Porifera

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Porifera are a Phylum of Sessile (permanently affixed) and mostly marine Invertebrate Animals. Poriferans are commonly known as 'Sponges'. They are one of the most primitive multicellular aquatic Animals. There are approximately 9,000 known Species of Porifera of which: about 400 are Glass Sponges; about 500 are Calcareous Species and the rest are Demosponges. Majority of Porifera Species are Marine with only a few Species found in fresh water. Fossils and molecular data put their origin at somewhere around 650 million years ago, nearly back to the dawn of Animal life. DNA analysis indicates that the Sponge’s immediate evolutionary predecessors are the 'Protistan Choanoflagellates'.

Sponges in temperate regions live for at most a few years, but some tropical species and perhaps some deep-ocean ones may live for 200 years or more. Early Europeans used Soft Sponges for many purposes, including padding for helmets, portable drinking utensils, municipal water filters, applicators for paints and ceramic glazes and discreet contraceptives. In modern times Sponges are used mostly in pottery and jewellery making, painting and decorating, and in surgical medicine. Most valuable Sponges are found in the eastern Mediterranean area. They also are harvested off the west coast of Florida and the Florida Keys, in the West Indies, off Mexico and Belize, and in some areas of the Philippines. Since many Sponges exist on Coral Reefs some are threatened by Reef destruction.

Scientific Classification

Domain - Eukaryota.
Kingdom - Animalia.
Phylum - Porifera.

Classes and Subclasses of Porifera

1.  Calcarea - These have skeletons made of Calcite. There are about 300 Species.

Subclass - Calcinea.
Subclass - Calcaronea.

2.  Hexactinellida (Hyalospongiae) - They are also known as Glass Sponges. They have silicate spicules, the largest of which have six rays and may be individual or fused. There are about 500 Species.

3.  Demospongiae - These have silicate spicules or spongin fibres or both within their soft tissues. Some Demospongiae also have massive external skeletons made of aragonite, another form of calcium carbonate. There are about 4,200 Species.

Porifera Examples

  • Ciliona
  • Euplectella (glass sponge)
  • Euspongia(bath sponge)
  • Leucosolenia
  • Sycon
  • Spongilla(fresh water sponge)
  • Thena

Porifera Characteristics


  • Multi-Cellular Animals with Undefined Symmetry - Sponges are one of the simplest Multi-Cellular Animals. Their multicellular body is a loose aggregate of cells without true tissues. The body of a Sponge is a collection of a few different types of cells loosely arranged in a gelatinous matrix called a 'Mesohyl', 'Mesoglea' or 'Mesenchyme'. This 'Mesohyl' is the connective tissue of a Sponge body and it is supported by the skeletal elements. Throughout the body run canals through which water flows, there is considerable variation in the complexity of these canals. The canals have openings to the outside which are called pores, where the water enters the Sponge system these pores are usually small and are called 'Ostia' and where the water leaves the Sponge system the pores are larger, often singular and are called 'Oscula' (singular osculum). Most of these canals are lined with special flagellated cells called 'Choanocytes'. These choanocytes keep the water flowing through the canals in the correct direction by beating their flagellum, they are also important in trapping food items.

Sponges are built up from relatively few cell types. These are:

a)  Choanocytes - These are vase shaped cells with a collar of fine fibrils connected by microvilli. It strains out the smallest food items from the water such as individual Bacteria. Extending from the centre of this collar is the single flagellum whose beating drives the water currents that keep the Sponge alive and healthy.

b)  Pinacocytes - These form much of the epidermis of Sponges and are as close as a Sponge gets to having a tissue. Generally they cover the exterior and some interior surfaces. They can change their size (contractile) and can therefore change the size of the openings of the ostia thus controlling the flow of water through the Sponge. Pinacocytes are also implicated in the absorption into the Sponge of larger food items.

c)  Amoebocytes - These come in several forms, they are alike in that they are mobile and move around within the Sponge body. Archaeocytes are the basis of some asexual reproductive gemmules. If an amoebocyte secretes the spongin fibres of the skeleton they are called a 'Fibroblast', if it secretes spicules it is called a 'Scleroblast' and if it is star shaped and secrete collagenous fibrils then it is called a 'Collencyte'.

d)  Lophocytes - These are a type of amoebocyte, they are the most motile of the Sponge cells moving around relatively freely within the mesohyl where they are important in the secretion of fibrils.

Adult Sponges are Asymmetrical or Radially Symmetrical. Sponges come in a variety of shapes. Some form a crust on their rocky habitat. Some form a single straight tube. Others are vase shaped or cup shaped while others are massive clumps. Some others are fan shaped, while others have mitten-shaped or finger-like bulges on the body wall. Others are treelike or bushy.

