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Phylum Porifera Definition, Characteristics, Classification

The Porifera can be described as an multicellular asymmetrical or radially symmetrical organism having a cellular degree of organization that lacks welldefined...

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Phylum Porifera Definition, Characteristics, Classification
Phylum Porifera Definition, Characteristics, Classification

Definition of Phylum Porifera

The Porifera can be described as an multicellular asymmetrical or radially symmetrical organism having a cellular degree of organization that lacks welldefined organs and tissues that are exclusively aquatic, mostly sea-based, sedentary, single or conical creatures with body perforated through canals, pores and cambers that allow water to flow with at least one internal cavity filled with choanocytes and with a distinctive skull made up of calcareous spikes siliceous spicules and the horny fibers of spongin.

Characteristics of Phylum Porifera 

  • Porifera is all aquatic generally marine, with the exception of one family called Spongillidae that is found in freshwater.
  • They are sedentary and sessile and are able to grow as plants.
  • A body’s shape can be described as cylinder or vase-like and asymmetrical or the radially uniform.
  • The body’s surface is perforated with numerous pores, including the Ostia by which fluid can enter the body. There are also one or larger openings and the oscula through which water is able to pass through.
  • The multicellular organism that has the multicellular structure of the body. Organs and tissues are not distinct.
  • They are composed of the an outer ectoderm as well as an inner endoderm, with mesenchyme as an intermediate layer Therefore, they are diploblastic.
  • The inside of the body may be hollow or surrounded by many canals that are lined with Choanocytes. The inside of the body’s sponge is known as the spongocoel.
  • A skeleton with a distinctive character, made up of fine, flexible spongin fibers siliceous spicules or calcareous siliceous spicules.
  • Mouth absence and digestion is intracellular.
  • Organs for respiratory and excretory are not present.
  • Vacuoles of contractile origin are found in a variety of freshwater forms.
  • The sensory and nerve cells are likely to not be differentiated.
  • The basic nervous system that comprises neurons that are arranged in a distinct system of multipolar or bipolar cells, however, it is in doubt about its validity.
  • The sponges are monoecious.
  • Reproduction can be achieved through both sexual and sexual methods.
  • Asexual reproduction is triggered by gemmules and buds.
  • The sponge has a powerful capacity for regeneration.
  • Sexual reproduction happens through the ovum and sperms.
  • All sponges are hermaphrodites.
  • Fertilization is internal , but cross-fertilization may occur.
  • Cleavage holoblastic.
  • The development process is indirect and involves the free-swimming larva known as parenchymula or amphiblastula.
  • The structure of sponges is divided into three categories that are ascon type, Sycon type and leuconoid type in part due to simple and complicated forms.
  • Examples: Clathrina, Sycon, Grantia, Euplectella, Hyalonema, Oscarella, Plakina, Thenea, Cliona, Halichondria, Cladorhiza, Spongilla, Euspondia, etc.

Classification of Phylum Porifera

The phylum comprises about five thousand species of sponges divided into 3 categories based on the types of skeletons that are that they contain. The classification here is based upon Storer as well as Usinger (1971) and seems to be a variation of Hyman’s classification.

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

  • Small-sized calcareous sponges below 10 centimeters in height.
  • Conical or single form; body shape vase-like, or cylindrical.
  • They can show asconoid Syconoid or leuconoid structures.
  • A skeleton that is composed of distinct one , three, or four-rayed calcareous spicules.
  • All marine.

Order 1. Homocoela (=Asconosa)

  • Asconoid sponges that have cylindrical and circularly similar bodies.
  • Body wall thin, but not folded. Choanocytes are found in the Spongocoel.
  • Often conical.
  • Examples: Leucosolenia, Clathrina.

Order 2. Heterocoela (=Syconosa)

  • Leuconoid and syconoid sponges have vase-like bodies.
  • The body’s wall is thick and folded. Choanocytes are found in those flagellated chambers (radial canals) only.
  • Spongocoel is an elongated line formed formed by flattened cells of the endoderm.
  • Conical or solitary
  • Examples: Sycon or Scypha, Grantia.

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

  • Moderate -sized. Some exceed 1 Meter in length.
  • Glass sponges that are called.
  • The body form cup, urn or vase-like.
  • Skeleton is made up of siliceous particles which have a triaxon that has 6 Rays. In certain cases, the spicules fuse to create a lattice-like skeleton.
  • There is no epidermal epithelium.
  • Choanocytes line finger-shaped chambers.
  • Shaped like a funnel or cylinder
  • Usually found In deep tropical seas.

Order 1. Hexasterophora

  • Spicules are also hexasters i.e. like stars with axes that branch into Rays at their ends.
  • Chambers with flagellated walls are frequently and radially organized.
  • Usually, it is attached to Substratum straight.
  • Examples: Euplectella (Venus’ flower basket), Farnera.

