 | This article includes a list of general references, but it lacks sufficient corresponding inline citations .(June 2011) |
| Enopla | |
|---|---|
 | |
| Terrestrial nemertean Geonemertes | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Nemertea |
| Class: | Enopla Schultze, 1851 [1] |
| Subgroups | |
Enopla is one of the classes of the worm phylum Nemertea, characterized by the presence of a peculiar armature of spines or plates in the proboscis.
The record of nemerteans is extremely sparse, as would be expected from a soft-bodied animal. The Cambrian fossil, Amiskwia , has been interpreted as a nemertean based on its resemblance to some pelagic ribbon worms; however, this interpretation is disputed by many paleontologists. The enoplan nemerteans have been regarded as highly derived based on a more complicated muscle arrangement in the body wall and a more complex nervous system. However, whether this is a plesiomorphic or apomorphic character is not clear, and recent molecular studies are inconclusive in this respect.
Class Enopla used to be divided in two subclasses, Hoplonemertea and Bdellonemertea, but recent phylogenetic analyses based on nucleotide sequences show that Bdellonemertea should be included in Hoplonemertea. Hoplonemertea (in the old sense) contains two suborders, Monostilifera and Polystilifera. The encompasses those animals with a proboscis armature consisting of a single central stylet on a large cylindrical basis. The Polystilifera are armed with a pad, or shield, bearing numerous small stylets. The Polystilifera are further divided in two taxa, one (Pelagica) containing the pelagic species, and the other (Reptantia) with crawling or burrowing forms.
The class is currently divided into 30 families and 155 genera with approximately 650 described species. The two largest genera, Amphiporus and Tetrastemma contain 230 species, i.e., one third of all named species in the class. However, it must be made very clear that the systematics and classification of nemerteans are not based on a phylogenetic approach, and recent studies question the classification.
Enoplan nemerteans are generally small, from less than 1 centimetre (0.4 in) up to 10 centimetres (4 in), although larger species exist. While most nemerteans are rather drab in color, others are more conspicuous with striking pigment patterns and coloration. However, the more brightly colored forms are more common in the class Anopla. A nemertean is generally recognized in the field by the way it moves. Its normal movement is gliding over the surface by help of cilia on the ventral side in combination with mucus produced by the worm. Some species may, under certain circumstances, swim with undulating movements, but only for a short period of time. Enoplans are differentiated by the proboscis, which is armed (i.e., there is a stylet attached to it) in enoplans but unarmed in anoplans. Enoplans have a common opening for the proboscis and mouth, whereas anoplans have separate openings for the two structures.
Enoplan nemerteans are known from all continents and all seas. Terrestrial nemerteans are mainly known from islands in the tropical and subtropical regions, although there are few more widespread species. Freshwater species are also reported from all continents, except the Antarctic.
Enoplan nemerteans are typically found in the sea, in the littoral among algae. While larger species may be found simply by turning over boulders, smaller species are not found unless special techniques are utilized. An easy way of collecting nemerteans is to place seaweed and smaller algae in a bucket of sea water and let it stand for a few hours, and up to a couple of days, depending on weather and temperature. The worms will crawl to the sides of the bucket, where they are easily observed and collected, as the oxygen concentration decreases in the water.
Although nemerteans are abundant, especially in temperate waters, their presence is often overlooked because they are not easily observed. Enoplan nemerteans do not appear to be equally common sublittorally, but this may be a result of biased sampling (less accessible environments). The majority of enoplan ribbon worms are marine and benthic, but there are approximately 100 named and described species of pelagic nemerteans. These creatures inhabit the water column of the world oceans, commonly found at depths of between a few hundred feet and several thousand feet, and they are most abundant at 2,130 to 8,200 ft (625 to 2,500 m).
There are a few freshwater species recorded, of which most are placed in the genus Prostoma . This genus is also by far the most widespread, especially the two species, Prostoma eilhardi and Prostoma graecense . The latter has been recorded from Europe, Africa, Japan, and Australia. The spreading of these animals is probably a result of the exportation and importation of freshwater vegetation.
