KINGDOM ANIMALIA (Phylum Chordata) - Part V

 Characteristics of Chordates:

All chordates have a number of structures in common:

• A notochord (noto = the back; chord = string) is present in all embryos, and may be present or absent/reduced in adults. This is the structure for which the phylum was named.
• A dorsal, hollow, ectodermal nerve cord (compare with Annelida and Arthropoda which have ventral, solid, mesodermal nerve cords) typically forms by an infolding of the ectoderm tissue, which then “pinches off” and becomes surrounded by mesoderm. Spinal bifida is the failure of the nervous system to close.
  
• The pharangeal slits (pharynx = throat) originally functioned in filter feeding: water is taken into the mouth and let out via the pharangeal slits. The slits filter out food particles and keep them in the animal’s body so they can be put into the digestive tract. In fish, these have become modified as gills, and in humans as our ears and eustachian tubes.
• A postanal tail (post = behind, after; anal refers to the anus) is present and extends behind the anus in many taxa, thus the anus isn’t at posterior tip of body. In humans, the tail is present during embryonic development, but is subsequently resorbed. 

Taxonomy of Chordates:

 

• Subphylum Cephalochordata (cephalo = head), which doesn’t have a “head.” This subphylum includes lancelets (or lancets), so-named for their shape. These are in genus Branchiostoma (branchio = gill, fish; stoma = mouth) which was formerly know as genus Amphioxus (amphi = on both sides, double) Lancets look a lot like the generic chordate described above. They have a notochord, but no bones. They are about one inch long, and live in the muddy ocean floor.
• Subphylum Urochordata (uro = tail) are called the tunicates. Their larvae show typical chordate characteristics, but the adults have lost many of these organs, and what they do still have have become highly-modified.
• Subphylum Vertebrata may have come from an Amphioxus-like ancestor, however vertebrates have a definite head and Amphioxus doesn’t. Another theory suggests that vertebrates may have come from a larval form similar to tunicate larvae that were capable of reproduction in the larval stage, that is, they are sexually mature prior to metamorphosis, which is referred to as paedogenesis (paedo = child — same root as in pediatrician; genesis = origin, birth), defined as the precocious attainment of sexual maturity in a larva. Vertebrate characteristics include:
  • vertebrae, the skeletal units surrounding the nerve cord
  • a brain, enclosed within a skull
  • an endoskeleton which will grow along with the animal (unlike arthropods which must molt)
  • a closed circulatory system with a ventral heart
  • excretion via kidneys
  • separate males and females with sexual reproduction in most, with a few cases of parthenogenesis
  The Classes in Subphylum Vertebrata include:
  
