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Animal Kingdom Cheat Sheet (DRAFT) by

Salient features and classification of animals-non chordates up to phyla level and chordate up to class level (three to five salient features and at least two examples).

This is a draft cheat sheet. It is a work in progress and is not finished yet.


Taxonomy is the branch of science that deals with the study of nomenc­lature, classi­fic­ation, and principles of classi­fic­ation. Taxonomy word was given by "­Can­dol­le"
(Taxis - arrang­ements. Nomia-distr­ibu­tion).


Aristotle:- He is known as the "father of zoology". (Book Historia Animalium).
He is also known as the father of ancient taxonomy. He classified animals into two groups on the basis of the
color of blood.
(1) Anaima - Those animals which don't have red blood or in which RBC are absent. e.g. Invert­ebrates like
Sponges, Cnidaria, Mollusca, Arthro­poda, Echino­der­mata.
(2) Enaima :- These animals have red blood. This group includes all verteb­rates and it has been further divided into two subgroups.
(a) Vivipara:- It includes animals that give birth to young ones. e.g. Mammals.
(b) Ovipara:- It includes animals that lay eggs. e.g. Pisces, Amphib­ians, Reptiles, Aves, etc.


When any plane that passes through the centre does not divide the body of animals into two equal halves.
e.g : most of the sponges are asymme­trical.
Radial symmetry
When any plane passing through the central axis of the body divide the animal into two identical halves.
e.g : Coelen­ter­ates, Ctenop­hores and Echino­derms (adult)
Bilateral symmetry
When the body can be divided into identical left & right halves in only one plane.
e.g : Platyh­elm­inthes to Chordates.

Body plan

Cell-a­ggr­egate type
e.g. Sponges
Blind Sac type
Animals in which digestive system is incomp­lete, it has only single opening to the outside of the body that serves as both mouth and anus.
e.g. Coelen­terates to Platyh­elm­inthes
Tube-w­ith­in-tube type
Found in those animals having complete digestive tract i.e. with separate openings mouth and anus.
e.g. Nemath­elm­inthes to Chordates

Germinal layers

Animals in which the cells are arranged in two embryonic layers ectoderm and endoderm with an interv­ening undiff­ere­ntiated mesoglea
e.g. Coelen­terates and Ctenop­hores.
Those animals in which the developing embryo has a third germinal layer–­Mes­oderm in between the ectoderm and endoderm
e.g. Platyh­elm­inthes to Chordates.

Level of body organi­sation

Protop­lasmic level
In protoz­oans, unicel­lular body performs all biological activities
Cellular level
In sponges, cells are arranged as loose cell aggregates and division of labour occurs among cells (Tissues absent)
Tissue level
In coelen­terates and ctenop­hores, cells performing the same function are arranged into tissues
Organ level
In Platyh­elm­inthes tissues are grouped together to form organs.
Organ system level
In higher animals, organs further organise to form organ systems e.g. Aschel­min­thes, Annelida, Arthro­poda, Echino­dermata and Chordata


e.g. Tapeworms
In Annelids, Arthropods and Chordates. In these animals, the body is externally and internally divided into segments with a serial repetition of atleast some organs, this is called metameric segmen­tation and the phenomenon is known as Metame­rism.


Animals without notochord
e.g. Porifera to Hemich­ordata
Animals with notochord.
eg. Chordata
The notochord is a mesode­rmally derived rod-like structure formed on the dorsal side during embryonic
develo­pment in some animals.

Circul­atory system

Open type
In which the blood is pumped out of heart and the cells & tissues are directly bathed in it.
e.g. Arthro­pods, Molluscs, Echino­derms, Hemich­ordates and some lower Chordates like tunicates
Closed type
In which the blood is circulated through a series of vessels of varying diameters i.e. arteries, veins and blood capill­aries
e.g. Annelids, Cephalopod molluscs, Verteb­rates etc.

