Invertebrate Anatomy OnLine

Glycera dibranchiata ©



Copyright 2001 by

Richard Fox , Lander University

Edward Ruppert, Clemson 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, Aciculata, Phyllodocida O, Glyceridae 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. These are lacking in the sister taxon, Scolicida.


     Aciculata is a large taxon containing many worms well-known to marine biologists and invertebrate zoology students. The parapodia are well-developed and biramous.   The prostomium has antennae.   Aciculates were once known as “errant” polychaetes because they are active and mobile.

Phyllodocida O

            These are the polychaetes with a muscular eversible pharynx.

Laboratory Specimens

            Glycera is common on the coasts of North America and elsewhere.   These animals are known as "bloodworms" by fisherman who purchase them or dig them for bait.   A commercial bloodworm industry exists in Maine and the Canadian Maritime Provinces where one species, Glycera dibranchiata, attains large sizes and high population densities.  

            Living or preserved specimens are suitable for the study of Glycera.   Preserved animals are available from biological supply companies.   Courses taught on sedimentary coasts may collect living specimens or they may be purchased from coastal bait shops or ordered from supply companies such as the Woods Hole Marine Biological Lab or from wholesale bait distributors in the northeast (See Supplies chapter).  Glyceridae is a homogeneous taxon and any species can be used for this study.


            Glycerids are derived polychaetes that have diverged in many ways from the more typical polychaete plan as exemplified by Nereis.   The coelom is unpartitioned with vestigial septa, the hemal system is vestigial, osmoregulation is with protonephridia instead of metanephridia, and gametes are shed by rupture of the body wall.                             

            Bloodworms are active raptorial species that excavate and inhabit galleries of tunnels in soft sediments (Fig 13-39B). These worms capture food and dig with a powerful, eversible pharynx which can be expelled forcefully through the mouth (Fig 1, 13-39C).   The pharynx is a key feature in the life and evolution of glycerid worms.  

            Most of the adaptations exhibited by glycerids are ultimately consequences of the presence of the eversible pharynx.   1. A spacious and unpartitioned coelom is necessary to accommodate the retracted pharynx. The transverse septa that divide the coelom of most other polychaetes are necessarily lost or reduced in Glycera to make room for the pharynx.   2. The coelom, since it is not interrupted by septa, can function as a fluid transport system and it replaces the hemal system, which is vestigial.   3. The absence of a pressurized blood vascular system necessitates the substitution of protonephridia for metanephridia since there is no heart or blood pressure to drive ultrafiltration into the coelom.   4. Finally, gametes must be shed by rupture of the body wall since there are no metanephridial ducts to conduct them to the exterior.

            In spite of its unusual features, Glycera is included in this collection as the representative of the polychaetes because it is an easy dissection that reveals much about the organization of polychaete bodies.   It is easily handled alive and is useful for observations of behavior and physiology.  


              Glycera is an ambush raptor that uses the eversible pharynx for both prey capture and burrowing. Glycera is unusual among the many taxa of burrowing polychaetes because it uses the pharynx to enter the sediment and pull itself through it.   It does not generate peristaltic contractions in the body wall as do most other burrowing annelids. Glycera constructs a system of interconnected burrows, called a gallery (Fig 13-39B), and occupies one of the branch burrows where it waits in ambush for unsuspecting prey which it seizes with its pharyngeal jaws.   It detects the presence of prey by sensing vibrations in the water with its four tiny antennae.           

            >1a. Annoy the animal by pushing it (gently) with an applicator stick or a probe.   Be careful, Glycera has poison glands and a large one can bite and, although by no means lethal, the bite is not pleasant.   Observe the explosive protrusion of the pharynx and be sure to notice the four jaws at the expanded tip of the pharynx.   Each jaw receives a duct from a poison gland in the pharynx wall.   The dark jaws can be seen through the body wall when the pharynx is retracted.   Look for them and note their position well posterior of the anterior end. <   

            Glycera begins burrowing with a rapid eversion of its pharynx into the sediment.   Once into the sediment, contraction of pharyngeal circular muscles causes the pharynx to swell and form a terminal anchor.   Contraction of longitudinal muscles in the wall of the body pulls the rest of the worm forward to the anchor.                                                                    

