Phylum: Porifera (sponge), its classification and characteristics
March 13, 2018
- Multicellular, eukaryotic with cellular grade of body organization.
- Aquatic, mostly marine few found in fresh water.
- Solitary or colonial, free living.
- Sedentary and sessile.
- May be asymmetrical (Spongilla) or radially symmetrical (Leucosolenia).
- Body greatly varies in shape. They may be vase-like, cylindrical, tubular or cushion like.
- Body is provided with large number of small inhalant pores called ostia (sing- ostium).
- One or few large exhalent pores are present called oscula (sing- osculum).
- Inter hollow body is present called spongocoel, lined by flagellated cells called choanocytes.
- Diploblastic. Outer layer is pinacoderm (ectoderm) and inner layer is choanoderm (endoderm).
- In between these layers, jelly like layer is present called mesenchyme (mesohyl or mesogloea).
- Mesenchyme contains collagen fibers, skeletal elements, and amoebocytes.
- Nervous and sensory cells are absent.
Image source: weebly
- Skeletal elements are calcareous, silicious or formed of spongin fibers.
- Well developed water canal system which help them in feeding, respiration, excretion, etc.
- Have great power of generation.
- Reproduction occurs asexually by budding or formation of gemmules. sexual reproduction occurs by fusion of gametes.
- Indirect development occurs which include free swimming, larval forms called amphiblastula or parenchymula.
Classification:
Poriferans are divided into 3 classes on the basis of spicules or skeletal elements. They are :
Class 1 : Calcarea
- exclusively marine.
- calcareous spicules.
- solitary or colonial.
- osculum is always encircled by a fringe of upstanding spicules.
- small sized sponges, less than 10 cm in length.
- body shape cylindrical and vase-like.
- examples: Sycon (crown sponge), Grantia, Leucosolenia, Clathrina
Image source: blogsubc
Class 2 : Hexactinellida
- exclusively marine.
- six rayed triaxoned glass like silicious spicules.
- mostly solitary.
- commonly called glass sponges.
- grow up to 92 cm in length.
- cylindrical or funnel shaped or vase-like.
- examples : Euplectella (venus flower basket), Hyalonema (glass rope sponge).
Image source: faunafondness
Class 3 : Demospongiae
- mostly marine, few are found in fresh water.
- skeletal elements formed of calcareous spicules, monoaxoned or tetraaxoned silicious spicules, spongin fibers or both or absent.
- spicules are never six rayed.
- small or large sized.
- solitary or colonial.
- examples : Euspongia (bath sponge), Spongilla (Fresh water sponge), Plakina, Oscarella.
References:
ii) https://www.embibe.com/exams/phylum-porifera/