Embryonic develo­pment

Animals in which mouth is formed first (Blastopore→Mouth)
e.g. Platyh­elm­inthes to Mollusca
Animals in which anus is formed earlier than mouth (Blast­opore → Anus)
e.g. Echino­derms, Hemich­ordates and Chordates.
On the basis of the fate of blasto­pore, animals can be divided into two categories :
(i) Protos­tom­iates
(ii) Deuter­ost­omiate

Body Cavity or Coelom

Animals in which the body cavity is absent
e.g. Porifera, Coelen­terata, Ctenno­phora, Platyh­elm­inthes
In same animals body cavity is not lined by mesoderm, instead, the mesoderm is present as scattered pouches in between the ectoderm and endoderm. Such a body cavity is called pseudo­coelom.
e.g. Aschel­min­thes.
Animals possessing coelom i.e. the body cavity which is lined by mesoderm on all sides
On the basis of embryonic develo­pment, the coelom is of two types:
(i) Schizocoel – Coelom formed by splitting of a mesodermal mass
e.g. Annelida, Arthro­poda, Mollusca.
(ii) Enterocoel – Coelom formed by fusion of gut pouches during embryonic stage
e.g. Echino­der­mata, Hemich­ordata and Chordata.
The presence or absence of a cavity between the body wall and gut wall is very important in classi­fic­ation.

Important Phyla

Protozoa (Included in kingdom - Protista)
Amoeba , Paramo­ecium etc
Porifera (Kingdom - Animalia)
Sponges (Leuco­sol­enia, Sycon)
Hydra, Jellyfish, etc
Ctenophora (minor phylum)
Pleuro­bra­chia, Ctenoplana
Flatworms (eg: Tapeworm)
Roundworm (eg: Ascaris)
Earthworm, Leech, etc
Insects, Scorpion, Fly, etc.
Snail, Pila, Octopus, etc.
Fish, Snake, Birds, Monkey, etc

Test Your Knowledge 01

1. Which of the following phylum have radially symmet­rical organisms ?
(1) Coelen­terata
(2) Platyh­elm­inthes
(3) Aschelminthes
(4) Annelida
(1) Coelen­terata
2. Which of the following phylum possess true coelom ?
(1) Aschelminthes
(2) Annelida
(3) Ctenophora
(4) Platyh­elm­inthes
(2) Annelida
3. Loose cell aggregate type body plan is found in _____.
(1) Protozoa
(2) Porifera
(3) Coelenterata
(4) Platyh­elm­inthes
(2) Porifera
4. Which of the following phylum is pseudo­coe­lomate ?
(1) Aschel­minthes
(2) Arthropoda
(3) Annelida
(4) Platyh­elm­inthes
(1) Aschel­minthes
5. When any plane passing through the central axis of body and divides the animal into two identical halves. It is called as _____.
(1) Asymmetry
(2) Radial symmetry
(3) Bilateral symmetry
(4) Biradial symmetry
(2) Radial symmetry
6. Which of the following phylum have "Tube within tube" body plan ?
(1) Platyh­elm­inthes
(2) Coelenterata
(3) Porifera
(4) Nemath­elm­inthes
(4) Nemath­elm­inthes
7. Which of the following phylum has closed circul­atory system ?
(1) Arthropoda
(2) Annelida
(3) Mollusca
(4) Echino­dermata
(2) Annelida
8. Segmen­tation is found in :-
(1) Annelida, Arthro­poda, Mollusca
(2) Arthro­poda, Mollusca, Echinoderms
(3) Annelida, Arthro­poda, Chordata
(4) Arthro­poda, Echino­derms, Chordata
(3) Annelida, Arthro­poda, Chordata
9. Which of the following group is Deuterostome–
(1) Annelida, Arthro­poda, Mollusca
(2) Echino­der­mata, Hemich­ordata, Chordata
(3) Annelida, Mollusca, Chordata
(4) Arthro­poda, Mollusca, Echino­dermata
(2) Echino­der­mata, Hemich­ordata, Chordata
10. Incomplete digestive tract found in -
(1) Platyh­elm­inthes and Aschelminthes
(2) Platyh­elm­inthes and Ctenophora
(3) Aschel­minthes and Annelida
(4) Coelen­terates and Aschel­minthes
(2) Platyh­elm­inthes and Ctenophora


