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.


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.


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

Feeding Behavior of Balanus nubilus

Balanus nubilus (Arthropoda, Crustacea, Thecostraca, Cirripedia, Thoracica, Sessilia)

The giant barnacle, Balanus nubilus, is a sessile organism that attaches itself on a chosen substrate and remains there for the duration of the organism’s lifespan (Figure 1). They do not leave their shell, yet open it up for life functions such as: feeding, spawning, and respiration. They are suspension feeding animals that use their feet to extract food from the water column. My observations are based upon organisms with apertures or openings that are around 4cm in length. The giant barnacle has long and short cirripedia showing a clear distinction between the two (Figure 2). Under the short cirri are feeding appendages composed of maxillae and a mandible, which looks very sturdy in comparison to the cirri (Figure 3).

Figure 1. Balanus nubilus with open scutum opercular plates.

Figure 1. Balanus nubilus with open scutum opercular plates.

Figure 2. View of cirripedia, feeding appendages of Balanus nublius.

Figure 2. View of cirripedia, feeding appendages of Balanus nublius.

Figure 3. Dissected Balanus nubilus' feeding appendages, a view into the mouth.

Figure 3. Dissected Balanus nubilus‘ feeding appendages, a view into the mouth.

When feeding, the giant barnacle first opens its operculum and then extends and uncurls its cirripedia into the water column (Figure 4). The cirri still retain a slight curve when fully extended into the water column. I found when orienting the water flow from the sea table in the test barnacles direction, verses turing the water flow off, the feeding rate changed. The giant barnacle extends its cirri more frequently when there is less water movement. This appears to increase the water flow around the cirri and helps the barnacle to feed more efficiently. When there is ample water flow, barnacles seem to keep their cirri extended into the water column for longer periods, therefore beating them less frequently. The cirripedia can be swiveled to either side once extended (Figure 5). This action seems to better orient the cirri and face into the current’s flow. Smaller barnacles species feed more rapidly than larger barnacle species. They frequently extend their cirri at a rate of more than once per second whereas larger barnacles beat their cirri at a slower rate.

Figure 4. Ventral view of Balanus nubilus feeding with cirripedia.

Figure 4. Ventral view of Balanus nubilus feeding with cirripedia.

Figure 5. Ventral view of Balanus nubilus orienting cirri in the water column

Figure 5. Ventral view of Balanus nubilus orienting cirri in the water column

Barnacles are likely to stop feeding and narrow the operculum if they sense a predator above them. They seem to most likely sense predators by an interruption of light and shadows being cast over them. An agitated barnacle is timid to readily feed again and may cautiously take many minutes to resume feeding activity.

If a barnacle is poked along the soft tissue under the edge of the operculum, it swivels its operculum around the aperture in order to hide the soft and vulnerable tissue from a predator (Figure 6). On large barnacles this sometimes means they expose a vulnerable area of soft tissue on the other side of their opercula. The swiveling movement seems very quick for such a large barnacle.

Figure 6. The soft tissue of Balanus nubilus exposed.

Figure 6. The soft tissue of Balanus nubilus exposed.

Bailey Navratil
University of Washington

Introvert Behavior in Phascolosoma agassizii (Sipuncula)

Figure 1: Phascolosoma agassizii with its introvert fully evaginated from the body cavity (coelom). At the most anterior end of Phascolosoma spp., a notch in the crown of red tentacles indicates the dorsal orientation (Kozloff, 1990).

Figure 1: Phascolosoma agassizii with its introvert fully evaginated from the body cavity (coelom). At the most anterior end of Phascolosoma spp., a notch in the crown of red tentacles indicates the dorsal orientation (Kozloff, 1990).

One of the major features of the phylum Sipuncula, or the Peanut Worms, is the presence of an introvert extending from a round, vermiform trunk.  The introvert has two pairs of retractor muscles that connect the apical portion of the introvert (which bears the tentacles) to the inner trunk body wall. This allows the animal to retreat into the coelomic cavity or extend its introvert and nearly double its length. To extend its introvert, the retractor muscles relax; this allows the internal pressure within the coelom to force the introvert outwards. (Kozloff, 1990)

Phascolosoma Internal Anatomy

Figure 2: Diagram shows a pictorial representation of the internal anatomy of P. agassizii. Two pairs of large retractor muscles attach low within the trunk body wall and allow for retraction of the introvert. The dissection this image reflects is the result of cutting along the dorsal body wall.

The specimen I observed was collected July 9th, 2013 at Argyle Beach on San Juan Island, WA. My specimen was found under a rock in a cobble slew connecting the Argyle Bay to the Argyle Lagoon. I observed this specimen in both its habitat and in a water table. My observations focused on the morphology and behavior of the introvert.

