Invertebrate Anatomy OnLine

Eudistylia vancouveri ©

Fan worm


Copyright 2003 by

Richard Fox

Lander University


            This is one of many exercises available from Invertebrate Anatomy OnLine , an Internet laboratory manual for courses in Invertebrate Zoology.   Additional exercises, a glossary, and chapters on supplies and laboratory techniques are also available at this site. Terminology and phylogeny used in these exercises correspond to usage in the Invertebrate Zoology textbook by Ruppert, Fox, and Barnes (2004).   Hyphenated figure callouts refer to figures in the textbook.   Callouts that are not hyphenated refer to figures embedded in the exercise. The glossary includes terms from this textbook as well as the laboratory exercises.  


AnnelidaP, Polychaeta C, Palpata, Canalipalpata, Sabellida O, Sabellidae F (Fig 13-7A)

Annelida P

            Annelida consists of the segmented worms in the major taxa Polychaeta (bristleworms), Oligochaeta (earthworms and relatives), Branchiobdellida (crayfish ectosymbionts), and Hirudinea (leeches) with a total of about 12,000 known species in marine, freshwater, and terrestrial environments.   The segmented body is composed of an anterior prostomium, a linear series of similar segments, and a posterior pygidium.   The prostomium and pygidium are derived from anterior and posterior ends of the larva whereas the intervening segments arise through mitotic activity of mesodermal cells in the pygidium.  

            The body wall consists of a collagenous cuticle secreted by the monolayered epidermis. A connective tissue dermis lies beneath the epidermis. The coelom is lined by a peritoneum which may be specialized to form the body wall muscles.   Most annelids have chitinous bristles, or chaetae, secreted by epidermal cells, that project from the body. The coelom is large, segmentally compartmented, lined by peritoneum, and well developed in polychaetes and oligochaetes but reduced in leeches.   Successive coelomic spaces are separated by transverse bulkheads known as septa which consist of double layers of peritoneum with connective tissue in between.   The right and left sides of each segmental coelom are separated by longitudinal mesenteries which, like septa, are double layers of peritoneum with connective tissue between.    

            The gut is a straight, regionally specialized tube that begins at the mouth at the anterior end and extends for the length of the body to end at the anus on the pygidium.   It penetrates each septum and is supported by dorsal and ventral mesenteries. Like that of most invertebrates, the gut consists of ectodermal foregut, endodermal midgut, and ectodermal hindgut.   The nervous system consists of a dorsal brain in or near the prostomium, a pair of circumpharyngeal connectives around the anterior gut, and a double, ventral nerve cord with paired segmental ganglia and nerves.   The hemal system of most annelids is a set of tubular vessels, some of which are contractile and serve as hearts.   The hemal system is absent or greatly reduced in leeches.   The system includes a dorsal longitudinal vessel above the gut in which blood moves anteriorly, a ventral longitudinal vessel below the gut, in which blood moves posteriorly, and paired segmental vessels that connect the dorsal and ventral vessels. The digestive, hemal, and nervous systems are continuous and pass through the segments.  

            Respiration is accomplished in a variety of ways.   In some, the general body surface is sufficient but gills are present in most polychaetes, many leeches, and a few oligochaetes.  Excretory organs are metanephridia or protonephridia and typically one pair is present in each segment. These osmoregulatory organs are best developed in freshwater and terrestrial species.  The sexes are separate in polychaetes but oligochaetes and leeches are hermaphroditic.   In the ancestral condition paired submesothelial clusters of germ cells were present in each segment and released developing gametes into the coelom.   In derived taxa reproductive functions tend to be confined to a few specialized genital segments. Gametes mature in the coelom or its derivatives and fertilization is external.   Gametes are shed through ducts derived from metanephridia or by rupture of the body wall.   Spiral cleavage follows fertilization. Clonal reproduction is common.  