1. Members of this phylum are commonly known as "­Spo­nge­s". The study of sponges is known as Parazo­ology.

2. All are aquatic and Sessile, mostly marine but few are found in fresh water also. They are solitary or colonial. The entire body with pores i.e. numerous small Ostia for entry and one large opening Osculum for the exit of water.

3. Sponges have various body forms and shapes with irregular shapes mostly Asymme­trical. (Radial symmetry in Sycon and Leucosolenia)

4. Sponges are primitive multic­ellular acoelomate animals and have a cellular level of organi­zation.

5. Body wall encloses a large central cavity the spongocoel or paraga­stric cavity with small hollow canals.

6. Canal system or water transport system: It is a unique feature of sponges, water enters through Ostia in the body wall into the spongocoel and goes out through the osculum. This pathway of water transport is helpful in food gathering (Nutri­tion), respir­atory exchange, and removal of Wastes (excretion).

7. Choano­cytes form the lining of Spongocoel and canals. The ceaseless beating of flagella helps in mainta­ining the flow of water current.

8. Nutrition is holozoic. Digestion is intrac­ellular and occurs in food vacuoles of choanocytes.

9. Skeleton is internal, and consists of tiny calcareous spicules or siliceous spicules or fine spongin fiber located in the mesenc­hyme. Sclero­blast secretes spicules and spongi­oblast secretes spongin fibers.

10. Respir­ation and Excretion take place by diffusion of gases through the body surface. The excretory matter is Ammonia.

11. Reprod­uction takes place by means of-
(A) Asexual - By Budding or Fragme­ntation or by Special cell mass Gemmules containing Archae­ocytes.
• Endogenous buds of asexual reprod­uction in sponges are known as Gemmules (In unfavo­rable condit­ions).

(B) Sexual - Sponges are Hermap­hrodite, fertil­ization is internal and cross due to Protog­ynous condition and develo­pment is indirect having a larval stage which is morpho­log­ically distinct from adult.


• Coelen­terates are also known as Cnidarians due to the presence of stinging cells called Cnidoblast or Cnidocytes.

1. Mostly marine, few fresh-­water (Hydra) Carniv­orous, sessile or free swimming.

2. Radial symmetry.

3. Tissue level of organi­zation, acoelomate animals.

4. They develop from two germinal layers (1) Ectoderm (2) Endoderm i.e. they are Diplob­lastic (mesogloea between two layers) Inters­titial cells are totipotent cells found in both layers of the body wall.

5. Coelen­terates have two basic body forms (Dimorphic) -
(A) Polyp-
-Cylin­drical and sessile form
- May be solitary or Colonial
- Mouth directed upwards
e.g.- Hydra, Adamsia
- Umbrel­la-­shaped and free swimming
- Always solitary
- Mouth directed downwards
e.g. - Aurelia
• Either or both zooids may occur in a species.
• If both are found in a species, two forms alternate in life cycle, Polyps produce medusae asexually and medusae form the polyps sexually, this altern­ation of generation is called Metage­nesis eg:- Obelia
• Group of different types of zooids in polyp or medusa shows polymo­rphism.

6.Cnidoblast or Cnidocyte (contains stinging capsule as Nemato­cyst) present on the tentacles and body, which are used for anchorage (Attac­hment), defense and for the capture of Prey (Offence).
• Body of some coelen­terates may be covered by the exoske­leton of calcium carbonate. eg. :- Corals

7. A large central cavity called Coelen­teron is having a single aperture on hypostome i.e. Incomplete digestive tract (Blind sac).

