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Date & Time : 22, December 2024 17:15
General Characteristics of Arthropoda
- They are triploblastic,bilaterally symmetrical,metamerically segmented animals.
- Body covered with thick chitinous cuticle;forms exoskeleton.
- Body cavity is haemocoel , true coelom reduced to spaces of genital excretory organs.
- Digestive tract is complete. Mouth and anus lie at opposite ends.
- Circulatory system open with dorsal heart.Capillaries absent.
- Various means of respiration: by gills or general body surface in aquatic forms, tracheae or book lungs in terrestrial forms.
- Excretion by coelomoducts,malphigian tubules,green or coxal glands.
- Sexes generally separate.
- Internal fertilization with indirect development observed.
Classification of Arthropoda
A Few Examples
1.Limulus
Common name-King crab.
Habit and habitat- marine species, found burrowing in the sand.
IDENTIFYING CHARACTERS:-
- Body division- body is divided into prosoma and opisthosoma.
- Prosoma- anterior portion of the body, consisting of eyes and appendages.
- Eyes- There are two pairs of eyes in which one pair is of median eyes and other one is lateral.
- Appendages- There are six pairs of appendages in which first pair is of chelate chelicerae, four pairs of chelate legs and the last one of non chelate legs.
- Opisthosoma- it is hexagonal in shape and is the posterior portion of the body. It is articulated with prosoma. It consists of six mesosomal segments and unsegmented metasoma (caudal spine), and six pair of appendages
2.Sacculina
Common name-root headed barnacle.
Habit and Habitat-parasitic mode of life, live as parasite on crab
IDENTIFYING CHARACTERS:-
- Body- body is extremely degenerated.
- Segmentation-There is no segmentation in Sacculina.
- Mouth- mouth is absent.
- Appendages- absent.
- Ventral surface- There is a fleshy tumor attached by peduncle to the abdomen.
- Peduncle- it consists of delicate root -like filaments which absorbs nourishment from the host body.
- Mantle cavity- mantle cavity opens to the hind end of the parasite.
- Anus- anus is entirely absent.
- Reproduction- indirect (larval form iscirripede- nauplius). Sacculina is a hermaphrodite.
3. Palaemon
Common name:- prawn.
Habit and habitat:- it is freshwater species, like to live in ponds, rivers, lakes and ditches etc.
Distribution:- commonly found in India.
IDENTIFYING CHARACTERS:-
- Body- Body is elongated and compressed.
- Body shape- Body is spindle shaped.
- Body division- Body is divided into anterior and posterior parts. The anterior one is known as cephalothorax and the posterior one is called abdomen.
- Cephalothorax- It is the large anterior portion of the body which is rigid and unjointed. It consist of head( five segments), thorax(eight segments) and carapace which covers the whole cephalothorax.
- Thorax- It contain thoracic appendageswhich are maxillipedes( three pairs) and walking legs
- Abdomen- It is the posterior part of the body which consists of telsons ( six distinct and movable segments) and aterminal conical piece.It also bears six pairs of biramous pleopods.
- Each segment of the body contain a pair of joint appendages.
4.Palamneus
Common name:- scorpion.
Habit and habitat:- It is nocturnal in habit. It lives in burrows or under stones.
Distribution:- found on all major land masses except Antarctica.
IDENTIFYING CHARACTERS:-
- Body- Body is elongated and segmented but there is no internal segmentation.
- Body shape- catterpillar-like cylindrical.
- Body length- 2-3 inches.
- Skin- skin is velvety- like containing numerous papillae (with spines).
- Body division- Body is divided into mesosoma and metasoma.
- Mesosoma- It consist of seven segmented sternum.
sternum of 1st segment -genital opening
sternum of 2nd segment- pectine(one pair)
sterna of 3rd-6th segment- stigmata (one pair each).
sternum of 7th segment- opening of book lungs.
- Metasoma- It consists of five segments but there are no appendages. There is a sting containing ampulla and a spine at last segment.
- Excretion- Excretory organs are malphigian tubules and coxal glands.
- Sexes are separate having a network of gonads.
- Viviparous.
5.Julus
Habit and habitat- live in dark and damp places under stones.
IDENTIFYING CHARACTERS:-
- Body- elongated, cylindrical and perfectly segmented.
- Legs- each segment contain two pair of legs(exception- first four segment and last segment).
- Head- it consists of short and jointed antennae ( 7 in number), mandibles (one pair) and maxillae which constitute the gnathocholarium.
- Stick glands- present, located along the sides of the body.
- Jaws- absent.
- Genital pores- located at the third segment behind the head.
6.Queen termite
Habit and Habitat- inhabits underground galleries,termitaria or huge moulds.some may also be found burrowing in wood.
IDENTIFYING CHARACTERS:-
- It is sexually mature female of colony.
- Body- elongated and cylindrical,divided into head, thorax, abdomen.
- Head and thorax are comparatively small.