There are 13 known species of terrestrial nemerteans; a typical feature of these species is that their distribution tends to be restricted to a particular island. These species live in damp places under stones and in rotting wood.
Most nemerteans are solitary, free-living animals.
Nemerteans are common predators in a variety of habitats. Benthic marine enoplans are suctorial feeders and prey mainly on crustaceans. The proboscis is everted and the central armature (the stylet) is used to pierce and immobilize the prey. After inversion of the proboscis, the worm uses its head to probe among the crustacean appendages, seeking a place where it can penetrate the prey; eventually, the head is wedged past the opening and the anterior gut is everted into the opening. It is uncertain whether proteolytic enzymes are inserted through the stylet-produced hole in the exoskeloton—histology of central armature suggests this — but at some stage, enzymes are injected to dissolve the prey's body tissue. Free-living marine suctorial nemerteans appear to be food specialists feeding primarily on amphipods. There are some enoplan species known to feed upon barnacles, limpets, and polychaetes. There are also examples of macrophagus hoplonemerteans that engulf the entire prey after paralyzing it with a blow by the stylet. Freshwater hoplonemerteans are known to feed on oligochaetes, unicellular organisms, insect larvae, and other crustaceans. Very little is known about the ecology of pelagic nemerteans, including diet and feeding behavior.
There is one group of parasitic enoplan nemerteans (family Carcinonemertidae) found among the egg masses of certain crab species that feed on the host's embryos. There are also commensal enoplans (in family Bdellonemertidae) that live in the mantle cavities of bivalves where they feed on plankton from the mantle cavity. Obviously, the proboscis is not used to capture prey and has been (perhaps secondarily) reduced in these species.
Most nemerteans are dioecious, although there are a few hermaphroditic hoplonemerteans. Most species are oviparous, i.e., produce eggs that are laid and hatched externally. Mode of spawning is unknown for most species, but where known, it ranges from widespread release of gametes into surrounding waters, to pseudocopulation with eggs attached in a gelatinous matrix to a benthic substratum. A few species bear living young.
Very little is known about nemertean ecology, distribution, or abundance. It is clear, however, that certain species are the most abundant invertebrate group in some habitats/localities. Whether other species are threatened is almost impossible to say, but the 1996 IUCN Red List of Threatened Species includes six terrestrial nemerteans. Two species ( Antiponemertes allisonae and Katechonemertes nightingaleensis ) are considered Threatened, and Argonemertes hillii as Near Threatened.
There is very little direct significance of nemertean worms to humans. Some species in the family Carcinonemertidae are egg parasites of commercially important species of crustaceans, but the overall economic effect of nemertean parasites is small. [2] Also, many nemerteans produce toxins of which some are nicotinic agonists. Some of these toxins, originally found in a nemertean, have been synthesized and tested in pre-clinical trials as a possible memory enhancer in the treatment of Alzheimer's disease.
Nemertea is a phylum of animals also known as ribbon worms or proboscis worms, consisting of 1300 known species. Most ribbon worms are very slim, usually only a few millimeters wide, although a few have relatively short but wide bodies. Many have patterns of yellow, orange, red and green coloration. The foregut, stomach and intestine run a little below the midline of the body, the anus is at the tip of the tail, and the mouth is under the front. A little above the gut is the rhynchocoel, a cavity which mostly runs above the midline and ends a little short of the rear of the body. All species have a proboscis which lies in the rhynchocoel when inactive but everts to emerge just above the mouth to capture the animal's prey with venom. A highly extensible muscle in the back of the rhynchocoel pulls the proboscis in when an attack ends. A few species with stubby bodies filter feed and have suckers at the front and back ends, with which they attach to a host.
Amiskwia is a genus of soft-bodied animals known from fossils of the Middle Cambrian Lagerstätten both in the Burgess Shale in British Columbia, Canada and the Maotianshan shales of Yunnan Province, China. It is interpreted as a member of the clade Gnathifera sensu lato.
The bootlace worm is a species of ribbon worm and one of the longest known animals, with specimens up to 55 m (180 ft) long being reported, although this has not been confirmed. Its mucus is highly toxic.