8. Digestion is extrac­ellular as well as Intrac­ellular i.e. takes place in Coelen­teron as well as in food vacuole. The mouth serves both purposes.
• Coelen­teron is also respon­sible for the distri­bution of food besides partly digesting it. Due to this dual role, it is named coelen­teron or Gastro­vas­cular cavity.

9. Respir­ation and Excretion take place by diffusion of gases through body surface. The excretory matter is Ammonia.

10. Nervous system diffused type and consists of non-polar neurons (Nerve net).

11. Reprod­uction
– Asexual by budding
– Sexual by the production of gametes
– Develo­pment is indirect with larval stages
– Larva of Obelia - Planula (free living).
– Larva of Aurelia - Ephyra.


1. Ctenop­hores are known for their beauty and delicate nature. In sunlight, their comb-p­lates give the effect of a rainbow. They are commonly known as "­Sea­-go­ose­ber­rie­s" or "­Com­b-j­ell­ies­" or "­Sea­-wa­lnu­ts".

2. Nemato­blasts are absent, so they are also called "­acn­ida­ria­ns".

3. They are exclus­ively marine.

4. Biolum­ine­scence (The property of a living organism to emit light) is well marked.

5. Body is soft transp­arent jelly-­like. They are radially symmet­rical, Diplob­lastic organisms with tissue grade body organi­zation.

6. Locomotion takes place by the presence of 8 ciliary comb plates on the body surface.

7. Digestion is both extrac­ellular and intrac­ell­ular.

8. Skeletal, Excretory and Respir­atory systems are absent.

9. They are carniv­orous. A pair of long solid tentacles are present. In place of nemato­blasts, special types of cells are present on tentacles, called Lasso cells (Collo­blasts) which help in catching the prey.

10. Sexes are not separate. Reprod­uction takes place only by sexual means. Fertil­ization is external.

11. Develo­pment is of the indirect type. The life cycle involves a free-l­iving Cydippid larval stage.

1. Pleuro­brachia
2. Ctenoplana
3. Beroe - Swimming eye of Cat.
4. Cestum -


1. They have dorsov­ent­rally flattened bodies and hence are called flatworms.

2. These are mostly endopa­rasites found in animals including human beings but some are Free-l­iving (aquatic).

3. Study of worms causing a parasitic infest­ation in humans is called Helmin­tho­logy.

4. Body is Bilate­rally symmet­rical and the body organi­zation is of organ /organ system grade.

5. Body is Triplo­blastic i.e. body is formed from three germinal layers i.e. Ectoderm, Endoderm & Mesoderm.

6. Locomotary organs are absent in these animals but adhesive organs like suckers, hooks, etc are present in the parasitic form.

7. Epidermis is sometimes ciliated. On the body wall of parasitic animals, a thick cuticle is present i.e. Tegument. A thick cuticle protects the parasite from the digestive enzymes of the host.
– Muscles in the body wall are mesodermal. Below the epidermis, longit­udinal, circular, and oblique muscles are present.

8. These are acoelo­mate. In between various organs a solid, loose mesodermal tissue called Mesenchyma or Parenchyma is present.

9. Digestive system is incomplete (Blind sac body plan) and without an anus but in Tapeworm digestive system is completely absent. They absorb nutrients from the host directly through their body surface.

10. Skeleton, respir­atory and circul­atory systems are absent.

11. They respire through the body surface. Anaerobic respir­ation is found in internal parasites like Taenia.

12. Excretion occurs through specia­lized cells called flame cells or Soleno­cytes (Proto­nep­hridia). They also help in osmore­gul­ation.

13. Nervous system is ladder­-like and consists of a nerve ring and longit­udinal nerve cords.

14. They are Bisexual. The reprod­uctive system is complex and well developed. Fertil­ization is internal. Develo­pment indirect through many larva stages.

15. Some members like Planaria possess a high regene­ration capacity.

16. Examples-
(A) Planaria -
Found in freshw­ater, nocturnal, cannib­alic, slow creeping, omnivo­rous. Reproduce sexually as
well as asexually (Trans­verse binary fission), with good power of regene­ration. The pharynx can be everted.

