are supplied by segmental ganglia of VNC.
¤ Some epidermal cells in earthworm are modified and perform sensory function.
 

Reproductive system

Earthworms are bisexual animals. But testes mature earlier and hence, they are called protandrous animals
 

Male reproductive organ:
a) There are two pairs of testes - one pair in 10th and the other in 11th segments
b) There are two pairs of seminal vesicles (11th , 12th segments) and two pairs of spermiducal funnels (10th & 11th segments).
c) Vasa deferentia arise from these funnels extend upto 18th segment and open out through a pair of male genital apertures.
d) The prostate ducts arising from prostate glands also opens out along with male genital apertures. e) There are accessory glands in 17th and 19th segments and opens out on genital papillae.
 

Female reproductive organs:
a) There is a pair of ovaries in 13th segment (attached to septum separating 12th , 13th segments)
b) There are two oviducal funnels in 13th segment oviducts arising from them unite and opens out through a female genital pore on the ventral side of 14th segments.
c) There are four pairs of spermathecae in 6th , 7th , 8th , 9th segments - one pair in each segment. They store the spermatophores (groups of sperms) received during copulation
 

Copulation, Fertilisation and cocoon formation:
¤ During copulation, two earthworms are attached along their ventral surfaces in opposite direction, in such a way that the male genital apertures of one earthworm opposes the spermathecal apertures of the other.
¤ Then, they exchange the spermatophores which are stored by spermathecae.
¤ Clitellum forms cocoon (egg case).
¤ Within 3 weeks, development is completed. About 4 earthworms will develop from each cocoon. There is no larval stage in earthworm.
 

Economic important:
¤ Earthworms are called friends of farmers, because, they make the soil pores and aerated. They brought the fertile subsoil to surface as worm casting. Earthworms are also used in production of vermicompost.
¤ Earthworms are used as bait to catch fishes
¤ Medicine prepared from earthworms is used to cure gout disease
 

PHYLUM - ARTHROPOD 

General Characters:
¤ The term Arthropod (arthos = joined; podos = legs/ appendages was proposed by Voi siebold.
¤ Arthropod is the largest phylum and Insecta is the largest class in animal kingdom (about 80% of animals on the earth are arthropods).
¤ These are triploblastic, bilaterally symmetrical and metamerically segmented animals.
¤ These are coelomates (schizocoelom) and coelom is confined to gonads only.
There is a spacious perivisceral cavity filled with blood and is called haemocoel.
¤ Bodies of Arthropods are covered by hard, exoskeletal plates. Arthropods periodically undergo moulting (ecdysis). It allows growth.
¤ Body of most of the arthropods is divisible into head, thorax and abdomen (e.g.: cockroach). In some forms (e.g.: prawn) head and thorax are fused to form cephalothorax (In some (e.g.: scorpion), cephalothorax is called prosoma and abdomen is called opisthosoma).
¤ Respiration is effected by trachea (e.g.: cockroach), gills (e.g.: prawn) or book lungs (e.g.: scorpion).
¤ a. Circulatory system is of open type.
    b. There is a heart on the dorsal side of the body.
    c. In most of the arthropods blood is colourless due to absence of pigments. In the blood of crustaceans (e.g.: prawn) blood contains haemocyanin (a pigment with copper)
¤ Striated muscles are first developed in arthropods.
¤ Nervous system is like that of annelids (nerve ring + ventral nerve cord).
¤ Sense organ include antennae, compound eyes, statocysts etc.
¤ Excretory organs are Malpighian tubules, green glands or coxal glands.
¤ These are unisexual. Fertilization is internal. Development is direct (without larva) or indirect with (larva)
e.g.: Periplaneta (cockroach) Palaemon (prawn)
         Cancer (crab),
         Palamnaeus (scorpion)
        Araneae (Spider)
 

Economically Important Insects:
Apis (Honey bee): Bombyx (Silkworm Moth)
Kerria (Lac Insects)
Vectors for some pathogens:
Mosquitoes: Anopheles, Culex, Aedes
Housefly: Musca
Gregarious Pest: Locusta
Living Fossil: Limulus (king crab)
 

Classification:
Phylum Arthropod is divided into 3 sub phyla:
 

Subphylum - 1: Trilobita
¤ It Includes extinct arthropods.
¤ Many pairs of biramus appendages are present.
¤ Body is divided into three lobes along the length hence the name, trilobita.
    e.g.: Trianthrus, Dalmanites.
 

