Holothuroid doliolaria

I found this gastrula in a plankton sample taken from the Charleston marina docks on May 17th.  We speculated that it may be a sea cucumber (class Holothuroidea; phylum Echinodermata) because of its unusual shape.  One can see in this picture that the gastrula is longer than wide and tapers toward the animal pole (upper left).  In holothuroids, gastrulation begins by invagination whereby cells at the vegetal pole (bottom right) fold into the blastocoel (the cavity within the embryo) as a layer, rather than ingress individually (McEuen 1987).  One can see these invaginating cells in this gastrula as an opaque area.  This embryo later confirmed our suspicions and developed into a lecithotrophic (non-feeding) doliolaria (planktonic larva of some holothuroids). 

Doliolariae are shaped like a barrel (hence the name) and are ciliated. Cilia may cover the entire surface (uniform ciliation) or form 2-5 discrete transverse bands.   Ciliated bands often develop from an initially uniformly ciliated area of epidermis (Miller 2001).  On May  23rd (left) two ciliary bands were present in this larva in addition to a uniformly ciliated anterior area (left on this image). 

By May 25th, the uniformly ciliated region had developed into yet another discrete band of cilia (three in total), seen in the third photograph.The duration of the doliolaria larval stage is species specific, ranging from six to thirteen days in the local species with described development (Miller 2001). The end of planktonic period is marked by the protrusion of five primary tentacles from the larval vestibule.  One can see several curved projections in the larval epidermis (upper left in the third image) through which these tentacles will eventually emerge. At that point the larva will be called a pentactula.

Although sea cucumbers are relatively soft bodied, internal calcareous ossicles are used for structure and support.  In this polarized light image, one can see a small ossicle as well as a larger ring of ossicles that will surround the pharynx in the adult sea cucumber (Ruppert et al. 2004). 

Miller, B. 2001. Echinodermata. In: An Identification Guide to the Larval Marine Invertebrates of the Pacific Northwest. Edited by Alan Shanks. OSU Press, Corvallis.

McEuen, SF.  1987.  Echinodermata: Holothuroidea.  In: Reproductive and Development of Marine Invertebrates of the Northern Pacific Coast by Megumi Strathmann.  University of Washington Press, Seattle. 

Ruppert, E. E., R. S. Fox and R. D. Barnes.  2004.  Invertebrate Zoology: A Functional Evolutionary Approach.  Brooks Cole, Belmont, CA.

Identifying crustacean nauplii

The first picture is that of a copepod nauplius from a plankton tow collected at the mouth of Coos Bay, OR on Saturday, May 5th. The nauplius is the first larval stage of many crustaceans (although many species pass through this stage while still enclosed in the egg capsule). Nauplii are characterized by having three pairs of appendages: a pair of uniramous (not forked) antennules, and a pair of antennae and manidibles, both of which are biramous (i.e. forked). Nauplii are some of the most common organisms one encounters while sorting plankton samples. In Coos Bay we often encounter the nauplii of both barnacles and copepods.

In the second picture we see the nauplius of a barnacle.  Typically barnacles go through four to six naupliar stages depending on species. The distinguishing characteristic of a barnacle nauplius is the pair of fronto-lateral horns at the anterior end. Copepod nauplii do not have any such horns. Being able to distinguish between the two kinds of nauplii is important because both have a biphasic life cycle, but copepods are holopelagic (meaning they spend the entire life cycle in the water column) whereas barnacles are benthopelagic (adults are benthic, while larvae are planktonic) so different ecological questions can be addressed by studying these two kinds of organisms.

After the nauplius barnacles go through an additional larval stage called the cyprid (left). The final nauplius stage molts into the cyrpid stage, which is non-feeding. Cyprid larva has a pair of large appendages at the anterior end (left side of this photo) called antennae  - one can see these sticking out from the carapace. The cyprid will use these to “walk” around on the substrate while  looking for an ideal spot to settle. Once it finds a spot it will cement itself to the substrate and undergo metamorphosis into an adult (permanently attached) stage.