  • Class Agnatha (a- = not, without; gnatho = jaw) which is the lampreys. They do not have jaws, are eel-shaped, prey on fish, and have larval forms which are different from the adults.  
  • Class Chondrichthyes (chondro = cartilage; ichthys = fish) which includes sharks and rays. They have a cartilage skeleton, not bone. They are not buoyant like other fish so they must swim or sink. Like other fish they have a lateral line system which detects differences in water pressure, the equivalent of our hearing.
  •  Class Osteichthyes (osteo = bone) is the bony fish. This is the most numerous of all vertebrate classes. In fish, O₂ is exchanged via the gills, which are covered by an operculum which helps to draw water across/through the gills. Their swim bladder is an air sac used to control buoyancy, thus unlike the sharks, bony fish can hold still at any depth and not sink. 
  • Class Amphibia (amphi = on both sides, double; bios = life) is frogs, newts, and salamanders. They were the first land vertebrates. Frogs, especially, go through metamorphosis. Their eggs have no egg shells, so the sperm can swim through the water to the eggs, and the embryos must develop in water.  
  • Class Reptilia (reptili = creeping) is the dinosaurs (dino = terrible; saur = lizard), snakes, turtles, crocodiles, and lizards. Reptiles have scales and are dry to the touch. Their eggs have leathery shells. Reptiles are exothermic (exo = out, outside), that is they maintain their body temperature through external means such as sunning on a rock or seeking shade. Reptiles need less food/energy to live and live longer than a comparable-sized mammal. Some dinosaurs may have been endothermic. 
  • Class Aves (avi = a bird) is the birds. It is thought that birds are descended from dinosaurs, as evidenced, in part, by the scales on their feet. Also, feathers are modified scales: a key characteristic of birds is that they have feathers. (It is also now known that many kinds of dinosaurs had feathers.) Birds’ bones are light weight for flight. Birds are endothermic (endo = within, inner), that is, they control their body temperature from within (they’re “warm-blooded”). Birds’ vision is the best of all vertebrates: soaring hawks can spot small mice scrambling through the grass in a field far below them. Birds have shelled eggs and so must have internal fertilization — the egg muct be fertilized before the hen’s reproductive tract secretes an eggshell. Generally, mating is accompanied by an elaborate courtship ritual. Eggs and often young birds are more exothermic (are not able to control their body temperatures from within) and so must be brooded/incubated by parents. 
  • Class Mammalia (mamma, mammil = teat, nipple) is the mammals. Key characteristics of mammals are the presence of fur/hair and mammary glands, derived from modified sweat glands, which produce milk for the young. Mammals have a diaphragm to aid in respiration. They are endothermic. Most mammals bear live young.
  • • Subclass Monotremes (trema = hole) includes the platypus and spiny anteater. These mammals lays eggs like reptiles, but do have fur and milk. However, they have no nipples: their mammary glands just secrete milk onto the fur, from which the babies lick it. They have one posterior opening for their digestive, urinary, and genital tracts, hence the subclass name. 
    • Subclass Marsupials (marsupi = a bag, pouch) includes opossums, kangaroos, koalas, etc. The young are born as very immature embryos and must crawl to their mother’s pouch to continue their development. Typically, once in the pouch (marsupium) a baby would find a nipple there. Because of continental drift, there is a wide variety of marsupials in Australia, yet few elsewhere on Earth.  
    • Subclass Placentals (placent = a round, flat cake) contains most of the animals with which we are familiar. In this taxon, young complete embryonic development within the mother’s uterus and are nourished across a placenta.
    
      Source : http://biology.clc.uc.edu/courses/bio106/chordate.htm

KINGDOM ANIMALIA (Phylum Arthropoda) - Part IV

Characteristics of the Arthropoda:-
1)Bilaterally symmetrical (in most cases).
2)Body has more than two cell layers, tissues and organs.
3)Body cavity a true coelom.
4)Most possesses a through straight gut with an anus (in most cases).
5)Body possesses 3 to 400+ pairs of jointed legs.
6)Body possesses an external skeleton (in most cases).
7)Body is divided in 2 or 3 sections.
8)Nervous system includes a brain and ganglia.
9)Possesses a respiratory system in the form of tracheae and spiracles (in most cases).
10)Possesses a open or lacunnar circulatory system with a simple heart, one or more arteries, and no veins, (in most cases).
11)Reproduction normally sexual and gonochoristic, but can be parthenogenetic.
12)Feed on everything.
13)Live everywhere.