  • Lack of Respiratory Organs - Porifera lack Respiratory organs and oxygen is supplied by a direct exchange between the tissues and the surrounding water. Excretion occurs through both the oscula and the surface of the Sponge. Special amoebocytes (mobile cell) disintegrate in the mesohyl, and their granules are expelled through the canals. The excretory products of the Sponges like ammonia and other nitrogen-containing substances, account for their characteristic unpleasant odour.
  • Absence of a Nervous System - The lack of coordination in the oscula, pores, and choanocytes and the slow reaction of Sponges to stimuli confirm the absence of a Nervous System. They also don't have a any distinct circulatory, digestive and excretory systems.
  • Filter Feeders - Most Sponges are Filter Feeders. Water is drawn into the Sponge by tiny hair-like flagella. It passes through small pores and chambers into central cavities. These cavities are lined with cells which can digest small food particles and plankton suspended in the water.  Some Sponges trap roughly 90 percent of all Bacteria in the water they filter. A large quantity of food is absorbed by a Sponge, and it can use several litres of water a day.
  • Unique Flagellated Cells - Possess unique flagellated cells, 'Choanocytes' which create water flow through a water current system. These choanocytes keep the water flowing through the canals of the body in the correct direction by beating their flagellum, they are also important in trapping food items. The water-current system in  Porifera is efficient. The water flow into and out of the  is maintained by continuous movement of the flagella of the choanocytes; flagellar movement pushes water into the choanocyte chambers, creating in them a pressure that extends to the excurrent canals, as water passing into the pores is drawn along the system of incurrent canals. Water flow is also regulated by contraction and expansion of the pores and of the oscula.
  • Sessile - Generally, they are sessile, however some are able to move slowly (up to 4 mm per day) within aquaria.
  • Typically Marine - 98% of all Sponge Species are predominantly marine. Rest like the family, Spongillidae are an extant group of fresh-water Demosponges.
  • Regeneration - Sponges can regenerate after being fragmented, and each part will grow into a new individual. Sponges can not only regenerate a damaged or lost parts but can also completely regenerate from an adults fragments or even single cells. In order for small fragment of cells to form larger organism, the cells generally attach themselves to a surface, where they flatten and develop an envelope of special cells (pinacocytes), which is known as the 'Diamorph Stage'. Reconstitution of the choanocyte chambers and of the canal system follows soon afterward, resulting in a young Sponge that is functional and able to grow.
  • Plant-Like Appearance - Sponges look like plants, but are in fact huge colonies of cells which are capable of living in isolation. The colony is supported by an internal skeleton-like structure.
  • Porifera Skeleton - Porifera Body is supported by a skeleton provided by spicules, composed of calcium carbonate or silicon. There are two main components of a Sponge skeleton, a protein called Spongin which forms a tough fibrous network throughout the Sponge and normally works in conjunction with the spicules. Spicules are non-living aggregates of a chemical nature, secreted and made from either silica or calcium carbonate as calcite or aragonite.

Skeletal Arrangement in Porifera

a)  Calcarea Sponges - They have spicules of calcium carbonate that have 1, 3 or 4 rays, a a skeleton that involves a single large lump of calcium carbonate rather than spicules.

b)  Demospongiae - They have their spicules made from silica and they have 1, 2, or 4 rays.

c)  Hexactinellida or 'Glass Sponges' - They have spicules made from silica that are 6 rayed.

  • Defence Mechanism - Sponges are sedentary and move very little. As a result, they have developed quite complex defence mechanisms. Some have sharp silicon spikes within their tissue which makes it hard for predators to eat them. Others have developed toxic chemicals. Some of these chemicals have been tested by the pharmaceutical industry and found to have curative properties.
  • Association with other Animals - Some Sponges bore into the shells of Bivalves, Gastropods, and the colonial skeletons of Corals by slowly etching away chips of calcareous material. Most commonly the Crabs, use Sponges for camouflage by removing a piece of a living Sponge and holding it against their shell. One of the most well known association occurs between the Sponge 'Suberites domuncula' and Hermit Crabs. Hermit Crabs live in the shells of Gastropod Mollusks on which the Sponge is placed. It is a mutually beneficial association as the Hermit Crab gains protection of the Sponge which has an unpleasant smell and taste which discourages attack by fishes and other enemies. On the other hand the Sponge gets benefit of transportation. Sometimes Porifera kill those they cover; the Sessile (attached) Barnacle 'Balanus balanoides', for example, may be killed in this way. Various Plants and Animals may live on the surface of the Sponge or inside its canals and cavities. Some of these  Animals are Crustaceans, Nematode, Polychaete Worms, Ophiuroid Echinoderms (brittle stars), and Bivalve Mollusks.

Colour - Porifera come in a variety of colours.  Deep-water Sponges are usually of neutral colour, drab or brownish. While shallow-water Sponges are frequently brightly coloured, ranging from red, yellow, and orange to violet and occasionally black. Most calcareous Sponges are white. Some Sponges like, the Spongillidae, are often greenish because green Algae live in a symbiotic relationship within them; others are violet or pinkish, because they harbour symbiotic blue-green Algae. These symbionts endow the Sponges with colour as long as light is available; the Sponges become white in the dark when no photosynthesis occurs and the Algal pigments utilized in photosynthesis are no longer produced.

