Phylum Porifera: The Most Primitive Animals

Distribution of Phylum Porifera

The Porifera are all pore-bearing creatures, commonly referred to as the sponges. All are aquatic. Sponges are globally distributed, living in a vast array of sea habitats, from the polar regions to the tropics. Many are living in silent, clean seas because sediment or rocks broken by waves could obstruct their pores, so which makes it problematic to allow them to breathe and feed.

Most of the sponges usually are found on hard surfaces such as rocks and stones, but a few sponges may hook themselves into soft sediment by means of a root-like base.

This is part 3. See part 1 of this series: Classification of Living Organisms See part 2 of this series: Classification of Kingdom Animalia Take 50 MCQs of Phylum Porifera

Sponges are abundant but not as diverse in temperate waters than in tropical seas, perhaps because creatures that predate on sponges are richer in tropical waters. Glass sponges are the most frequent in temperate waters and at the depths of tropical and temperate waters, as their porous structure lets them extract food from these types of resource-poor waters with the minimum of work.

Demosponges along with calcareous sponges are diverse and abundant in shallower non-Polar waters. Out of absolute 5000 species, 150 species reside in freshwater whereas others are marine.

General characteristics of Phylum Porifera

Grade of organization: Sponges are composed of many cells hence are multicellular. But they are the simplest organisms. They have no tissue organization and lack organs.

Shape and Symmetry: Sponges lack symmetry or they are asymmetrical. They have various kinds of body shapes but the mostly cylindrical body and tube or vase-like.

Body cells:

Pinacocytes: Pinacocytes are the cells that made the outer layer of the body wall which is known as pinacoderm.

Choanocytes: Choanocytes are the flagellated collar cells that made the inner body wall layer which is known as choanoderm.

Amoeboid cells: The gelatinous mesenchyme present between pinacoderm and choanoderm contains amoeboid cells or spicules or sometimes called sponging fibers.

Spongocoel: The single cavity in the body of sponges, it is sometimes divided by choanocytes into chambers or canals.

Size: The phylum Porifera ranges from few millimeters to more than a meter. So, some of them are macroscopic and can be seen by the naked eye.

 

Do you know? Scolymastra joubini-is more than a meter found in Antarctica

Ostia and Osculum:

The pores through which water enters in the body of the sponge are called Ostia and the pores through which the body emits water are called the osculum.

Organs and Organ Systems:

Sponges are the simplest organisms so they do not have respiratory or circulatory organs.

Movements: The adult poriferans are sessile and stationary spend their lives by attaching to rocks or stones. But their larvae are capable of swimming.

Nervous system:

Because of the simplest organisms, they do not have nervous systems but neurons and neurosensory cells are present for the coordination of the body.

Endoskeleton:

These organisms have needle-like spicules (calcareous or siliceous) which act as endoskeleton and provides support. These spicules are also present around Ostia and osculum.

Reproduction in porifera:

Asexual: This type of reproduction is by budding. Buds may be external or internal. Internal buds are known as gemmules.

Sexual reproduction:

Some sponges are hermaphrodites.

hermaphrodites are those organisms which contain both male and female sexes.

Most of the hermaphrodite poriferans are protandrous, i.e. male sex cells develop first.

Fertilization: Fertilization is internal i.e. occurs in mesenchyme and zygote is formed. The embryo development includes blastula and larval stages.

Some common sponges are:

Sycon: It is a marine sponge.

Leucoselenia: A sponge that consists of a group of erect tubes.

Euplectella: It is a delicate sponge made up of a glassy framework and is commonly called Venus flower basket.

 Spongilla: It is a freshwater sponge.

Classification of Phylum porifera

• Class 1: Calcarea or Calcispongiae
• Class 2: Hexactinellida or Hyalospongiae
• Class 3: Demospongiae

Calcarea or Calcispongiae

These are cellular sponges characterized by spicules made up of calcium carbonate. Generally, sponges of this class are small and mostly colorless or dull colored.

Example: Clathrina Clathrus

 

Hexactinellida or Hyalospongiae

Hexactinellid sponges are sponges having four- or six-pointed siliceous spicules, frequently known as glass sponges. They chiefly located at 450 to 900 meters in the depth of oceans.

Example: Hyalonema

Demospongiae

This class is the most diverse class in phylum Porifera. Round about 76% of all sponges are demosponges. They are soft from inside but their outer layer is hard and made of calcium carbonate. They are mostly marine.

Example: Spongia officinalis

Economic Importance of Sponges

The skeleton of sponges has always been applied by men mostly for bathing and washing purposes. Even though a lot of artificial sponges are grown from synthetic material, but there is a great demand for pure natural sponges and is a significant industry in many regions of the world.

The finest commercial sponges are located in the hot waters of the Mediterranean Sea. Sponges have an amazing capacity to absorb water. They are utilized in surgical operations for absorbing fluids along with blood. Also, they are used for noise absorption in buildings.

 

Do you know? SpongeBobSquare Pants is also a sponge and the creator of this series was a marine biologist who animated the marine life in this series.

 

 

This is part 3. See part 1 of this series: Classification of Living Organisms See part 2 of this series: Classification of Kingdom Animalia

Summary

Porifera from Latin word meaning pore bearing is the phylum containing all porous organisms with multicellular organization, simple asymmetrical and cylindrical body plan and are aquatic mostly inhabiting marine waters. The body of poriferan has specialized cells such as pinacocytes, choanocytes, and amoeboid cells.

There is a single cavity in the body called spongocoel. They can be from few millimeters to more than a meter. The pores through which water enters the body are called Ostia and through which exit the body is Osculum. They do not have a nervous system but neurosensory cells are present for coordination.

As the simplest organisms, they also do not have respiratory or circulatory systems. The adult poriferans are sessile and stationary but their larvae can move. Sponges are hermaphrodites but also reproduce by budding the asexual method of reproduction. There are three classes of this phylum 1) Calcarean 2) Hexactinellida 3) Demospongiae. Sycons are the common sponges in phylum Porifera.