Brachiolaria larva of Pisaster ochraceus

Pictured here is a dark field image of a four-week old Pisaster ochraceus (a kind of sea star) brachiolaria larva that is 2.35 mm long. This is a ventral view with the anterior end up. The central V-shaped structure is the mouth, which leads into esophagus (a clear tube just below), which in turn leads to the stomach (light pink oval shape below), and finally the intestine (dark pink tube), which opens outside via an anus (out of focus) on the ventral side. The convoluted circumoral ciliary band is particularly obvious (clearly in focus) along the sides of the larval body in the middle part of the image. It is divided into the pre-oral (anterior to the mouth) and the post-oral (posterior to the mouth) portions.  

The second image is a rare side view (left side) of the larva. Located near the anterior portion of the larva is the attachment complex that characterizes the difference between the brachiolaria and the preceding bipinnaria larval stage. Below is a close up of this attachment complex. There are three brachiolar arms capped by the dark colored suckers that test the substratum and provide temporary adhesion during settlement. These arms are differentiated from other larval arms by containing an extension of the anterior larval coelom (which

one can clearly see in the second picture). The dark circle between the two bottom arms is the adhesive disk which contains glands that secrete a cement-like substance for more permanent attachment during metamorphosis.

The last image is a close up of a developing spicule located just near the larval stomach. See an earlier post by Lara Macheriotou for context. This is interesting because asteroids lack the ability to make larval spicules, unlike the pluteus larvae of echinoids and ophiuroids that have a calcareous skeleton.  See a post by Nick Hayman about the underlying developmental mechanism. The spicule pictured here is part of the developing juvenile rudiment, and will be incorporated into the adult skeleton.

Sipunculid pelagosphera larva

This sipunculid (peanut worm) pelagosphera larva was found in an open ocean plankton sample that was collected during our class boat trip on April 17, 2012 – a few miles south of the mouth of Coos Bay, OR. Pelagosphera larva is found only in the phylum Sipunculida. They develop from trochophore larvae and can be lecithotrophoic or planktotrophic. I have kept this larva for a few weeks and fed it unicellular algae Dunaliella tertiolecta and Rhodomonas lens.  Since there is only one known species of peanut worm that has a long-lived, planktotrophic pelagosphera larva in the Pacific Northwest, this larva likely belongs to Phascolosoma agassizii.

The body of this pelagosphera larva can be divided into four regions: the head, the mid-region that includes the metatrochal ciliary band, the trunk, and the terminal organ.  The head, mid-region and terminal organ can be simultaneously retracted into the trunk (left) when the larva is disturbed. A cuticle covers the epidermis of the entire larval trunk. This pelagosphera has numerous cuticular papillae covering the entire trunk. The digestive system can be seen through the cuticle and is indicated by the green hue in the esophagus, stomach and intestine. 

The second picture (left) shows the pelagosphera with extended head, and the metatroch, which these larvae use to swim. The third picture shows the larvae with the head and lip extended. The head is covered by cilia on the ventral surface and divided into two ventral lobes by a ciliated groove that leads into the mouth. The lip is just below the head and is typically covered with cilia on the medial and proximal surfaces. The lip along with lip glands, gland cells of the oral cilature and buccal organ are believed to be involved in feeding.

The terminal organ (not shown) is usually retracted when the larva is swimming or inactive. The primary function of the terminal organ seems to be attachment to the substratum. I was not able to take a picture with the terminal organ of the pelagosphera visible.

Jaeckle, W & Rice, M. 2002. Phylum Sipuncula. In: Atlas of Marine Invertebrate Larvae. Edited by Craig M Young. Academic Press.

Johnson, K. 2001. Sipuncula: The Peanut Worms. In: An Identification Guide to the Larval Marine Invertebrates of the Pacific Northwest. Edited by Alan Shanks. OSU Press, Corvallis.

