Question

1. For each of these groups, describe the basic morphology, feeding, skeleton, reproduction, and ecological role:  porifera, cnidaria, platyhelminthes, Mollusca, arthropoda, Echinodermata.  

Answer 1

PORIFERA-primitive multicellular animal.All aquatic(mainly marine but few found in freshwater). They are sessile, solitary or colonial.whole body covered with many pores(mouth lets opening) called Ostia and one central opening of exit osculum. They have various forms and shape with an irregular shape generally Asymmetrical( Leucosolenia -radial symmetry). the body wall consists of 1)outer ectoderm (dermal layer)/ pinacoderm-pinacocytes(flat cell) and porocytes (oval) 2)inner ectoderm(choanocytes layer)/choanoderm-collar cell or choanocytes (flagellated ) 3) between two-layer there is gelatinous material Mesenchyma. Mesenchyma consist of different amoebocytes cells and these are - Scleroblast(for skeleton), spongioblast(for skeleton),thesocytes(for food storage),phagocytes (to engulf by phagocytosis)trophocytes (for distribution of food), archaeocytes(formation of ova and spermatozoa),colonocytes(connective tissue cell),chromocytes(pigmented),myocytes(highly contractile).Body wall encloses a large central cavity -spongocoel/paragastric cavity having small cavitied canals. collar cell with flagella is lined in the spongocoel cavity. this canal system helps in nutrition, respiration, and excretion.SKELETON is internal consist of small calcareous Spicules-calcoblast/siliceous or fine spongin fibre-sponginoblast, located in the mesenchyme. REPRODUCTION-asexual by budding or fragmentation.special cell mass Gemmules containing archaeocytes.in an unfavorable condition, they undergo internal budding called gemmulation, Sexual -hermaphrodite, fertilization internal and cross-fertilization(protogynous condition)

CNIDARIA-named on the basis of stinging cells. Mostly marine, few freshwater(Hydra), carnivorous, some are fixed or free-floating.dimorphic-POLYP -cylindrical in shape, mostly sessile (some motile), may be solitary or colonial, asexual or mouth and tentacle upward orientated, and MEDUSA -umbrella-like, free swimming, always solitary, sexual, mouth and tentacles downward directed. if both form found in a species- alternation of generation/ metagenesis. polyp produces medusa asexual and medusa form polyp sexually eg obelia. generally radial symmetry, some Anthozoans have biradial symmetry.they have 2 germ layers (ectoderm and endoderm) i.e diploblastic(mesogloea between 2 layers).TISSUE LEVEL OF ORGANISATION.cindoblast or chidocyte (contain stinging capsule as nematocyst)present on the tentacle and body, which are used for anchorage, defense and for the capture of prey.BODY may by supported by horny/calcareous exoskeleton eg corals.cavity have a single aperture. mouth serve both purposes (incomplete digestive tract/ blind sac. REPRODUCTION-asexual by budding(under favourable condition) and sexual (under unfavourable condition), bisexual, external and cross-fertilization(protandrous condition) and indirect. fertilization

PLATYHELMENTHES-include flatworm (dorsoventrally flattened), most primitive bilateral animals, free-living or parasite.oORGAN LEVEL OF ORGANISATION. TRIPLOBASTIC-body is formed from 3 layers(ectoderm endoderm and mesoderm)BILATERALLY SYMMETRICAL. locomotion organ absent but the adhesive organ is present like a sucker, hook( in the parasitic form). SKELTON SYSTEM IS ABSENT.BISEXUAL, REPRODUCTION-is complex and well developed.fertiliztion may be self or cross and internal, cleavage is spiral and determinate .development may be direct or indirect.some member have high regeneration capacity

ARTHROPA-found in water, land, sea, in plants and animals. they are colonial, gregarious, show parental care.BODY -BILATERAL, TRIPLOBLASTIC WITH ORGAN LEVEL OF ORGANISATION.consist of well-developed sense organs such as simple eye, compound eye, antennae, statocyst or balance organ. a compound eye consists of many similar units OMMATIDIA each having lense and capable of forming an image. they have a various shape with the externally segmented body. the body is mainly divided into 3 region-head, thorax and abdomen.some or all segment bear jointed appendages. BODY IS COVERED BY CHITINOUS EXOSKELETON.they are most successful invaders of terrestrial environment in invertebrate due to presence of cuticle, appendages and wings. SEX ARE SEPARATE. fertilization internal but few aquatic has external. gonads have ducts. larval stage undergoes a degree of metamorphosis.sexual dimorphism may be present .moslty oviparous, few viviparous.

MOLLUSCA-marine, some freshwater or on land.BODY is unsegmented with variety of shape. Neopilina is exceptionally segmented. BILATERAL SYMMETRY, few are asymmetrical. TRIPLOBALSTIC WITH ORGAN SYSTEM LEVEL.body is covered with calcareous shell with the district- head with sense organ (eye, tentacles), dorsal visceral mass/hump containing organ system, and ventral muscular foot for locomotion.thin fleshy fold or soft and spongy layer of skin form mantle or pallium. space between hump and mantle called the mantle cavity. mantle secretes an externally limy shell.shell is made up of calcium carbonate and conchiolin protein.SEX separate mostly oviparous fertilization external or internal

ECHINODERMATA-all marine, generally live at bottom and show moving.body shape is star like ,cylinderical like ,melon like disc like, flower like,bilateralin larva