Size - The height and width of Sponges ranges from less than one inch (a few millimetres) to about 6.5 feet (2 meters).

Diet - Most of Porifera feed on Bacteria and other food particles in the water, some host photosynthesising micro-organisms as Endosymbionts and these alliances often produce more food and oxygen than they consume. A few Species of Sponge that live in food-poor environments have become carnivores that prey mainly on small Crustaceans. They capture small Crustaceans with their spicules (Small pointed structures) which act like Velcro when they come in contact with the Crustacean exoskeletons. Cells then migrate around the helpless prey and digestion takes place extracellularly. Other Sponges harbour symbionts such as Green Algae, Dinoflagellates, or Cyanobacteria, from which they also derive nutrients.

Porifera Distribution (geographical range & habitat)

Sponges are found worldwide, from the polar regions to the tropics. They occur in rivers and streams, from rock pools to the deep ocean depths, from frozen arctic seas to the warm tropical seas. The greatest numbers of Sponges are usually found on firm surfaces such as rocks. Sponges are more abundant but less diverse in temperate waters than in tropical waters, possibly because organisms that prey on Sponges are more abundant in tropical waters.

Poriferans: History and Evolution

It is widely considered that Poriferans arose from Flagellated Protozoans. The primitive structure of the Porifera indicates affinities with certain types of Protozoan colonies; both lack integration of parts, mouths, and digestive systems, and both have a type of skeletal formation in which single elements are produced by a single cell or by a small group of cells. The earliest evidence of Poriferans in the fossil record consists of traces of 24-isopropylcholestane, a chemical formed by the breakdown of lipids in Sponges, that date back to the Cryogenian Period of the Proterozoic Era (about 635 million years ago). The first Sponge skeletons, however, appear in rocks that date to the Ediacaran Period (630 million to 542 million years ago). Calcareous Sponges appear in the Carboniferous Period (about 345 million to 280 million years ago). The first members of order Pharetronida from the Permian Period (about 280 million to 230 million years ago) had compact calcareous skeletons and spicules. Present day Sponges do not differ substantially from many groups in the Paleozoic Era.

Porifera Reproduction

Some Sponges start sexual reproduction when only a few weeks old, while others wait until they are several years old. Sponges reproduce by both asexual and sexual means, however they are only one gender at a time, being either Male or Female or neuter. Some Species like 'Halichondria moorei' change colour when they change sexes though most do not. Sponges have no permanent gonads, instead a number of areas of the Sponge will during the reproductive period become differentiated (changed) to produce either sperm or ova (eggs). Sperm are frequently 'Broadcast' into the water column, i.e. the sperm are created, concentrated and sent out the excurrent openings, sometimes in masses so dense that the Sponges appear to be smoking. These sperm are subsequently captured by Female Sponges of the same Species. Inside the Female, the sperm are transported to eggs by special cells called 'Archaeocytes'. Fertilization occurs in the mesenchyme and the zygotes develop into ciliated larvae. Some Sponges release their larvae, where others retain them for some time. Once the larvae are in the water column they settle and develop into juvenile Sponges. Sponges that reproduce asexually produce buds or, more often, gemmules, which are packets of several cells of various types inside a protective covering. Fresh water Sponges of the Spongillidae often produce gemmules prior to winter. These then develop into adult Sponges beginning the following spring.


Sponges have three asexual methods of reproduction:

i)  After Fragmentation - Fragments of Sponges may be detached by currents or waves, and perhaps by predators. They use the mobility of their Pinacocytes and Choanocytes and reshaping of the mesohyl to re-attach themselves to a suitable surface and then rebuild themselves as small but functional Sponges over the course of several days.

ii)  By Budding
- Very few Species reproduce by budding. Budding is possible only if a Sponge fragment contains both collencytes to produce mesohyl and archaeocytes to produce all the other cell types.

iii)  By Producing Gemmules - Gemmules are 'Survival Pods' which a few marine Sponges and many freshwater Species produce by the thousands when dying. Spongocytes make gemmules by wrapping shells of spongin, often reinforced with spicules, round clusters of archaeocytes that are full of nutrients. The gemmules then become dormant, and in this state can survive cold, drying out, lack of oxygen and extreme variations in salinity. Freshwater gemmules often do not revive until the temperature drops, stays cold for a few months and then reaches a near-"normal" level. When a gemmule germinates, the archaeocytes round the outside of the cluster transform into 'Pinacocytes', a membrane over a pore in the shell bursts, the cluster of cells slowly emerges, and most of the remaining archaeocytes transform into other cell types needed to make a functioning Sponge. Gemmules from the same Species but different individuals can join forces to form one Sponge. Some gemmules are retained within the parent Sponge, and in spring it can be difficult to tell whether an old Sponge has revived or been recolonized by its own gemmules.