Unknown Advanced Actinotroch

This picture shows a lateral view of an unknown actinotroch larva of a phoronid worm that was found on May 10th in plankton sample taken off the F Dock in the Large Boat Basin of Charleston, OR.   This picture clearly shows a ring of tentacles (called the lophophore) at the anterior end of the larva (up). The lophophore is used for feeding and each tentacle is ciliated. The oral hood is visible just anterior to the lophophore. It is pulled over the mouth, much like a hood, and is used in feeding as well. This picture also shows the telotroch,  a ciliated ring at the posterior end of the larva which is used for swimming.

The second picture is a ventral view of the same larva. The telotroch, lophophore, and oral hood are clearly visible. It also shows the achtinotroch’s digestive tract. The stomach is the large internal cavity, and the narrow, tapered end toward the postrior is the intestine. The structure that is wrapped around the posterior part of the stomach (partially outlined by yellow pigment granules) is the metasomal sac. Metasomal sac grows inside the larva, is everted at metamorphosis and becomes the trunk of the juvenile. For a view of an early metasomal sac, see an earlier post by Mark Inc.

The third photo is a dorsal view of the larva. The metasomal sac is now on the far side of the stomach, though it is still visible. The anterior-most end of the sac opens to the outside via the metasomal pore. The sac is everted through this pore. The mouth of the larva is visible as a triangular shape at the anterior end, just below a cluster of pigment granules. It is inside the oral vestibule formed by the oral hood.

Nephtys sp. metatrochophore

This is a metatrochophore larva of a nephtyid polychaete (family Nephtyidae).  In April and May 2012, we frequently encountered these larvae in plankton samples from Coos Bay, OR.  These larvae are propelled by two ciliary bands - an anterior prototroch and a posterior telotroch. The prominent red pigment bands near the prototroch and pygidium (the posterior-most segment) inspired me to look at them more closely.  Upon closer inspection, one can see striking blue (!) pigment in the lining of the gut.  Also in the gut, is this larva’s most recent meal, a centric diatom.  We determined that this larva belongs to the genus Nephtys due to the distinct red and blue pigments mentioned above as well as the dome shaped episphere and a single pair of red eyes (Crumrine 2001).  

In one week, this planktonic larva turned into a benthic juvenile polychaete (left) displaying additional characteristics of Nephtys species.  These predatory worms commonly found burrowing in mudflats use an eversible pharynx armed with a pair of jaws (visible in the third picture as two glowing arrowheads) to capture and subdue prey such as mollusks, crustaceans or other polychaetes.  Furthermore, we noticed that the juvenile possessed an anal cirrus (looks like a small sphere on the pygidium in the bottom photograph).  The presence of an unpaired anal cirrus is  characteristic of Nephtys species, although it is often lost when adults are handled.  

There are more than six species within this genus in the NE Pacific, but N. caeca and N. caecoides are most common (Rudy and Rudy 1983).  To identify species within this genus, one must examine the interramal cirri (slender projections between parapodial branches) on the adult parapodia (Carlton 2007), which was not possible for this juvenile stage.    

Crumrine, L.  2001.  Polychaeta. In: An Identification Guide to the Larval Marine Invertebrates of the Pacific Northwest.  Edited by Alan Shanks.  OSU Press, Corvallis.

Carlton, J T.  2007.  The Light and Smith Manual:  Intertidal Invertebrates from Central California to Oregon 4th Edition.  University of California Press, Berkeley. 

Rudy, P and L Rudy.  1983.  Oregon Estuarine Invertebrates: An Illustrated Guide to the Common and Important Invertebrate Animals.  Oregon Institute of Marine Biology, Charleston, OR.   

Metamorphosed juvenile of Strongylocentrotus purpuratus

These pictures show a newly metamorphosed juvenile of the purple sea urchin Strongylocentrotus  purpuratus, a common intertidal organism in Oregon.  Take note of the red pigment granules dispersed aborally and the green coloration of the internal structure though the transparent distal plates.  Purple urchin pluteus larvae swim and feed in the plankton for several weeks prior to settlement on the seabed and metamorphosis into the juvenile stage. This particular specimen was cultured in the lab from gametes collected from induced spawning via injection of adults with a KCl solution and fertilized in vitro on April 3, 2012.  Like the adults, the juveniles of this species are benthic feeders and have acquired traits adapted to their environment, for example, tube feet, and juvenile (splayed) and adult (pointed) spines.  At this early stage, the juvenile possesses four adult spines per interambulacrum, two juvenile spines, a single  unpaired primary podium per ambulacrum, and five to eight additional juvenile spines located on the aboral surface (Miller and Emlet, 1999).  The juvenile spines are four-pronged, shorter, and located more orally compared to the longer, barbed adult spines.