Polychaeta C

            Polychaeta is a large (8000 species) and diverse taxon of marine annelids thought to be the most primitive of the annelid taxa and the most like the ancestral annelid.   The body of a typical polychaete is divided into segments, each of which bears a pair of fleshy appendages, or parapodia.   The head is often equipped with abundant, well-developed sense organs.   The anterior gut is muscular, sometimes eversible, and frequently equipped with chitinous jaws.   Polychaetes are gonochoric and gametes ripen in the coelom from which they are shed through ducts or by rupture of the body wall.  


            The prostomium has a pair of sensory palps which are lacking in the sister taxon, Scolicida.


     The prostomium has palps with longitudinal grooves.  Although derived from the sensory palps of ancestral polychaetes, these are adapted for either deposit or suspension feeding. Canalipalpatans were once known as “sedentary” polychaetes because they are sessile and live in tubes or burrows which they rarely, if ever, leave.

Sabellida O

            Sabellidans are suspension feeders with the mouth surrounded by a ring or feeding tentacles.   The prostomium is fused with the peristomium. They inhabit permanent tubes which may be constructed of parchment, sediment particles, calcium carbonate, sand, or shell fragments.

            Sabellida includes some of the most beautiful worms including the fan worms, feather duster worms, and Christmas tree worms.

Laboratory Specimens        

            Sabellids are derived, tube-dwelling, suspension-feeding polychaetes.   The head bears a funnel-shaped lophophore-like, ciliated branchial crown composed of numerous featherlike gills arranged in a circle around the mouth (Fig 13-51A, 13-52).   The crown is sometimes called a fan or feather duster, hence the common names "fan worm" and "feather duster worm" for these exquisitely beautiful animals.   Parapodia, the characteristic polychaete segmental appendages, are reduced and inconspicuous but are nevertheless important to the worm and bear well developed specialized chaetae.   The sabellid tube is composed of a secreted parchment-like organic material but often has inorganic material such as sand or silt incorporated in it.   Most species never leave the tube.  

            Sabellid polychaetes are found on most coasts and some species are quite large and easily dissected.   Eudistylia vancouveri is a large sabellid from the North American west coast.   It occurs from Alaska to California in shallow water and can often be found in large numbers on floating docks where it is easily collected.   This account is written specifically for Eudistylia but can be used with a little modification for other sabellids.   If possible, study a living specimen relaxed in isotonic magnesium chloride if possible.  

External Anatomy

            1. Eudistylia constructs and inhabits a thick, pale, leathery, parchment tube which must be removed.   Carefully use scissors to make a longitudinal cut along the length of the tube.   Be careful you do not cut the worm.   It is delicate and easily damaged.   Remove the worm and place it in a long, narrow dissecting pan of magnesium chloride.

            There are three regions of the sabellid body.   The small head consists of the fused prostomium and peristomium.   It is difficult to distinguish between these two regions but the dorsal anteriormost part of the head is the prostomium.   The head bears the mouth and the branchial crown of feeding tentacles.   The second region of the body is the short thorax composed of a few segments posterior to the head.   Most of the body is the abdomen, which is very long and relatively uniform along its length.   The thorax and abdomen are easily distinguished from each other.

            Before proceeding, orient your worm so you can recognize the major axes and directions.   Anterior and posterior are easy.   The branchial crown is anterior and the opposite end is posterior.   The ventral surface of the body is covered by large, pale, rectangular pads of secretory tissue known as ventral shields.   Those of the posterior body are divided by a midventral groove. The ventral shields of the ventral surface of the thorax and abdomen are the best landmarks for recognizing the venter. You should now be able to find the major axes of your specimen and distinguish right from left.    


            The head is composed of the reduced prostomium and the peristomium to which it is fused.   The prostomium is the anteriormost region of the body.   Its embryological origin is different from that of the remainder of the body and it is not considered to be a true segment.   The peristomium is the first true segment of the annelid body.   As its name suggests it surrounds the mouth.   It does not bear setae in sabellids.  