I have found there are three major methods in distinguishing trunk from introvert. The first and most obvious method is to observe the extent of invagination by the introvert. The second method in distinguishing the two features is by an abrupt narrowing of the body from trunk to body. Unfortunately, when the animal is relaxed, this difference in body width can be difficult observe. In the specimen I observed, Phasolosoma agassizii (Kozloff, 1974), the introvert could be distinguished from the trunk by the stripe pattern emerging and becoming prevalent as you moved anteriorly. A striping pattern was readily visible on the introvert, whereas the trunk was more or less spotted.

The behavior of the introvert is variable depending on the environment. When the animal is placed on a flat surface in a saltwater tank, it will evert and withdraw its introvert frequently in what superficially looks like a blind animal’s “sniffing” behavior. If given enough time, P. agassizii will move, using a series of rolls and tumbles assisted by the introvert, to a rock or sediment. It will then use its introvert to anchor itself underneath the rock, or in the sediment, and bury itself (anterior positioned down in the case of sediment burrowing). Often, I would find my specimen hiding underneath a rock. Similarly, P. agassizii in the field can be found under rocks anchored to the underlying rocks and sediments.

Side-by-side with scale copy

Figure 3: Image shows the discrepancy in length of the same specimen of P. agassizii when its introvert is near fully invaginated (left, 6 cm) and fully evaginated (right, 11 cm).

When the animal is underneath an object, it will remain there with no obvious effort to escape. Rather, it will evert its introvert completely. Moreover, despite it appearing to be in a rather uncomfortable situation, if one were to remove P. agassizii from its “pinned” state, it will ultimately roll, tumble, and pull its way back and resume being pinned with its introvert fully extended. Not only do these behaviors show the versatility of the introvert, they are also indicative of the durability of the body wall as the animal positions itself tightly under large stones.

Introverts are expressed in other animal phyla, so it appears to be a rather efficient organ. Morphologically, the introvert allows the animal to keep its trunk, which is full of essential viscera, stationary while the introvert may be extended and retracted as it searches for food in sediments. It also allows for rather unique forms of locomotion and a method to hide a large portion of its body from disturbance. Despite the basic morphology of the introvert, the behaviors are diverse and contribute to a very unique organism.

Michael Tassia

University of Washington


Kozloff, Eugene N. “Phylum Sipuncula: Peanut Worms.” Invertebrates. Philadelphia: Saunders College Pub., 1990. 345-347. Print.

Kozloff, Eugene N., Linda H. Price, and Eugene N. Kozloff. “Phylum Sipuncula.” Marine Invertebrates of the Pacific Northwest. Seattle: University of Washington, 1987. 181. Print.

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.


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


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.


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.


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.


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.

Beauty may be skin deep, but peculiarity isn’t: a close look at Armina californica (Mollusca, Gastropoda, Arminidae)

Meet Armina californica: 

Figure 1: Pleased to meet you!

Figure 1: Pleased to meet you!

If the nudibranch world was a high school, the arminids would be the misfits. With their distinct lack of frills and gills and unique lifestyle, they don’t blend in with any other clique—the fancy aeolids, the sweet dorids (don’t even get me started on those sea-huggin’ dendronotids). However, the arminids don’t seem to mind the exclusion. Measuring up to around 10 cm in length, these sand-cruisin’ sea slugs can easily chomp away on a sea pen alone; but they are often found clustering together sharing a yummy Ptilosarcus meal.

It’s not only their peculiar appearance that sets them apart; their eccentricity runs much deeper than mere physical characteristics. The bauplan of A. californica seems exceedingly simple and inconspicuous, but the internal features make biologists scratch their heads.

External Anatomy

The body of A. californica is typically grayish-pink in color with white peripheral margins and meridional ridges. The striated bulbous rhinophores protrude tightly from a small notch at the anterior dorsum. Unlike the aeolids and dendronotids which have respiratory structures within their cerata and the dorids which have distinctive branchial plumes, the arminids do not possess obvious gills. Instead, the strategy involves sets of lamellae that act as respiratory structures (branchial and hyponotal lamellae) located on the underside of the dorsal flaps. The right side of the foot contains both the anal opening and a gonopore complex that is host to both the female opening and the penis. On the ventral side, the foot extends laterally beyond the edges of the dorsum and anteriorly into a veil-like structure covering the mouth. This gives the animal an overall two-tiered structure.

Figure 2: External anatomy. A) left is anterior; B) right side of the animal (right is anterior).

Figure 2: External anatomy. A) left is anterior; B) right side of the animal (right is anterior).

Internal Anatomy

Figure 3: Dorsal dissection with inset of digestive system detail.

Figure 3: Dorsal dissection with inset of digestive system detail.

