Diversity of Parapodia in Polychaete Worms

One of the most distinctive features of polychaetes are their parapodia. Parapodia are the paired “legs” of a polychaete that are outgrowths of each body segment. They can have a variety of functions and thus take on a variety of forms. The purpose of this blog post is to explore the diversity in the morphology and function of parapodia in different polychaete families.

The General Parapodium

Parapodia are biramous. They have a dorsal notopodium and a ventral neuropodium. These lobes usually have chaetae (notochaetae or neurochaetae), which are bristles made of chitin and protein. The notopodium can have a dorsal outgrowth called a dorsal cirrus while the neuropodium can have a ventral cirrus. These cirri generally have sensory functions. Parapodia can also have branched outgrowths called branchia which often function as gills.

Errantia

Errantia is one of the two major groups of polychaetes. They generally have large, well-developed parapodia.

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Nereididae—Nereis brandti: Parapodia are large and are used for fast crawling and swimming. The dorsal cirri get progressively larger in the posterior direction, with the posterior segments having very prominent lobe-shaped dorsal cirri. that may help with locomotion by increasing the surface area of the parapodia.

Nephtyidae

Nephtyidae—Nephtys: Parapodia are also quite large. Nephtys have rigid, muscular bodies and are active burrowers. Their large parapodia are relatively simple and facilitate movement through substrate.

Glyceridae

Glyceridae—Glycera: Glycerids are generally carnivorous. They have elaborate burrow systems to lie in wait for prey, and presumably use their large parapodia to dig and move quickly. They have a huge eversible pharynx. I observed a red tuft that resembled branchia on the ventral side of the parapodium. However, the literature describes this tuft to be on the dorsal side. Regardless, these filamentous red structures are not true branchiae because they contain no circulatory system, which has been lost in this family. Instead, they are known as coelomic loops, and are red because the coelomic fluid that flows through it contains hemoglobin.

Lumbrineridae

LumbrineridaeLumbrineris: These worms are long, stringy and fairly firm. They have small uniramous parapodia, with only the neuropodium present. Reduction of the notopodium occurs in several families, since the ventral neuropodium is usually more important for locomotion. Like Nephtys, they use their well-developed musculature to burrow. They are generally found in masses under rocks.

Polynoidae

PolynoidaeHalosydna brevisetosa (the scale worm): This polychaete family has scales, called elytra, that are secreted from parts of the notopodium. This particular species have 18 pairs of elytra. Parapodia are large, with a wide bunch of chaetae on the neuropodium. The notopodium is also reduced and the dorsal cirri are present on every other parapodium. They are found sticking to the undersides of rocks.

Eunicidae

EunicidaeEunice: These worms construct tubes in the sediment, from which they extend to feed. They have long branchiae for respiration. The notopodium is reduced to just the dorsal cirrus.

Onuphidae

Onuphidae—Diopatra: These worms live in tubes that can get very deep and deoxygenated. Ours was found in a tube that was arm’s-length deep into the mud. Thus, they have very large gills anteriorly for respiration but the gills get progressively smaller down the length of the body.

Sedentaria

Sedentaria is the other major group of polychaetes. They generally have smaller, simpler parapodia than Errantia. Two major groups of these sedentary worms are Canalipalpata and Scolecida.

Canalipalpata generally live in tubes.

Terebellidae

TerebellidaeThelepus (the spaghetti worm): Terebellids live in tubes and stick their head tentacles out to feed. The neuropodium is a compressed, long, thick structure that extends ventrally. When the neuropodium takes this form, it is called a torus. The tori bear hook-like chaetae called uncini, while the notopodium is smaller and bears the regular, long chaetae. The uncini help anchor the worm in its tube, while the long chaetae help it to move around in the tube.

Sabellidae

Sabellidae—Eudistylia (the feather duster worm): The thoracic and abdominal sections of this worm are distinct because of chaetal inversion. In the thorax, the notopodium has the long chaetae while in the abdomen, the neuropodium has it. The thoracic neuropodium and abdominal notopodium are tori and have uncini.

Cirratulidae

Cirratulidae—Cirratulus: The most characteristic feature of this worm are the long branchia, which function in respiration.  Cirratulids live in mud or sand underneath rocks. Though they don’t have very active lifestyles, they still seem to need lots of gills. I observed they tend to tangle themselves up in their gills. The notopodium and neuropodium are reduced to just the chaetae.

Scolecida are earthworm-like polychaetes.

Arenicolidae

Arenicolidae—Abarenicola pacifica (the lugworm): These worms are deposit feeders. Because they live in burrows, oxygen can be limited so their parapodia have large branchia. Like the Lumbrineris and Nephtys, they rely on musculature to burrow. Their neuropodia are tori.

