Phylum Porifera: Classification, Characteristics, Examples

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Definition of Porifera

Porifera are asymmetrical or radially symmetrical multicellular organisms with a cellular grade of organisation lacking well-defined tissues as well as organs; exclusively aquatic; mostly marine, sedentary, solitary or conical animals with a body perforated by pores, canals, as well as cambers through which water flows; with one or more internal cavities lined with choanocytes; as well as with a cellular grade of organisation lacking well-defined tissues as well as organs; exclusively aquatic; mostly marine

Characteristics of the Porifera Phylum

  1. Except for one family, the Spongillidae, which lives in freshwater, Porifera are entirely aquatic, mostly marine.
  2. They are sessile as well as sedentary, as well as they grow in the same way which plants do.
  3. Vase or cylinder-like body shape, asymmetrical or radially symmetrical.
  4. Numerous pores, the Ostia, through which water enters the body as well as one or more big apertures, the oscula, through which water exists, perforate the body surface.
  5. The cellular level of body organisation in a multicellular organism. There are no distinguishable tissues or organs.
  6. They are diploblastic since they are made up of outer ectoderm as well as inner endoderm with a layer of mesenchyme in between.
  7. The body’s internal area is either hollow or pervaded by many choanocyte-lined canals. The spongocoel is the sponge body’s internal area.
  8. Fine flexible spongin fibres, siliceous spicules, or calcareous spicules make up the distinctive skeleton.
  9. Due to the lack of a mouth, digestion takes place within the cells.
  10. There are no excretory or respiratory organs.
  11. Some freshwater forms contain contractile vacuoles.
  12. The nerve as well as sensory cells are most likely not separated.
  13. In some cases, the primitive nervous system consists of neurons organised in a specific network of bipolar or multipolar cells, however this is debatable.
  14. The sponges are monoecious.
  15. Both sexual as well as asexual ways of reproduction are used.
  16. Buds as well as gemmules both reproduce asexually.
  17. The sponge has a great capacity for regeneration.
  18. Ovum as well as sperms are used in sexual reproduction.
  19. Hermaphrodite sponges are all the same.
  20. Internal fertilisation is possible, but cross-fertilization is also possible.
  21. Cleavage holoblastic.
  22. The amphiblastula or parenchymula, a free-swimming ciliated larva, is responsible for indirect development.
  23. Due to their basic as well as complicated morphologies, sponges are divided into three types: ascon type, sycon type, as well as leuconoid type.
  24. Clathrina, Sycon, Grantia, Euplectella, Hyalonema, Oscarella, Plakina, Thenea, Cliona, Halichondria, Cladorhiza, Spongilla, Euspondia, as well as others are a few examples.

Porifera Phylum Classification

There are over 5,000 species of sponges in this phylum, which are divided into three classes based on the type of skeleton they have. The classification used here is based on Storer as well as Usinger’s (1971) classification, which appears to be a refinement of Hyman’s.

Class 1. Calcarea (L., calx=lime) or Calcispongiae (L., calcis= lime+ spongia= sponge)

  • Calcareous sponges with a height of less than 10 cm.
  • Solitary or conical; vase-like or cylindrical body form.
  • Structures such as asconoid, syconoid, as well as leuconoid may be present.
  • A skeleton made up of individual calcareous spicules with one, three, or four rays.
  • Exclusively marine.

Order 1. Homocoela (=Asconosa)

  • Sponge bodies which are cylindrical as well as radially symmetrical.
  • The body wall is thin as well as unfolded. The Spongocoel is lined with choanocytes.
  • Frequently conical.
  • Leucosolenia as well as Clathrina are two examples.

Order 2. Heterocoela (=Syconosa)

  • Vase-shaped sponges of the syconoid as well as leuconoid families.
  • The folds in the body wall are thick. Only the flagellated chambers (radial canals) are lined by choanocytes.
  • A line of flattened endoderm cells is known as a spongecoel.
  • Conical or solitary
  • Sycon or Scypha, Grantia are two examples.