The dissection of this animal is performed as a simple longitudinal incision of the dorsal surface. The most striking aspect of the internal structures may be the fact that many organs, including the cerebral ganglia, are colored bright orange due to the abundance of carotenoids from the armind’s diet of Ptilosarcus. At the most anterior end, the bright orange 4-ganglia brain sits atop the buccal mass (which contains the pharynx, radular sac, and all related mouthparts). Moving posteriorly, the salivary gland mass conceals the esophagus and its connection to the stomach. A bundle of organs that lies behind the salivary gland includes a clear ventricle and the genital complex—a set of glands and structures that aid in reproduction in addition to the male gonad. Connected to the genital complex is a large, orange gonad which houses the female reproductive components. Both the female gonad and the genital complex are connected via a paired gonoduct to the exterior gonopore complex.

The digestive system includes the anteriormost esophagus which leads directly into the stomach. The stomach extends uninterrupted into the central digestive gland forming one large continuous structure from which emerges the intestine. The branches of the central digestive gland connect back to the stomach, and to a pair of large, orange, lateral digestive glands, the function of which is as of yet unclear and makes this organism quite peculiar. It has been suggested that these glands play a role in the processing of the A. californicus’s odd diet of sea pens, a prey item that can fight back with stinging cells known as nematocytes. Much to the sea pen’s dismay, the arminid seems immune to its venom. The placement of the lateral digestive glands on the body wall may also hint at a further function: are these organs somehow retaining the nematocysts? Perhaps this foreshadows a reuse-recycle defense mechanism similar to that of other gastropods that feed upon cnidarians. The idea is definitely some some food for thought when considering these eccentric bumblers of the sea.

Rhi LaVine
University of Chicago

Paranemertes peregrina (Nemertea, Hoplonemertea)

Paranemertes peregrina is a species of ribbon worm that inhabits some of San Juan Island’s intertidal zones. I observed these worms in situ and collected them at Eagle Cove and False Bay. The individual pictured in the drawing, one from False Bay, measured approximately 8 cm in length when relaxed and about 11 cm when completely outstretched. In general, most worms that our class collected were about this size, but some ranged up to about 10 cm in length when relaxed. They are dorsoventrally thinned, only measuring 1 to 2 mm in height but about 5 mm in width. Dorsal color is brown/purple, and they have a peach-colored ventral side (see Figure 1). Under a dissecting microscope with a good light source, it is possible to see the coelom-based circulatory system in the form of darker brown lines within the body wall.


Figure 1. Dorsal view of a whole P. peregrina specimen, approximately 8 cm long, collected from False Bay.

These animals are slow movers on land and in water; they use circular and longitudinal muscles arranged down the length of their bodies to inch along sand and rock. The worm that I examined moved by contracting the circular and stretching the longitudinal muscles to elongate its body lengthwise and then doing the opposite to shorten the body, effectively pulling the posterior end anteriorly. At this pulling motion, the anterior end became especially flat, evidently gripping the surface beneath with the added surface area. I saw movement characteristic of only longitudinal muscle action when the individual put its head into the air and moved it side to side, evidently looking to change direction.

Mucus Secretion
When moving, the animal secreted mucus, which could be a mechanism to keep traction with the surface beneath it. I noticed more mucus on the tank walls (smooth, vertical surfaces with little traction) than sand beneath the worm. On the latter, gravity and the rough, moist sand grains aided the animal’s traction. Then, when I picked up the worm it responded by secreting a mucus covering, and I almost lost hold of it. Likely, this would be repeated against any predatory action, enabling the worm to make a slimy escape. In addition to traction and getaway, a mucus covering also helps the worms retain moisture on hot days in the harsh intertidal environment.

At False Bay, a muddy intertidal flat, there were hundreds of individuals on the beach at low tide. It was rainy and overcast, so the nemerteans could be on the sand surface without the risk of desiccation. Eagle Cove, the other location, is a rocky intertidal zone. Although there was not nearly the abundance of Paranemertes there (possibly due to the hot weather that day) we found some living on the large rocks in the high intertidal. Although there were not comparable population sizes at the two locations, it is impressive that the species can survive in both muddy and rocky habitats. One factor enabling their habitat diversity is the presence of their prey in both of these habitats.

P. peregrina feeds on nereid polychaetes that burrow in the intertidal sand or live in the subtidal. In the lab, we put a P. peregrina individual (9 cm long) in a dish with a nereid worm (8 cm long). After a minute or so of the nereid laying in front of P. peregrina‘s mouth, the ribbon worm everted its proboscis and latched onto its prey at the anterior end (Figure 2). At this point the nereid began to thrash, likely due to Paranemertes piercing it and injecting the neurotoxin, anabaseine (Cowles 2009). The Paranemertes individual reacted to the movement by elongating its proboscis more and more until it wrapped around the nereid, trapping it until the anabaseine took hold and the worm ceased to move. The proboscis extended to a length of a few centimeters during this process, about one third of the length of the worm. Finally, it retracted its proboscis and ingested the nereid through its mouth, anterior end first (Figure 2 and 3).