Introduction

Among the living animals of the world Crabs and Prawns, Woodlice, Spiders, Scorpions, Insects, Millipedes and Centipedes are all Arthropods, linked together by the possession of a hard jointed exoskeleton, a through-gut and jointed limbs.
Arthropods are currently thought to have evolved from Annelids. Both groups have the same sort of central nervous system, a similar circulatory system along with metameric segmentation and tagmatization (see below).
The phylum Arthropoda is huge in terms of both numbers of species and in terms of numbers of individuals. They have diversified to live in every habitat imaginable, from the tropics to the poles, from the bottom of the oceans to the tops of mountains, both underground and inside other animals and plants, where ever you look Arthropods are ubiquitous. Most of the invertebrates you encounter during your life will be Arthropods, in fact if you only noticed them you would realise that most of the living things you encounter in your life are Arthropods. With an amazing 1 million named species (and estimates of total species numbers rising to 30 million) the Arthropods represent over 80% of the Animal Kingdom and probably at least half of all living organisms.
Arthropods are amazingly diverse in form and function and in many cases fundamental characteristics have been secondarily lost, either completely or are only visible in embryonic form, hence the suite of '(in most cases)' in the list above. Most of these problems are generated by the Crustacea whose variability is incredible.
Because of their huge numbers, and the density at which they occur in many habitats, on land, in the soil, in fresh water and in the sea, arthropods are of immense importance to the ecology of the whole planet. It is true to say that without them complicated multicellular life on this planet would simply collapse and probably disappear all together. Their economic importance to mankind is also beyond measure, they are important in nutrient recycling in both aquatic and terrestrial environments, comprising the key workers in most ecologies. They supply food directly for huge numbers of Amphibians, Fish, Birds and Mammals and Reptiles and indirectly for more still. As insects their value as pollinators of flowering plants and therefore as preservers of floral diversity is incalculable, while there contribution to modern biological and ecological research is equally extensive.
The arthropoda have been around for a long time and several major, and many minor lineages are now extinct, perhaps the most well know of these are the Trilobites. The first arthropods evolved in the warm seas of the Cambrian period about 540 million years ago. Amongst the first arthropods were animals called Euthycarcinoids, creatures that appear to have been halfway between insects and crustaceans. Trace fossils, fossils left by animal activities, indicate that around 500 million years ago these long extinct arthropods were possibly the first animals to colonize the terrestrial environment. Certainly scientists believe that arthropods, first as detritivores (feeding on dead plants and micro-organisms) and then as carnivores were the first animals to live on land.
The living Arthropoda can be divided into three subphyla, 16 classes and innumerable orders and families. The higher level classification of the Arthropoda is given below along with links to pages containing more specific information on each of the groups.

• Phylum Arthropoda

  • Subphylum Chelicerata

    Body in two parts, no antennae.
    • Class Merostomata (Horseshoe Crabs)
    • Class Arachnida (Spiders, Mite, Scorpions e.t.c.)
    • Class Pycnogonida (Sea Spiders)

    Subphylum Crustacea

    Body in three parts, thorax in eight segments.
    • Class Cephalocarida (Small primitive shrimps only discovered in 1955)
    • Class Branchiopoda (Small primitive animals with gills on their feet i.e. Daphnia)
    • Class Ostracoda (small animals which look like miniature bivalves)
    • Class Mystacocarida (Minute thin shrimp like creatures)
    • Class Copepeda (Important small crustaceans such as Cyclops)
    • Class Branchiura (Small blood sucking ectoparasites)
    • Class Cirripeda (Barnacles)
    • Class Malacostraca (75% of all Crustaceans, Crabs, Lobsters, Shrimps and Prawns as well as Woodlice)

    Subphyllum Uniramia

    Body in three parts, thorax in three segments.
    • Class Insecta (Insects)
    • Class Chilopoda (Centipedes)
    • Class Diplopoda (Millipedes)
    • Class Symphyla (Small centipede like creatures which live in leaf litter)
    • Class Pauropoda (Small soft bodied animals of the forest floor)

Metameric Segmentation and Tagmata

Metameric segmentation is where the body is divided into a series of repeated segments, as in a millipede for instance. Each segment then performs all the functions of the body trunk sections, has legs, nerves, breathing apparatus, a unit of digestive tract and all the same organs and tissues. Each segment is in fact a copy of the one before it and the one behind. This is obvious in some arthropods like millipedes but not so obvious in others. What has happened in the others is called tagmatization. This is where groups of segments become specialised to perform specific functions for the whole body, these groups of segments are called Tagmata (Singular = Tagma). Careful dissection and analysis can reveal the underlying form of the original metameric segment in most cases. Some tagmatization occurs in the annelids, i.e. the head with its various appendages, however in the arthropods it has become far more advanced, reaching its ultimate expression in animals like Spiders and Barnacles which do not appear to have any segmentation at all to the casual observer.