Branchial Feeding Crown

            The sabellid head bears conspicuous right and left bundles of pinnately branched, ciliated radioles (Fig 13-52A).   Together the radioles form the branchial crown, the more or less circular crown of ciliated tentacles that is both the filter-feeding and gas exchange apparatus.   The radioles of the right form half of the branchial crown and those of the left form the other half.  Each bundle of radioles arises in a spiral row around a branchial stalk attached to the head.   The large funnel-like mouth lies ventrally, posterior to the base of the two branchial stalks.   In some species the two halves of the branchial crown are semicircles instead of spirals.

            Each radiole consists of a long central axis from which arise short, pinnately arranged, ciliated side branches, or pinnules (Fig 13-52A,B). In Eudistylia the central axis bears tiny, irregularly arranged, maroon eyespots.   The presence of eyes on the radioles is typical of sabellids although they are not universally present.   The crown can be rapidly retracted into the tube when the eyespots detect danger.              

            Skeleton, nerves, muscles, connective tissue, and blood vessels are present in the radioles.   The branchial crown is supported by an internal connective tissue skeleton.   A slender skeletal rod extends from the head skeleton into each radiole.   The most easily demonstrated part of the head skeleton is a thick bar extending transversely across the head just ventral to the prostomium.   Probe for it with a nadel to locate it and demonstrate its firm consistency.   Most of the muscles operating the branchial crown attach to this skeleton.                                                 

            >1a . The skeletal rods of the radioles of fresh specimens can be revealed by allowing the soft tissues to decompose in isotonic magnesium chloride.   After soaking for 24 hours, the soft tissues can be removed with fine forceps or a brush.   <

Feeding and Respiration

            The deployed branchial crown of sabellids is more or less funnel-shaped, with the mouth at the narrow, posterior apex of the funnel (Fig 13-52A, 13-51A).   The walls of the funnel are formed by the radioles and pinnules.   The axis of each radiole bears the medial, longitudinal radiolar food groove (Fig 13-52B).  

            Each pinnule in turn bears an inconspicuous ciliated pinnular food groove on its medial surface.   This groove leads to the radiolar groove which transports food particles to the mouth.  

            The pinnules bear two types of cilia.   Long lateral cilia on the sides of the pinnule generate the feeding current that moves through the walls of the funnel, between the radioles.   Much shorter frontal cilia in the center of the groove move captured food particles and mucus toward the radiolar groove.   Another set of cilia, the abfrontals, is present on the outer surface of the pinnules to generate a water current toward the tip of the pinnules.   The feeding current generated by the lateral cilia moves into the funnel across its walls and exits through the large open base of the funnel.   Food particles trapped by the mesh of pinnules are moved by laterofrontal cilia to the pinnular groove on the medial surface of the pinnule where they are then moved by the frontals toward the groove of the radiole.

            All the longitudinal grooves of the radioles of each side (right or left) empty into a large stalk groove that spirals down the branchial stalk and empties into the mouth.   The borders of this groove are elaborated at the base of the stalk to form dorsal and ventral lips, passing transversely across the midline, above and below the mouth respectively.   Food collected by the filter of pinnules is sorted and transported to the mouth by this system of grooves.                                                                            

            This is a downstream collecting system in which food is collected on the downstream side of the filter.   It contrasts with the upstream collecting system of lophophorates, pterobranchs, and sipunculans in which water enters the open end of the base of the funnel, exits by crossing the walls, and food is collected on the upstream side of the filter.


            A palp lies beside the first radiole of each branchial stalk and probably represent modified radioles. In Eudistylia these palps are very short, broad, and inconspicuous but in some species they are long.   The palps are ciliated and function in transport of fecal material and gametes from the fecal groove out of the tube as will be seen presently.  