Andrea Wong

University of Washington

Cell circulation in branchiae of Glycera americana

Perhaps to many it may come as a surprise that the glycerid polychaete is a fascinating subject to study. What might seem like a simple worm at first glance, it comes in at about 7 inches in length with a silver sheen on the somewhat pinkish body, and flaunts a gnarly proboscis containing four black jaws used in feeding.

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Fig.1 Glyceridae americana

Expecting the generic annelid characteristics with the particular worm I was looking at, I was very quickly drawn to the parapodia and branchia along the sides of the animal. The parapodia are lateral outgrowths along the worm’s body that are involved in respiration and locomotion while the branchiae are dorsal extensions of the parapodia, essentially the gills.glycera body:parapodia

Fig.2 Illustration of G. americana with a close up of a parapodium and its associated branchia

The branchiae clearly had movement of cells occurring inside of them when viewed under the dissecting microscope, and I was curious to see what kind of cells were circulating and how they were being driven. I snipped off one of the branchiae from an anterior segment of the worm and prepared a slide to view it under the compound microscope. The action going on inside just the single outgrowth was really exciting; numerous, small, red disc-shaped cells, fewer large white disc-shaped cells, and several small circular green cells were circulating around in what seemed to be a patterned flow.brachia pic

Fig.3 Even closer view of the branchia with the direction of cell flow of the three different cell types observed
Although the branchia was removed from the body and therefore possibly altered the movement of blood, the cells continuously flowed up one side and down the other of each individual groove or inlet of the branchia, with the smaller red cells passing around the larger white cells. The red cells seemed to move the fastest, with the smallest extracellular green cells a bit slower, and the large disc-shaped white cells barely moving by. The flow itself was not pulsating, and as polychaetes do not have a heart or cardiovascular system, ciliary movement was the force smoothly pushing the cells along the coelomic cavity. Also amazing was the fact that the movement of cells continued after the branchia was removed from the body for about 40 minutes. The video below shows the circulation of cells.

The next thing I was interested in finding out was the likely function(s) of each cell type, assuming at least one type was a part of the blood system. In their book Polychaetes, Greg Rouse and Fredrik Pleijel confirm that “Glyceridae lack a circulation system, the respiratory pigment is located in disc-shaped erythrocytes floating in the coelom” determining that one of the cells are indeed involved in respiration and that cilia are the driving force rather than muscular pulsing (112). An email from Jenna Moore, a polychaete expert, explained that the “glycerids [do] have hemoglobin…[and the] green [cells] could be chlorocruorin, another blood pigment” however the large translucent white cells still remain to be identified. The glycerids display a great visual of blood flow in the worms through their branchia and seeing all of this and how it worked under the microscope was great. Further research in this area of blood cells and the circulatory pathways involved in invertebrates would be fascinating.

Ashley Shiner

University of Washington

Literature Cited:

Pleijel, Fredrik and Greg Rouse. Polychaetes. New York: Oxford University Press, 2001. 112. Print

Naked and exposed spaghetti worms, Eupolymnia heterobranchia (Annelida, Canalipalpata, Terebellida, Terebellidae)

The first worm that comes to peoples’ minds is often the earthworm. Unknown to many non-biologist and marine scientists (and non-worm enthusiasts), the oceans are teeming with a diversity of worms and some of these worms are the most curious and beautifully colored inhabitants of the marine world.

A spectacular group of these animals are the spaghetti worms of the family Terebellidae. True to their name, these worms appear to be a splay of spaghetti noodles on the seafloor. Terebellids live in tubes or burrows on the seafloor and spread their spaghetti-like tentacles (palps) across the sediment surface from the opening of their tube. A terebellid of approximately 6 cm can have dozens of tentacles over 15 cm long (Figure 1). Each tentacle has a longitudinal central groove lined with cilia. The tentacles feel the seafloor for materials that will help construct a sturdy tube or burrow, such as shell fragments, small rocks, and mud that stick to their body with a secreted mucus. Tentacles also search surface sediment for tasty organic matter. The worms bring particles and food back to the burrow via the cilia in a manner similar to a conveyor belt.

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Figure 1. Terebellid with tentacles extending 360° about its body. Dashed ellipse outlines the extent of the tentacles’ reach. The tentacles spread covers approximately 518 cm2, estimating the radii of the ellipse is 15 cm and 11 cm. The body length of the terebellid is 6 cm, not including the tentacles or fire red branching gills.

