Priapulida

(redirected from Priapulids)

Priapulida,

phylum consisting of 17 species of predatory, unsegmented marine worms that live in the sand and mud at the sea bottom. The largest are 4 to 6 in. (10–17 cm) long, but the majority of species are less than .05 in. (.13 cm) in size. The animals consist of a spiny body with an anterior that can be everted or inverted into the trunk for locomotion or feeding. Spines around the mouth and in the pharnyx are everted to capture prey. The sexes are separate and the egg is fertilized externally, hatching into a larval stage in all but one species. Fossil species can be traced to the Cambrian period, but zoologists do not agree on an interpretation of the lining of the body cavity. This would determine if priapulids are coelomates or pseudocoelomates.
The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/

Priapulida

One of the minor groups of wormlike marine animals, now regarded as a separate phylum of the animal kingdom with uncertain zoological affinities. The phylum is a small one with only two genera, Priapulus and Halicryptus.

Priapulida inhabit the colder waters of both hemispheres. They burrow in mud and sand of the sea floor, from the intertidal region to depths of 14,850 ft (4500 m).

Priapulidaenlarge picture
Priapulida

Priapulids are small to medium-sized animals, the largest specimen attaining 6 in. (15 cm) in length. The body of Priapulus is made up of three distinct portions: proboscis, trunk, and caudal appendage (see illustration). Separated by a constriction from the trunk, the bulbous, introversible proboscis usually constitutes the anterior third of the body and is marked by 25 longitudinal ridges of papillae or spines. The mouth is located at the anterior end of the proboscis and is surrounded by concentric rows of teeth. The cylindrical trunk is annulated, but not segmented, and is often covered with irregularly dispersed spines and tubercles. At the posterior end of the trunk there are three openings: the anus and two urogenital apertures.

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Priapulida

 

a small relict group of marine worms of indeterminate taxonomic position. The body ranges in length from a few millimeters to 20 cm. The anterior third of the body, the proboscis, can be drawn inside by means of special muscles (retractors) and can extrude by pressure of cavitary fluid. The presence of a coelom links priapulids to the higher worms; however, unlike most higher worms, priapulids have an unsegmented body. The circulatory system is absent. Respiration occurs through the surface of the body or by means of posterior gill appendages. The nervous system consists of an esophageal ring and a ventral cord, and the excretory and sexual organs are united in a urogenital system. The sexes are separate. Some zoologists believe that the worms are closely related to Nemathelminthes owing to their type of egg cleavage.

There are 8 species of priapulids, embracing 6 genera. In the seas of the USSR, usually two genera, Priapulus and Halicryptus, are encountered.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

Priapulida

[‚prī·ə′pyül·əd·ə]
(invertebrate zoology)
A minor phylum of wormlike marine animals; the body is made up of three distinct portions (proboscis, trunk, and caudal appendage) and is often covered with spines and tubercles, and the mouth is surrounded by concentric rows of teeth.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
In the sea and along its shores swarm organisms of the other living world -- marine diatoms, crustaceans, ascidians, sea hares, priapulids, coral, loriciferans and on through the still mostly unfilled encyclopedia of life.
Hox genes in brachiopods and priapulids and protostome evolution.
Thus, most of the taxa herein are nested within a part of the lophotrochozoan tree, whereas priapulids are near the base of the ecdysozoan clade that includes arthropods (Halanych, 2004; Dunn et al., 2008; Kocot et al., 2010).
(46) The oldest known lobopodian bears certain similarities to a distinctive group of worms called the palaeoscolecid priapulids that also bore small plates or tubercles along their bodies.
The organisms forming those burrows were likely priapulid worms, a worm phylum that is well represented among the Chengjiang and Burgess fossils.
(52) These beds contain abundant and diverse sponges and cnidarians, as well as priapulid worms, annelid worms, lobopods, stem mollusks such as Wiwaxia, and brachiopods.
Hundreds of thousands of fossils representing a myriad of species of soft-bodied algae, sponges, worms (annelids and priapulids), primitive arthropods (a group that today includes insects and shrimps), and primitive members of the group humans belong to, the chordates, have been collected.
Chordates and molluscs also are more diverse today, while poriferans, priapulids, cnidarians and hyolithids are absent from the modern community.
Shale biovolume was dominated by arthropods, with poriferans, echinoderms and priapulids following.
Oblique striation has been described for muscles of platyhelminths, nematodes, gastrotrichs, nematomorphs, priapulids, pogonophora, chaetognathes, annelids, molluscs, brachiopods, and an echinoderm (3-7, 9), and dense bodies are an obvious feature in all taxa.
Invertebrates with erythrocytes are relatively rare, but phylogenetically diverse; they include representatives of the annelids, brachipods, echinoderms, echiurans, molluscs, priapulids, and sipunculans.
Our survey encompasses annelid, brachiopod, echinoderm, echiuran, molluscan, priapulid, and sipunculan representatives among the invertebrates (Table 1), as [TABULAR DATA FOR TABLE I OMITTED] well as a wide range of vertebrates including fish, amphibians, reptiles, birds, newborn marsupials, and placental mammals (Cohen and Nemhauser, 1985; Cohen et al., 1990).