Calcarea

(invertebrate zoology) A class of the phylum Porifera, including sponges with a skeleton composed of calcium carbonate spicules.

(Calcareous sponges)

Phylum: Porifera

Class: Calcarea

Number of families: 22

Thumbnail description:
Marine sponges with calcareous skeletal elements (spicules)

Evolution and systematics

The fossil record of unambiguously identified Calcarea is relatively poor and fragmented. Most calcareous sponges in the fossil record were classified as either stromatoporoids, chaetetids, archaeocyaths, inozoans, pharetronids, or sphinctozoans. They are common in the Paleozoic and Mesozoic, however, rare in the Cenozoic. It is now established that many of these forms actually belong to several groups of demosponges because of the possession of primary siliceous spicules, and only few to Calcarea (pharetronids and some sphinctozoans). Identification of "true" calcareous sponges in the fossil record is difficult because fossil remains often lack diagnostic spicules at all. Heteractinida, characterized by a spiculate (consisting of six-rayed heteractinid octactines, polyactines) and aspiculate calcitic skeleton, are now regarded as an extinct order of Calcarea, restricted to the Paleozoic. The oldest probable calcareous sponge with affinities to modern subclass Calcaronea (Gravestockia pharetroniensis Reitner, 1992) was described from the lower Cambrain of South Australia. The assignment of many records of so-called "Pharetronida," calcareous sponges with a rigid calcareous skeleton, to subclasses Calcaronea or Calcinea is difficult if they do not possess characteristic spicules to allow precise assignment. However, most Pharetronids probably belong to subclass Calcaronea. The majority of modern spiculate calcareans would be found as dissociated spicules in the fossil record; there is only one record from the middle Jurassic at King's Sutton, Northamptonshire, where the form and arrangement of a calcareous sponge was preserved (Leucandra walfordi Hinde, 1893).

Calcarea are regarded as one of four classes of the phylum Porifera (three extant [Demospongiae, Hexactinellida, Calcarea] and one fossil [Archaeocyatha]), distinctive in possessing a spicule skeleton composed exclusively of calcium carbonate and being the only poriferan taxon realizing all three stages of development of the aquiferous system (asconoid-syconoid-leuconoid). There is still dispute about the true phylogenetic relationships of the three extant sponge classes, including also the relationship of the class Calcarea to other (higher) diploblastic taxa like Ctenophora and Cnidaria. Two competing hypotheses group a) Hexactinellida + Demospongiae more closely together based on the possession of silicious spicules ("Silicea") in contrast to Calcarea ("Calcispongia") and b) Demospongiae more closely with Calcarea based on the possession of a cellular pinacoderm ("Cellularia"/"Pinacophora") to the exclusion of Hexactinellida, which possess a cyncitial tissue structure ("Symplasma"). Both proposals, however, assume poriferan monophyly. More recently, several authors have suggested from ribosomal DNA sequence data that Calcarea might be more closely related to the phyla Ctenophora/Cnidaria than to the other two extant classes of Porifera, rendering phylum Porifera paraphyletic. Class Calcarea was elevated to phylum status ("Calcispongia," a term that was already used in the mid-nineteenth century) (Zrzavy, et al., 1998; Borchiellini, et al., 2001), but as yet without robust statistical support (e.g., Medina, et al., 2001). However, this proposal is not followed in the most comprehensive systematic treatment of sponges to date, the Systema Porifera (Hooper and Van Soest, 2002) and the issue of sponge paraphyly is at the time of writing (2003) far from being resolved. Therefore, it should be regarded as still contentious until further corroboratory data, such as a molecular multi-locus approach, is presented. However, new chemotaxonomic data from lipid biomarkers (Thiel, et al., 2002) support a closer relationship of Hexactinellida and Demosponges. Although this confirms that Calcarea are chemotaxonomically different from "Silicosponges" or "Silicea" (Demospongiae + Hexactinellida), it does not necessarily imply sponge paraphyly.

Number of classes and families: 1 class (Calcarea); 2 subclasses (Calcinea, Calcaronea); 5 orders (2 in Calcinea: Clathrinida, Murrayonida; 3 in Calcaronea: Leucosoleniida, Lithonida, Baeriida); 22 families; 75 genera; about 500 described species.

Physical characteristics

Calcareous sponges are mostly small and inconspicious; they occur in a variety of forms, as single tubes, sometimes vase shaped, a mass of small tubes ("cormus"), a bushy arrangement of single tubes, or sometimes massive without any apparent symmetry. Three types of aquiferous system are realized in Calcarea: asconoid, all internal cavities are lined by choanocytes (flagellated cells) without folding of the choanoderm; syconoid, simple folding of the choanoderm; and leuconoid, choanocytes are arranged in discrete "choanocyte chambers."

