Phylum echinodermata

Phylum echinodermata:

The echinoderms are mostly marine animals. They include the sea stars, sea lilies, feather stars, star fishes, sea cucumber, sea urchin .some live in oceans and at great depth.

      Echinoderms are the most abundant group of animals that are available on the deep sea floor. Most of  them are slow moving animals and most use the tube feet(podia) for attachment in the bottom of the  sea.

      Although their free living larval stages are bilaterally symmetrical, most adult echinoderms show a basic five -point (pentamerous) radial symmetry. As radially symmetrical animals ,they lack cephalization. Thus adult echinoderms generally do not have anterior and posterior ends. Instead, the body surfaces are designated as being with either oral or aboral.

They have an internal skeleton compose largely of calcium carbonate. Typically, this skeleton bears projecting spines which give the body surfaces a spiny appearance.

       Their most distinctive feature is the WATER VASCULAR SYSTEM which consists of a series of fluid -filled canals. During  locomotion, the water vascular Canal operates like a hydraulic system. Echinoderms lack definite excretory system.

Characteristics of the   echinodermata

* Most echinoderms are typically pentamerous, that is the body is usually with five -radiating areas.

* They have skeleton  made of calcareous materials. The exoskeleton carries spines on them.

* The digestive tract is complete.

*Most echinoderms are dioecious (sex are separate) and fertilization is commonly external.

Classification of the phylum echinodermata

There are quite  a huge number of classes but five (5) classes of existing echinoderms are usually recognized

* Class of Asteroidea

* Class of Ophiuroidea

* Class of Echinoidea

* Class of Holothuroidea

* Class of Crinoidea

Class of asteroidea: They are the star fishes. They possess arms and a basically star-shaped body.

Class of Ophiuroidea :They are the brittle stars and the basket stars. They lack the anus and the tube feet lack suckers.

Class Holothuroidea :They are the sea cucumber. They are soft bodied animals. They have slender bodies which are elongated at both ends.

Class of Crinoidea : The Crinoids are the most primitive. They include the sea lilies  and the feather stars.

Class of Echinoidea :These are the sea urchins and the sand dollar. They are heart-like in shape  and the tube feet end with suckers.

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Preservation of animal species

Preservation of animal species 

Preservation  can be defined  as the use of chemical, physical or other            Processes to prevent  microbial
and physical damages to biological specimens with a view of retaining their  original  form and prolonging their  storage life.

    The procedure  for preservation of animal  specimens varies greatly from  one animal group  to another.
      In most cases, the animal must first be killed or narcotised in a suitable  way so as to leave the tissues  in a state ,which is proper for display.
     The specimen is then fixed in this  condition and finally preserved. This final preservation is normally made either in a solution of ethanol or methanal (formalin).

Techniques  in fixing and preserving animal materials
     Fixation is a chemical process, which stops autolysis  and stabilizes protein components of tissues so that in
subsequent processing the tissue retains as fully possible the form they had in life.
     Preservation allows materials to be stored indefinitely by destroying any microbial action, which could degrade the specimen.
    The choice of fixation will depend upon the animal material to be fixed and the purpose for which it is being fixed.
Narcotisation :This is also known as relaxation and is an interim technique for animals since many are highly contractile and assume  grossly distorted  postures if placed straight into fixative.

The main factors to be considered in 

Speed of penetration : This determines the size of specimen that can be fixed.
Hardening: Some chemical like ethanol  is particularly liable to cause tissues to harden on prolonged exposure to high concentration.
Shrinkage :Certain fixatives such as ethanol and mercuric chloride  cause  tissues to shrink thus distorting the specimen  significantly.

Preservation techniques

Wet preservation : Fhis is used mainly for animals and is usually preceded by narcotisation. The process of fixation is then comparatively straight forward. Most times, it is necessary to arrange the body and appendages of the animals using tape.

* A 5-10%v/v aqueous solution of formalin(=40% v tv aqueous  formaldehyde neutralized with calcium carbonate to prevent any acidity in the solution resulting in the slow dissolution of calcareous  structures.)
*50-70% ethanol : Ethanol is inflammable, highly volatile and tends to cause shrinkage and decolorization in soft bodied animals. Pass  them slowly through a graded series of concentrations to minimize this problem.

Dry preservation
This form of preservation is used mainly for vertebrate taxidermy and for arthropods  and other invertebrate species. The hard exoskeleton of arthropods are easily preserved in dry state since the skeleton  prevents collapse and loss of form upon drying.

Taxidermy : it is a type of dry mounting where the vertebrate is carefully skinned to remove the body and then replace with false body made of polystyrene, foam or cork etc.

Storage : Careful maintenance of specimen after fixation /preservation process is very important. The storage conditions for materials preserved either in wet or dry state.

Labelling : labelling must be comprehensive and contain information on the fixative and preservation processes  as well as ecologically and taxonomic details.

Reasons for animal preservation

* it prolongs the storage life of the  specimens.
*it prevents  the attack of micro–organisms like bacteria  and fungi that causes  spoilage.
* it helps in the preservation of large quantities of specimen needed for laboratory studies.
*extinct animals specimens can be preserved  for future study.

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