Phylum Porifera

Definition

The phylum Porifera commonly referred to as sponges and these animals contain pores in their body. They are the first multicellular animals.

Phylum Porifera – General Characters

• All sponges are aquatic and sedentary in habit.
• Two types of symmetry were found – Asymmetrical and Radially Symmetrical
• Porifera exhibit cellular grade of organization
• They are diploblastic: The body wall is formed of two layers, an outer ectoderm and an inner endoderm, which are connected by a jelly-like substance called Mesenchyme.
• The inner endoderm is made up of flagellated cells called Choanocytes
• The body of Porifera contains several minute pores called Ostia.
• Ostia leads into a large cavity known as Spongocoel.
• The spongocoel leads to a broad opening known as the osculum.
• The sponge body is supported by an endoskeleton in the form of Calcareous Spicules.
• Respiration and Excretion in porifera occur through the process of diffusion.
• Reproduction occurs through either asexual or sexual methods, depending on porifera’s reproductive strategy.
• Asexual reproduction involves the growth of new individuals through the process of budding or gamule formation.

L.S of Leucosolenia

Phylum Porifera – Classification

• Based on Spicule the Phylum Porifera is divided into three main groups 1.Calcarea 2.Hexactinellida 3.Demospongia

1. Calcarea

• The skeleton of some Porifera, is formed of calcareous spicules, which are made up of calcium carbonate crystals.
• Organisms in this class are radially symmetrical animals.
• Choanocytes are largely visible and apparent.
• Single cavity, spongocoel opening to outside through a single opening called osculum.
• Examples: Sycon, Leucosolenia, Clathrina.

2. Hexactinellida

• Skeleton is formed of six rayed triaxon, siliceous spicules.
• Canal system in this class is either branched or unbranched.
• Radially symmetrical.
• These are also called as Glass Spones.
• Example : Euplectella Phylum Porifera

3. Desmospongia

• The skeleton of this class is either present or absent, and when present, it can be composed of either spongin fibers or a silicious spicules.
• The canal system is complicated because its a type of Rhagon.
• Example: Spongilla Cliona

Canal System in Sponges

Definition

The body of the sponge is characterized by a network of numerous canals that open to the outside through several small pores, which together forms the canal system of Phylum Porifera. canal system in sponges bsc 1st year

Functions of canal system

The canal system creates a constant flow of water in and out of the organism through the pores, creating a continuous water current.

This water current serves the follow functions:

• Nutrition : Constant flow of water brings in food particles
• Respiration : The cell absorbs Oxygen from the water current and gives out Carbon Dioxide.
• Reproduction : The water current carries the sperm from one sponge to the other sponge.
• Excretion : The water current helps to remove the Nitrogenous waste and Solid wastes from the Porifera.

Types of Canal System

There are four types of canal systems in Phylum Porifera canal system in sponges

1. Ascon Type

• Simplest Type
• Cylindrical in shape
• Three layers of body wall found: 1. Ectoderm, 2. Mesenchyme 3. Choanocytes (Endoderm).
• Pores(Ostia) are intracellular because each pore is formed of single cell called Porocyte and openes into a cavity called spongocoel.
• Spongocoel opens into outside by a opening called osculum
• Beating of flagella in choanocytes creates a water current.

Water Flow: Ostia —–> Spongocoel —–> Osculum

2. Sycon Type

• Formed by outward protrusions from an ascon sponge, creating radial canals.
• Radial canals initially open to outside water, then fuse to form incurrent canals.
• These incurrent canals, lined by epidermis, represent the original sponge surface.
• Radial canals, lined by choanocytes, are better termed flagellated canals.
• Interior forms a large hollow spongocoel, lined by flat epithelium.
• Radial canals open into spongocoel through internal ostia, leading to a single osculum. canal system in sponges
• Wall between incurrent and radial canals pierced by small prosopyles pores.
• Syconoid structures appear in two stages: The first stage seen in some heterocoelous calcareous sponges like the Sycon genus. The second stage involves the spreading of the epidermis and mesenchyme over the outer surface, forming a cortex with cortical spicules. canal system in sponges helps in

Water Flow: Incurrent canal —–> Prosopyle —–> Radial canal —–> Apopyle —–> Spongocoel —–> Osculum.

