Phylum Echinodermata

20.6.8

ECHINODERMATA

q Non-segmented animals. Adult with radial symmetry characterized by five or more radiating area. The larvea echinoderms were bilaterally symmetrical.

q The animals show no cephalization and no head or brain.

q  They are at the organ system level of organisation.

q The echinoderms are enterocoelomic, triploblastic deuterostomes

q There is no anterior or posterior, right or left, dorsal or ventral. Instead there is an oral surface and an aboral surface.

q They have a complete digestive system.

q They have an endoskeleton of dermal calcareous ossicles covered by an epidermis.

q The echinoderms possess a water vascular system and tube feet. The tube feet are the major locomotory system for most echinoderms.

§  The coelom is extensive, involving the water

vascular system and a large perivisceral cavity.

§  The circulatory and excretory systems are reduced or absent.

§   Respiration is via the general body surface or special gills, tube feet, papulae, and etc.

§  The nervous system consists of a nerve ring and 5 radial nerve cords.

§   Locomotion is by tube feet, spines or arm movement.

 Sexes are separate, fertilisation external and development involves a free-swimming, bilaterally symmetrical larva

Classification of Echinodermata

•        Five classes:

                              i.            Class Asteriodea ( Asterias)

                           ii.            Class Holothuroidea ( Holothuria )

                        iii.            Class Crinoidea ( Sea lily)

                         iv.            Class Echinoidea ( Sea urchin )

                            v.            Class Ophiuroidea ( Ophi

ECHINODERMATA

v     ASTEROIDEA

v     HOLOTHUROIDEA

v     CRINOIDEA

v     ECHINOIDIA

v     OPHIUNOIDEA

ASTEROIDEA

CHARACTERISTICS :

·    STAR SHAPED WITH ARMS,NOT SHARPEDLY MARKED OFF

·    AMBULACRAL GROOVE OPEN,TUBE FEET ON ORAL SIDE

·    TUBE FEET OFTEN WITH SUCKERS

·    EXAMPLE : SEA STARS

HOLOTHURIDAE

CHARACTERISTICS :

·    CUCUMBER SHAPE WITH NO ARMS

·    SPINE ABSENT

·    AMBULACRAL GROOVES CLOSED

·    TUBE FEET WITH SUCKERS

·    EXAMPLE : SEA CUMBER

CRINOIDEA

CHARACTERISTICS :

·    FIVE ARMS BRANCHING AT THE BASE AND BEARING PINNULES

·    CILIATED WITH AMBULACRAL GROOVES ON ORAL SURFACE WITH TENTACLES LIKE TUBE FEET

·    EXAMPLE : SEA LILIES

ECHINODIA

CHARACTERISTICS :

·    MORE OR LESS GLOBULAR OR DISC SHAPED WITH NO ARMS

·    MOVABLE SPIRES

·    AMBULACRAL GROOVE IS CLOSED

·    TUBE FEET WITH SUCKERS

·    EXAMPLE : SEA URCHINS,PURPURATUS

OPHIUNOIDEA

CHARACTERISTICS :

ü     STAR SHAPED WITH ARMS SHAPED MARKED OFFCENTRAL DISC

ü     AMBULACRAL GROOVE IS CLOSEDTUBE FEET WITH SUCKERS AND NOT FOR LOCMOTION

•        Most echinoderms have calcite skeleton.  such as ophioroids (brittle stars).

•        The coelom of Echinodermata importance not only in carrying and distributing nutrients, respiratory gases, excretory and storage products but also in functioning as a water‑vascular system.

•        Skeleton in form of rods supporting arms and other projections; such as:

•        Asteroids get from the starfish and echinoids can get from sea urchins.

•        It forms more‑or‑less rigid capsule.

•        isolated spicules in the integument.

•        Star fish can threaten the coral reef.

•        Holothuria function in the medical field.

•          Holothuroids can be found in sea cucumbers.