(B) Fasciola hepatica (Liver fluke)
• Life history involves two hosts (Digenetic parasite)
(1) Primary host - Sheep & Goat
(2) Secondary host - Garden snail (Plano­rbis, Lymnea)
• Adult fluke is found in the bile ducts and liver of Sheep and causes Liver-rot or Cirrhosis disease.
• Shows many larval stages namely Miracidium (enters into snails body) →Sporocyst → Redia →Cercaria
→ Metace­rcaria →Eaten by sheep and develops into adult fluke.
• Infective stage for Primary host (Sheep) - Metace­rcaria
• Infective stage for Secondary host (Snail) - Miracidium (Free swimming)

(C) Schist­osoma (Blood fluke):
Found in veins of human bladder and intestine. Unisexual, Large male
carries female in a groove gynaec­ophoric canal on the ventral side. It shows sexual dimorp­hism.
• Life history involves two hosts (Digenetic parasite)
(1) Primary host - Man
(2) Secondary host - Garden snail (Plano­rbis, Lymnea)
MiracidiumSporocystCercaria larvae are found.
• Larva enters the human body by boring in the skin while bathing in ponds.
It damages the liver & causes intestinal disorder - Schist­oso­miasis or Bilharzia disease.

(D) Taenia solium (Pork tapeworm):
Flat, white ribbon­-like.
• Body divided into (1) head or scolex with hooks & suckers (2) Neck-for forming new proglo­ttides
(3) long strobila approx 850 proglo­ttides. T. solium is a human gut parasite, Attached to the intestinal wall by hooks
& suckers. Anaerobic respir­ation. Hermap­hro­dite, Self-f­ert­ili­zation.
• Life history involves two hosts (Digen­etic)
(1) Primary host - Man
(2) Secondary host - Pig
• Develo­pment through many larval stages namely: Onchos­phere, Hexacanth, Bladder worm and
• Man gets an infection from underc­ooked pork containing encysted larvae cystic­erci.
• Infective stage for the primary host (Man) - Cystic­ercus.
• Infective stage for the secondary host (Pig) - Onchos­phere
• It causes the disease Taeniasis and Cystic­ercosis


1. Phylum includes roundworms that appear circular in cross-­sec­tion.

2. Nematodes are found everyw­here, they may be free-l­iving (aquatic and terres­trial) or parasites in plants and

3. They have long, cylind­rical bodies with tapering ends and without segmen­tation.

4. Symmetry - Bilateral,
Germ layer - Triplo­blastic,
Level of organi­zation - Organ-­system level and having tube within tube body plan.

5. Anterior end does not show a distinct head (Cepha­lis­ation absent).

6. Body wall consists of
(i) Cuticle - Nonliving, thick, and resistant to the digestive enzymes of the host.
(ii) Epidermis - Syncytial i.e. a continuous layer of cytoplasm having scattered nuclei.
(iii) Muscle layer - Only Longit­udinal muscle fibers present

7. They are Pseudo­coe­lomate animals, the body cavity is there between the body wall and digestive tract which is not lined by a mesodermal epithelium i.e. Pseudocoel (developed from embryonic blasto­coel)

8. Skeleton is absent but fluid pressure in the pseudo­coelom maintains body shape. It is called Hydros­kel­eton.

9. Digestive tract is complete and differ­ent­iated into mouth, pharynx, intestine, and anus.
The pharynx is muscular and well developed. It is used to suck liquid food. The intestine is non-mu­scular.

10. Respir­ation is through the body surface by diffusion.

11. Excretory system is H-shaped and consists of excretory canals (Proto­nep­hridia) which remove body wastes from the body cavity through excretory pores. They develop from an embryonic "­Renette cell". The excretory matter is ammonia.