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Class 2. Hexactinellida (Gr., hex=six + actin=ray) or Hyalospongiae (Gr., hyalos=glass+ spongos= sponge)

  • The size is moderate. Some grow to be over a metre long.
  • Glass sponges are what they’re called.
  • Body shape cup, urn, or vase-like.
  • The skeleton is made up of triaxon siliceous spicules with six rays. The spicules in some of them are fused together to form a lattice-like skeleton.
  • There is no epidermal epithelium present.
  • Finger-shaped chambers are lined with choanocytes.
  • Funnel-shaped or cylindrical
  • Deep tropical seas are home to this creature.

Order 1. Hexasterophora

  • Spicules are hexasters, meaning they have axes which branch into rays at their ends.
  • Flagellated chambers are organised in a radial pattern.
  • Usually directly linked to the substratum.
  • Examples:Euplectella (Venus’ flower basket), 

Order 2.  Amphidiscophora

  • Spicules are amphidiscs, meaning they have a convex disc on one end as well as backwardly pointed marginal teeth on the other.
  • Flagellated chambers are slightly different from the typical type.
  • Root tufts anchor the plant to the substratum.
  • Hyalonema as well as Pheronema are two examples.

Class 3. Demospongiae (Gr., dermos= frame+ spongos= sponge)

  • The most sponge species are found here.
  • Small to huge in size.
  • Solitary or conical.
  • A vase, cup, or cushion is the body form.
  • Skeleton composed of siliceous spicules or spongin fibres, or both, or none at all.
  • Spicules are never 6-rayed; they are monaxon or tetraxon, with huge megascleres and minuscule microscleres.
  • The bodily canal system is of the leucon variety.
  • Choanocytes are only found in small spherical chambers.
  • There are a few freshwater forms, but most are marine.

Subclass I. Tetractinellida

  • Sponges are mainly solid, spherical cushion-like flattened shapes which are usually devoid of branches. Colors range from drab to vibrant.
  • The skeleton is mostly made up of tetraxon siliceous spicules, however the order Myxospongida is missing.
  • The Canal system is a form of leuconoid.
  • The majority of the time is spent in shallow water.

Order 1. Myxospongida

  • A simple structure.
  • Spicules are missing.
  • Oscarella, Halisarca are two examples.

Order 2. Carnosa

  • Simple structure.
  • Megascleres as well as microscleres are not distinguished in spicules.
  • It’s possible which there will be asters.
  • Plakina as well as Chondrilla are two examples.

Order 3. Choristida

  • Spicules of various sizes are present.
  • Geodia as well as Thenea are two examples.

Subclass II. Monaxonida

  • Occurs in a range of morphologies, including spherical masses, branching varieties, and elongated or stalked with funnel or fan-shaped leaves.
  • Monaxon spicules Spongin is present or not.
  • Spicules are classified as megascleres or microscleres.
  • Found in abundance all throughout the planet.
  • Mostly in shallow water, but also in deep sea and freshwater.

Order 1. Hadromerina

  • Tylostyles of Monaxon megascleres.
  • When asters are present, microscleres are present.
  • Spongia is not present.
  • Cliona, Tethya are two examples.

Order 2. Halichondrina

  • Monaxon megascleres are frequently divided into two types: monactines and diactines.
  • Microscleres are not present.
  • Spongia is present but sparse.
  • Halichondria is an example (crumb-of-bread sponge).

Order 3. Poecilosclerina

  • Monaxon megascleres are classified into two types: those found in the ectoderm and those found in the choanocyte layer.
  • Chelas, sigmas, and toxas are common microscleres.
  • Cladorhiza is one example.

Order 4. Haplosclerida

  • Monaxon megascleres have only one kind, which is diactinal.
  • There are no microscleres.
  • Spongia fibres are commonly seen.
  • Examples include Chalina, Pachychalina, and Spongilla.

Subclass III. Keratosa

  • The body is large and huge, with several prominent oscula.
  • Spongy sponges with a skeleton made of spongin fibres.
  • There are no spicules.
  • Found in shallow, warm, tropical and subtropical seas.
  • Examples include Euspongia and Hippospongia.

 

 

Phylum Porifera Citations 

  1. Jordan EL and Verma PS. 2018. Invertebrate Zoology. 14th Edition. S Chand Publishing.

 

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