A Spineless Column by Ronald L. Shimek, Ph.D.

Featherless Duster Worms and Lamp Shells

Some of the oddest types of animals found on coral reefs belong to what are called, by biologists, the Lophoporate phyla. There are several discrete and different types of animals found in this group, but they all share a specialized feeding and respiratory structure consisting of a circular or horseshoe-shaped band of thin tentacles called a lophophore. Most taxonomic authorities consider that there are three to five discrete groups of animals with such a structure, and I will be describing two of those groups, the Phoronida and the Brachiopoda.

Figure 1. Phoronopsis harmeri from the N.E. Pacific, showing the animal extending from its tube and feeding. The lophophore tentacles are clearly visible as is the red line of the major internal blood vessel.

A lophophore is a band of ciliated tentacles found along a ridge slightly elevated from the surface of the animal. This ridge is centered on the mouth so that the tentacles are found in a symmetrical pattern on either side of the mouth. These tentacles are covered with tracts of microscopic cilia and mucous producing cells creating "food grooves" to convey tiny particulate material to the mouth. The tentacles are extended into the water and collect small particles, bacterial particulates and phytoplankton cells. The particles stick to the mucus and the mucus is moved by the cilia. The food grooves run down the inner center surface of each tentacle and meet a larger "collection" groove at the tentacle base. The two collection grooves run along the bases of all the tentacles on each side of the lophophore and one enters each side of the mouth. This arrangement of mucus, cilia, food grooves, and tentacles is called, for obvious reasons, a ciliary-mucous suspension feeding apparatus. The tentacles of the feather-duster worms have a similar architecture and function, but unlike the feather dusters, the tentacles of the lophophorate animals are generally smaller, unbranched, more numerous for the size of the animal, and they don't have a feather-like appearance. The tentacles of lophophorates may appear quite like those of hydroids or most other small cnidarian polyps; however, there are distinct differences. The polypoid tentacles lack food grooves, so they can't be ciliary-mucous suspension feeders, and the lophophore tentacles lack nematocysts, so they cannot sting.

Figure 2. The lophophore of a phoronid living in sediments. The mouth of the animal is located in the triangular-shaped structure on the inside of the middle of the "back" of the "C" shaped ridge of tentacles.

The animals with lophophores are small, but complex, beasts. All lophophorates possess organs arranged into digestive, reproductive, excretory, circulatory and nervous systems. There are three major groups of lophophorate animals, each put into one of the major taxonomic groupings called a phylum. These three phyla are the phoronids, the lamp-shells (or brachiopods), and the moss animals or bryozoans. The most successful and widespread of these groups is the Phylum Bryozoa, and it will be discussed it in a later column. The other two phyla are the subject of this column.

The Phylum Phoronida

Nobody sets out to purchase phoronids: they are really a curiosity that may incidentally enter an aquarium. The Phylum Phoronida is probably the least successful major animal group in terms of species number and diversity. There are only two genera, Phoronis and Phoronopsis, and there are probably less than 30 species known. However, total species diversity is only one measure of success, for while there are less than fifty species of phoronids, there are phoronids in darn near every marine habitat. Occasionally very abundant, such as along the sand and mud flats of the California coast, most often they are patchy and rare, but they are almost always present.

These creatures are all tube-dwelling, sessile worms. They form their tubes by secretions from the glandular epidermis of the body surface using a combination of some organic matrix and inorganic materials such as sand grains. The tubes are straight and are typically longer than the animals. Differing species may exist either as solitary animals or as aggregations, and in some cases they form "colonies" from asexual reproduction and budding. If they are aggregated, the tubes are often intertwined into an inseparable mass.

Here is an image of a phoronid worm, with its tube removed:

Here is some information about phoronids, including some interesting images of the worms and their tubes: http://www.ucmp.berkeley.edu/brachiopoda/phoronida.html

The body wall is highly muscular, and the animals are capable of rapid retraction into the tube, which is often buried in sediments. Typically, the buried bulbous bottom portion of the worm is anchored deeply in the sediments. Strong longitudinal muscles run from the bulb to the upper portion of the animal. When some threat is sensed, the muscles contract and rapidly pull the animal down into the sediments. The nervous system has some giant fibers allowing for very rapid conduction of nervous impulses, and this can result in the worm being able to retract completely into the sediments within a few thousandths of a second. The tentacles are not retractile, and when the animal withdraws into its tube, the tentacles are simply pulled along with the rest of the body.