Calcareous sponges range from minute size an inch or less (few millimeters), to about a maximum of about 12 in (30 cm) (Pericharax heteroraphis). They are mostly colorless (whitish to beige), sometimes bright yellow (Leucetta chagosensis), dark greenish-brown (Pericharax heteroraphis), or fluorescent red/orange (Leucetta microraphis, sometimes).

Calcareous sponges have a skeleton that is made of calcium carbonate (calcite), composed of free diactines, triactines, tetracines, and/or polyactine spicules, to which a solid basal calcitic skeleton may be added, with either cemented basal spicules or which is fully embedded in an enveloping calcareous cement. Calcareans are viviparous and have blastula larvae.

Distribution

Calcareous sponges are found globally in all oceans, from intertidal to the deep sea, but not the abyss.

Habitat

Calcareous sponges live in diverse habitats. In tropical coral reefs, they dwell mainly in shaded and/or cryptic habitats and prefer calmer waters.

Behavior

Not applicable; calcareous sponges are sessile filter feeders.

Feeding ecology and diet

Calcareous sponges are sessile filter feeders, whose main diet is dissolved organic matter and small particulate matter (bacteria) filtered from seawater by pumping activity.

Reproductive biology

Calcareous sponges have internal fertilization, with egg size ranging from 25 to 100 µm. They are sexual and viviparous, with some species probably asexual by budding.

Conservation status

No species are listed by the IUCN.

Significance to humans

There is no known significance of calcareous sponges to humans.

Species accounts

Resources

Borojevic, R., N. Boury-Esnault, M. Manuel, and J. Vacelet. "Order Baerida." In Systema Porifera, edited by J. N. A. Hooper and R. W. M. Van Soest. New York: Plenum, 2002. ——. "Order Clathrinida Hartman, 1958." In Systema Porifera, edited by J. N. A. Hooper and R. W. M. Van Soest. New York: Plenum, 2002. ——. "Order Leucosolenida Hartman, 1958." In Systema Porifera, edited by J. N. A. Hooper and R. W. M. Van Soest. New York: Plenum, 2002.

Fell, P. E. "Porifera." In Reproductive Biology of Invertebrates. Volume I: Oogenesis, Oviposition and Oosorption, edited by K. G. Adiyodi, and R. G. Adiyodi. New York: John Wiley and Sons, 1983. ——. "Porifera." In Reproductive Biology of Invertebrates. Volume IV: Fertilization, Development, and Parental Care (Part A), edited by K. G. Adiyodi, and R. G. Adiyodi. New York: John Wiley and Sons, 1989. ——. "Porifera." In Reproductive biology of invertebrates. Volume 6 Part A: Asexual propagation and reproductive strategies, edited by K. G. Adiyodi, and R. G. Adiyodi. Chichester, New York: John Wiley and Sons, 1993. ——. "Poriferans, the Sponges." In Embryology: constructing the organism, edited by S. F. Gilbert, and A. M. Raunio. Sunderland, MA: Sinauer Associates, Inc., Publishers, 1997.

Hooper, J. N. A., and R. W. M. Van Soest, eds. Systema Porifera. Guide to the Supraspecific Classification of Sponges and Spongiomorphs (Porifera). New York: Plenum, 2002.

Lévi, C., ed. Sponges of the New Caledonian Lagoon. Paris: Orstom, 1998.

Manuel, M., R. Borojevic, N. Boury-Esnault, and J. Vacelet. "Class Calcarea Bowerbank, 1864." In Systema Porifera, edited by J. N. A. Hooper and R. W. M. Van Soest. New York: Plenum, 2002.

Pickett, J. "Fossil Calcarea. An overview." In Systema Porifera, edited by J. N. A. Hooper and R. W. M. Van Soest. New York: Plenum, 2002.

Vacelet, J., R. Borojevic, N. Boury-Esnault, and M. Manuel. "Order Lithonida Vacelet, 1981, recent." In Systema Porifera, edited by J. N. A. Hooper and R. W. M. Van Soest. New York: Plenum, 2002. ——. "Order Murrayonida Vacelet, 1981." In Systema Porifera, edited by J. N. A. Hooper and R. W. M. Van Soest. New York: Plenum, 2002.

Borchiellini, C., M. Manuel, E. Alivon, N. Boury-Esnault, J. Vacelet, and Y. Le Parco. "Sponge paraphyly and the origin of Metazoa." Journal of Evolutionary Biology 14, no. 1 (2001): 171–179.

Medina, M., A. G. Collins, J. D. Silberman, and M. L. Sogin. "Evaluating hypotheses of basal animal phylogeny using complete sequences of large and small subunit rRNA." Proceedings of the National Academy of Science of the USA 98, no.17 (2001): 9707–9712.

Thiel, V., M. Blumenberg, J. Hefter, T. Pape, S. A. Pomponi, J. Reed, J. Reitner, G. Wörheide, and W. Michaelis. "A chemical view on the most ancestral Metazoa—biomarker chemotaxonomy of hexactinellid sponges." Naturwissenschaften 89 (2002): 60–66.