The second image is a close up of the aboral surface of the juvenile, showing the five tube feet and the transparent distal plates.  After settlement, the juvenile is not able to feed for 5 to 6 days due to an incomplete gut. You can see that the distal plates and the anus are not entirely formed in this specimen (Leahy 1986). 

Leahy, PS.  1986.  Laboratory culture of Strongylocentrotus purpuratus adults, embryos, and larvae.  Methods in Cell Biology, 27, 1-12.         

Miller, BA., and Emlet RB.  1999.  Development of newly metamorphosed juvenile sea urchins (Strongylocentrotus franciscanus and S. purpuratus): morphology, the effects of temperature and larval food ration, and a method for determining age.  Journal of Experimental Marine Biology and Ecology. 235(1): 67-90.

Hoplonemertean embryo and larva

This is a hoplonemertean (ribbon worm) embryo. I collected several of such embryos from plankton obtained off of a dock in Charleston, OR on February 8, 2012. In general, nemertean eggs cleave circumferentially, but in some species with large yolky eggs, the cleavage furrow cuts in from one side. This is referred to as “unilateral cleavage”. The embryo shown here is doing just that - it is in the process of dividing from one to two cells, and the cleavage furrow is deeper on one side than on the other.  Many hoplonemerteans encase their eggs in some sort of envelope, or chorion. The embryo shown here has an inner chorion (which is tight around the embryo) and a larger outer chorion. 

The second picture shows a uniformly ciliated multicellular embryo after one day of development. The embryo rotates inside the egg chorion at this stage. It also has an apical tuft of longer cilia (seen at about 5 o’clock). A clear vesicle inside the chorion at about 2 o’clock is likely a polar body (a product of meiosis). The larvae that hatched from these eggs (after 4 days of development) had a transitory larval epidermis which they shed when slightly compressed under a coverslip. 

The third picture shows two ciliated cells of transitory larval epidermis left behind by a larva that is just about to exit the frame (at upper left). Other hoplonemertean larvae are known to have similar transient epidermal covering; in some it is reabsorbed, in others it is shed (Maslakova & von Döhren 2009; Hiebert et al. 2010).

The bottom photograph is of a week-old larva. It is uniformly ciliated and possesses a prominent apical tuft, a caudal cirrus, three pairs of eyespots, cerebral ganglia (large clear areas), gut, and a proboscis. It is essentially a planktonic juvenile. This type of development is referred to as “direct” because the planktonic stage (if present at all) possesses a body plan essentially similar to that of the adult (unlike the nemertean pilidium larva).

Hiebert LS, Gavelis G, von Dassow G and Maslakova SA. 2010. Five invaginations and shedding of the larval epidermis during development of the hoplonemertean Pantinonemertes californiensis (Nemertea: Hoplonemertea). Journal of Natural History. 44: 2331–2347.

Maslakova SA, von Döhren J. 2009. Larval development with transitory epidermis in Paranemertes peregrina and other hoplonemerteans. Biological Bulletin. 216:273–292.

Viviparous brittle-star Amphipholis squamata

Amphipholis squamata are simultaneous hermaphrodites, which means they produce both eggs and sperm at the same time, and they self-fertilize. The exciting part is that this tiny brittle star is also viviparous. We dissected adults in class to find brooded embryos.

The long slender arms are made up of a series of flexible joints and can bend and coil. This brittle star will unexpectedly fold up to conceal itself or reach out quickly to make a sneaky escape. In preparation for these photos, I  immersed the brittle star in a solution of MgCl2 to anesthetize it. It almost immediately relaxed and stayed still through the subsequent dissection.