Because the tentacles serve these two purposes, I tested the hypothesis that terebellids will preferentially extend tentacles and move their body toward sediment rich in nutrients or materials useful in the construction of their tubes. To test this hypothesis, I placed two individuals of the species Eupolymnia heterobranchia, collected from Argyle Lagoon, San Juan Island, WA, in a sea table cleaned of debris, sediment, and other organisms (with the exception of a persistent sea anemone). At one end of the table, I lined the walls with a boarder of sediment, approximately 7 cm wide. The worms were removed from their self-constructed mud tubes and placed naked in the sea table. Each spaghetti worm was positioned to face their own sediment wall at a distance of 10 cm (Figure 2).

I observed the worms every 15 minutes for an hour and both of the worms’ movements about the sea table were random. Neither worm transported sediment along their tentacles for feeding or to construct a new body tube during the period of observation. Moreover, the tentacles did not extend in a preferential direction toward sediment; instead tentacles surrounded the body in 360° (Figure 1). Potential reasons for the lack of interest in the sediment include: sediment did not suit the habitat type of the worms, animals were in shock after being stripped of their outer tubes, and/or no predators were present in the sea table to encourage the worms to build tubes. Although I observed no particle transport along the tentacles, these two terebellids did show an unexpected amount of movement (~2 cm/min) about the sea table for being tube/burrow dwellers (Figure 2). However, it remains unclear if this movement was via cilia or body contractions.

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Figure 2. Photos of the two terebellids (A & B) in the sea table experimental set-up at their initial placement and for each sequential 15 minutes for the following hour: t0, t15, t30, t45, and t60 (top to bottom). The dimensions of the sea table are 60 cm wide by 120 cm long. The blue and white rulers are both 15 cm for scale. Note the distance covered by these worms in the span of 1 hour: estimated average velocity for these two terebellids is 1.9 cm/min, ranging between 0.5 – 6.0 cm/min.

Caitlin Keating-Bitonti, Stanford University

The Dissection of Abarenicola claparedi (Annelida, Polychaeta)

On a quiet sunny day, my class went to Eagle Cove, San Juan Island to dig Abarenicola claparedi for our first dissection. The best and easiest way to find these worms is looking for their burrow openings and fecal castings on the surface of the sand. Then we used the shovels to dig as much sand as we could and searching them.

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Figure 1. Photo of A. claperedi. Anterior right and posterior left.

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Figure 2. Drawing of live A. claperedi. Dorsal side. Anteiror left, posteiror right.

Abarenicola claparedi belongs to the class Polychaeta, phylum Annelida. Figure 1 and 2 shows the appearance of the A. claperedi. The whole worm is 20cm long, and1cm wide at the head. The first segments, including the head, are green, followed by yellow body segments. The color of the mouth is red and the anus is orange-red. There are red branchia on both sides of the middle region.  A. claperedi lives in borrows in the sand. It swallows the sediment and feeds on the organic material. Its feces can be seen as sandy ropes outside of the opening to its burrow. Meanwhile, the sand will collapse a little because of the swallow.

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Figure 3. Drawing of dorsal view with branchia. At 15x magnification of dissecting scope. Also shows the complete part of parapodium

Looking closely to the skin, there are orange dots covering the skin. The parapodium consists of a ventral neuropodium with chaetae and a dorsal brachium (gill).  Figure 3 shows the details of the branchia. Lots of branches increase the surface area for gas exchange. The red color is respiratory pigment in capillaries that go through each branch, transferring oxygen while “breathing”. Observed at 15x magnification on the dissecting scope, the skin of the A. claperedi is translucent yellow: you can see the gut but not clearly underneath the skin.

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Figure 4. Drawing of a maturing spermatocyte finding in the body liquid of A. claperedi. At 400x maginification of compound scope.

Finishing observations of external features, we started to dissect the A. claperedi. We cut a small hole with fine scissors and sucked some liquid flowing out from the worm. Figure 4 shows what we saw under the compound scope. We didn’t see mature gametes, but think that the cell in figure 4 is a maturing spermatocyte.  The season that A. claperedi spawn sperms is spring and we dissected it in summer.

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Figure 5. Drawing of the opening body of A. claperedi after dissection. Anterior up, posterior down. Not the compelet worm with part of bottom left. Shows all the organs and muscles. Differenciated by color pencle.

Figure 5 shows the internal structure of A. claperedi. The organs are clear and organized inside its coelom. From the posterior, you can see the intestine, with black sediment in it. It is connected with the stomach. Our worm’s stomach broke in to two parts, maybe in the process of digging it out from the sediment. Anterior to the stomach, you can see the esophageal caeca. There are around 10 to 13 small caeca arranged along the esophagus, posterior to two long, large caeca. Both the stomach and the small caeca are yellow and the large caeca are brown. Between the stomach and the caeca is the heart, in dark red. On the surface of that organ, a relative thick dorsal vessel goes along in the coelom from the anterior to posterior. Furthermore, on the heart side, a line of white nephridia arrange along the skin. You can also see white muscle underneath the skin and also beside the chaetae.

http://www.beachwatchers.wsu.edu/ezidweb/animals/Abarenicolapacifica2.htm

Nightlighting at FHL

The LED nightlight, just below the surface draws in a couple fast-swimming neirids and a shrimp of the Pandalus genus.