Here is a diagram of a phoronid showing some of the internal structures:

The gut is "U-shaped" with the mouth and the anus on the upper exposed surface of the animal. The digestive system is regionated with specialized digestive regions. Phoronids collect particulate organic material with the lophophore, and their food is rich in diatoms and bacteria. Unlike mollusks and some other invertebrates, the digestion of food occurs in the gut cavity and digested food is absorbed across the gut lining, much as in vertebrates or annelid worms. They have a well-developed circulatory system, which allows the distribution of dissolved nutrients to all parts of the body. They also possess hemoglobin, in corpuscles, as a respiratory pigment, and the lophophore functions as a respiratory organ as well as a food gathering one.

Figure 3. A colonial mass of phoronids living in a clam shell. The bright white objects are embryos being protected in the bases of the lophophores. Each lophophore is about one tenth of an inch across.

Aquarium Occurrences

Nobody sets out to purchase phoronids: they are really a curiosity that may incidentally enter an aquarium. The most likely way for them to enter our aquaria is either in burrows in live rock or associated with some other animals. Many species of Phoronis are capable of burrowing into calcareous rock or shells, and colonies might well be imported with the rocks. Occasionally, they are found living with other animals; Phoronis australis is found living in the tubes of tropical cerianthids, or tube anemones.

Phoronids are long worms which, like feather dusters, have a crown of tentacles at the head end. The tentacle crowns of phoronids are distinctive, but close examination is required to distinguish them from feather-dusters. Generally, these are small animals, with a tentacle crown less than a centimeter in diameter. The tentacles are absolutely straight; they cannot curl or bend. The most significant diagnostic feature is their lack of side branches. So, unlike the feather-like tentacles of the feather dusters, phoronid tentacles are perfectly straight without side branches. No other worms with tentaculate crowns have unbranched tentacles. The tentacle crowns may be white, translucent gray, green, brown or black depending on the species. When viewed from above, the crowns often look horseshoe-shaped, usually with the ends of the horseshoe coiled in on themselves a few times.

These are suspension-feeding animals, living on fine plankton and will need supplemental small plankton, such as phytoplankton, to survive in captivity. Phoronids should be kept with their associated animals or rock and should not be manipulated as they tend to break easily. If the species is Phoronis australis, living on cerianthid tubes, a deep sand bed will provide both the appropriate habitat and supplemental food in the form of suspended bacterial particulates. For species acquired on live rock, supplemental microplankton feeding will be necessary. Given an appropriate habitat and sufficient food, these animals are capable of living indefinitely in aquaria.

The Phylum Brachiopoda

Figure 4. Some individuals of the temperate articulate brachiopod, Terebratalia transversa, on a rock.

This phylum has a large fossil record (30,000 species) but relatively few living species (250 species). Some ancient brachiopod fossils from the species Lingulella have been used to define the beginning of the Cambrian period about 525 million years ago and are effectively identical to those of the living Lingula, which makes Lingula a true living fossil. It is rather mind-boggling to consider that this species may not have changed much in morphology for over 500,000,000 years.

All brachiopods are marine animals, and most are found in relatively shallow water. They have bivalved shells, similar to clams. Unlike the mollusks, however, where the shells are found laterally on each side of the animal, brachiopod shells are dorsal and ventral to the body between them.. In some of these animals, one of the shells has a hole in it for some tissue to pass through. These particular shells may look a bit like an ancient oil lamp, and have given the whole group the common name of "lampshells." Brachiopod individuals may be large with the shells of some species that attach to rocks reaching up to four inches (10 cm) across. While the free-living forms typically have smaller shells, they have an equally long stalk or peduncle extending into the sediments.

Brachiopods are probably closely related to the phoronids discussed above, and may be considered to be basically phoronid-like animals enclosed in a pair of shells. They have an exceptionally complex lophophore enclosed within the valves. Where the phoronid crown of tentacles is generally in the shape of a simple horseshoeor slightly coiled horseshoe, that of the brachiopods is much larger, and looks like a horse-shoe with the ends rotated and spiraled, so that the tentacles on each lateral branch look something like the tentacle arrangement in a Christmas tree worm. Such a structure is structurally very complex, and it is quite difficult to understand just exactly how it works.