12. Nervous system comprises a nerve ring (Brain) and longit­udinal nerve cords. Sense organs like Papillae (tango­rec­ept­ors), and Amphids (chemo­rec­eptors) are present on lips while Phasmids (chemo­rec­eptors) are found on
the tail.

13. Reprod­uction system is developed and the sexes are separate (Dioec­ious). Fertil­ization is internal and develo­pment may be direct or indirect.

14. Sexual dimorphism is present.
In Ascaris male is smaller than the female and curved from its caudal end. Male has Pineal setae for copula­tion. The genital tract joins with the digestive tract to form the cloaca. Female is larger than male and straight at both ends. Genital and digestive tract open indepe­ndently (Cloaca absent).

15. Eg.
(1) Ascaris - Roundworm (in the small intest­ine), larva - Rhabdi­tif­orm­/Rh­abd­itoid
(2) Ancylo­stoma - Hookworm (in the small intestine)
(3) Wuchereria - Filarial worm (Vivip­arous)
• Digenetic parasite that causes Filari­asi­s/E­lep­han­tiasis disease.
• Carrier host is a female Culex mosquito.
• Adult mainly infects lymph vessels and lymph nodes in humans.
(4) Dracun­culus - Guinea worm (Madina worm) or Fiery serpent (Digenetic - Cyclops as interm­ediate host)
(5) Enterobius - Pinworm or seat worm (in the large intestine)
(6) Trichuris - Whipworm (in the intestine)
(7) Rhabditis - Free-l­iving nematode
(8) Trichi­nella - Infection in intestines and striated muscles (vivip­arous)


1. Free-l­iving is found in moist soil (Terre­str­ial), freshwater or marine but few are parasites.

2. Body is soft elongated, cylind­rical, and divided into segments or metameres by ring-like grooves called Annuli.

3. They are bilate­rally symmet­rical, triplo­blastic, and have an organ system level of organi­zation with the tube within the tube body plan.
• They are metame­rically segmented and coelomate animals.
• Anterior end has a distinct head with sense organs in a few annelids. (eg: Nereis)

4. They have Chitinous Setae and lateral muscular appendages called Parapodia for locomo­tion.

5. Body wall consists of
(i) Cuticle - Moist and elastic
(ii) Epidermis - Living layer that secretes dead cuticle outside
(iii) Muscle layer - Contains circular and longit­udinal muscles which help in Locomotion

6. Body cavity is a true coelom lined by mesodermal coelomic epithe­lium. (Schiz­oco­el/­First Eucoel­omate). It is filled with coelomic fluid that serves as a hydros­tatic skeleton.

7. Digestive tract is complete, straight, and extends through the entire body. Digestive glands are developed for the first time in Annelida.

8. Respir­ation is through moist skin (Cutaneous respir­ation), Some have gills (branchial respir­ation).

9. Circul­atory system is the closed type and a pulsatile heart is present.
• The blood is red with hemogl­obi­n-like pigment which remains dissolved in plasma (Eryth­roc­ruo­rin). It has amoeboid corpuscles only. (RBCs absent)

10. Excretory organ is Nephridia (sing. nephri­dium). They also help in osmore­gul­ation. Excretory matter (1) Ammonia in aquatic form (2) Urea in landform

11. Nervous system consists of a nerve ring (Brain) and a solid, double, and ventral nerve cord with ganglia.

12. Reprod­uction is sexual, Nereis is dioecious but earthworms and leeches are monoec­ious.
• Develo­pment is direct or indirect with free swimming ciliated trocho­phore larva.