            >1b. You can observe burrowing and gallery construction in an observation chamber made from two pieces of window glass and a length of rubber tubing (Fig 5).   Place the apparatus upright, open end up, in a seawater aquarium, so you can see it easily.   Place a healthy worm on the sediment surface and watch it burrow, recording your observations.   Does the burrow seem to be lined with silk or mucus to stabilize its walls?   <

External Anatomy

            1. If your animal is living, place it in magnesium chloride and allow it to relax comp­letely. This will take 15-30 minutes depending on the size of the speci­men.   Alternatively, use a worm that was relaxed by the teaching staff prior to the beginning of the laboratory period.   The worm should be in a transparent dish of magnesium chloride.   Study the relaxed animal with the dissecting microscope.

If your worm is preserved it should be in tapwater.

            Note the sleek, tapered, vermiform shape (Fig 13-39A). The body includes an anterior head, posterior pygidium, and a large number of short, similar segments in between.   The head is one of the simplest among the polychaetes and consists of the long, conical prostomium plus the peristomium.   It bears the mouth but the sensory appendages are reduced.  


            The prostomium is the anterior end of the worm (Figs 1, 2, 13-39C).   Because of its embryological origins it is not considered to be a true segment.   It is anterior and dorsal to the mouth and is long, conical, and divided into rings by shallow transverse grooves.  

            Preserved worms often have the pharynx everted, giving the animal an awkward and unnatural appearance that is anything but streamlined and tapered (Fig 1).   When fully everted, four black, chitinous jaws are visible at the tip of the pharynx, which has temporarily become the anterior end of the animal.   If the pharynx of your specimen is everted, the prostomium will be located at its base and be dwarfed by it.   Figures 2 and 13-39A show worms whose pharynges are not everted. Four tiny vibration sensitive antennae are visible at the tip of the prostomium (Fig 2).  Use the anterior, dorsal prostomium as a landmark to help locate ventral and posterior.   Some glycerid species have tiny eyes on the apex and base of the prostomium but Glycera dibranchiata and G. americana do not.  

Figure 1.   Dorsal view of the anterior end of Glycera dibranchiata with the enormous pharynx everted.  The prostomium is the actual anterior end of the worm and the pharynx is usually retracted and out of sight. Poly80L.gif


            The peristomium, which is the first true segment, is immediately posterior to the prostomium and is much wider (Fig 2).   It is fused with the proximal end of the prostomium and appears to be part of it.   The mouth is encircled by the peristomium and overhung by the prostomium.   Note the paired, horseshoe-shaped slits, the nuchal organs, which are presumed to be chemoreceptors, situated laterally on the dorsal surface of the peristomium.   The nuchal organs are ciliated pits which can be everted to form ciliated papillae.   The peristomium bears neither parapodia nor chaetae.   The first segment with parapodia and chaetae is the one immediately behind the peristomium and is the second true segment.  

            In living specimens, the large brain, surrounded by red, neuroglobin-rich tissue can sometimes be seen through the dorsal body wall at the base of the prostomium.   It is easiest to see in small individuals with thin integument.


            Each of the numerous short segments making up the body of the worm is superficially divided into two rings, or annuli, by a shallow transverse groove circling the body.   As a consequence, there seem to be twice as many segments as actually are present.   Each true segment, except the peristomium, bears one pair of fleshy parapodia which protrude from the sides of the segment.   Observe the parapodia, noting that, with the exception of those of the anteriormost two segments, they are biramous; that is, composed of two branches.  

            (In living specimens look for a midventral line extending the length of the worm.   It is red and conspicuous.   It resembles, but is not, a blood vessel.   It is neuroglobin-rich tissue surrounding the ventral nerve cord.   There may also be a middorsal longitudinal, red line on your animal but it is not a blood vessel either, but neither is it a nerve cord as you will soon see.)