A close view of the aboral side shows the tiny central disc of an adult (4 mm in diameter). The disc isn't strictly circular but pentagonal. The whole body has a five-fold symmetry so there are five (or multiples of five) of every structure, as is characteristic of the phylum Echinodermata, in general.

A close view of the oral side shows a smaller pentagon at the center. This is made up of five triangular teeth which, when open, reveal the mouth. On either side of each arm are dark lines. These are bursal slits, entrances to ten sac-like spaces called genital bursae. 

Ovaries and testes flanking the bursae release sperm and eggs into the bursae through gonopores. Fertilization happens internally and the embryos develop and grow inside the parent's body. The juvenile emerges from the bursal slit when mature. Amphipholis squamata is fertile year-round and is able to brood multiple young at different stages of development.

Using sharp forceps, I searched for brooded embryos by pulling back the tissue between two bursal slits. After my third try I was pleased to find this tiny juvenile. See also a post by Amanda Clark which shows two dissected juveniles of A. squamata at different stages of development.

Field Trip to South Cove

The Pacific Northwest is a particularly rich location to experience the biodiversity of marine life.  Spring is when many species reproduce making it an excellent time of the year to study embryonic and larval development of marine invertebrates. A point of interest is the South Cove of the Cape Arago headland as it offers students here at the OIMB an opporunity to observe and study a diverse array of organisms.  On April 24 at 8:30 a.m., with our gear in tow, we left for the South Cove to catch the -0.3 foot low tide at 9 a.m.  By van we made our way six miles south of the OIMB campus down Cape Arago highway to look for particular species of brooding bryozoans. 

Sticking close to more experienced students and our instructor Svetlana, I saw many interesting species including this morning sunstar, Solaster dawsoni, being held up by my classmate Ashley (left). Other common species of the South Cove intertidal zone we observed include the worlds largest chiton, Cryptochiton stelleri, commonly known as the gumboot chiton, the worlds largest sea star, Pycnopodia helianthoides, commonly known as the sunflower seastar, and a model organism for developmental biologists, Strongylocentrotus purpuratus, commonly known as the purple sea urchin, to name a few. After two hours in the intertidal, we headed back to the lab to study our specimens. In addition to finding the brooding bryozoans we were looking for, we found many other interesting species that we will study in class. 

A rather noteworthy member of this menagerie pictured in the center of the glass dish is the veiled chiton, Placiphorella velata. It is a rare find because this species typically occures in the very low intertidal or subtidal. Unlike most chitons which graze on algae, this predatory chiton waits for small crustaceans and worms to wander under its veil and rapidly (less than a second) lowers the hood to trap its prey. It then swallows the smaller bits whole or uses its radula to scrape and break apart parts of larger prey.

Identifying pinnotherid crab larvae

The first picture is of a larva of a crab from the family Pinnotheridae collected from the plankton on April 19th, 2012 from the boat basin in Charleston, Oregon.  Pinnotherids, commonly known as pea crabs, are crabs that live commensally with a variety of organisms e.g. mollusks, annelids and echinoderms.  This zoea has relatively short rostral and dorsal spines in addition to two lateral spines. Studies have shown that lateral spines likely serve to reduce predation by planktivorous fishes. Additionally, one can see one of the two large compound eyes of this larva.Pea crab zoeas are some of the most ubiquitous zoea larvae encountered in plankton tows in this part of the world.  However, zoea larvae of many brachyuran crabs are very similar and identification can be tricky. The two bottom pictures highlight the differences between zoea larvae of a pea crab and a crab from the family Cancridae.

In the second picture we see a close up of the telson (terminal segment) and the two preceding abdominal segments excised from a pea crab zoea. The enlarged last abdominal segment (wider than the telson) that you can clearly see on this picture is a the identifying feature of pea crabs in the Northeast Pacific.  Furthermore, most pinnotherid zoeas have small narrow telson.

In the third picture we see the telson and last four abdominal segments of a zoea from the genus Cancer.  One can see a pair of spines on each of the abdominal segments, however none of the segments is expanded to the point of being wider than the telson.  Additionally, the telson  of a cancrid zoea is wider than that of the pinnotherid zoea and is forked.

