FSc Notes Class XI Biology Phylum Echinodermata

FSc Notes Class XI Biology Phylum Echinodermata 1st Year Biology Notes Online Taleem Ilmi Hub Class 11

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Phylum Echinodermata

GENERAL CHARACTERS

HABIT AND HABITAT

The Echinodermates are exclusively marine including the largest invertebrate “Giant Squids.”

EXTERNAL FEATURES

• Symmetry usually radial, nearly always pentamerous.
• Body shape is rounded to cylindrical or star like.
• Surface of the body is rough.
• Body wall consists of an outer epidermis, a middle dermis and inner lining of peritoneum.

INTERNAL FEATURES

• Endoskeleton consists of closely fitted plates forming shell usually called “THECA,” may be composed of separate small “OSSICLES.”
• Coelom is spacious, lined by peritoneum and occupied mainly by digestive and reproductive systems.
• Presence of “Water Vascular System” is most characteristic feature.
• Alimentary tract is usually coiled.
• Circulatory or Haemal or blood lacunar system is typically present.
• Excretory system is wanting.
• Nervous system is primitive, consists of ganglionated nerve cord.
• Sense organs are poorly developed.
• Sexes are usually separate.
• Reproduction is usually sexual, fertilization is external.

WATER CANAL SYSTEM

Water canal system is unique in possessing an internal closed system of canals containing a watery fluid.

REGENERATION

Regeneration of lost part is common

IMPORTANCE OF WATER CANAL SYSTEM

These canals are provided with tubular protrusions called “Tube Feet,” which serve a number of functions like locomotion, anchoring to hard surfaces, grabbing the prey, diverting food particles towards mouth and in some cases also respiration. The watery fluid is drawn from the surrounding water through a perforated disc called the “Madreporite.”

EXAMPLE

Star Fish, Brittle stars, Sea urchins, Sea-cucumbers, Sea-Dollar, Sea-lilies and Feather stars.

LARVA

Bipinnaria larva