Figure 2.   The anterior end of Glycera dibranchiata with the pharynx retracted.   Poly81La.gif


            Increase the magnification and look at the anterior surface of a parapodium of a segment near the middle of the body.   Each parapodium is composed of two branches, or rami.  These are the dorsal notopodium and the ventral neuropodium (Fig 3).   They are close together and may be difficult to distinguish from each other.   Each has a bundle of chaetae and the notopodium has a small dorsal cirrus.  

            With your fine forceps, hold a parapodium so you see it in side view and look at the well-developedchaetae.   The parapodium is supported by a pair of short internal rods, the acicula, which cannot be seen at present.

            The gills (= branchiae) are thin-walled coelomic sacs protruding through the body wall of the parapodium.   Glycera dibranchiata has two unbranched digitiform gills extending from each parapodium, one dorsal and one ventral, hence the name "dibranchiata".   If the gills are otherwise, your specimen belongs to another species.

Figure 3.   Anterior view of the 55 th right parapodium of Glycera dibranchiata. Poly82La.gif

            >1c. If you have a living specimen, red hemoglobin-laden coelomic fluid will be visible through the thin walls of the branchiae.   Find a parapodium with pink gills and examine the gill with your highest power using transmitted light.   Experiment with the light to achieve the best view of the interior of the gill.   Observe the motion of the red coelomocytes in the coelomic fluid in the gill.   If you look carefully, you may also see some of the white cells that are often clumped in the gills.   Spherical white ova are often visible in the gills.   The coelomic fluid is circulated by the ciliated peritoneum lining the coelom. <   


            The pygidium is the posterior end of the animal.   Like the prostomium, it is not considered to be a true segment.   It is small and bears two short tentacle-like anal cirri and a tiny anusdorsal to the cirri.   The pygidium is often damaged and may be incomplete in your specimen.

Internal Anatomy

             Transfer your specimen from the glass dish to a long narrow dissecting pan of tapwater (if preserved) or magnesium chloride (if living). Arrange it in the dissecting pan so that, once pinned, all parts will be visible with the dissecting microscope.   Working under a dissecting microscope, orient the specimen with its dorsal side up.   It is easy to confuse dorsal and ventral but it is important to do so, so be careful.   The best landmark is the dorsal prostomium.

            Temporarily secure the anterior end by pressing two #1 insect pins through the bases of the parapodia of segment 5 or 6 and into the wax of the dissecting pan.   It may be necessary to impale part of the lateral body wall in order to anchor the specimen securely.   Similarly, pin the specimen to the wax at two points well behind the pharyngeal region (about segment 60-70) stretching the animal slightly as you do so.  

"     Using your finest scissors, make a dorsal longitudinal incision, starting at about midbody and working anteriorly.   Initiate the incision by pinching the body wall with fine forceps and then snip through the fold with fine scissors.   The incision should be shallow and slightly to one side of the middorsal line but must pass completely through the body wall.  

            >1d. If your animal is alive, red coelomic fluid will gush from the body but you should not wash it away as it is useful in visualization of ciliary currents.   As soon as you open the coelom, pipet some coelomic fluid onto a slide and apply a coverslip.   Observe the preparation with high power of the compound microscope and find coelomocytes. Note the size of the cells and look for bits of phago­cytized material inside them.   Gametes, either gigantic spherical ova with conspicuous nucleii, or tiny flagellated spermatozoa, may also be present. <

            If your specimen is preserved, the coelomic fluid will be coagulated into irregular gray masses filling the body cavity.   Wash this material away with squirts of water from a pipet. Advance the incision as far as possible anteriorly, to the base of the prostomium, but do not cut into the prostomium. The absence of septa makes the dissection much easier that it would be inLumbricus or Nereis.     

            Extend the incision a short distance laterally on either side of the anterior end of the worm so the body wall can lie flat on the dissecting pan.   Be careful that you do not cut more deeply than the body wall.  

            Remove the original pins, center the worm in the dissecting pan ventral side down, and pin aside the two flaps of body wall.   Insert the pins at 45 ° angles and use as many as necessary to hold the body cavity open.   Stretch the body wall slightly as you pin it.   If convenient, pull the gut to one side and secure it temporarily with a single pin.   Extend the incision posteriorly, pinning as you go, to the end of the worm.