(Source : http://www.earthlife.net/inverts/arthropoda.html

KINGDOM ANIMALIA (Vermes) - Part III

The term worm /ˈwɜrm/ is used in everyday language to describe many different distantly related animals that typically have a long cylindrical tube-like body and no legs. Worms vary in size from microscopic to over 1 metre (3.3 ft) in length for marine polychaete worms (bristle worms), 6.7 metres (22 ft) for the African giant earthworm, Microchaetus,and 58 metres (190 ft) for the marine nemertean worm (bootlace worm), Lineus longissimus.Various types of worm occupy a small variety of parasitic niches, living inside the bodies of other animals. Free-living worm species do not live on land, in marine or freshwater environments, or burrow.
In biology, "worm" refers to an obsolete taxon (vermes) used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, and stems from the Old English word wyrm. Most animals called "worms" are invertebrates, but the term is also used for the amphibian caecilians and the slow worm Anguis, a legless burrowing lizard. Invertebrate animals commonly called "worms" include annelids (earthworms), nematodes (roundworms), platyhelminthes (flatworms), marine polychaete worms (bristle worms), marine nemertean worms ("bootlace worms"), marine Chaetognatha (arrow worms), priapulid worms, and insect larvae such as grubs and maggots.
Worms may also be called helminths, particularly in medical terminology when referring to parasitic worms, especially the Nematoda (roundworms) and Cestoda (tapeworms) which reside in the intestines of their host. When an animal or human, is said to "have worms", it means that it is infested with parasitic worms, typically roundworms or tapeworms.

Classification

In everyday language, the term worm is also applied to various other living forms such as larvae, insects, centipedes, shipworms (teredo worms), or even some vertebrates (creatures with a backbone) such as blindworms and caecilians. Worms can be divided into several groups, but are still technically decomposers.

• The first of these, Platyhelminthes, includes the flatworms, tapeworms, and flukes. They have a flat, ribbon- or leaf-shaped body with a pair of eyes at the front. Some are parasites.
• The second group contains the threadworms, roundworms, and hookworms. This phylum is called Nematoda. Threadworms may be microscopic, such as the vinegar eelworm, or more than 1 metre (3 feet) long. They are found in damp earth, moss, decaying substances, fresh water, or salt water. Some roundworms are also parasites. The Guinea worm, for example, gets under the skin of the feet and legs of people living in tropical countries.
• The third group consists of the segmented worms, with bodies divided into segments, or rings. This phylum is called Annelida. Among these are the earthworms and the bristle worms of the sea.

In earlier taxonomic classification, all the above were included in the now obsolete group Vermes.
There are hundreds of thousands of species that live in a wide variety of habitats other than soil. Over time this broad definition narrowed to the modern definition, although this still includes several different animal groups.
To most people the most familiar worms^{[citation needed]} are the earthworms, members of phylum AnnelidaEarthworms in general have been around for 120 million years. They enrich and aerate the soil; Charles Darwin found that worms turn over the top six inches (15 cm) of topsoil every 20 years in a field near where he lived. In less favourable conditions, such as waterlogged soils or hard soil deficient in suitable organic matter, or in seasonally dry soils, they cannot achieve anything like that. They lack a brain in the sense of the vertebrate brain, but have nerve centers (called ganglia); they also lack eyes but can sense light with photoreceptors. Worms are hermaphrodites (both sexes in one animal) but can cross fertilize.
Other invertebrate groups may be called worms, especially colloquially. In particular, many unrelated insect larvae are called "worms", such as the railroad worm, woodworm, glowworm, bloodworm, inchworm, mealworm, silkworm, and wooly bear worm.
Worms may also be called helminths, particularly in medical terminology when referring to parasitic worms, especially the Nematoda (roundworms) and Cestoda (tapeworms). Hence "helminthology" is the study of parasitic worms. When a human or an animal, such as a dog or horse, is said to "have worms", it means that it is infested with parasitic worms, typically roundworms or tapeworms. Deworming is a method to kill off the worms that have infected a human or animal by giving anthelmintic drugs.
"Ringworm" is not a worm at all, but a skin fungus.