            A single nephridiopore serves the two metanephridia of sabellid polychaetes.   It is median in position and is located dorsally in the dorsal excretory pit beneath the anterior edge of the prostomium.   The pit is between the bases of the two palps and under the transverse bar of the head skeleton.   It is easily seen with magnification.   The nephridiopore inside it is difficult to see. 


            The thorax lies immediately posterior to the head and consists of about 8 chaeta-bearing segments, or setigers.   The number of thoracic setigers varies with species and individual.  The first thoracic setiger bears a conspicuous flangelike collar that fits around the mouth of the tube.   This setiger is known as the collar segment.  

            Polychaetes are characterized by possession of a pair of fleshy, setose, paddlelike parapodia arising from the sides of each segment.   A typical parapodium is biramous, consisting of two branches, or rami.   These are the dorsal notopodium and the ventral neuropodium.   Each ramus is provided with chitinous chaetae; notochaetae in the notopodium and neurochaetae in the neuropodium.   Sabellid parapodia are reduced and do not protrude from the body but nevertheless are composed of the usual two rami. In sabellids, the thoracic notochaetae are long and bristlelike.   They are grouped in a tuft, whereas the neurochaetae are short hooks arranged in a vertical row.

            >1b. Later, when you have finished your study of the internal anatomy, use fine scissors to excise a piece of body wall containing a parapodium.   Make a wetmount and study it with the compound microscope.   Find the two types of chaetae characteristic of sabellids.   You should see a cluster of long, hairlike capillary setae in the notopodium (of the thorax, neuropodium of the abdomen).   Find the long row of hooklike uncini characteristic of thoracic neuropodia (and abdominal notopodia).   Capillary setae are used to move the animal back and forth in the tube whereas the uncini anchor the worm in position in the tube.   <

            Posterior to its collar, the collar segment bears a bundle of long hairlike setae on each side.   These setae are associated with the much reduced parapodium of this segment and belong specifically to its notopodium.   The neuropodium and its setae are absent from the collar segment.

            The ventral surface of each segment (both thoracic and abdominal) is covered with a rectangular pad of thick, glandular epithelium called a ventral shield.   These are covered with secretory epithelium that produces mucus.   Deep transverse grooves separate the shields of adjacent segments.   There is a deep midventral groove on the abdomen but none on the thorax.

            The dorsal surface of the thorax bears a broad middorsal thoracic fecal groove which extends anteriorly over the prostomium and connects with the fecal grooves of the palps, which you saw earlier on the head.   This groove is deepest anteriorly and in preserved specimens may be difficult to discern posteriorly.   The groove is ciliated and moves waste materials anteriorly, to the mouth of the tube.   It will be discussed more fully later.

            >1c.   If your specimen is alive, place a drop of carmine/seawater suspension on the posterior end of the thoracic fecal groove and watch for motion of the particles in the groove.   Note the direction of motion and the destination of the particles.   <


            The remainder of the body is the long, many-segmented abdomen.   The posterior end of the abdomen is the small, inconspicuous pygidium.   Like the prostomium, the pygidium is not considered to be a true segment.   It bears the large anus.

     Note that the positions of the capillary chaetae and uncini are reversed in the abdomen.   Here the dorsal setae are hooks and the ventral setae are bristles.   Note also that the ventral shields are split on the ventral midline by the ciliated abdominal fecal groove.   This ciliated groove extends anteriorly from the anus along the ventral midline for the entire length of the abdomen.   At the junction of abdomen with thorax however, the fecal groove swings to the right, as the lateral fecal groove, runs obliquely across the right side of the body, and joins the posterior end of the thoracic fecal groove, which, you remember, is dorsal.


            The entire fecal groove, consisting of abdominal, lateral, thoracic, and palpal regions, moves feces and gametes anteriorly to the mouth of the tube where they are released from the palps release into the exhalent current exiting the branchial crown.   Animals inhabiting one-ended tubes must, in one way or another, prevent the accumulation of wastes (and gametes) in the closed posterior end of the tube.   Often this is accomplished by a U-shaped gut as in the lophophorates, pterobranchs, and sipunculans, or with a U-shaped body as in the sabellariid polychaetes, or with an anteriorly directed, external transport mechanism, such as the fecal grooves of sabellid and serpulid polychaetes.  