Body Wall

            Examine the cut edge of the body wall along the middorsal incision.   The outermost layer of the thick body wall is the cuticle.   Inside it is the epidermis and a layer of connective tissue. The cuticle is secreted by the epidermis.

            The body wall musculature lies inside the connective tissue layer and resembles that of other annelids.   First is an outer layer of circular muscles divided into rings by the annulations in the cuticle and epidermis.   The longitudinal muscles lie inside the circular muscles and are arranged into four broad, flat, longitudinal bundles that extend uninterrupted from anterior to posterior.   Two dorsolateral bundles lie on either side of the dorsal midline and extend laterally to the dorsal edge of the parapodia (Fig 4).   These are easy to see on the inner surface of the body wall.   Two ventrolateral bundles lie beside the ventral midline and extend laterally to the ventral edge of the parapodia.   They are not so evident as the dorsolateral bundles.   Later you can use scissors to cut across a dorsal and ventral bundle to get a better look.   The ventral bundles are easily seen in such a cross section.   The peritoneum is the innermost layer of the body wall but is not apparent in gross dissection.  

            Although polychaete peritoneum is usually not ciliated, that of Glycera is.   The coelom and coelomic fluid are the fluid transport system of these worms. Circulating coelomic fluid and is responsible for distributing gasses, nutrients, and wastes throughout the body.   Mesothelial cilia generate the necessary currents in the coelomic fluid to transport these materials.  

            >1e. If you have a living worm, look at the mesothelial lining of the coelom for evidence of ciliary activity.   If red coelomocytes are still present, their motion can easily be followed along the wall of the coelom.   If no cells remain in the coelom, try to find some that spilled from the animal earlier and pipet them back onto the peritoneum. <


"     Use your fine scissors to remove a complete parapodium and make a wetmount with it.   Select a parapodium from a segment in the posterior half of the worm.   Study it with 40X of the compound microscope and distinguish the notopodium from the neuropodium (Fig 3).   Find the  dorsal and ventral gills.   Find the small dorsal cirrus on the dorsal base of the notopodium.   There is no ventral cirrus.   Study the chaetae with 100X and distinguish between the simple (unjointed) notochaetae and the compound (jointed) neurochaetae.   If the thickness of your preparation permits, look at the chaetae with 400X and then change back to 100x.   Each ramus is supported by a heavy, stiff, internal chitinous rod called an aciculum.   Adjust the light so you can see the acicula (Fig 3).


            The large space revealed by opening the body is the coelom.   It is filled with coelomic fluid and contains the viscera.   The coelom of Glycera is spacious and, unlike that of most polychaetes, nearly free of septa or mesenteries.   Septa are present, nevertheless, but are reduced to small, transparent, transverse membranes on the coelom floor.   Gently drag the tip of aminuten nadel along the floor of the coelom to demonstrate the presence of the reduced septa.  

            Figure 4.   Dorsal dissection of the anterior end of Glycera dibranchiata.   The nephridia and chaetal sacs of the left side are hidden by the gut.   poly83La.gif


            The coelomic fluid contains abundant coelomocytes, most of which contain hemoglobin and are red (in life).   The red coelomic fluid is the reason for the common name "bloodworm" for these animals.   The so-called "blood" of the name is actually coelomic fluid.   Ironically, bloodworms do not have blood.

Chaetal Sacs

            The conspicuous rows of segmentally repeated structures projecting into the sides of the coelom are the acicula and chaetae associated with the parapodia.   The chaetal protractor muscles are thin, whitish bands arranged around each bundle like guy wires around a tent pole.   A cap of secretory tissue, the chaetal sac, sits atop the two acicula, which it secretes (Fig 13-5A).   Find the two acicula associated with a chaetal sac.  

Digestive System

            The long gut tube is the most conspicuous feature in the coelom (Fig 4).   It is longer than the body and its anterior end may be coiled loosely in the anterior coelom.   The extra length permits the protrusion of the pharynx during burrowing, feeding, or defense.   In preserved material the anterior gut is usually everted from the mouth.  