Subphylum - 2: Chelicerata
¤ The Body of these animals is divisible into prosoma (head + thorax) and opisthosoma (abdomen).
¤ Prosoma has 6 pairs of appendages, in which, first pair is called chelicerae.
¤ Chelicerata is divided into two classes.
 

Class - A. Xiphosuria:
¤ Most of these animals became extinct.
¤ Limulus (king crab) is one of the living xiphosurians and is marine.
¤ Prosoma is covered by horseshoe shaped plate called carapace.
¤ Ventrally prosoma has a pair of chelicerae, four pairs of walking legs and a pair of pusher legs.
¤ Respiratory organs are book gills.
    e.g.: Limulus (king crab - horseshoe crab) - living fossil. 
 

Class - B. Arachnida:
¤ This class includes terrestrial arthropods like scorpions, spiders etc.
¤ Body is divisible into prosoma and opthosoma.
¤ Prosoma has a pair of chelicerae, a pair of pedipales and 4 pairs of walking legs.
¤ Respiratory organs are book lungs or trachea or both.
¤ Excretory organs are malpighian tubles and coxal glands.
¤ Scorpions are viviparaus.
    e.g.: Palamnoeus (scorpion)
             Aranea (Spider)
            Sarcoptes (Mite) 

 
Sub Phylum - 3:
Mandibulata: It is divided into four classes.
Class - A. Crustacea:
¤ These are aquatic arthropods.
¤ Body is divisible into cephalothorax and abdomen. cephalothorax is covered by a broad carapace.

¤ There are two pairs of antennae: (first pair- antennules, second pair- antennae).
¤ Each segment of the body has a pair of jointed appendages.
¤ Respiratory organs are gills and excretory organs are greenglands.
¤ Blood contains haemocyanin.
¤ Typical larva is Nauplius.
e.g.: Palaemon (fresh water prawn)
         Cancer (Crab)
         Balanus (Barnacle)
 

   Class - B: Chilopoda                                         Class - C: Diplopoda 

1. These are terrestrial arthropods                      1. These are terrestrial arthropods. 

2. These are commonly called centipedes.         2. These are commonly called millipedes. 

3. Body is long and dorsoventrally flattened.     3. Body is long and cylindrical. 

4. Body is divisible into head and trunk.            4. Body is divisible into head and trunk. 

5. Each segments has a pair of legs.                   5. Each segment has two pairs of legs. 

6. Legs end with poison claws.                          6. Poison claws are absent. 

7. Gnathochilarium is absent.                            7. Maxillae are modified into gnathochilarium. 

8. Respiration by trachea.                                  8. Respiration by trachea. 

9. Excretion by malpighian tubules.             
e.g.: Scutigera  Scolopendra                             9. Excretion by malpighian tubules.
                                                                             e.g.: Julus Spirostreptus. 
 

Class - D. Insecta or Hexapoda  

1. Insecta is the largest class in the animal kingdom.
2. Body is divisible into head, thorax and abdomen.
3. Head possess compound eyes, antennae, mandibles etc.
4. Thorax has 3 pairs of jointed legs. Hence the name Hexapoda.
5. Study of Insects is known as Entomology.
6. Respiration by trachea and excretion by malpighian tubules.
7. Insects excrete uric acid (For water conservation).
8. Development may be direct or indirect.
e.g.: Periplaneta (Cockroach), Musca (Housefly), Lepisma (Silver Fish)
 