Figure 1: The LED nightlight, just below the surface draws in a couple fast-swimming nereids and a shrimp of the Pandalus genus.

Night Lighting at Friday Harbor Laboratories

By Dan Lombardo

The bulky power supply is connected to the 24” tube of super-bright LEDs, causing students to cry out and cover their eyes, surprised and momentarily stunned by the blinding white flash.

Figure 2: A tiny nauplius larvae that turned out, a few days later, to be a crab of the Cancer genus.

Figure 2: A tiny megalopan larvae that turned out, a few days later, to be a crab of the Cancer genus.

It’s a dark, clear evening, and the nightlight is slowly being lowered off of the floating dock and into the waters of Friday Harbor.  As the afterimages fade, a new world is revealed:  In this world, tiny animals (probably ostracods) race through tight curves beneath the surface like turbo-charged sesame seeds.  The eerie glow of the nightlight is surrounded and smothered in swarms of nauplii (an early larval stage of some crustaceans), while larger and less numerous, the pea-sized final stage of decapod larvae, the megalopa, drift along, their tiny pereopods outstretched in a chibi caricature of adulthood.

Deeper down, just below the nightlight, a churning school of Sandlance, Ammodytes hexapterus, the “potato chip” of the Salish Sea, is beginning to assemble.

As the ebb-tide drains the harbor it brings other planktonic drifters into the submarine halo; Ctenophores (or “comb jellies” if you prefer), of the Bolinopsis and Pleurobrachia genera cruise by, navigating the current with their eight rows of fused cilia in search of prey.  Medusoid hydrozoans, Mitrocoma and Aequoria, like living glass paperweights, pulsate in the moving water column.  As Aqueoria drifts out of the light and toward San Juan Channel, a sudden blue-green flash indicates that its hunt has been successful; its tightly coiled cnidocysts are deployed at amazing speed, impaling and envenomating its planktonic quarry in a horror-movie scene that is thankfully invisible to the naked eye.

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Figure 3: A coon-stripe shrimp (Pandalus danae) retrieved from the floating dock.

Coon-stripe shrimp, Pandalus danae, crawl, swim, and dart in typical caridoid fashion along the edges of the floating dock.  They are beautifully unaware of our 2-dimensional terrestrial world, and orient themselves in the water column without regard for the illusions of “up” and “down”.  The relative silence is suddenly broken as voices raise to a shout: The creature many of us have been hoping to see is coming into view; writhing and undulating, out of the darkness below, a huge Nereid worm!  The 50cm long giant winds its way through the scene, blindly crashing into the light, the dock, the shrimps, and anything else in its path, in its eagerness to spawn.  This specimen is clearly male, indicated by the milky trail of sperm it leaves behind; the skywriting of a perverted barnstormer, desperately seeking a mate before its terminal disintegration.

Figure 3: The creature everyone wants to see: A massive neirid worm, approaching its spawning phase.

Figure 4: The creature everyone wanted to see: A massive Neanthes brandti!

The best (or easiest to catch) specimens of numerous crustacean larvae, polychaete worms (including our lusty monster Nereid), a few ctenophores, an Aqueoria, and some total unknowns are transferred to our collection jars and buckets and taken to the labs for later evaluation.  It has been a productive evening, and I am looking forward to the chance to practice my diagrammatic drawing during tomorrow’s lab.  While it’s poorly understood why marine animals are drawn to the nightlight, my own attraction is clear:  The nightlight opens the door to an entirely new and fascinating world, a world seldom seen or appreciated by those who aren’t a part of it.  The cryptic nocturnal realm floating just beneath my feet reminds me that there is always more to learn, that the world Is not a simple place, and that the seemingly important complications of my everyday life pale in comparison to the desperate struggles of the quadrillions of tiny creatures more numerous than myself.  It is a scene to be appreciated with awe and humility.

Animals Collected and Identified While Nightlighting in Friday Harbor

Phylum Class Order Family Genus/Species
Annelida Errantia Phyllodocida Nereidae Neanthes Brandti
Arthropoda Malacostraca Decapoda Pandalidae Pandalus danae
  Cancridae Cancer spp.
Cnidaria Hydrozoa Leptomedusae Aequoriedae Aequoria spp.
  Mitrocomidae Mitrocoma cellularia
Ctenophora Tentaculata Cydippida Pleurorachiidae Pleurobrachia bachei
Lobata Bolinopsidae Bolinopsis infundibulum