            The gut is divided into three regions.   There is an anterior foregut, whose lining is ectodermal and cuticularized, a very long, middle midgut with an endodermal, non-cuticularized lining, and a very short, posterior hindgut which, like the foregut, is ectodermally derived and lined with cuticle.  The midgut is by far the longest of the regions and its anterior end is attached to the dorsal body wall by numerous dorsal mesenterial muscles derived from the dorsal mesentery (Fig 4).   These muscles, along with others in the gut wall, are the retractor muscles for the pharynx.

            The foregut extends from the mouth to the point where the first mesenterial muscle originates (Fig 4).   It consists of the buccal cavity, pharynx, and esophagus.   The walls of the buccal cavity and anterior pharynx are longitudinally striated and cannot be distinguished from each other until the gut is opened.   The anterior sixth of this longitudinally striped region is buccal cavityand the remainder is the anterior pharynx.  

            The posterior pharynx, which is not striped, has thick muscular walls and its junction with the anterior pharynx is marked by four delicate flaps of tissue attached to the gut wall.   The surface of this part of the pharynx bears four large, swollen, longitudinal ridges.   Each ridge contains a long pouch that itself contains a jaw, its musculature, and its poison gland.   A black, chitinous jaw can sometimes be seen through the pharynx wall at the anterior end of each of these fleshy ridges.   The poison gland may also be visible as a whitish area in the middle of the ridge.  

            Posterior to the pharynx, the foregut narrows and becomes the esophagus (Fig 4).   The exposed surface of the esophagus is marked with faint transverse bands.   The esophagus extends posteriorly to its junction with the midgut.    

            The midgut, or intestine, is easily recognized by the presence of the numerous dorsal mesenterial muscles and the yellow (in life) chlorogogen tissue in the peritoneum investing it.  The mesenterial muscles originate from the dorsal midline of the midgut and insert on the dorsal midline of the body wall.  

            The pharynx is extended when contraction of circular muscles in the body wall pressurizes the coelomic fluid and force the anterior foregut (pharynx) to turn inside out through the mouth.  Contraction of the mesenterial muscles pulls the midgut posteriorly in the coelom and retracts the foregut.  

            The midgut is the region of hydrolysis, absorption, and feces formation.   Its anterior end is specialized for secretion of hydrolytic enzymes and digestion of food molecules.   The middle region is specialized for absorption.   The dorsal mesenterial muscles are relatively small and weak in the absorptive region.  

            Chlorogogen tissue, usually yellowish and a characteristic feature of annelid peritoneum, functions metabolically like the vertebrate liver.   It stores glucose as glycogen and releases it when needed, synthesizes hemoglobin, detoxifies toxins, deamifies amino acids to produces ammonia and synthesize urea, and stores lipids.

            The short posteriormost region of the gut is the rectum, or hindgut, but it is difficult to distinguish it from the midgut.   The rectum opens to the exterior via a very small anus.

"     Open the anterior gut with a longitudinal incision beginning at the mouth.   Make the cut a little to one side of the dorsal midline and avoid the brain in the prostomium.   Extend the cut posteriorly, studying the interior of each region before proceeding farther.  

            The buccal cavity is lined with a thick, iridescent cuticle with wavy, irregular ridges.   Its iridescence is due to microscopic striations on its surface.

            The cuticle of the anterior pharynx is transversely ridged and bears a dense covering of minute papillae.   The cuticle is thinner and less evident in this region.

            Look for the black tips of the four chitinous jaws protruding into the lumen of the pharynx.   The jaw tips may be visible where they emerge from deep pouches in the gut wall.   Push the folds of tissue aside and reveal the opening of the pouch and look for the jaw within.   With your fine forceps, grasp the tip of one of the jaws and gently pull it into view.   You will be resisted by powerful muscles.  

"     Insert the tip of your finest scissors into the opening from which a jaw protrudes and cut posteriorly to reveal the interior of the pouch, its musculature, jaw, and poison gland.  

            The thick muscular walls of the posterior pharynx are lined with a thick cuticle.   The walls of the esophagus are thinner and less muscular than those of the pharynx but are also cuticularized, most heavily anteriorly.   The cuticle is irregularly ridged.