- Abdomen enormously swollen;has a large no. of fertilised eggs.
- Mouth parts biting type
7.Melolontha
Common name:- cockchafer beetle.
Habit and habitat:- it is a terrestrial and burrowing insect.
Distribution:- commonly found in India.
IDENTIFYING CHARACTERS:-
- Body- Body is ovate,divided into head , thorax and abdomen.
- Head- Small and flexed ventrally,consists of a large pair of compound eyes and a pair of antennae.
- Mouth parts biting and chewing type.
- Thorax- consists of legs(3 pairs) and wings(2 pairs).
- Elytra the hard leathery fore wings form elytra; not used in flight.
- Hind wings membranous andcovered by elytra during resting conditions.
- Abdomen consists of 10 segments.
8.Scolopendra
COMMON NAME- centipede.
HABIT AND HABITAT-live in damp places under stones.
FOOD-feed on insects, worms,and spiders etc.
IDENTIFYING CHARACTERS:-
- Body- elongated, dorsoventrally flattened and segmented.
- Body division- Body is divided into head and trunk.
- Head- it consists of antennae (one pair), mandibles ( one pair) and maxillae ( two pair).
- Trunk- it consists of numerous segments, trunk appendages (maxillipedes) containing poison glands.
- Claw- sharp, located at the 1st pair of trunk appendages.
- Legs-one pair of leg at each and every segment.
- Genital aperture- located posteriorly at the end of body.
9.Hippa
Common name- mole crab
Habit and Habitat-lives in burrows in sand in the sea.
Food-feeds like an earthworm swallowing the sand through which it burrows.
IDENTIFYING CHARACTERS:-
- Body- ovate with large cephhalothorax
- Carapace is smooth and mouth parts are poorly developed.
- Head- it consists of eyes,biramous antennules(1 pair) and uniramous large antennae(1 pair)
- Rostrum simple and pointed.
- Legs- flattened and curved.
10.Squilla
Habit and habitat- it is predatory and marine in nature. It is found in burrows of sand or mud.
IDENTIFYING CHARACTERS:-
- Body- Body of Squilla is elongated and segmented.
- Body division- Body is divided into three regions i.e. head, thorax and broad abdomen.
- Carapace - thin and uncalcified; last three segments uncovered.
- Rostrum- covers anterior head region.
- Pleopods large and biramous; first five bear gills, sixth forms large uropods.
11.Balanus
Common name- rock barnacle.
Habitat- live below high water mark (attached to rocks).
IDENTIFYING CHARACTERS:-
- Body-calcareous shell.
- Shell- consists of six plates, lateral plates (two pairs), a single carina and a rostrum.
- Scuta and terga are present in the folds of shell.
- Thoracic legs (six pairs) sweep in food particles via shell opening.
- Shell is directly attached to rocks, no peduncle.
12.Daphnia
Common name-water flea.
Habit and Habitat-fresh water species, found in ponds and streams.
IDENTIFYING CHARACTERS:-
- Body- Body covering- enclosed in a bivalved carapace.
- Length- 1-2mm in length.
- Segmentation- imperfectly segmented.
- Carapace- bivalved, and ends into a pointed dorsal spine.
- Head- rounded, bearing antennae, antennules and a compound sessile eye.
- Thorax- consist of 5 pairs of appendages.
- Abdomen- bears no appendages.
13.Lepas
Common name- goose barnacle or ship barnacle.
Habit and Habitat- found all over the world.
Food- feed on minute organisms.
IDENTIFYING CHARACTERS:-
- Body- divided into pedicel and capitulum.
-Pedicel:- consist of body proper, and wrinkled skin covers it.
-Capitulum:- it consist of 5 calcareous plates, 2 scuta (proximal), 2 distal terga and adorsal carina. A bivalved carapace covers it.
- Mouth- it consists of mandibles (one pair) and maxillae ( two pair).
- thorax consists of jointed biramous appendages ( six pairs).
14.Pediculus
Common name:- human louse
Habit and Habitat- may be found as ectoparasite of man
IDENTIFYING CHARACTERS:-
- Body- dorso ventrally flattened,pale in color.
- Head consists of a pair of compound eyes and a pair of five segmented antennae.
- Mouth parts piercing and sucking type.
- Abdomen nine segmented.
- Sexes are separate. In males post. end is turned upwards.
15.Apus
Common name- tadpole fish or tadpole shrimp.
Habit and Habitat- freshwater species, found in all over the world.
IDENTIFYING CHARACTERS:-
- Body- elongated.
- Length- 20-30 mm.
- Carapace- horse- shoe shaped, covers the 2/3 of dorsal surface, bearing shell glands on its lateral surface.
- Head- broad and depressed. It consist of eyes (a pair), a median eye and a dorsal organ above.
- Antennae- antennules and antennae are present below the head.
- Reproduction- parthenogenesis occurs.
- Swimming appendages- present, but absent in few segments in females.
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