The simplest animals include the sponges (Porifera) and the Cnidaria. Sponges are unsymmetrical or radially symmetrical, with many cell types but no distinct tissues; their bodies contain numerous pores and sharp protective spicules.
Characteristics. All coelenterates are aquatic, mostly marine. The bodyform is radially symmetrical, diploblastic and does not have a coelom. The body has a single opening, the hypostome, surrounded by sensory tentacles equipped with either nematocysts or colloblasts to capture mostly planktonic prey.
Porifera are known informally as "sponges." Gas exchange: The gas exchange in sponges happens by diffusion from the exterior to the cells that absorb molecular oxygen and liberate carbon dioxide. They take up food from the water, digest it, carry nutrients to other cells.
Only sponges (phylum Porifera) have asymmetrical body plans. Some animals start life with one type of body symmetry, but develop a different type as adults; for example, sea stars are classified as bilaterally symmetrical even though their adult forms are radially symmetrical.
Diploblastic organisms are organisms which develop from such a blastula, and include cnidaria and ctenophora, formerly grouped together in the phylum Coelenterata, but later understanding of their differences resulted in their being placed in separate phyla. The endoderm allows them to develop true tissue.
Hydra is a diploblastic animal,i.e., it is derived from two germ layers, the ectoderm and endoderm . These germ layers form two distinct cellular layers, i.e., outer epidermis and inner gastrodermis respectively.
Among animals, sponges show the simplest organization, having a single germ layer. Although they have differentiated cells (e.g. collar cells), they lack true tissue coordination. Diploblastic animals, Cnidaria and Ctenophora, show an increase in complexity, having two germ layers, the endoderm and ectoderm.
Porifera is a diploblastic . They have only 2 germ layers during development and no mesoderm.
Taxonomic level: phylum Porifera; grade of construction: cellular, with no distinct tissues or organs; symmetry: variable; type of gut: none; type of body cavity other than gut: none; segmentation: none; circulatory system: none; nervous system: none; excretion: diffusion from cell surface.
Origins and evolutionThe majority of animals more complex than jellyfish and other Cnidarians are split into two groups, the protostomes and deuterostomes. Chordates (which include all the vertebrates) are deuterostomes.
Platyhelminthes is commonly known as flatworm or tapeworm. Gegenberg gave the term Platyhelminthes. They are advanced diploblastic or lower triploblastic, acoelomate and bilaterally symmetrical metazoan.
Characteristics of Rotifera:Bilaterally symmetrical. Body has more than two cell layers, tissues and organs.
Roundworms (Nematoda) and rotifers (Rotifera) have a body cavity (coelom) where organs are found and that can serve as a hydrostatic skeleton. Their coelom is called a pseudocoelom because it is not completely lined by mesoderm.
The body wall consists of a thin cuticle. Tufts of cilia at the anterior end make up the corona, which is used for feeding and locomotion. Small organisms are extracted as food from water currents created by the ciliated corona. Larger organisms, such as other rotifers, crustaceans, and algae, are also eaten.
Human beings are Eucoelomates and that means they have a true coelom. Lying inner to the mesodermal wall, coelom surrounds the body track of humans and is divided into three parts. Similarly, coelom surrounding the lungs is pleural cavity and the one surrounding digestive organs is called as peritoneal cavity.
Diploblastic: Diploblastic animals do not have body cavities. Triploblastic: Most triploblastic animals develop a body cavity, the coelom. Diploblastic: Endoderm of the diploblastic animals forms true tissues and the gut.
A coelom is a fully-encased, fluid-filled body cavity (gut) lined with mesodermic tissue. Most complex, multicellular animals have a coelom. Cnidarians are not considered to have a coelom because they are diploblastic, so they don't have any mesodermic tissue.
Coelenterates are diploblastic because their boy is mainly composed of two cells layers namely, ectoderm and endoderm.
Body cavities of any sort only exist in triploblastic animals. The Mesoderm gives rise to the skeleton, the muscles, the dermis of the skin, blood and blood vessels, mesenteries and the lining of the coelomic cavity.
Triploblastic animals don't have a false coelom, as they are all true coelomates.
The mesoderm forms skeletal muscle, bone, connective tissue, the heart, and the urogenital system. Due to the evolution of the mesoderm, triploblastic animals develop visceral organs such as stomachs and intestines, rather than retaining the open digestive cavity characteristic of diploblastic animals.
: having three primary germ layers.
Sponges do not have a coelom. A coelom is the cavity within the body in which the intestines, lungs, heart, kidney, etc., are located, and it is sealed off from the outside world. Porifera means pore-bearing. Sponges are covered with tiny pores on the outside called ostia (2).
The bilaterian tree unites two major clades, deuterostomes (e.g. humans) and protostomes (e.g. flies) [1]. Protostome species such as insects, nematodes, annelids, and mollusks have served as invaluable model organisms.
Fossil cnidarians have been found in rocks formed about 580 million years ago, and other fossils show that corals may have been present shortly before 490 million years ago and diversified a few million years later.
Although they have specialized cells for particular functions, they lack true tissues in which specialized cells are organized into functional groups. The cnidarians, or the jellyfish and their kin, are the simplest animal group that displays true tissues, although they possess only two tissue layers.
In Summary: Phylum PlatyhelminthesFlatworms are acoelomate, triploblastic animals.
Any of a major group of animals defined by its embryonic development, in which the first opening in the embryo becomes the mouth. Protostomes are one of the two groups of animals having a true body cavity (coelom) and are believed to share a common ancestor. They include the mollusks, annelids, and arthropods.
Sponges are similar to other animals in that they are multicellular, heterotrophic, lack cell walls and produce sperm cells. Unlike other animals, they lack true tissues and organs. Some of them are radially symmetrical, but most are asymmetrical.
To clarify these issues, the researchers studied nematocyst discharge with an electronic framing-streak camera at a framing rate of 1,430,000 frames per second. They show discharge kinetics of nematocysts in Hydra to be as short as 700 nanoseconds, creating an acceleration of up to 5,410,000 g.
The protostomes are a large and diverse group, classified by their shared characteristics. This is because protostomes are animals such as flatworms, nematodes, segmented worms, mollusks, and arthropods.