Brachiopods have two distinct functional modes of living; they are either attached to rocks or burrowed into sediments. There are also two taxonomic types of brachiopods which are distinguished by their internal anatomy. To make things a bit difficult, however, these two internal divisions don't correspond to the two functional modes of life. Both taxonomic groups may be found attached to hard substrata, but only one type can burrow into sediments.

All brachiopods are suspension-feeding organisms. The gut has a large digestive gland extending from the stomach, and unlike the situation in the phoronids, digestion appears to occur largely within the cells of some digestive glands which sit adjacent to the gut. In one group of brachiopods, those with shells connected with a hinge, the gut is blind-ending and lacks an anus; in the other group, the shells are not connected yb a hinge and there is an intestine and anus. As in the phoronids, brachiopods are large enough to require a circulatory system, with a pulsating vessel which moves the blood, to move nutrients, wastes, and dissolved gases around the inside of the body. Some of them have a blood pigment present in cells or corpuscles. They have no specific respiratory system, but the blood circulates in the lophophore and, as in the phoronids, gas exchange undoubtedly occurs across the tentacle surfaces. Sexes are separate and they generally have planktonic larvae, although some may brood their young in the shells. The nervous system in both brachiopod groups is in the typical invertebrate pattern with the major nerves connected to a nerve ring found surrounding the esophagus. This ring has a small ventral ganglion which is dignified with the name of brain. Sensory reception is poorly known, but they have chemosensory and photosensory capabilities, even though no discrete sensory organs are known.

Here is a link to a diagram of an articulate brachiopod showing some of the internal structures: http://www.biology.ucsc.edu/classes/bio136/brachiopoda/brachiopoda.gif

Here is a link to an articulate brachiopod opened to show the internal structures, as well as to provide a good discussion of articulate brachiopod structure and anatomy:

The shells may be made of either calcium phosphate or calcium carbonate and are opened and closed by muscle action, from different muscle groups. Contrast this with the bivalved mollusks where the shells are closed by muscles, but opened by the hinge ligament.

For a wealth of brachiopod information, images, and data, see this website:

Articulate Brachiopods or Brachiopods Whose Shells Are Connected By A Hinge

Figure 5 . An articulate brachiopod, Hemithiris psittacea, from the North Pacific. The animal is about one inch wide and is fastened to the rock by a fleshy stalk.

Articulate brachiopods look superficially like clams, as they have two shells. The doral/ventral orientation of the shells results in one characteristic that makes these particular brachiopods easy to recognize, and which may be used to distinguish them from clams. In clams the two shells are generally very similar in shape, while in brachiopods, they are always dissimilar. Additionally, while clams may be fastened to rock by proteinaceous byssal threads or calcium carbonate cement, articulate brachiopods are ALWAYS fastened to the substrate with a fleshy stalk, and they are unable to move from the position to which they are cemented.

Articulated brachiopods must remain attached to their rock for survival. If removed from the rock, they will die shortly thereafter. They are typically found in areas of relatively high current, often on rock rubble. If such rubble is collected and used as live rock in an aquarium, the brachiopod comes along for the ride.

One common tropical species is Frenulina sanguinolena. This particular species may be recognized by its basically orange, tan or golden shell coloration, often with a contrasting zigzag pattern of darker coloration, and reaches a width of 2 to 3 cm. However, there are number of other brachiopods with similar shell shapes and colors.

Here is an image of Frenulina sanguinolenta:

Articulate brachiopods feed by using the cavity within the shells to assist the lophophore in collecting their food, and need to be oriented correctly in relation to current flow to filter efficiently. Frenulina sanguinolena needs rather strong, consistent, currents blowing over it. It will pivot on its stalk or peduncle to orient for maximum feeding efficiency. Articulate brachiopods will need dietary supplements of phytoplankton in most aquaria, and will benefit from being in an aquarium with a well-established deep sand bed community where planktonic bacterial aggregates are produced by the sand bed fauna.

Inarticulate Brachiopods or Brachiopods With Their Shells Connected Together Only By Muscles

Figure 6. An adult and several juvenile inarticulate brachiopods fastened to a rock. These are Neocrania californica, and the adult is about an inch across.