            >1d. Place some carmine/seawater suspension in the anterior end of the abdominal fecal groove and watch its motion.   You should see it pass along the the lateral fecal groove to the thoracic groove.   The particles are mixed with mucus to facilitate transport.   Do you see evidence of this?   Is the system capable of transporting materials away from the pull of gravity?   <

            >1e. Use a carmine/seawater suspension to test other areas of the body surface for ciliary particle transport.   You may find evidence of such flow in the grooves between thoracic segments and along the dorsal midline of the abdomen.   All these flows move particles and water toward the thoracic fecal groove and thus aid in keeping the tube cleared of undesirable materials that would otherwise accumulate.   <

Internal Anatomy

            Use a pair of #1 insect pins to anchor the worm ventral side down in the center of a long, narrow wax-bottom dissecting pan.   Insert the pins at 45° angles through the lateral body wall at the posterior end of the thorax or anterior abdomen.   Be sure to plan ahead and position the worm so all regions of the body can eventually be pinned to the wax and observable with the dissecting microscope.

"     Carefully insert the finest point of your fine scissors through the body wall a little to one side of the dorsal midline. You must penetrate the thick layer of muscles without damaging the organs in the body cavity. The incision should be a little to the right of left of the dorsal midline. The gut tube is attached tightly to the dorsal body wall by a very short dorsal mesentery and a median incision will open the gut as well as the coelom.   This is to be avoided.   Extend the cut anteriorly and posteriorly through the thorax and anterior abdomen.  

            Push the cut edges of the body wall apart and look inside.   The space you see is, of course, the coelom.   It is partitioned by numerous transverse septa which isolate the coelomic space of each segment from that of its neighbors.   In addition, the coelom is partitioned longitudinally into right and left segmental compartments by dorsal and ventral mesenteries.   The dorsal mesentery extends from the dorsal body wall to the gut whereas the ventral mesentery runs from the gut to the ventral body wall.   The dorsal mesentery is very short so that the gut as held tightly to the dorsal body wall as already mentioned.  



            Note the large, tubular, gut filling most of the space in the coelom.   Look for darkly pigmented blood sinuses in the wall of the gut and for dark blood vessels, especially on the septa and body wall.  

            Avoid cutting into the gut tube.   Most of the blood volume is contained in large lacunae in the gut wall and if these are cut, much of the blood will escape.  

            After you have seen the septa, pull the two sides of the body wall apart, tearing or cutting the septa as necessary, and pin the walls to the wax with # 1 insect pins.   Try to avoid damaging the hemal, or any other, system while doing this.   There is no dorsal, longitudinal, blood vessel in sabellids but there is a ventral longitudinal vessel below the gut.   Note that the segmental coelomic compartments are partitioned into right and left halves by the gut and the dorsal and ventral mesenteries.   The procedure will open and expose only one side of the coelom, either right or left, depending on which you chose for your initial incision.   Note the abundant orange chlorogogen tissue on the septa, lateral body wall, and gut tube.

Hemal System

            Because it is easily destroyed, the hemal system should be examined first, before proceeding to other systems.   To study the hemal system, you need to recognize the esophagus and stomach, even though we have not yet studied the digestive system.   Both are located in the thorax.   The esophagus occupies the first 2-3 thoracic segments.    The stomach follows it and is in the posterior thorax.

            The blood of sabellids contains the respiratory pigment chlorocruorin which is a type of hemoglobin.   Chlorocruorin is a green or red pigment.  