Paranemertes eating

Figure 2. Dorsal view of P. peregrina in the first stage of feeding with its proboscis everted, attacking and wrapping around a nereid worm. This is the point at which Paranemertes injects anabaseine.

Paranemertes Eating (2)

Figure 3. P. peregrina during the ingestion of the nereid (dorsal view). The red line on the nereid is its large dorsal blood vessel, and the posterior end of the worm is the portion still remaining to be eaten. The individual has expanded itself slightly to ingest this worm, visible by the peach colored ventral side being slightly visible in this dorsal view.

Paranemertes finishing

Figure 3. P. peregrina finishing the ingestion of the nereid (dorsal view). The feces of the nereid is visible at its anus; This Paranemertes individual squeezed the worm so that a large amount of its feces was deposited exteriorly and not consumed.

Maggie Doolin, Hamilton College

Cowles, Dave. Paranemertes peregrina. Walla Walla University, n.d. Web. 11 Jul 2013.

The morphology of the Lopholithodes mandtii (Arthropoda, Crustacea, Malacostraca, Decapoda, Anomura)

Members of the Decapoda are crustaceans that have five pairs of walking legs which include the chelipeds, three pairs of maxillipeds that function as mouthparts, two pairs of maxillae, a pair of mandibles which could also be described as jaws for eating, and two pairs of antennae. This general organization varies from species to species.

Crabs are benthic decapods that have a highly reduced abdomen and often a large, wide carapace. “True” crabs are members of the Brachyura.  Members of the Anomura have also evolved crab like features making them a sister group of the Brachyura. A decapod means ten-legged. Brachyura are true crabs because they have five pairs of visible pereiopods, however an Anomura have only four pairs of pereiopods that are visible and a fifth pair that have been reduced to been hiding under the carapace. Lopholithodes mandtii is a large anomuran crab that lives along the pacific northwest cost from Alaska to California and found in the subtidal areas up to 137m (Cowles 2004).  I examined the morphology of one specimen collected subtidally (15 m depth) from Pt. George, Shaw Island.

The most obvious feature of this large crab is that the cuticle of its carapace and legs has large bumps that could make it look or be described as the rough surface of a rock. It seems that this feature of the crab is so that it would be well camouflaged in its rocky habitat. This crab also has a hard, triangular abdomen that is curled under the thorax; it fits into a depression in the thorax but can be pulled away. I examined the appendages of the crab from anterior to posterior.  The first two pairs of appendages are antennae.  The first pair is unbranched (uniramous) and the second pair has two branches (biramous). Behind the antennae is a pair of mandibles, which were hard and rounded, each with a small branch projecting anteriorly.  Posterior to the mandibles are three pairs of appendages that all look similar: they were very thin and leaf-like.  These are called the first and second pairs of maxillae, and the first pair of maxillipeds.  Posterior to those appendages were maxillipeds 2 and 3, which both are biramous bear appendages, modified to function as mouthparts. The first pair of walking legs, which bear  pinching claws, are called chelipeds.  The next three pairs of walking legs have pointed dactyls which are used to grip to hard substrate. At first observation, a fifth pair of pereiopods was not noticeable; however closer observation showed that the reduced fifth pair of pereiopods is hidden under the thorax by the abdomen.

The ecological morphology of the Lopholithodes mandtii is not well studied due to the rareness of its species. However in summary, the morphology of the king crab has been adapted to so that it has the ability to survive and function with ease amongst its rocky deep water environment.

Figure A. Hand drawn diagram of L. mandtii illustration major morphological features of the organism.

Figure 1. Hand drawn diagram of L. mandtii illustrating major morphological features of the organism.

Figure B. Apical view of the organism's mouth parts.

Figure 2. Anterior view of the organism’s mouth parts.

Figure C. Apical view illustrating the asymmetry of the organism.

Figure 3. Anterior view of the organism observing its asymmetry and  its pereopods/dactyl used for hard substrates.

Figure D. Ventral view observing counter shading in the organism L. mandtii.

Figure 4. Ventral view

Figure E. Dorsal view of the L. mandtii observing counter shading.

Figure 5. Dorsal view of the L. mandtii

Figure 6. Ventral view of abdomen/thorax, also showing fifth pereiopod reduced

Figure 6. Ventral view of abdomen/thorax, also showing fifth pereiopod reduced

Literature Cited

Cowles, D. Lopholithodes mandtii (Brandt, 1849). 2004.


Aleisha Setka, Auburn University