Coronate larva of Crisia sp.

This picture shows a fragment of a bryozoan colony Crisia sp. I collected it at South Cove just south of Charleston, OR during low tide in April 2012. The colonies of Crisia sp. look like upright branching whitish tufts about 1.5 cm tall on the underside of rocks and under rock ledges. One can see openings of many individual feeding zooids (autozooids) and one zooid specialized for reproduction (gonozooid). Gonozooid is larger than the autozooids and looks like a yellow “pouch”. Crisia is interesting because it exhibits an unusual reproductive strategy called polyembryony. A single zygote is initially deposited within the gonozooid, it receives nutrients from the mother zooid via a kind of placenta, grows, and buds off secondary embryos, which, in turn, can bud off tertiary embryos. In this way each gonozooid ends up  filled with many genetically identical small embryos - a kind of embryonic cloning.  The calcareous wall,  which protects the gonozooid (much like the other zooids in the colony), is clearly visible.

The second picture shows a gonozooid in which I cracked and removed part of the wall with a pair of sharp forceps to expose the embryos. Each of the small yellow spheres is a brooded embryo. These embryos are tightly packed inside the gonozooid and readily spill out when it is opened. These brooded embryos emerge as ciliated coronate larvae.


The bottom image is a side view of a coronate larva I removed from a gonozooid of Crisia. Most of the larval surface is covered by a ciliated epithelium called corona ciliata. Corona ciliata is used for locomotion. Coronate larvae do not have a shell (unlike the other kinds of bryozoan larvae (cyphonautes and pseudocyphonautes), or a gut (so they do not feed). They spend only a few hours in the plankton before settling. Coronate larvae of Crisia are anatomically very simple. Aside from the corona ciliata they have an internal sac (not visible here) and an aboral non-ciliated region clearly visible here (top). A portion of this non-ciliated region is invaginated in a circular groove, which corresponds to pallial epithelium.   The coronate larva of Crisia sp. lacks the pyriform organ and vibratile plume found in coronate larvae of some other bryozoan species (e.g. Bugula and Schizoporella).

Nectochaete larva of Harmothoe sp.

This polycheate nectochaete larva was found in a plankton tow collected in the Charleston, OR boat basin. Using a plankton identification guide (Crumrine 2001) with a dichotomous key I identified this larva as belonging to the genus Harmothoe (Family Polynoidae, commonly known as scale worms). This larva has nine setigers (segments bearing setae) and five pairs of elytra (scales that characterize the worms of this family).

The first picture was taken on the day when the larva was collected – April 12, 2012. It is a dorsal view, so one can clearly see the five pairs of large scales (elytra) running along the anterior-posterior axis. The third pair of elytrae is unpigmented, whereas the rest of them have a pigmented margin (appears golden in dark field). The larva has three pairs of large ocelli (two of which are in focus). There are also three pointed antennae on the anterior-most segment (called prostomium), all tinted with the same golden pigment as the elytrae.

The second picture was taken six days later. This is a ventral view, so one can clearly see the nine pairs of parapodia (appendages) with chaete (setae), the two ventral palps with bulbous base – one on each side of the mouth, and the two anal cirri (appendages on the posterior-most segment, called the pygidium). Worms in the genus Harmothoe either brood early embryos or spawn (release eggs and sperm) directly into the plankton. I hope to continue to follow this larva through its development during the course and try to determine which species it belongs to.

Crumrine, L. 2001. Polychaeta. In: An Identification Guide to the Larval Marine Invertebrates of the Pacific Northwest. Edited by Alan Shanks. OSU Press, Corvallis.

Unidentified actinotroch larva

Our class collected plankton on April 12, 2012 using a 153-μm mesh size net towed behind a boat two miles outside Coos Bay, OR. The two pictures show the 0.7 mm long unidentified actinotroch larva of a phoronid worm that I found in this sample.