Phylum Molusca

Kingdom Mollusca

Characteristics

·         Multicellular animals

·         Bilaterally symmetrical

·         Reached an organ system level of organization

·         Triploblastic

·         Protosmial

·         Scizocoelomates

·         Head with eyes usually on tentacles

·         Have a complete digestive system with extracellular digestion

·         Largest phylum of living organisms outside of the Athropoda

·         Primarily aquatic organisms found in almost all marine and freshwater habitats

·         Also live in terrestrial environments although they avoid direct sunlight areas

·         Open circulatory system that has a heart, several major arteries, blood sinuses and respiratory blood pigments

·         Gas exchange is across gills, lungs, or the mantle wall

·         Excretion through the use of metanephridia

·         Nervous system of most consists of 3 or 4 pair of ganglia, interconnecting fibres and sensory cells

·         The muscles pull against the shell or a hydrostatic skeleton

·         Dioecious and reproduce only sexually

Classification of Mollusca

                     I.        Class Gastropoda (snails, sea slugs)

                   II.        Class Bivalvia (clams, mussels, oysters, scallops)

                 III.        Class Cephalopoda (squids, octopus, nautilus, cuttlefish)

Class Gastropoda

Characteristics

·         Have shells

·         Asymmetrical

·         Have a single, often spirally coiled shell (univalve), undergo a developmental process called torsion, possess a mantle and a muscular foot used for locomotion

·         Use radula to scrape food

Torsion (twisting) in Gastropoda

·         Twisted nearly 180 in a counterclockwise direction

·         Gills, anus and reproductive glands, which lie directly over the head

Advantages and disadvantages of tortion

·         Increased water currents

·         Allowing the animal to withdraw more deeply into the shell

·         Disadvantages is the excrete from the anus comes out just above the head

·         The mantle cavity is designed so the poisonous wastes are quickly dispersed into the water and are quickly washed away from the Mollusca

Class Chephalopoda

·         Cephalopoda means “head foot”

·         Completely merged head and foot, with a ring of arm and/or tentacles surrounding the head. The arms, tentacle and funnel are all derivatives of the foot

·         The mantle surrounds the visceral sac and possesses strong muscles required for contraction of the cavity and respiration

Class Bivalvia

·         Includes clams, oysters, mussels, and scallops

·         Have a shell consisting of two rounded plates called valves joined at one edge by a flexible ligament called the hinge

·         Have no head, very little cephalization and no radula

·         A foot is present but laterally compressed

·         Generally have a large mantle cavity with ciliated gills that hang down on either side of the visceral mass

·         All bivalves are filter feeders

                                               

Phylum Annelida

Phylum annelida

UNIQUE CHARACTERISTIC OF ANNELIDA

-         The phylum Annelida contains segmented worms

-         Bilaterally symmetrical and tiploblastic

-         Body cavity is a true coelom,often divided by internal septa

MERISTEM

-         Have an anterior prostonium and posterior pygidium both nonsegmented

-         Each segmen usually bears one or more chitinous bristles called setae; help anchor segments

NERVOUS SYSTEM

-         Consists of  brain which is connected to a pair of ventralnlongitudinal nerve cord with a ganglion in each segmented

CIRCULATORY SYSTEM

-         Closed circulatory system in which the blood is always enclosed within blood vessel that run the length of the body and branch to every segmented

EXCRETORY SYSTEM

-         With ciliated funnels that remove waste from the coelomic fluid open to the outside via excretory pores

REPRODUCTIVE SYSTEM

-         Most annelids are hermaphoroditic but their usually cross fertilizers

THERE ARE THREE MAJOR CLASSES WITHIN THE PHYLUM ANNELIDE

CLASS POLYCHAETA

-         Mostly marine worms such as Nereis

-         Each segment is equipped with a pair of fleshy paddle-like structures-parapodia used in locomotion

-         Most are marine

CLASS HIRUDINEA

-         The leeches such as hirudo

-         Prostomium is well equipped with sensory and fedding structure

-         Body is dorso-ventrally flattened

CLASS OLIGOCHAETA

-         Many of the morphological structures are reduse when compared to the polychaetes

-         Prostomium lacks sensory structure

-         Parapodia are absent each segmented usually contains one or more pairs of setae used in locomotion