Phylum - Mollusca 

General Characters
¤ The term Mollusca (mollis = soft body) was proposed by Johnston. Mollusca contains soft bodied animals and Mollusca is the second largest Phylum.
¤ Most of the Molluscs are marine. Some live in fresh water, some are terrestrial, few are amphibious and very few are parasitic.
¤ These are triploblastic, bilaterally symmetrical, unsegmented and are coelomates.
¤ Molluscs are provided with a calcareous (CaCO3) shell.
    a. Shell may be external (e.g.: Pila), internal (e.g.: Sepia) or absent   (e.g.: Octopus).
    b. Shell may be univalve (e.g.: Pila), bivalve (e.g.: Unio) or Multivalve  (e.g.: Chitin)
¤ Body is divisible into head, foot (muscular) and visceral mass.
¤ Soft body of Molluscs is covered by an ectodermal membrane called mantle (pallium). The space between mantle and soft body is called mantle cavity.
¤ The buccal cavity contains a rasping organ called radula, that helps in feeding.
¤ Respiratory organs of aquatic molluscs are ctenidia. In terrestrial forms pulmonary sac acts as respiratory organ. In amphibious forms both ctenidia and pulmonary sac are present.
¤ Perivisceral cavity is haemocoel. Circulatory system is open type. Blood contains haemocyanin.
¤ Nervous system consists of many ganglia and nerves.
¤ Sense organs include eyes, tentacles, osphradium etc. (Osphradium is a sense organ of molluscs, that tests the purity of water.)
¤ Excretory organs are metanephridia.
¤ Some are unisexual and some are bisexual.
¤ During development, a veliger larva is formed (modified trochophore larva)
    e.g.: Pila (apple snail)
             Pinctada (Pearl Oyster)
             Sepia (Cuttle Fish)
            Octopus (Devil Fish)
 

Classification: Phylum Mollusca is divided into 7 classes.

Class - 1: Aplacophora
¤ These are worm like marine animals.
¤ Shell, mantle, Foot etc. are absent.
¤ Skin contains calcareous spicules.
    e.g.: Neomenia, Chaetoderma     
 

Class - 2: Monoplacophora
¤ Scientists believed that these animals became extinct. But in 1952 a mollusca of thin class was collected by scientists from Pacific Ocean from the ship- Galathea.
¤ That animal was named as Neopilina Galathea. It exhibits both annelidian and molluscan characters. Hence, it is called connecting link between Annelida and mollusca. 
¤ Internal segmentation, nephridia etc. are annelidian characters.
¤ Shell, Foot, Ctenidia hearts etc. are molluscan characters.
    e.g.: Neopilina
 

Class - 3. Polyplacophora:
¤ These are oval, dorso ventrally flattened, bilaterally symmetrical and marine animals.
¤ Shell is dorsal and is in the form of a series of 8 plates.
¤ 6 to 88 pairs of ctenidia are present around foot.
    e.g.: Chitin, Lepidopleurus 

 
Class - 4. Gastropoda:
¤ Gastropods are marine, fresh water, terrestrial, amphibious or parasitic.
¤ Shell is univalve; it may be external or internal
(e.g.: Aphysia) or absent (e.g.: Doris)
¤ Head and Foot are well developed.
¤ During development, larvae undergo Torsion and hence, the adults are asymmetrical.
¤ Larva is veliger.
e.g.: Pila (apple snail), Aplysia (Sea hare),
Doris (Sea Lemon) 

Class - 5: Scaphopoda
¤ These are marine forms and are commonly called tusk shells.
¤  Foot is conical and helps in burrowing.
¤  A large number of thread like capitula help in food collection.
    e.g.: Dentalium, Pulsellum 

 
Class - 6: Pelecypoda or Bivalvi
¤  These are marine or fresh water forms.
¤  Head and radula are absent.
¤  Foot is axe shaped (hence the name pelecypoda)
¤  Shell is bivalve (hence the name Bivalvia)
¤  Stomach contains a rod like crystalline style, which helps in digestion of starches.
¤  Ctenidia help in respiration and in food collection and they are plate like
¤  Larva is glochidium, veliger or trochophore.
     e.g.: Unio         (Fresh water mussel)
               Mytilus    (Marine mussel)
               Pinctada Vulgaris (Pearl oyster)
 