Characteristics

Some species of earthworms have a tongue-like lobe above the mouth called prostomium. The prostomium is actually a sensory device. Earthworms do not have a nose, eyes, ears, or hands to gather sensory information about their environment. Instead, they depend on their prostomium and sensory receptors in their skin to "feel" their way through the soil. Worms usually have a cylindrical, flattened, or leaf-like body shape and are often without any true limbs or appendages. Instead, they may have bristles or fins that help them move. A few have light-sensing organs. Worms vary in size from less than 1 mm (0.04 inch) in certain aschelminths to more than 30 m (100 feet) in certain ribbon worms.
Some worms reproduce sexually. Hermaphroditism, the condition in which a single individual possesses both male and female reproductive parts, is common in many groups of worms. Asexual reproduction, whereby new individuals develop from the body cells of another, also occurs in some worms.
Worm species differ in their abilities to move about on their own. Many species have bodies with no major muscles, and cannot move on their own—they must be moved by forces or other animals in their environment. Many other species have bodies with major muscles and can move on their own; they are a type of muscular hydrostat. Many species of worms are decomposers; they break down dead plants and animals to return nutrients to the soil. They have also been known to infiltrate households feeding on food in the early stages of decomposition, namely breads and cheeses^{[citation needed]}.
Earthworms are divided into three different categories. The first are the surface dwellers, the Epigeic worms. Then there are the upper soil worms, the Endogeic worms. Finally, there are the deep burrowing species, the Anecic.

(Source : http://en.wikipedia.org/wiki/Worm)

KINGDOM ANIMALIA (Phylum Cnidaria) - Part II

Cnidaria (Source : http://www.earthlife.net/inverts/cnidaria.html)    Characteristics of Cnidaria:- 1)Radially Symmetrical. 2)Body multicellular, few tissues, some organelles. 3)Body contains an internal cavity and a mouth. 4)Two different forms exist, medusa and polyp 5)Reproduction is asexual or sexual. 6)Has a simple net like nervous system. 7)Has a distinct larval stage which is planktonic. 8)Lives in aquatic environments, mostly marine. 9)Mostly carnivorous otherwise filter feeders. 10)May have a minimal skeleton of chiton or calcium carbonate.

Introduction

The Cnidaria (pronounced nidaria)as a group of animals are well known to many people under their common names, Sea Anemones, Corals and Jellyfish are all Cnidarians as are Hydras, Sea Whips, Sea Fans and Sea Pansies. They are linked together by their carnivorous feeding habits their simple anatomical design and the possession of nematocysts, though one species of Ctenophora possesses nematocysts as well.

 