Order 2.  Amphidiscophora

  • Spicules are also known as amphidiscs, i.e. having a convex disc with marginal teeth that are directed backwards on both sides.
  • The flagellated chambers differ from the usual kind.
  • Connected to the substratum via roots tufts.
  • Examples: Hyalonema, Pheronema.

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

  • The largest variety of sponge species.
  • Sizes range from small to large-sized.
  • Conical or single.
  • The body shape is vase or cup or cushion.
  • Skeleton composed of siliceous spicules, or fibers of spongin or both, or even none.
  • Spicules do not have 6-rays They are monaxon or tetraxon. They are further divided into small megascleres as well as large microscleres.
  • The system of the body canal is a leucon type.
  • Choanocytes are confined to small, round chambers.
  • The majority of freshwater types.

Subclass I. Tetractinellida

  • Sponges are generally solid and straightforward, with a cushion-like shape flattened shape, usually with no branches. They can range from dull to vibrantly colored.
  • Skeleton consists mainly of tetraxon siliceous particles, however not present in the order Myxospongida.
  • It is the Canal canal system belongs to a type of leuconoid.
  • The majority of them are found in shallow water.

Order 1. Myxospongida

  • It has a Simple structure.
  • Spicules are absent in Myxospongida.
  • Examples: Oscarella, Halisarca.

Order 2. Carnosa

  • It has a Structure simple.
  • Spicules do not differ into microscleres or megascleres.
  • Asters could be present.
  • Examples: Plakina, Chondrilla.

Order 3. Choristida

  • Small and large spicules are present.
  • Examples: Geodia, Thenea.

Subclass II. Monaxonida

  • The species is found in many forms, from rounded mass to branches or stalks that are elongated, funnels or fan-shaped.
  • Spicules monaxon. Spongin is present or absent.
  • Spicules can be distinguished into megascleres as well as microscleres.
  • All over the world.
  • Most of the time found in shallow waters, certain in deep seas and others in freshwater.

Order 1. Hadromerina

  • Monaxon megascleres in the shape of Tylostyles.
  • Microscleres can be found are in form of asters.
  • Spongia is absent.
  • Examples: Cliona, Tethya.

Order 2. Halichondrina

  • Megascleres from Monaxon tend to be comprised of 2 kinds i.e. diactines and monactines.
  • Microscleres do not exist.
  • Spongia present and minuscule.
  • Example: Halichondria (crumb-of-bread sponge).

Order 3. Poecilosclerina

  • Monaxon megascleres can be classified into 2 kinds, one located in the ectoderm, and another kind in the choanocyte layer.
  • Microscleres are usually chelas, Sigmas, and toxas.
  • Example: Cladorhiza.

Order 4. Haplosclerida

  • Monaxon megascleres can be found in only one kind i.e. diactinal.
  • There are no microscleres.
  • Spongia fibers can be found in the majority of cases.
  • Examples: Chalina, Pachychalina, Spongilla.

Subclass III. Keratosa

  • The body is round and massive, with a multitude of prominent pores.
  • The Skeleton of fibres of spongin.
  • There are no stipulations.
  • They are found in warm and shallow waters of subtropical and tropical regions.
  • Examples: Euspongia, Hippospongia.

Examples of Phylum Porifera

A few of the most common Porifera examples include:

Sycon

They are colonial or solitary marine sponges that are found in shallow waters , and are attached to their rocks. Its body has a cylindrical with many spores. The canals radial comprise from flagellated cells. The body’s water is absorbed through Ostia and then reaches the radial canals via prosopyles. The species that reproduce sexually and asexual reproduction.

Hylonema

They are also known for their glass-like sponges, which are found in marine waters. The body is either round or oval, with twisting root tufts. Small amphidiscs can be found within the skeleton.

Cliona

They are also referred to as Boring Sponges, which are found in coral Skeletons, Mollusc Shells, and other calcareous items. They are purple, green as well as light yellow hue. Canals are the hallmark of the leuconoid species of sponges. They reproduce sexually and sexually

Euplectella

These are also referred to as Venus flower baskets and are found in deep water. The body is long, cylindrical and curving, which is anchored in the mud beneath the ocean. It is a a simple synconoid type. The skeleton comprises siliceous spicules that are fused at the ends, creating the three-dimensional structure with gaps in the parietal region.

Spongilla

They are found in streams, ponds, and lakes that are formed by the submerged plant and stick. The body wall is comprised of a thin dermis that is surrounded by pores referred to as Ostia. They are equipped with a rhagon canal system. They reproduce sexually and sexually.

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