Wörheide, G., and J. N. A. Hooper. "Calcarea from the Great Barrier Reef. 1: Cryptic Calcinea from Heron Island and Wistari Reef (Capricorn-Bunker Group)." Memoirs of the Queensland Museum 43, no. 2 (1999): 859–891. ——. "New species of Calcaronea (Porifera: Calcarea) from cryptic habitats of the southern Great Barrier Reef (Heron Island and Wistari Reef, Capricorn-Bunker Group, Australia)." Journal of Natural History 37 (2003): 1–47.

Zrzavy, J., S. Mihulka, P. Kepka, A. Bezdek, and D. Tietz. "Phylogeny of the Metazoa based on morphological and 18S ribosomal DNA evidence." Cladistics 14, no. 3 (1998): 249–285.

Atlas of Sponges. (2 July 2003).

[Article by: Gert Wörheide, PhD]

A class of the phylum Porifera, including sponges with a skeleton composed of spicules of calcium carbonate. Calcarea vary from radially symmetrical vase-shaped species to colonies made up of a reticulum of thin tubes to irregular massive forms. Calcareous sponges are mostly of small size and inhabit the shallow waters of all seas, from tidal areas to depths of 600 ft (200 m), with a few species extending down to at least 12,000 ft (4000 m).

Primitive calcareous sponges with an ascon grade of construction consist of colonies of upright tubes with unfolded walls made up of an outer epidermis of pinacocytes and an inner lining of choanocytes. Between these layers of cells is a stratum of mesoglea containing amebocytes and spicules. Cells called porocytes, each perforated by a tubular canal, pierce the walls at intervals and allow water to enter the central cavity or spongocoel. Water leaves by way of a terminal osculum.

A somewhat more complicated structure is seen in calcareous sponges of the sycon grade of construction. Syconoid sponges are usually individual vase-shaped forms with a thick wall enclosing a large central spongocoel opening out through a terminal osculum. In the simplest forms the wall is pushed out at intervals into fingerlike projections, called radial canals, in which the choanocytes are localized. Water enters the radial canals directly through pores without the intervention of special inhalant canals. In most syconoid species, however, a dermal membrane made up of pinacocytes and mesenchyme forms a cortex of greater or less thickness which joins the outer ends of the radial canals. Pores or ostia pierce the dermis and open into inhalant canals which are simply the spaces between the radial canals in some cases.

The leuconoid grade of construction has probably evolved independently among the several lines of calcareous sponges. In those with a syconoid ancestry, the radial canals subdivide into many small flagellated chambers which arise as outpocketings of the radial canal wall.

Fossils clearly referable to the class Calcarea do not appear before the Carboniferous, later than any other class of sponges. The dominant Calcarea preserved from the late Paleozoic (Carboniferous and Permian periods) are the Sphinctozoa. In the Permian probable Calcinea with the pharetronid type of skeleton first appear. Both the Sphinctozoa and the pharetronids become highly varied and abundant in the Permian and Triassic periods. Calcareous sponges remained fairly abundant in shallow water and reefy deposits until the end of the Cretaceous. After that time the Sphinctozoa became extinct and the pharetronids became gradually less abundant. See also Porifera.

Calcareous sponges
"Calcispongiae" from Ernst Haeckel's Kunstformen der Natur, 1904
Scientific classification
Kingdom: Animalia Phylum: Porifera Class: Calcarea
Orders
Subclass Calcinea Clathrinida Leucettida Murrayonida Subclass Calcaronea Baerida Leucosolenida Lithonida Sycettida

The calcareous sponges of class Calcarea are members of the animal phylum Porifera, the cellular sponges. They are characterized by spicules made out of calcium carbonate in the form of calcite or aragonite. While most have three points, the spicule of a calcareous sponge may have two to four points.

All sponges in this class are strictly marine dwellers. All three sponge body plans are represented within class Calcarea : asconoid, syconoid, and leuconoid. Typically, the Calcarea are very small, measuring about 3-4 inches in height. Of the 15,000 or so species of Porifera that exist, only 400 of those are Calcareans.

Species of Calcarea vary from radially symmetrical vase-shaped body types to colonies made up of a reticulum of thin tubes or irregular massive forms. Calcareous sponges are generally sedentary filter feeders, lacking any real tissues. Calcareous sponges are most commonly found in shallow tropical waters. Generally, Calcarea are small sponges. The different shapes of calcareous sponges are relatively simple, either purse, vase, pear or cylinder-shaped. The skeleton has either a mesh or honeycomb structure. Unlike most other sponges, calcareous sponges lack hollow canals, which makes the sponge stronger.

Calcarean sponges first appeared during the Cambrian and their diversity was greatest during the Cretaceous Period. Recent molecular analysis suggests that the class Calcarea should be delegated as a phylum, in particular the first to have diverged in the Kingdom Animalia; the other sponges belong to the phylum Silicarea.

External links

• UCMP: Calcarea

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Calcarea

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