Phylum Arthropoda : General Characters

what are the general characters of phylum arthropoda

Arthropoda is a largest Phylum of Kingdom Animalia, includes about 80% of all known animal species in the biosphere including terrestrial and aquatic biomes. The phylum includes insects, crustaceous, centipedes, millipedes, spiders etc. The word Arthropoda is derived from two Greek words, ‘arthro’ = joint and ‘podo’ = foot. Phylum Arthropoda is characterized by:

@. Segmented body plan

@. Paired jointed appendages

@. Chitinaceous exoskeleton


General characters of Phylum Arthropoda:

@. Cosmopolitan distribution

@. Presence of exoskeleton, made of chitin

@. Chitin= a structural homo-polysaccharide of N-acetylglucosamine linked by β-1, 4 glycosidic bond

@. Segmented appearance of body

@. Body bears paired jointed appendages

@. Bilateral body symmetry

@. Segmentation is heteronomous metameric (metamers are grouped to do similar functions)

@. Members show tagmosis (= grouping of multiple segments to a single functional unit)

@. Usually three tagmas (head, thorax and abdomen)

@. Members show ecdysis or moulting (= shedding of exoskeleton periodically)

@. Primary body cavity is hemocoel

@. Hemocoel accommodate internal organs

@. Compound eye present, however no image formations in the eyes

@. Eyes are only able to detect the direction of light

@. Image formation occurs in the main eyes of spiders

@. Ciliated structures are completely absent

@. Respiration is by gills (aquatic forms) or trachea or book lungs (terrestrial)

@. Circulatory system open, no blood vessels

@. The blood analogue is called haemolymph

@. Blood pigment is Hemocyanin (a copper containing pigment to carry oxygen)

@. Excretion is by green glands or by malpighian tubules

@. Nerve system ladder like with paired ventral cords running through all segments and form paired ganglia in each segment

@. Brain present, formed by the fusion of ganglia

@. Reproduction varies (internal or external fertilization)

@. Eggs are centrolecithal (yolk placed in the centre of the cytoplasm of ovum)

@. Triploblastic development (= blastula contain three primary germ layers – ectoderm, mesoderm and endoderm; triploblastic development results in bilateral body symmetry)

@. Scorpions are viviparous (eggs hatched inside the body of mother)

@. Scorpions show prolonged parental care

@. Larval stage present, which generally lack jointed limbs

@. Larvae undergo total metamorphosis to produce the adult form


Classification of Phylum Arthropoda:

Arthropods are classified into Five Sub-phylum and each then subdivide into classes (a total of 16 classes according to recent classification of animal taxa)


Phylum Arthropoda:

Sub-phylum (1). Trilobitomorpha (extinct arthropods)

Sub-phylum (2). Chelicerata (spiders, horseshoe crabs)

Sub-phylum (3). Myriapoda (centipedes, millipedes)

Sub-phylum (4). Crustaceae (crabs, prawns, shrimps)

Sub-phylum (5). Hexapoda (insects)

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