The name Cnidaria has now pretty much replaced the older term of Coelenterata (pronounced selenterata) which these days is often applied to both the Cnidaria and the Ctenophora together, these two phyla are also known as the Radiate Animals because they both have radial or biradial symmetry. The word Cnidaria refers to Cnidocysts, specialised cells which contain the Nematocysts, the stinging organelles that allow the Cnidaria to subdue their prey.
The Cnidaria are the oldest of the true metazoan phyla. A fossil Hydrozoan from South Australia called Ediacara is 700 million years old, while numerous fossil Cnidarians exist from the Cambrian 500 million years ago. The Cnidarians, particularly the corals often make up an important component of the shallow marine fauna of tropical and subtropical seas. All the Cnidaria are aquatic and nearly all are marine. Corals because of their shallow marine environment and their habit of accumulating a mineralised skeleton (coralite) tend to fossilize well and we know quite a bit about their evolution.
The Cnidarian body is basically a U shape with intact walls that surround a central digestive area and a mouth at the opening, generally surrounded by tentacles, there is no distinct anus. In Anemones the mouth faces up, and in Jellyfish it faces down. The Cnidarians show a more complicated arrangement of cell layers as well as a greater range of cell types than the Porifera. Their bodies show two distinct layers of cells and thus they are called 'Diploblastic animals'. The two cell layers are an outer Epidermis or Ectoderm, and an inner Gastrodermis or Endoderm. These two layers are separated by the mesoglea a non-cellular fibrous jelly like material that is thin in some groups such as the Hydras but can be quite thick in other such as the Jellyfish where it helps provide negative buoyancy (makes the animal more likely to float). The ectodermis consists of five basic cell types, Epitheliomuscular cells which supply some of the muscular capabilities of the animal, Interstitial cells which are basic cells that give rise to the other cell types, Cnidocysts (see below), Mucous glands and sensory or nerve cells. The endodermis consists of three or four basic cell types Gastromuscular cells which help digest food items and provide some muscle power, Gland cells that secrete enzymes for digestion, Mucous cells and in Anemones but not in Hydras, Cnidocytes.
One of the most important distinguishing characteristics of the phylum are the Nematocysts. Nematocysts, and their enclosing Cnidocysts come in about 24 different forms, the differences play a functional role in the classification of the phylum. A Cnidocyst is a cell that secretes a nematocyst within it. A basic Nematocyst is a capsule made of something like chitin within which rest a coiled thread. This thread can be shot out of the capsule to encounter prey items, or in some cases to repel predators. The Cnidocyst has either a modified flagellum called a Cnidocil, or a cone as a sensory trigger. If this trigger is touched the nematocyst thread is rapidly ejected. Nematocyst threads come in 3 basic types. The fundamental nematocyst is a thin tubular thread with barbs at the far end, though there may be barbs near the base as well. When the nematocyst is discharged, the barbs penetrate the skin of the prey and a toxin can be injected. Ptychocysts are uncommon, occurring only in the Ceriantharians, they lack spines or barbs but are adhesive and can be used to line the tubes the Ceriantharians live in as well as to entangle prey. Spirocysts also lack barbs or spines, they are an enclosed tube that is adhesive, they are used to trap prey in a tangled net of sticky threads.
Though a few people get stung by jellyfish every year, and a very few of these stingings may be fatal, the only Cnidarians to have a real impact on human beings are the corals. Corals and the reefs they form are important breeding areas for fish, some of which are commercially important, they are also important in terms of biodiversity because of the wide range of creatures that live preferentially, or only in or near coral reefs. Thirdly they are of importance because of their beauty and thus their use as a tourist attraction, coral reefs are among the most beautiful and colourful places on the planet. It is a sad truth, and a condemnation of humanity that these structures which take hundreds or thousands of years to develop are rapidly being destroyed in one way or another by mankind, over 75% percent of reefs are now suffering some sort of damage, many are completely dead. To add to their troubles reef building corals, which live in a delicate balance with the dinoflagellate Symbiodinium microadriaticum have a very narrow temperature range within which they produce new coral skeleton faster than the rest of nature whereas it away. This temperature range is 23 to 29 degrees C, or 73 to 84 degrees F. There are fears that global warming could have a disastrously destructive effect on the world's remaining coral reefs.
The Cnidaria come in two basic forms, a 'Polyp' form typified by the Sea Anemones and a 'Medusa' form typified by Jellyfish. Generally speaking Polyps are tube shaped and sedentary with a ring of tentacles around the mouth, Medusae are umbrella or bell shaped, free living and have a central projection on the inside of the umbrella which supports the mouth and their tentacles around the rim of the umbrella.
The Cnidarians are either carnivores or omnivorous filter feeders.The the carnivorous forms do not hunt their prey, instead they use various 'sit and trap' or 'float/swim and trap' strategies, using their Nematocysts, which are not only found on the stinging tentacles but can be all over the animals body, to stun and or kill their prey. There are about 10, 000 species of Cnidarians divided between 3 classes Hydrozoa, Scyphozoa and Anthozoa.

Class	Life Style	Form	Habitat	Genera
Hydrozoa	Solitary or colonial, sessile as adult	Sexual polyps and asexual medusa either of which may be absent.	Freshwater and Marine	Hydra, Obelia, Physalia, Tubularia
Scyphozoa	Solitary, nearly all free swimming	Sexual medusa with a reduced or absent polyp	Marine only	Aurelia, Cassiopeia, Chironex, Rhizostoma
Anthozoa	Solitary or colonial sessile as adult	Polyp only	Marine only	Adamsia, Cerianthus, Gorgonia, Renilla

KINGDOM ANIMALIA (The Opening and Phylum Porifera) - Part I

Kingdom Animalia 
(Source : http://biology.tutorvista.com/organism/kingdom-animalia.html)
The major group of animals are classified under the Kingdom Animalia, also known as Metazoa. This kingdom does not contain prokaryotes. All the members of this kingdom are multicellular, eukaryotes. They are heterotrophs, they depend on other organisms directly or indirectly for food. Most of the animals ingest food and digest in the internal cavity. Most of the organisms are motile which means they can move independently and spontaneously.