            >1f. If the blood accumulating in the coelom of your animal is red, remove some of it to a small culture dish and note its color again.   It may change to green.   The perceived color of this pigment depends, in part, on its concentration.   It is red in high concentration but appears green when dilute. <

            The hemal system of sabellids differs in some respects from the typical annelid plan although it is a variation on that plan.   It is similar to the pattern in Amphitrite, another canalipalpatan polychaete (Fig 13-20). Chief among these differences is the presence of a large blood sinus in the gut wall instead of the usual dorsal longitudinal vessel.   Find the blood sinus in the wall of the gut.   It will be obvious in your specimen, if it is still filled with blood.   It covers all of the gut posterior to the esophagus and is dark due to the chlorocruorin in its blood.   A large ventral longitudinal vessel can be seen in the mesentery ventral to the gut.   There is no dorsal longitudinal vessel except in the head.   A series of paired segmental vessels run from the ventral blood vessel dorsally over the lateral body wall to the gut sinus.   At the anterior end of the stomach the gut sinus ends.   A short dorsal blood vessel arises from it on the dorsal midline and extends into the head.   Laterally a large esophageal plexus of vessels arises from its anterior end.   The dorsal vessel gives rise to a pair of circumesophageal vessels which run around either side of the esophagus to join ventrally and form the ventral blood vessel.   Arising from the anterior end of the dorsal vessel are the vessels supplying the branchial crown. Ultimately, there is one blind branchial vessel for each radiole.



            Blood moves anteriorly in the gut sinus propelled by contractions of muscles in its outer wall.   It is forced into the short dorsal vessel and the esophageal plexus.   Blood in the dorsal vessel goes to the radioles, or into the circumesophageal vessels to the ventral vessel.   Blood enters the branchial vessels due to pressure generated by the gut sinus but cannot return to general circulation from the blind vessels of the crown by this mechanism.   Circular muscles in the wall of the branchial vessels contract to force blood (now oxygenated) back into general circulation.   A valve prevents its entry into the dorsal vessel and requires it to join the flow in the circumesophageal vessels to the ventral longitudinal vessel.   Blood in the ventral vessel moves posteriorly as it does in other annelids and exits via the segmental vessels to the gut sinus.   You will probably not see all these vessels, especially those in the head, but the gut sinus, ventral longitudinal vessels, segmental vessels, and esophageal plexus are usually easily demonstrated in living specimens with intact hemal systems.  

Numerous small blind capillaries extend as tiny papillae from some of the vessels of the body wall into the coelom and are easily seen.   They are clustered in little tufts on the lateral body wall, especially in the thorax.

Digestive System

            The gut tube runs longitudinally from mouth to anus, both of which you should already have seen.   The gut is regionally specialized.   Its epithelium is ciliated.   It is best studied by opening it with a longitudinal incision.   Begin with a middorsal incision through the head to the mouth.  

"     Cut posteriorly through the gut on the side exposed earlier.   Identify the regions of the gut as you move posteriorly.  

            The mouth opens into a short buccal cavity occupying the interior of the head.   The buccal cavity opens posteriorly into a relatively longer esophagus in the anterior 2 or 3 thoracic segments.   Its inner walls are longitudinally ridged.   There is no blood sinus in the walls of the esophagus but the network of vessels of the esophageal plexus are present and should be visible if still filled with blood.   A conspicuous sphincter separates the esophagus from the stomach.   The gut sinus is present in the walls of the stomach and all posterior gut regions.   The sinus may leak blood when you cut the stomach wall.   The inner walls of the stomach are not ridged, making it easy to distinguish stomach from esophagus.  

            The stomach changes imperceptibly into the intestine at about the level of the junction of thorax and abdomen.   The two can be distinguished only by histological examination of their epithelia, something beyond the scope of this study of gross anatomy.   The stomach epithelium is characterized by possession of secretory cells, in addition to the ciliated cells found throughout the length of the gut.   The intestine lacks secretory cells.

            The intestine extends for almost all the remaining length of the abdomen.   In the posterior few segments it becomes the rectum, although this cannot be determined by gross inspection.  The epithelium of the rectum contains gland cells that secrete mucus.   The rectum opens to the exterior via the anus.  