3. Rhagon Type

• This type of canal system found Rhagon which is the larval form of Spongilla.
• Rhagon type sponge: broad base, conical shape with single osculum at summit.
• Basal wall called hypophare lacks flagellated chambers.
• Upper wall bears row of small oval flagellated chambers, termed spongophare.
• Spongocoel bordered by oval flagellated chambers opening via wide apopyles.
• Dermal pores open into subdermal spaces extending below body surface.
• Branching incurrent canals lead from subdermal spaces to small flagellated chambers formed from breakdown of radial canal, lined by choanocytes, leading into spongocoel.
• Spongocoel opens via single osculum.

Water Flow: Dermal ostia —–> Prosopyles —–> Flagellated chamber —–> Apopyles —–> Spongocoel —–> Osculum

4. Leucon Type

The leucon type of canal system is derived from the Rhagon type with some advance characteristics:

• The dermal ostia open into subdermal spaces.
• The subdermal spaces open into incurrent canals.
• The incurrent canals open into flagellated chambers.
• Choanocytes are located only in the flagellated chambers.
• The flagellated chamber leads into excurrent canalas.
• The excurrent canals open into spongocoel.
• The Spongocoel opens to the outside by an Osculum

There are three variant of leucon type of canal system:

A. Euryphylous type

• In the eurypylous leuconoid canal system, flagellated chambers are broad and thimble-shaped. Each chamber directly opens into the excurrent canal via a wide aperture called apopyle and receives water supply directly from the incurrent canal through the prosopyle.
• Water Flow: Dermal Ostia —–> Subdermal spaces —–> Incurrent canal —–> Prosopyles —–> Flagellated chamber —–> Apopyle —–> Excurrent canal —–> Spongocoel —–> Osculum.

B. Aphodal Type

• In the aphodal leuconoid canal system, flagellated chambers are small and rounded. Each chamber’s opening into the excurrent canal extends into a narrow tube, typically of limited length, known as the aphodus. The arrangement of the flagellated chambers with respect to the incurrent canals remains unchanged. Phylum Porifera
• Water Flow : Dermal ostia —–> Subdermal spaces —–> Incurrent canal —–> Prosopyles —–> Flagellated chambers —–> Aphodus —–> Excurrent canal —–> Spongocoel —–> Osculum.

C. Diphodal Type

• In certain cases, there exists a narrow current tube, known as the prosodus, between the incurrent canal and the flagellated chambers. This condition is termed diplodal. Examples of organisms with this type of canal system include Oscarella and Spongilla. Phylum Porifera
• Water Flow: Dermal ostia —–> subdermal spaces —–> Incurrent canal —–> Prosodus —–> Flagellated chamber —–> Aphodus —–> Excurrent canal —–> Spongocoel —–> Osculum.

Skeleton in sponges

One of the most important features of the sponge is its skeleton. It helps to support and protect the sponge body. It is also the most commonly used diagnostic feature for the classification of sponges, consisting of spicules or sponging of both.

Spicules

Spicules and sclerites are crystalline structures composed of rays or slices that arise from a point. They’re either calcareous or siliceous. Both contain a core of organic matter around which calcium carbonate or silica is deposited. Traces of other materials such as manganese zinc, copper etc. is also present.Phylum Porifera

The spicules are divided into larger macroscleres and small microscleres, in proportion to their sizes.

Macroscleres

Macroscleres are made up of a support structure for the sponge, whereas microsclerres exist throughout the mesenchyme. Macroscleres can be classified into different types based on their shape.

Monaxons

• These are simple spicules that are rod-like or needle-like in shape.
• They grow in one or both directions along a single axis. If the growth has only occurred in one direction, the spicule is known as monactinal monaxon or style. Phylum Porifera
• Styles have a rounded end at one end and a pointed end at the other. If the broad end is knobbed, the style is called tylostyles. Acanthostyles are styles that are covered in thorn.
• Spicules are referred to as diactinal monaxons or rhabdoids when they grow in both directions.
• Rhabds pointed at both the ends are known as oxeas, lance shaped at each ends are termed tornotes, round at the ends are strongyles; and knobed at each end are called tylotes. ias zoology optional notes