Probably the most abundant of the tropical inarticulate brachiopods, Lingula reeve is very abundant in many tropical sand and mud flats where it lives buried in the sand within a burrow, with just the tip of the shells exposed. Lingula is an inarticulate brachiopod, and these animals differ from articulate brachiopods in having symmetrical shells. It may be recognized by its paired glossy greenish or greenish-yellow to tan shells, which have a long stalk or peduncle projecting from their rear. The stalk is the burrowing and anchoring organ, and it allows the animal to move up and down in its burrow.

For an image of Lingula, see this link: http://paleo.cortland.edu/tutorial/Brachiopods/Brachiopod%20Images/lingula.GIF

For an image of fossil Lingula or Lingulella follow this link:

Here is an image of Glottidia, a Gulf of Mexico animal related to Lingula:

As with other totally infaunal animals, Lingula is a very decidedly null pet. On the other hand, as a curiosity for the scientifically inclined, it is a VERY neat animal, indeed. Shells effectively identical to modern Lingula are found in some of the earliest fossil beds dating from around a half a billion years old. This makes this species a living fossil, and as such makes an interesting addition to an aquarium.

As with many suspension-feeding animals, individuals of Lingula will need supplemental small plankton such as phytoplankton, and they should be housed in a tank with a deep sand bed. The deep bed will provide both the appropriate habitat and supplemental food in the form of suspended bacterial particulates. Given a deep sand bed, and sufficient food, these animals are capable of living indefinitely in aquaria.


The larger Lophophorates, such as brachiopods and phoronids, could make interesting additions to either "species" tanks or to more diverse reef community tanks. Phoronids are occasionally food for some fishes such as bat rays, but probably are not eaten by most reef aquarium animals, and should persist in reef tanks if given sufficient food. Sand- or mud-dwelling brachiopods in the genera Lingula or Glottidia are common in shallow areas in the tropics, where they live in burrows. They can be kept in a tank with a deep sand bed, and certainly could easily be collected. However, I don't know of anybody that has actually been sold one. If they were not purchased specifically, it is possible, but unlikely, that individuals could enter the tank with some uncleaned tropical sand. They do survive well in captivity, however, as numerous individuals have been kept in research aquaria for varying lengths of time. In contrast, the attached brachiopods are mostly found on rocks, and have been brought into aquaria with live rock, where they survive well. I have maintained temperate species in tanks for several years. In nature, brachiopods appear to have a long life expectancy, 20 years or more. Provided they get the appropriate food, there is no reason to suggest that they won't live a long life in a reef aquarium.

If you have any questions about this article, please visit my author forum on Reef Central.



Kozloff, E. N. 1990. Invertebrates. Saunders College Publishing. Philadelphia. 866 pp.

Ruppert, E. E. and R. D. Barnes. 1994. Invertebrate Zoology. Saunders College Publishing. Philadelphia. 1056 pp.

Tasch, P. 1973. Paleobiology of the invertebrates. John Wiley and Sons. New York and London. 946 pp.

  Specific References Which May Lead You To Other Interesting Information:

Bailey-Brock, J. H. and C. C. Emig. 2000. Hawaiian Phoronida (Lophophorata) and their distribution in the Pacific region. Pacific Science. 54:119-126.

Carlson, S. J. 1995. Phylogenetic relationships among extant brachiopods. Cladistics. 11:131-197.

Jin, Y., X. Houx and H. Wang. 1993. Lower Cambrian pediculate lingulids from Yunnan, China. Journal of Paleontology. 67:788-798.

Johnson, A. 1997. Flow is genet and ramet blind: consequences of individual, group and colony morphology of filter feeding and flow. In: Lessions, H. A. and I. G. Macintyre. Eds. Proceedings of the eighth international coral reef symposium, Panama, June 24-29, 1996. Smithsonian Tropical Research Institute. Balboa, Panama. pp. 1093-1096.

Nielsen, C. 1991. The development of the brachiopod Crania anomala (O. F. Muller) and its phylogenetic significance. Acta Zoologica (Stockholm). 72:7-28.

Raup, D. M. 1969. Modeling and simulation of morphology by computer. Proceedings of the North American Paleontological Convention. September 1969:71-83.

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Featherless Duster Worms and Lamp Shells by Ronald L. Shimek, Ph.D. - Reefkeeping.com