13. Examples:
1. Nereis - Sandwarm/ Ringworm
(a) Cephal­isation is present.
(b) Parapodia helps in locomo­tion.
(c) Unisexual
(d) Larva is trocho­phore
2. Pheretima - Earthworm
(a) Cephal­isation absent
(b) Setae for locomotion
(c) Bisexual or hermap­hrodite
3. Hirudi­naria - Freshwater leech (Blood­sucking leech)
(a) Cephal­isation and setae absent
(b) Parapodia and setae absent
(c) Bisexual
(d) Hirudin (antic­oag­ulant) present
4. Aphrodite - Sea mouse


1. Arthropoda is the largest phylum of Animalia which includes insects. Over two-thirds of named species on earth are arthro­pods.
2. They may be aquatic (marine and freshw­ater) or terres­trial, free-l­iving, and sometimes parasitic.
3. Body is Bilate­rally symmet­rical, Triplo­blastic with organ system level of organi­zation
4. They are metame­rically segmented and coelomate animals.
5. Body is divided into three regions Head, thorax & abdomen, but in some head and thorax are fused to form cephal­othorax (Prosoma)
6. Unique features
(i) They have jointed appendages for different functions. (arthro - jointed, poda - foot/a­ppe­nda­ges).
(ii) The body of Arthropods is covered by a Chitinous exoske­leton.
7. Body cavity around the viscera contains blood and the coelom filled with blood is called the haemocoel.
8. Digestive Tract is complete and they can feed upon all kinds of food substa­nces.
9. Respir­ation by gills (e.g. Prawn), Book-gills (e.g. King crabs). The tracheal system (e.g Insects), Book-lungs (e.g. Scorpion), The trachea carries oxygen directly to the body cells.
10. Circul­atory system is Open type i.e. blood flows in open tissue spaces and haemocoel instead of blood vessels. Blood is colourless and called Haemolymph (e.g. Insect). Respir­atory pigment absent. Copper­-co­nta­ining pigment haemoc­yanin is found in some arthropods (e.g. Prawn).
11. Excretory organs are - Antennary or green glands (e.g. Prawn), Coxal gland (e.g. Scorpion), Malpighian tubules (e.g. Insects) opening into the gut.
12. Excretory matter is Ammonia in aquatic animals and Uric acid in land animals.
13. Nervous system comprises a nerve ring and a double, solid, and ventral nerve cord bearing ganglia.
14. Head is distinct [ High degree of cephal­iza­tion]
15. Sensory organs like simple eyes, compound eyes or both, antennae, statocyst, and anal cerci are found.
16. They are mostly dioecious. Fertil­ization is usually internal but few aquatic forms have external fertil­iza­tion. Gonads have ducts. Sexual dimorphism may be present. They are mostly oviparous.
17. Develo­pment may be direct or indirect.
18. Animals of Arthropoda are the most successful invaders of terres­trial enviro­nments among invert­ebrates due to the presence of (i) Cuticle (ii) Appendages (iii) Wings

19. Examples:-
• Econom­ically important insect - Apis (Honey bee), Bombyx (Silkw­orm), Laccifer (Lac insect)
• Vectors - Anopheles, Culex, and Aedes (mosqu­itoes)
• Gregarious pest - Locusta (Locust)
• Living Fossil - Limulus (King crab)
• Others - Butterfly, Scorpion, Prawn, Spider, Cyclops, Centipede, Millipede, Peripatus, etc.

(i) Biting and chewing - Grassh­opper, Cockroach, Termites, Caterp­illars.
(ii) Piercing- sucking - Mosqui­toes, Bugs, Tse-tse fly
(iii) Chewing- lapping type - Honey Bee
(iv) Sponging type - Housefly.
(v) Siphoning type - Butter­flies, moths

21. Muscles are stripp­ed/­str­iat­ed/­vol­untary (first time developed in Arthro­pods)

22. Due to the presence of joints, muscles are separate or arranged in bundles in them.

23. Class Arachnida (Octapoda)
- Cephal­othorax bears 1 pair of Chelic­erae, 1 pair of Pedipalps for feeding & 4 pairs of walking legs
– Antennae absent
- Respir­ation - Trachea or book lungs
- Excretion - Coxal gland or Malpighian Tubules or both
- Develo­pment- Direct
1. Palamnaeus - Scorpion (vivip­arous and last segment modified into poison sting)
2. Lycosa­/Ag­elena– Spider
3. Ticks and Mites