Triaxons

• Triaxons are a defining characteristic of the Hexactinellida class. Six rays are produced by the intersection of three equal axes at a right angle to form triad spicules. Many changes are brought about by the growth of knobs, spines, and other features, as well as the reduction, loss, branching, or curving of rays. canal system in sponges develops due to

Tetraxons

Tetraxons are made up of four rays that radiate in various directions from a single common center. When all four rays of the spicule are roughly equal, it is referred to as a calthrops. When a single, elongated ray has three smaller rays in its crown, it is referred to as triaenes. A diaene is created when a smaller ray is lost; an amphidisc spicule is created when an elongated ray has a disc at both ends. The triod, or triradiate spicule, is generated when the elongated ray is lost.

Polyaxons

polyaxons have a number of axes running from the center.

Spheres

These are rounded spicules in which the growth is circular around a central point. canal system in sponges ppt

Desma

When silica is deposited in an uneven layer over regular monaxon triradiate or tetraxon spicules, modified macroscleres known as desma develop. Typically, a network known as lithistid connects it. canal system in sponges long question

Micoscleres

Microscleres develop in the mesenchyme and may protrude across the canal. They are also referred to as flesh spicules or auxilia. these are two kind:

1.Spires

they are curved in a single plane or spirally twisted, with numerous variations, these are:
Sigmas – C shaped form
Toxas – Bow Shaped
Chelas – Curved hooks, plates, flukes at each end
isochelas – two ends are alike the chelas
Sigmaspires – Spirally twisted sigmas

2.Asters

These microscopic structures are called “multiaxinate microsclerites.” The type of actin filaments that radiate outward from a central point are called “euasters.”

There are two main types of asters: one with small centers and long rays, and the other with large centers and short rays.

Among the small-centered asters, there are several subtypes, including oxyasters with pointed rays, strongylasters with rounded ends, and tylasters with knobbed rays.

Large-centered asters include spherasters with distinct rays and terrasters with reduced rays that appear as small projections on the spherical surface.

Among monaxons, there are several types of asters. Short spring asters are known as streptasters, while spirally twisted streptasters are called spirasters. Rod-shaped asters are called sanidasters, and streptasters with a few spines from a very short axis are known as plesioasters. when the spines are at the both the ends are called amphiasters.

Development of spicules

The cells responsible for secreting spicules, known as scleroblasts, play a crucial role in the formation of these calcium carbonate structures. During the process, a binucleate scleroblast secretes a small piece of calcium carbonate around an organic axis thread between the two nuclei. As the spicule grows, the two nuclei separate until the scleroblast divides into two cells: one at the inner end of the spicule, known as the founder, and the other at the outer end, called the thickener. The founder cell gradually shapes the spicule’s form and length, while the thickener adds additional layers of calcium carbonate to provide thickness. Once the spicule is fully formed, both cells pass into the mesogloea.

A triradiate spicule is formed by three scleroblasts which meet in a triangle and divide to form six cells. A small spicule is secreted by each pair of cells. Later the three spicules or rays unite together to form a triradiate spicule.

Tetraradiate spicule is secreted similarly by four scleroblast cells.

A hexactinal spicule is secreted within a multinucleate syncytial mass which is perhaps derived by repeated nuclear divisions of an original scleroblast.

spongin

Spongin is an organic, thorny, and elastic substance with a chemical composition similar to silk. It is produced by specialized cells called spongioblasts, which secrete the fibers in the form of fine threads. After secreting the spongin, the spongioblasts become vacuolated and eventually degenerate. Spongin can be found in various forms within demospongia, including as a cement binding together siliceous spicules in some Monaxonida, or as branching fibers with embedded siliceous spicules in others. In keratosa, the spicules are absent, and the spongin alone forms a continuous, elastic framework for the body.

Phylum porifera – Reproduction

Scypha exhibits asexual and sexual methods of reproduction.

Asexual Reproduction

It occurs by budding. The bud develops from the base as an outgrowth. The free end develops an osculum. The daughter either remains within the parent or it is detached from the parent and forms a new sponge.

Sexual Reproduction

Scypha is hermaphrodite. Gonads are absent. Gametes are produced by the archaeocytes of mesogloea. The ovum remains in the wall of the radial canal. But the sperms are released into the water.