There are around 9 to 10 million species of animals, and about 800,000 species are identified. Fossil records of animals were found in the era of the Cambrian explosion, about 540 million years ago. Animals are divided into various sub-groups, biologists have identified about 36 phyla within the animal kingdom including birds, mammals, reptiles, fish, amphibians etc.

Phylum Porifera

(Source : http://www.earthlife.net/inverts/porifera.html)

 

Characteristics of Porifera:-
1)No definite symmetry.
2)Body multicellular, few tissues, no organs.
3)Cells and tissues surround a water filled space but there is no true body cavity.
4)All are sessile, (live attached to something as an adult).
5)Reproduce sexually or asexually, sexual reproduction can be either gonochoristic or hermaphroditic.
6)Has no nervous system.
7)Has a distinct larval stage which is planktonic.
8)Lives in aquatic environments, mostly marine.
9)All are filter feeders.
10)Often have a skeleton of spicules. 

Sponges are one of the better known groups of invertebrates, due to their usefulness in the bath many people who care nothing for invertebrates at least know name and may even have seen a sponges skeleton on sale in a shop. One of the more amazing things about sponges is there ability to suffer damage. Because the cells are not linked in a tissue it is possible for them to be separated an then come together again. Some species such as the freshwater sponge Ephydatia fluviatilis can be pushed through a sieve, then if given time the individual cells will come together again and make a new sponge.

A sponge is a simple organism that is easy to describe. A sponge is a sedentary, filter-feeding metazoan which has a single layer of flagellated cells that drive a unidirectional current of water through its body. such a brief description though does not do them justice. Sponges are an ancient and highly successful group of animals. In the Palaeozoic they are believed to have comprised more than half the biomass in marine reefs. They have been living in the waters of the world for more than 600 million years, and can now be found in all marine and many freshwater habitats. Sponges occur in rivers and streams, from rock pools to the deep ocean depths, from frozen arctic seas to the warm tropical seas. They are perhaps at their most beautiful in tropical marine seas. There are about 10,000 known species and though their basic organisation is pretty simple and remains fairly constant throughout the all species they do manage to show a great variety of forms.

Anatomy

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. The skeletal elements of sponges are variable and important in taxonomy. Throughout this 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). Many if not 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.
There are three main types of canal system in sponges. The simplest form is Asconoid, here the canals run straight through the sponge body and all the choanocytes line the central large space called the 'spongocoel'. The water enters the ostia, is drawn through to the spongocoel and leaves through a single large osculum. Asconoid sponges have cylindrical hollow bodies and tend to grow in groups attached to some object or other in relatively shallow seas.
Slightly more complicated are Syconoid sponges, externally they are fairly similar to asconoid sponges except that their body wall is thicker. The canals are branched however and do not allow the water to flow straight through in to the spongocoel. Instead the water flows a twisted route through a number of canals some of which are lined with choanocytes before being expelled into the spongocoel and out through the osculum. The spongocoel is not lined with choanocytes only the canals. Syconoid sponges go through a asconoid stage in their development suggesting that they evolved from some ancestral asconoid. Syconoid sponges do not normally form groups as do asconoid sponges.
Most modern sponge species are Leuconoid. In leuconoid sponges the canal system is more complicated again with the canals being longer and more branched, they lead to special chambers whose walls are lined by choanocytes, there are no choanocytes in the canals. There is no real spongocoel just a central exit canal leading to the osculum. Leuconoid sponges tend to live in large groups with each individual sponge having its own osculum, however the borders between individual sponges are often hard to define and the sponge may act more like a large communal organism.
Sponges are built up from relatively few cell types, the main ones being choanocytes, pinacocytes, amoebocytes and lophocytes.
Choanocytes are vase shaped cells with a collar of fine fibrils connected by microvilli. this is a filter which 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. 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 (they are 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.
Amoebocytes 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 spongioblast, 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.
Lophocytes 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.
Sponges have skeletons, if it were not so they would be just blobs. 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. These spicules are important in the classification of sponges, thus we can say that.
The Calcarea sponges 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.
The Demospongiae have their spicules made from silica and they have 1,2, or 4 rays.
The Sclerospongiae have a compound skeleton of spicules of silica that is restricted to thin layer of living sponge supported on a large basal layer of calcium carbonate.
The Hexactinellida or 'Glass sponges' have spicules made from silica that are 6 rayed.
Individual spicules can be arranged loosely within the spongin or interlocking and fused together, siliceous spicules come in two sizes called megascleres and microscleres.

