Zoology

  CLASSIFICATION PHYLUM ARTHROPODA (Jointed appendages). SUB-PHYLUM CRUSTACEA (Biramous appendages). CLASS : BRACHIOPODA (Trunk appendages as gills). COMMENTS : • Commonly called 'water flea'. •Microscopic, attain a length of about 2 mm. • Body is oval & laterally compressed with a ventral beak on head & sharp caudal spine. •Head bears reduced uniramous antennules, & two very large biramous antennal. •A thin bivalved carapace covers the body except the head. • Carapace is transparent. • Sessile compound eyes are united to large structure. • 5 pairs of thoracic appendages food an efficient food gathering organ. • Abdominal appendages are absent. • Sexes are separate. • Brood pouch present in female but absent in males. Development of eggs take place in brood pouch.

CLASSIFICATION : Phylum :Arthropoda(Jointed legs) Sub-phylum :Chelicerata (Feeding appendages called chelicerae) Class : Arachinida (possess both lungs and tracheae). COMMENTS: • Commoly called as scorpion. • Body is elongated, segmented & differentiated into anterior prosoma and posterior opisthosoma. •Opisthosoma is sub-divided into a broad anterior mesosoma & a narrow posterior metasoma. •Prosoma is covered dorsally by a carapace. •Body is encased in chitinous covering. •Mesosoma is composed of 7 broad segments & metasoma of 5- narrow segments. • Last metasomatic segment is telson containing a sting. Ventrally the sternum of 1st segment contains a pair of genital openings. •Metastoma is limbless. •Sexes are separate without sexual dimorphism and Viviparous. • Habit & Habitat : It is a nocturnal arthropod. Found in sand. • Distribution : cosmopolitan distribution.

CLASSIFICATION : Phylum :Arthropoda (Jointed legs) Subphylum :Chelecerata (Feeding appendages called chelicerae) Class : Merostomata (exhibit pseudocopulation during mating). COMMENTS : • It is commonly known as king crab & it is a marine arthopod found burrowing in sand. • Body is comprised of anterior cephalothorax or prosoma & a posterior-opisthosoma. •Cephalothorax is broad, convex above & concave below & bears a pair of median & a pair of lateral eyes andthree longitudinal ridges above. •It also bears six pairs of non-locomotor limbs below around the mouth. All the legs,except the last pair, are chelate. •The opisthosoma is divided into mesosoma, metasoma & belson & is movably articulated with prosoma. • The first pair of appendages is united to form a genital operculum whereas remaining five pairs bear book gills or book lungs. • Malphigian tubules absent & excreation through coxal glands. •Regarded as living fossil. Indirect development.

 CO MMENTS : • Bilaterally symmetrical, primitively coelomate,Segmented protostomes. •Coelom reduced to the portions of the reproductive & excreatory systems. •Body segments primitively associated with one pair of jointed appendages. •Body divided into two or more tagmata (regions): -In mandibulates a head, with sensory and feeding functions, and trunk, often subdivided into a thorax (locomotory) & abdomen (digestive & respiratory functions). -In chelicerates a prosoma, with feeding & locomotary functions, and an opisthsoma, with digestive & respiratory function. •Exoskeleton typically chitinous (α-chitin) • Digestive system is complete with large stomodeal & proctodeal region lined by chitin in between it's midgut •Sense organs include sensillium & compounde eyes Brain tripartite. •Cardiovascular system (open) in which haemolymph is pumped by a heart. •Excreatory system includes saccular excreatory organs & Malphigian tubules. •Generally diocious, i...

  EVOLUTION OF COELOM Body cavity - A body cavity can mean any internal space or a series of spaces present inside body.   Coelom - The coelom is defined as a liquid filled cavity in the mesoderm. It develops in, and is surrounded by the embryonic mesoderm .  Pseudocoelom - The body cavity is formed by a persisting of the blastocoel . This is simply a space between the digestive tract and that part of the body wall not bounded by mesoderm. According to the nature of body cavities there are three major groups of triploblastic animals ↳ Acoelomata ↳ Pseudocoelomata ↳ Coelomata or eucoelomata 1) Acoelomata No body cavity or coelom is present. Embryonic mesoderm remains as a solid layer, space betweeen endoderm (gut wal) and ectoderm (bodywall) is filled with mesenchyme and muscle fibres . Ex. Porifera, Coelenterata, Ctenophora, Platyhelminthes and Nemertinea     2) Pseudocoelomata Body space is a pseudocoelom or false coelom . It is a persistent bla...