Current Affairs 11th Class

Category : 11th Class

(Gk. Porus = Pore; ferre = To bear)

Brief History : Robert Grant (1825) finally proved that sponges are animals, and coined the name ‘Porifera’ for these. Schulze (1878), Butschli (1884), Sollas (1884) and Delage (1898) separated sponges from other metazoans on the basis of embryological studies, and suggested a separate group, “Parazoa” for these.

General Characters  

(1) All the sponges are aquatic, sedentary, asymmetrical or radially symmetrical. First multicellular organisms and have cellular grade of organization.

(2) They are diploblastic. Ectoderm is formed by pinachocyte and endoderm is formed by choanocyte. Both layers are called pinachoderm and choanoderm. A gelatinous noncellular mesenchyme present in between them.

(3) Mesenchyme contains free amoebocytes and skeletal elements.

(4) Different types of amoebocytes are :

Archaeocytes                :   undifferentiated totipotent cells.

Chromocytes                 :   with pigment granules.

Thesocytes                     :   with reserve food granules.

Myocytes                        :   highly contractile, spindle-shaped cells.

Trophocytes                  :   supply nutrients to developing cells (nurse    cells)

Gland cells                     :   secrete slimy substance.

Sex cells                           :   develop from archaeocytes only during breeding season.

(5) The body is perforated by numerous minute pores called ostia.

(6) The ostia open into a large cavity called spongocoel or paragastric cavity.

(7) The spongocoel opens to the outside by a large opening called osculum.

(8) Sponges have a canal system and they need a continuous current of water flowing through their bodies for respiration, excretion, nutrition and reproduction.

(9) Different types of canal system in sponges are asconoid, syconoid and leuconoid.

(10) The simplest type of canal system in porifera is asconoid type.

(11) The course taken by the water current way be shown as under –

Ingressing water \[\xrightarrow{\text{Ostia}}\] Spongocoel \[\xrightarrow{\text{Osculum}}\] To outside

(12) The sponges possess an endoskeleton in the form of calcareous spicules.

(13) Excretion and respiration occur by diffusion.

(14) They have greater power of regeneration due to totipotent archaeocytes.

(15) Digestion in sponges is intracellular like protozoans.

(16) All sponges are hermaphrodite, reproduction takes place by asexual or sexual methods.

(17) Gemmules are internal buds containing archaeocytes, mostly found in fresh water sponges, concerned with asexual reproduction.

(18) Development is indirect or direct. The common larval forms are parenchymula (leucosolenia and Clathrina), amphiblastula (Sycon), etc.

Classification of porifera : On the basis of types of endoskeleton, phylum porifera is divisible into three classes

Class 1. Calcarea or Calcispongiae

(1) Skeleton is formed of Calcareous spicules. 

(2) Radially symmetrical.

(3) Choanocyte cells are large and conspicuous.

(4) Canal system asconoid (ascon) or syconoid (sycon) type.

(5) These are also known as limy sponges.

Examples : Clathrina, Leucosolenia, Sycon, Grantia, etc.,

• Leucosolenia is a smallest sponge with asconoid type of canal system.

Class 2. Hexactinellida Or Hyalospongiae

(1) Skeleton is formed of six rayed triaxon, silicious spicules,

(2) Canal system is branched or unbranched.

(3) Radially symmetrical.

(4) These are also known as glass sponges.

Examples : Pheronema, Hyalonema, Euplectella, etc.,

• Euplectella is the sponge which is given as a Gift in Japan and known as “venus flower basket”. It show commensalism with shrimps of the genus spongicola, ‘life upto death’.

Class 3. Demospongia

(1) Skeleton either absent or present. When present it is either formed of spongin fibres or combination of spongin fibres and silicious spicules.

(2) The silicious spicules when present are never six rayed.

(3) The canal system is complicated Rhagon type or leuconoid type.

(4) Rhagon larva is formed.

(5) These sponges are of great economic importance.

Examples : Cliona, Spongilla, Chalina, Euspongia, Hippospongia, Oscarella, etc.,

• Spongilla is a fresh water sponge.

• Cliona is harmful to oyster industry.

  Common Names