Respiratory System

            Gas exchange occurs across the general body surface and the branchial crown.   Approximately 40% of gas exchange occurs in the crown which is ventilated by the feeding current.   The body surface, which is enclosed in the tube, is ventilated by movements of the body.   In at least one sabellid species, a peristaltic wave of short wide segments moves from anterior to posterior and pushes water into the tube so that clean water flows around the collar at the anterior end of the tube.  

Excretory System

            Sabellids have a single pair of large metanephridia located in the anterior segments of the thorax.   They empty via a common duct to the single nephridiopore located in the excretory pit under the overhang of the prostomium.   Each nephridium consists of a large sac connected to the coelom by a ciliated nephrostome.   The sac empties into a duct which runs to the common excretory duct mentioned above.   Find the nephridia on the side of the animal you have been studying.   In living specimens they are green and can be found by cutting into the body wall beside the anterior esophagus.   The esophagus in this region adheres tightly to the body wall and must be cut free to expose the nephridium.   Be careful as you do so that you do not cut the broad, white circumesophageal connective of the nerve ring located in the anterior peristomium.   The anterior position of the nephridia and nephridiopore is an adaptation for the tube-dwelling habits of these worms.

Nervous System

            The nervous system, like that of other annelids, consists of a dorsal brain, circumenteric connectives, and a ventral nerve cord.   The brain is located on the dorsal midline in the posterior prostomium.   It was exposed, and sectioned, by the mid-dorsal incision you made to open the buccal cavity and esophagus.   It is a relatively large, white mass situated ventral to the skeletal supports of the branchial crown.   It is relatively deep below the integument.   A large circumesophageal connective arises via two roots from either side of the brain, passes obliquely around the esophagus, and joins its counterpart ventral to the gut on the floor of the posterior peristomium.   The union of the two circumenteric connectives forms the ventral nerve cord.   The two halves of the nerve cord run posteriorly well separated from each other but are difficult to demonstrate.  

            Sabellids, as sedentary, tubicolous worms, have poorly developed sensory systems.   Eudistylia has small eyespots on the outer edges of the radiole axes.   Some genera (e.g.Megalomma) have large compound eyes near the tips of the axes.   Fabricia, a small species which leaves its tube and crawls backwards has eyespots on its posterior end.  

Reproductive System

            Most sabellids, including Eudistylia, are gonochoric.   Fertilization is external.   The gonads are submesothelial in the abdomen, bulging into the anterior part of the coelomic compartments.   Two ciliated gonoducts exit the coelom of each segment and open ventrally via gonopores near the abdominal fecal groove.   Gametes accumulate in the coelomic spaces of the abdomen where they mature.   Gametes enter the gonoducts, exit the gonopores, and are carried anteriorly by the cilia of the fecal groove to be released into the sea with the exhalant current.  


            Abbott DA. 1987.   Observing Marine Invertebrates.   Stanford Univ. Press, Stanford.   380pp.

            Nicol EAT.   1930.   The feeding mechanism, function of the tube, and physiology of digestion of Sabella pavonina.   Trans. Roy. Soc. Edinburgh 56:537-598.

Ruppert EE, Fox RS, Barnes RB.   2004. Invertebrate Zoology, A functional evolutionary approach, 7 th ed. Brooks Cole Thomson, Belmont CA. 963 pp.  

            Thomas JG.   1940.   Pomatoceros, Sabella, and Amphitrite.   Liverpool Mar. Biol. Comm. Mem.   33:1-88, pls 1-11.


Dissecting microscope

Compound microscope

Slides and coverslips

Eudistylia or another large sabellid, about 10-15 cm

Dissecting pan.   Kippered herring tin poured with wax is a convenient size.

# 1 stainless steel insect pins

Isotonic magnesium chloride if using living Eudistylia

Dissecting set with microdissecting tools

Carmine/seawater suspension