Class - 7. Cephalopoda:
¤ These are more advanced molluscs and are marine.
¤ Foot is in head region in the form of arms.
¤ Shell may be external, internal or absent.
¤ Circulatory system is closed type.
¤ Montle Cavity contains on ink gland (help in escaping from enemies).
¤ Nervous system is well developed and brain is covered by a cartilaginous. Cranium
¤ Development is direct.
e.g.: Sepia (Cuttle fish - shell is called cuttle bone)
          Loligo (shell is called pen)
          Octopus (Devil Fish)
        Architeuthis (giant squid- the largest invertebrate)

 
PHYLUM - ECHINODERMATA 

General Characters
¤ The term Echinodermata (echinos = spiny, derma = skin) includes the animals having spiny skin.
¤ Echinoderms are marine animals.
¤ These are triploblastic and eucoelomates (enterocoelom)
¤ Larvae are bilaterally symmetrical and adults are pentaradially symmetrical)
¤ Some of the spines on the body are modified into forceps like structures called pedicellariae. They help in keeping the body surface clean.
¤ Echinoderms have a unique water vascular system (developed from coelom). It helps in locomotion, food collection, respiration and excretion. Sea water enters the system through madreporite.
¤ Circulatory system is of open type. Heart is also absent.
¤ Respiration takes place through dermal populae (dermal branchiae), tube feet or respiratory trees.
¤ Nervous system is poorly developed.
¤ These unisexual animals during development, a bilaterally symmetrical larva is formed (Ancestral larva of echinoderms is dipleurula).
     e.g.: Asterias (Star Fish)
         Cucumaria (Sea Cucumber)
         Echinus (Sea Urchin)

Classification: Phylum echinodermata is divided into two sub phyla:
Sub Phylum 1. Pelmatozoa: It includes primitive echinoderms. The existing pelamatozoans are included in one class.
Class - Crinoidea:
¤ These are commonly called sea lilies or Feather stars.
¤ Arms are biramus and face upwards. Arms have pinnules that helps in food collection.
¤ Central disc is attached to sub stratum by root like structures called cirri.
¤ Larva is doliolaria, which becomes pentacrinoid larva and then adult. 
         e.g.: Neometra (Feather Star)
                  Bathycrinus (Sea Lily)

Sub. Phylum 2 Eleutherozoa: Eleutherozoans are movable echinoderms. Eletherozoa is divided into 4 classes

S.No. Features		Classes
	A. Asteroidea	B. Asteroidea	C. Echinoidea	D. Holothuroidea
Common Name	Star Fishes(Sea Stars)	Brittle stars(Serpent Stars)	Sea Urchins (Spherical)Sand dollars (Flat)	Sea Cucumbers.
Arms	Short and not clearly marked from disc.	Long and flexible	Absent	Absent
Madreporite	Aboral	Oral	Aboral	Opens into coelom
Pedicellariae	present	absent	present	absent
Special Feature	-	-	Pharynx contains a masticatory organ called Aristotle's lantern	Respiratory trees are present
Larva	Bipinnaria	Ophiopluteus	Echiopluteus	Auricularia
Examples	Asterias Astropecten	Ophiothrix Gorgonocephalus	Echinus (Urchin) Echinodiscus (dollor)	Holothuria Synapia

PHYLUM HEMICHORDATA 

General Characters:
¤ Previously Hemichordata is one of the sub phyla in chordata. But now, it was included in non-chordates as a separate phylum.
¤ These are worms like marine animals
¤ These are triploblastic, bilaterally symmetrical and enterocoelomates.
¤ Body is divisible into proboscis, collar and trunk.
¤ Buccal cavity forms a buccal diverticulum (stomachord) which extends into proboscis.
¤ Respiratory organs are gills.
¤ Circulatory system is open type. There is a heart on the dorsal side.
¤ Development is indirect. Larva is TORNARIA
     e.g.: Balanoglossus, Saccoglossus
 

Classification.
Class I-Enteropneusta:
¤ These are commonly called acorn worms.
¤ These are solitary and burrowing animals.
¤ Larva is tornaria.
e.g.: Balanoglossus, Ptychodera
 

Class 2. Pterobranchia:
¤ These are sedentary, colonial or tube dwelling animals.
      e.g.: Rhabdopleura, Cephalodiscus