Ecology

All sponges are filter feeders on small to extremely small particles and most are sedentary or immobile as adults, i.e they spend their adult lives fixed to a substrate.
The reproductive ecology of most sponges has never been studied so the following generalisation is based on the few species that are reasonably well known and should not be taken as the last word in sponge reproductive ecology.
Sponges are generally hermaphroditic, however they are only one gender at a time, being either male or female or neuter, some species such as 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 is released into the canals and is then pumped out of the sponge through the osculum where it is likely to be drawn into the canal system of another sponge. Here incoming sperm of the same species are trapped by the choanocytes which then loose their flagellum and collar and migrate through the mesohyl to the ovocyte, a cell generating ova, where the sperm are transferred to the ova, assuming this is a sponge in its female form. Sperm release can be an individual act as in Verongia archeri or it can be a co-ordinated affair with many sponges in an area releasing their sperm simultaneously as in Neofibularia nolitangere.
The fertilised ova are retained within the adult sponge until some unknown signal indicates it is time for their release. They are then set free into the surrounding waters. Once an adult begins expelling its larvae it continues to do so for some time, thus Microciona coccinea releases 4 or 5 larvae per minute for 3 to 4 days.
Larval sponges are small 50 microns to 5 millimetres in diametre. all known sponge larvae are ciliated though the cilia may be longer, shorter or absent from different parts of their surface. After release they swim or crawl for a period of time before settling down to begin life as a new miniature sponge. Swimming species tend to have a crawling phase immediately before settling down. This free living stage may last as long as 18 to 20 days in Polymastia spp. or be as short as 4 to 6 hours in genera such as Ophlitaspongia. Larval sponges are not complicated organisms, and there is much variation between species however many species have a positive phototaxis when they first leave their parents body which switches to a negative one before they enter the presettling stage. Some species have been shown to have a preliminary negative geotaxis while most species have shown a preference for surfaces with an algal or bacterial film. As with the larval stage so the time taken for the larvae to reorganise itself into and functioning sponge varies between species so that Microciona spp. are up and running within two days while Polymastia spp. can take as long as 7 days to get themselves sorted.
Sponges also reproduce asexually by releasing fragments of themselves, or special groups of cells called gemmules. These gemmules, at least in freshwater species such as Ephydatia fluviatilis have protective coat of spongin and have particular environmental conditions they need to have met before they germinate.

 

Classes

(Source : Wikipedia)

Sponges were traditionally distributed in three classes: calcareous sponges (Calcarea), glass sponges (Hexactinellida) and demosponges (Demospongiae). However, studies have shown that the Homoscleromorpha, a group thought to belong to the Demospongiae, is actually phylogenetically well separated. Therefore, they have recently been recognized as the fourth class of sponges.
Sponges are divided into classes mainly according to the composition of their skeletons^:

	Type of cells	Spicules	Spongin fibers	Massive exoskeleton	Body form
Calcarea	Single nucleus, single external membrane	Calcite May be individual or large masses	Never	Common. Made of calcite if present.	Asconoid, syconoid, leuconoid or solenoid
Hexactinellidas	Mostly syncytia in all species	Silica May be individual or fused	Never	Never	Leuconoid
Demospongiae	Single nucleus, single external membrane	Silica	In many species	In some species. Made of aragonite if present.	Leuconoid
Homoscleromorpha	Single nucleus,  single external membrane	Silica	In many species	Never	Sylleibid or leuconoid