class 9  characteristics of  nematoda, artropoda,mollusca,echinodermata and protochordata

Nematoda is a phylum under Kingdom Animalia.

 These are a group of invertebrates without vertebrate column. 
General characteristics of Nemtoda
Nematoda are bilaterally symmetrical, triploblastic parasitic worms with a cylindrical body.
Nematoda get their name from two Greek words - “nema,” which means “thread,” and “ode,” which means “like”. Nematodes can be free living or parasitic. e.g. Ascaris. 
Nematodes are unsegmented round worms which are considered to be pseudocoelomate organisms.
Nematodes possess complete alimentary canal.
Sexes are separate in nematodes and they exhibit sexual dimorphism. Eggs are protected by thick walls to overcome unfavourable conditions.
e.g. Ascaris, Ancyclostoma, Dracunculus etc.

Phylum Arthropoda - Characteristics

·         EXOSKELETON In most arthropods the body is covered with chitonous. ...

·         METAMERISM. ...

·         JOINTED APPENDAGES. ...

·         DOUBLE VENTRAL NERVE CORD Ventral nerve cord with. ...

·         OPEN CIRCULATORY SYSTEM A dorsal (upper) vessel directs blood. ...

·         BILATERAL SYMMETRY.

 MOLLUSCA

  Unsegmented soft body with bilateral symmetry.

  Presence of an internal or external shell.

  A toothed tongue (made mostly of chitin) called the radula.

  A mantle which is a fold in the body wall that lines the shell.

eg; fresh water mussel  snail pila.

 ECHINODERMATA

• Free living exclusively marine forms.

• Adults are radially symmetrical while larvae are bilaterally symmetrical.

• Body is represented by a central disc covered by ossicles with spines called pedicellaria.

• Disc may bear extensions called arms.

• Digestive system is complete.

• A unique ambulacral or water vascular system is present.

• Tube feet are present for locomotion and respiration. Tube feet are extended and retracted by variation in hydraulic pressure of the fluid in them and contraction of their muscles.

• Nervous system has a central nerve ring with five radiating nerves.

• Reproduction is sexual. Sexes are separate. Development is indirect.

• Show very high power of regeneration.

• Tube feet are for feeding as well.

o    General characteristics of protochordata -

o     

·         Elastic, solid, ensheathed rod-like structure of vacuolated turgid cells callled notochord is present may be through out the life or only during early embryonic development mentioned above.

·         Paired pharyngeal gill slits( pharynx is perforated by gill slits) is present which takes part in circulation of water for respiraton and in higher chordates , they occur only in embryonic stage.

·         Ventral heart is present and gut lies ventral to nerve cord.

·         Post-anal tail is present and if present then it's for balancing.

·         They are bilaterally symmetrical, triploblastic, coelomate with organ system level of organisation.

Marine habitat.