Although Calcarea is considered the primitive group, and are the only sponges with asconoid and synconoid construction, the asconoid and synconoid forms are not necessarily considered primitive conditions.
Sponges will react by closing ostia or oscula, either because of direct physical stimulation or when suspended particles within the sponge are too large or highly concentrated. However, there are no known nerve structures. However, some sponges may respond to electrical impulses.
Perception Channels: chemical ; electric
Sediments effect sponges although they are resistant to hydrocarbons (including detergents) and heavy metals. Particular species have been overharvested.
Reproduction occurs asexually by budding and sexually. Development of fertilized eggs takes place within the sponge. The larval stage has outer flagellated cells, often with spicules. The young break out of the parent's mesohyl, and become free swimming larvae, but not for more than two days.
Sponges have different amoeboid cells in the mesohyl. Acheocytes are large cells with large nuclei. These cells are totipotent, meaning they can develop into any cell type. Sclerocytes, also in the mesohyl, accumulate calcium to produce spicules. Three sclerocytes will fuse to form spicules in intercellular spaces.
Development - Life Cycle: indeterminate growth
There are about 400 described species of sponges in the Calcarea group.
Sponges have been harvested for centuries by many civilizations. Compounds produced by sponges are being explored for pharmaceuticals.
Positive Impacts: body parts are source of valuable material
Sponges in general may make up a significant portion of the benthic biomass. For example, in Antarctica, at depths of 100-200 m, 75 per cent of the benthic biomass are sponges.
Ecosystem Impact: creates habitat
Because of the simple cells that make up sponges, cell types and water currents used by the sponges to obtain food have been extensively studied. Sponges in general use flagellated cells called choanocyte cells to create a current. Choanocytes are located in the interior part of the sponge. In the asconoid structure, the water is drawn in through the ostium (outer pores), goes through the spongocoel or atrium, and out the osculum (the opening in the top of the sponge). Outer pores are 50 micrometers or less, so larger particles and animals are not ingested.
As food or particles are moved through the sponges, amoemoid cells surround and engulf it (pinocytosis and phagocytosis). Particles are caught in the collar part of the choanocyte cells.
Foraging Behavior: filter-feeding
Primary Diet: planktivore ; detritivore
Calcarea sponges are found throughout the oceans, but are mainly in temperate areas.
Biogeographic Regions: arctic ocean ; indian ocean; atlantic ocean ; pacific ocean ; mediterranean sea
Exclusively marine and mainly in temperate regions, Calcarea sponges are usually found in shallower, sheltered waters less than 1000 m. In tropical regions they are associated with coral reefs.
Habitat Regions: temperate ; tropical ; saltwater or marine
Aquatic Biomes: benthic ; reef ; coastal
Other Habitat Features: intertidal or littoral
Calcarea is the only class with asconoid and syconoid construction. All others have leuconoid construction. The calcium carbonate spicules are only megascleres, or large structural spicules. Other groups of sponges have microscleres, which are smaller reinforcing spicules. Most Calcarea are 10 cm less in height, and are dull in color, although some colorful species are known.
Other Physical Features: ectothermic ; heterothermic
Sponges are preyed on by many animals. Spicules, and other compounds, including potential biotoxins, probably discourage most predators.
Most all sponges can reproduce asexually, by regenerating tissues. Sponges also reproduce sexually. Being hermaphroditic, sperm and eggs can be reproduced, sequentially or at the same time. Choanocytes give rise to egg and sperm cells, and archaeocyte cells also give rise to egg cells. Sperm and eggs are released in the water, and most species cross fertilize. Fertilized eggs will develop into free-swimming larvae.
Key Reproductive Features: simultaneous hermaphrodite; sequential hermaphrodite; sexual ; asexual ; fertilization (External ); viviparous
There is no parental investment beyond release of gametes.
The calcareous sponges[2] of class Calcarea are members of the animal phylum Porifera, the cellular sponges. They are characterized by spicules made of calcium carbonate in the form of calcite or aragonite. While the spicules in most species have three points, in some species they have either two or four points.
All sponges in this class are strictly marine, and, while they are distributed worldwide, most are found in shallow tropical waters. Like nearly all other sponges, they are sedentary filter feeders.
All three sponge body plans are represented within class Calcarea : asconoid, syconoid, and leuconoid. Typically, calcareous sponges are small, measuring less than 10 cm (3.9 in) in height, and drab in colour. However, a few brightly coloured species are also known.
Calcareous sponges vary from radially symmetrical vase-shaped body types to colonies made up of a meshwork of thin tubes, or irregular massive forms. The skeleton has either a mesh or honeycomb structure.
Of the 15,000 or so species of Porifera that exist, only 400 of those are calcareans.
Calcarean sponges first appeared during the Cambrian, and their diversity was greatest during the Cretaceous period. Recent molecular analysis suggests the class Calcarea should be designated as a phylum, in particular the first to have diverged in the Animalia.
The calcareous sponges are divided into two subclasses and six orders:
Class Calcarea
Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. p. 104. ISBN 0-03-056747-5.
The calcareous sponges of class Calcarea are members of the animal phylum Porifera, the cellular sponges. They are characterized by spicules made of calcium carbonate in the form of calcite or aragonite. While the spicules in most species have three points, in some species they have either two or four points.
