Phylum Porifera Definition

The Phylum Porifera can be described as asymmetrical or radially symmetrical multicellular organisms without clearly defined tissues and organs, exclusively aquatic, mostly marine, sedentary, solitary, or conical animals, with bodies perforated by pores, canals, and cambers through which water flows, with one or more internal cavities lined with choanocytes, and with a distinctive skeleton made of calcareous spicules, siliceous spicules

Phylum Porifera Characteristics

1. All the Porifera are aquatic, with the exception of one family, the Spongillidae, which is freshwater only.
2. They develop like plants and are sessile and sedentary.
3. The body is shaped like a vase or cylinder and may be radially symmetrical or asymmetrical.
4. Water enters the body via a number of pores called ostia and exits through one or more big holes called oscula on the surface of the body.
5. The multicellular creature that is organised at the cellular level, no discrete organs or tissues.
6. They are diploblastic because they have an intermediate layer of mesenchyme between the outer and inner endoderm.
7. Either the body’s interior is hollow or it is laced with many choanocyte-lined channels. Spongocoel is the name of the sponge body’s inside.
8. characterised by a skeleton made of siliceous spicules, calcareous spicules, or tiny, flexible spongin fibres.
9. Absence of the mouth; intracellular digestion.
10. Absent are the respiratory and excretory systems.
11. Certain freshwater forms include contractile vacuoles.
12. It’s likely that the sensory and nerve cells are not differentiated.
13. The existence of the primordial nervous system, which consists of neurons organised into a clear network of bipolar or multipolar cells in some, is questionable.
14. The sponges have a single egg.
15. Reproduction may take place in a sexual or asexual way.
16. Buds and gemmules both engage in asexual reproduction.
17. The sponge has a strong capacity for regeneration.
18. Ovum and sperm are used in sexual reproduction.
19. Sponge species are all hermaphrodite.
20. Internal fertilisation may also result in cross-fertilization.
21. The holoblastic cleavage
22. A free-swimming, ciliated larva known as an amphiblastula or parenchymula facilitates indirect development.
23. Sponge types are classified as ascon, sycon, and leuconoid based on their basic and complex morphologies.
24. As an example, consider the following species: Clathrina, Sycon, Grantia, Euplectella, Hyalonema, Oscarella, Plakina, Thenea, Cliona, Halichondria, Cladorhiza, Spongilla, Euspondia, etc.

Phylum Porifera Classification

The phylum has roughly 5,000 different species of sponges, which are divided into three divisions, mostly based on the kinds of skeletons they have. This classification seems to be a variation of Hyman’s classification and is based on Storer and Usinger’s (1971) categorization.

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

• calcareous sponges that are not taller than 10 cm.
• vase-like or cylindrical; singular or conical in form.
• Asconoid, Syconoid, or leuconoid formations may be seen.
• It is a collection of distinct, calcareous spicules with one, three, or four rays.
• Only maritime.

Order 1. Homocoela (=Asconosa)

• There are sponges with asconoid bodies that are cylindrical and radially symmetrical.
• The body wall is not folded but thin. The Spongocoel is lined with choanocytes.
• Commonly conical
• Leucosolenia and Clathrin are examples.

Order 2. Heterocoela (=Syconosa)

• Sponge species with syconoid and leuconoid bodies resembling vases
• Body walls are thick and folded. Only the flagellated chambers (radial canals) are lined by chonocytes.
• Endoderm cells that have been flattened form the spongecoel.
• Conical or isolated
• Examples include Grantia and Sycon.

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

• medium-sized. Some grow to a length of one metre.
• Known as glass sponges.
• Body form like a vase, cup, or urn.
• Siliceous triaxon spicules with six rays make up the skeleton. In some, the spicules are united to create a skeleton resembling a lattice.
• Epidermis epithelium absent.
• Choanocytes cover the chambers with fingers.
• Funnel- or cylindrical-shaped
• located in tropical deep waters.

Order 1. Hexasterophora

• The form of spicules is hexaster, or star-like, with axes that branch into rays at their ends.
• Regularly spaced and radially oriented flagellated chambers.
• Normally immediately linked to the substrate.
• Examples are Farnera and the flower basket that Venus carried.

Order 2. Amphidiscophora

• Spicules are amphidiscs, meaning they have a convex disc with marginal teeth pointing backwards at both ends.
• The characteristic kind differs somewhat from flagellated chambers.
• Root tufts that are anchored to the substratum.
• Hyalonema and pheronema are examples.

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

• It has the most varieties of sponges.
• From little to huge.
• Solitary or conical.
• A vase, cup, or cushion would describe the body form.
• Siliceous spicules or spongin fibres, or both, or none at all, make up the skeleton.
• Spicules are either monaxon or tetraxon and may be classified as either huge megascleres or tiny microscleres. They are never 6-rayed.
• It has a leucon-type body canal system.
• Confined to tiny, spherical chambers by choanocytes.
• Few freshwater forms; mostly marine species.

Subclass I. Tetractinellida

• Sponges are typically flat, circular cushions without branches that are primarily solid in composition. dull to vivid in hue.
• The order Myxospongida was missing from the skeleton, which was mostly made of tetraxon siliceous spicules.
• A leuconoid system, the Canal system.
• Mostly in small bodies of water.

Order 1. Myxospongida

• simple architecture
• Absence of spicules
• For instance, Oscarella and Halisarca

Order 2. Carnosa

• Simple structure
• Megascleres and microscleres are not distinguished among spicules.
• There may be asters.
• For instance, Chondrilla and Plakina

Order 3: Choristida

• There are both big and little spicules.
• For instance, take Geodia and Thenea.

Subclass II. Monaxonida

• It occurs in a variety of forms, including spherical masses, branching kinds, stalks that are elongated or funnel-shaped, and fans.
• monaxon spicules Spongin may be present or not.
• Megascleres and microscleres are two types of spicules.
• Found in great abundance all around the planet.
• Most often in shallow waters, but even occasionally in deep seas and freshwater.

Order 1: Hadromerina

• Tylostyles are monaxon megascleres.
• Asters, which are microscleres when they are present,
• Sponge is missing.
• For instance, take Cliona and Tethya.

Order 2. Halichondrina

• Monactines and diactines, two forms of monaxon megascleres, are often seen.
• There are no microscleres.
• There are few and scarce sponges.
• For instance, Halichondria (crumb-of-bread sponge).

Order 3. Poecilosclerina

• There are two varieties of monaxon megascleres; one type is found in the ectoderm and the other type in the choanocyte layer.
• Typically, chelas, sigmas, and toxas make up microscleres.
• Think about Cladorhiza.

Order 4: Haplosclerida

• There is just one kind of monaxon megasclere, called diactinal.
• microscleres are absent.
• There are often sponge fibres.
• For instance, take Chalina, Pachychalina, and Spongilla.

Subclass III: Keratosa

• The body is huge and spherical, and it has many obvious oscula.
• Spongin fibres form the backbone of horny sponges.
• Spicules absent.
• Found in tropical and subtropical seas that are warm and shallow.
• For example, Hippospongia and Euspongia

References

• Kotpal RL. 2017. Modern Text Book of Zoology- Invertebrates. 11th Edition. Rastogi Publications.
• Jordan EL and Verma PS. 2018. Invertebrate Zoology. 14th Edition. S Chand Publishing.