Anopla has long been used as name for a class of marine worms of the phylum Nemertea, characterized by the absence of stylets on the proboscis, the mouth being below or behind the brain, and by having separate openings for the mouth and proboscis. The other long used class of Nemertea are the Enopla. Although Anopla is a paraphyletic grouping, it is used in almost all scientific classifications. Anopla is divided into two orders: Palaeonemertea and Heteronemertea.
Palaeonemertea is a class of primitive nemertean worm. It may be para- or polyphyletic, consisting of three to five clades and totalling about 100 species.
Parborlasia corrugatus is a proboscis worm in the family Cerebratulidae. This species of proboscis or ribbon worm can grow to 2 metres in length, and lives in marine environments down to 3,590 metres (11,780 ft). This scavenger and predator is widely distributed in cold southern oceans.
Amphiporus lactifloreus is a species of ribbon worm in the phylum Nemertea. It is found on the lower shore, under stones, in shingle and amongst the fronds of seaweed.
Lineidae is a family of nemertean worms. It contains the following genera:
Prostoma jenningsi is a species of ribbon worm known only from one site near Croston, Lancashire. It was described in 1971, and is believed to be the county's only endemic species. It grows up to 20 mm (0.8 in) long, with 4–6 black eyespots, and has a long eversible proboscis.
Prostoma is a genus of freshwater nemerteans, containing the following species:
Gononemertes australiensis is a parasitic ribbon worm. It lives commensally in the ascidian Pyura pachydermatina found in the sublittoral waters of the New Zealand. G. australiensis was found in specimens of P. pachydermatina collected in Sydney harbor. These worms were found specifically in the atrium of P. pachydermatina. It is dioecious and has several gonads. Each of its gonads produce several oocytes while the male worms carry testes along its parenchyma. Fertilization is external.
Malacobdellidae is a monogeneric family within the phylum Nemertea. It is included with the order Hoplonemertea within the class Enopla.
Tubulanus polymorphus is a species of ribbon worm in the phylum Nemertea. It is found in the northern Atlantic Ocean and the northern Pacific Ocean. It occurs on the lower shore down to about 50 m (160 ft), on sand or gravel, under stones and among seaweed.
Tubulanus superbus, commonly known as the football jersey worm, is a species of ribbon worm in the phylum Nemertea. Found in the northern Atlantic Ocean, the North Sea and the Mediterranean Sea, it occurs from the lower shore down to about 80 m (260 ft), on sand or gravel.
Tubulanus annulatus, commonly known as the football jersey worm, is a species of ribbon worm in the phylum Nemertea. It ranges across the northern Atlantic Ocean, the North Sea and the Mediterranean Sea, being present from the lower shore down to about 40 m (130 ft), on sand, gravel and other habitats.
Cerebratulus lacteus, the milky nemertean or milky ribbon worm, is a proboscis worm in the family Lineidae. This ribbon worm has a wide geographical range on both sides of the northern Atlantic Ocean.
Gorgonorhynchus repens is a species of the proboscis worm in the subclass Heteronemertea and of the family Gorgonorhynchidae. It is to be found on the seabed in shallow water in the Pacific Ocean.
Carcinonemertes errans is a ribbon worm in the family Carcinonemertidae. It lives in symbiosis with the Dungeness crab, consuming the crab's developing eggs. In 1980 it was implicated in the collapse of the Dungeness crab fishery in central California.
Hoplonemertea is an order of ribbon worms in the class Enopla. It contains two suborders:
Dinonemertes arctica is a species of ribbon worm within the family Dinonemertidae. The species was described from a male holotype collected from the Arctic Ocean in its central region at a depth of 2980 meters. A male paratype was also collected in the Greenland Sea at a depth of 2800 meters. D. arctica is distinguishable from other members of the family Dinonemertidae from the common opening of the mouth and rhynchodeum. Its internal morphology is typical of the Dinonemertes genus, consisting of a rhynchocoel wall with three muscle layers.
| Authority control databases: National |
|---|
