Phoronida

(redirected from phoronid)
Also found in: Dictionary, Thesaurus, Medical, Wikipedia.

Phoronida

(fərŏn`ədə), small phylum of slender, wormlike marine tube-dwellers, typically found in temperate, shallow seas. About 10 species are known. Although the body is free in the tube, the organisms extend only a crown of ciliated tentacles (the lophophore) to capture food. Water currents generated by the lophophore cilia sweep food particles against mucus secreted at the base of the tentacles and ciliated grooves propel the food to the mouth. Phoronids have a U-shaped digestive tract, a blood-vascular system containing hemoglobin, and excretory organs called metanephridia. The coelom, or body cavity, is divided into compartments resembling those seen in the Ectoprocta and the Brachiopoda, which are phyla related to the Phoronida; the compartments also resemble those of the Echinodermata. Phoronids are ancient, and some zoologists have suggested they are the ancestors of the brachiopods because of similarities in embryology. Tubes seen in early paleozoic sandstones appear to be identical with modern phoronid tubes, but little is known of their history.

Phoronida

A small, relatively homogeneous group of animals now generally considered to constitute a separate animal phylum. Two genera, Phoronis and Phoronopsis, and about 16 species are recognized.

 Phoronopsis harmeri removed from its tubeenlarge picture
Phoronopsis harmeri removed from its tube

Phoronids may occur in vertical tubes placed just below the surface in intertidal or subtidal mud flats, or as feltlike masses of intertwined tubes attached to rocks, pilings, or old logs in shallow water. In both cases the tubes, composed basically of a secreted, parchmentlike material, are encrusted with small particles of sand or shell. A third living habit concerns those phoronids found inside channels, probably self-made, in limestone rock or the shells of dead pelecypod mollusks.

The geographical distribution of phoronids appears to be worldwide in temperate and tropical seas. There are no records of phoronids from the polar regions.

The body is more or less elongate, ranging in length from about 1.6 to 8 in. (4 to 20 cm), and bears a crown of tentacles arranged in a double row surrounding the mouth which is usually crescent-shaped (see illustration). The anus occurs at the level of the mouth and is borne on a papilla immediately outside the double row of tentacles. The digestive tract is therefore U-shaped, the mouth and anus opening close together at one end of the animal. The tentacles rest on a connective tissue base known as the lophophore. Associated with the mouth is a ciliated flap of tissue known as the epistome. See Lophophore

The phylum includes both dioecious animals and hermaphrodites. All phoronids may reproduce sexually, and in most cases the life history includes the pelagic actinotroch larva. Some species reproduce asexually by transverse fission.

Phoronida

[fə′rän·ə·də]
(invertebrate zoology)
A small, homogeneous group, or phylum, of animals having an elongate body, a crown of tentacles surrounding the mouth, and the anus occurring at the level of the mouth.
Mentioned in ?
References in periodicals archive ?
Moreover, molluscs and annelids form a clade with brachiopods, phoronids, and nemerteans, with ectoprocts more distantly related, but exact relationships between these taxa tend to vary based on the data and analytical approaches used (Kocot, 2013; Struck et al., 2014).
Phoronid larvae were exposed to 1:10 dilutions of bacteria in FSW and aqueous extracts of the hindgut gland.
Although phoronids, bryozoans, brachiopods, and rhabdopleurid pterobranchs each have a single bilateral tentacular feeding structure that surrounds the mouth but not the anus, the cephalodiscid pterobranchs have multiple arms bearing tentacles (6, 12).
This situation differs sharply from the one in lophophorates, where numerous such cells were found in the apical organ of phoronids, although peripheral cells comparable to those of the tetraneuralians have not been clearly identified (Santagata, 2002; Santagata and Zimmer, 2002).
bryozoans and brachiopods), but probably most closely to phoronids.
ABSTRACT Various red abalone shells (Haliotis rufescens) taken from Chiloe X Region, Chile, were examined revealing an enormous amount of vermiform organisms identified as phoronides (Phylum Phoronida) belonging to the genus Phoronis.
The more divergent morphologies present within the Lophotrochozoa confound traditional evolutionary interpretations of many larval and adult characters, especially with regard to the "lophophorates." More recent studies on the development and larval anatomy of phoronids and brachiopods have expanded our understanding of their evolutionary affinities (Santagata and Zimmer, 2002; Santagata, 2004b; Cohen and Weydmann, 2005).
Cornulitids have been affiliated with annelids, tentaculitids, microconchids, cnidarians, molluscs, bryozoans, and phoronids (Fisher 1962; Boucek 1964; Blind 1972; Dzik 1991; Vinn & Mutvei 2005; Vinn 2005, 2006).
For example, phoronids are not colonial, but these lophophorate suspension feeders can live in very dense aggregations (up to 20,000 [m.sup.-2]) (Johnson, 1997).
Induction of settlement and metamorphosis by natural external chemical cues has been demonstrated for species as diverse as cnidarians (e.g., Muller, 1973; Hofmann and Brand, 1987; Morse et al., 1988; Morse and Morse, 1991; Leitz et al., 1994; Fleck and Hofmann, 1995), polychaetes (Wilson, 1952; Jensen and Morse, 1990; Pawlik et al., 1991; Hadfield et al., 1994), sipunculans (Rice, 1988), bivalves (Grassle et al., 1992), gastropods (Scheltema, 1961; Morse and Morse, 1984; Hadfield, 1984), barnacles (e.g., Crisp and Meadows, 1962), crabs (Jensen, 1989; Brumbaugh and McConaugha, 1995), echinoids (Pearce and Scheibling, 1990a, 1991), phoronids (Herrmann, 1995), and ascidians (Young and Braithwaite, 1980).
In other species, sperm enter maternal individuals to fuse with eggs internally, as in some hydroids (see Miller, 1983), the sea cucumber Leptosynapta clarki (Sewell and Chia, 1994), the colonial ascidian Diplosoma listerianum (Bishop and Ryland, 1991; Burighel and Martinucci, 1994a, b), phoronids (see Zimmer, 1991), and the gymnolaemate bryozoan Membranipora membranacea (Temkin, 1994).