            An elevated ring of circular muscle, the midgut sphincter, marks the junction of the foregut with the midgut.   The walls of the midgut are thinner, softer, and much less muscular than those of the foregut and have no cuticle.

Excretory System

            The excretory organs of Glycera are protonephridia associated with modified coelomoducts (Fig 13-27C).   There is a pair of small and inconspicuous   protonephridia in each segment except for the first fifteen or so and the last few (Fig 4).   The protonephridia are attached to the body wall near the chaetal bundles by a vestigial septum.  

            >1f. To locate the protonephridia, first find the large chaetal protractor muscle on the anterior side of a chaetal bundle and the large protractor muscle on the posterior side of the adjacent chaetal bundle.   The two protractor muscles extend in opposite directions and cross each other near the body wall.   In Glycera dibranchiata the protonephridium is located at the point where they cross.   In life they are brown and white but these colors may be obscured by obsolescent red coelomocytes which accumulate in their tubules.   (In G. americana there may be two or even three nephridia associated with each chaetal bundle on the anterior retractor muscle and the septum.)   <   

Nervous System

            Find the white (in life) ventral nerve cord lying on the ventral midline on the floor of the coelom.   In life it is surrounded by red neuroglobin-rich tissue which forms a longitudinal red stripe along the midventral line outside the peritoneum.   Try to locate the delicate segmental nerves which extend laterally just posterior to each septum.  

            Follow the ventral nerve cord anteriorly to the large, bilobed brain in the prostomium dorsal to the pharynx.   The brain is also surrounded by red tissue in living animals.

"     Pin the prostomium and extend the middorsal incision into it to get a good view of the brain.   Free the brain from the surrounding tissues and find the two circumpharyngeal connectives extending laterally around the anterior gut from brain to nerve cord.

Fluid Transport System

            The fluid transport system of glycerids is the coelom.   The ciliated peritoneum circulates the coelomic fluid and transports materials from sources to sinks.   Oxygen, for example, is transported from the gills to the tissues, nutriment is transported from the midgut to the tissues, and ammonia is carried from chlorogogen to the gills.  

            There is a ciliated groove on either side of the dorsal midline that helps circulate coelomic corpuscles.   The faint red color (in life) of the middorsal line is due to concentrations of red coelomocytes in these grooves. Glycera is usually reported as having no hemal system but recent work has shown it to be present but vestigial.   There are no red corpuscles in the hemal system.

Reproductive System

            Glycerids are gonochoric and the submesothelial gonads are evident only during the reproductive season.   If gonads are present, they appear as opaque, white, globular masses attached directly to the body wall next to the chaetal bundles.   Gametes are shed from the gonads into the coelom where they mature.  

            When ripe, the worms release gametes from the coelom by rupture of the weakened body wall.   The adults do not survive the experience.   The tiny ducts associated with the protonephridia are not used for release of the gametes.


            Day JH. 1967.   A monograph on the Polychaeta of southern Africa, Part 1, Errantia.   British Mus. Nat. Hist.   458p. + index.

            Harrison FW, Gardiner SI (Eds.).   1992.  Microscopic Anatomy of Invertebrates vol. 7 Annelida.   Wiley-Liss, New York.   418p.

            Pettibone MH .   1963.   Marine polychaete worms of the New England region.   Bull. Mus. Nat. Hist.   227:1-356.

            Ruppert EE, Smith PR .   1988.   The functional organization of filtration nephridia.   Biol. Rev.   63:231-258.

            Smith PR.   1989.   Ultrastructure of polychaete nephridial organs with emphasis on structure and function of solenocytic protonephridia.   Ph.D. dissertation, Clemson Univ., Clemson, South Carolina.

            Westheide W, Hermans CO.   1988.   The Ultrastructure of Polychaeta (Microfauna Marina vol. 4).   Fischer Verlag, Stuttgart.   494p.

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


Dissecting microscope

Compound microscope

Slides and coverslips

Glycera, about 10-12 cm

Dissecting pan.   Kippered herring, sardine, or smoked oyster tins poured with wax are a good size.

# 1 stainless steel insect pins

Isotonic magnesium chloride if using living Glycera

Dissecting set with microdissecting tools