The top image is focused on the tentacles, each with a single black pigment spot. This larva had 14 tentacles total. At the anterior end (up) one can see the pre-oral hood, and at the posterior - the telotroch, a prominent ciliary band that surrounds the anus and propels the larva. The bottom picture shows the same individual, but focusing deeper in to show the internal structures. At the apex of the pre-oral hood, one can see a thickened region of epithelium - this is the apical sense organ (the larval brain). It may play a role in substrate selection during metamorphosis (Johnson and Zimmer, 2002).

On this picture one see almost the entire digestive tract. The oral hood encloses a funnel-shaped vestibule, at the tip of which is the mouth. The mouth leads into the stomach (a large oval shape that occupies the majority of space in the larval trunk). The stomach connects to the hindgut - a short straight tube which opens at the posterior end via an anus.One can also see a small but distinct mid-ventral (to the right on the picture) invagination just posterior to the tentacles (and next to a pigment granule). It is called the metasomal sac. This sac will grow throughout larval development and eventually wrap around the larval gut. At the onset of metamorphosis the metasomal sac is everted to form the trunk of the adult worm. The entire larval gut is pulled into the everted sac, thus shortening the larval axis, and bringing the mouth and anus closer together to form the U-shaped adult gut.

Johnson, KB and Zimmer, RL. 2002. Phoronida p.430. In: Atlas of Marine Invertebrate Larvae. Edited by C. M. Young. Academic Press. New York.

Phyllodocid metatrochophore

Polychaete metatrochophore larvae like this one were collected in plankton tows off the docks in Charleston, OR in April.  I identified them as members of the family Phyllodocidae, largely due to the presence of their leaf-like dorsal cirri.  Cirri are fleshy projections found on polychaete segments (e.g. prostomium, peristomium or pygidium) or their parapodia (appendages bearing chaetae).  Phyllodocid polychaetes have rounded dorsal (and sometimes ventral) cirri on each parapodium.  The cirri of this metatrochophore were particularly leaf-like in their shape and texture, which is a characteristic of the genus Phyllodoce (Crumrine 2001).  This image is a lateral view (anterior up) showing the distinct dorsal cirri, one of the two red eye spots, and the prototroch (a transverse ciliated band encircling the larva at its widest point).  One can also see the four pairs of long finger-like tentacular cirri just posterior to the prototroch.  The second image was taken at a higher magnification to show the leaf-like characteristics of the dorsal cirri.

I kept one of these metatrochophores in a sea table in our lab. When I checked in on it several days after collection, I discovered that it had grown into a juvenile worm and was crawling around on the bottom of the bowl.  At first glance this juvenile looks rather different from the metatrochophore in the above photographs.  But with closer examination, one can see the foliaceous dorsal cirri and the four pairs of long tentacular cirri just posterior to the oval prostomium (anterior-most segment bearing eyes).  The characteristics of both the metatrochophore and the juvenile suggest that this specimen belongs to the genus Phyllodoce.  Identification to species requires examination of the polychaete’s proboscis (the large semi-transparent shape that can be seen through the body wall in this picture).  The arrangement of papillae on the surface of the everted proboscis is a species-specific characteristic within this genus (Carlton 2007). But unfortunately this worm did not evert its proboscis while I was watching, and so the species remains undetermined.   

Crumrine, L.  2001. Polychaeta. In: An Identification Guide to the Larval Marine Invertebrates of the Pacific Northwest. Edited by Alan Shanks.  OSU Press, Corvallis.

Carlton, J T.  2007.  The Light and Smith Manual:  Intertidal Invertebrates from Central California to Oregon 4th Edition.  University of California Press, Berkeley. 

Brooded embryos of bryozoan Dendrobaenia lichenoides

The first image depicts a fragment of a colony of the bryozoan Dendrobaenia lichenoides with brooded embryos (pink).  The D. lichenoides specimens were gathered by hand in South Cove at Cape Arago State Park south of Charleston, Oregon on April 24, 2012.  Each globular ovicell (a calcified brood chamber attached to the maternal zooid) houses a single large embryo.  Ovicells tend to be in the center of the colony where the older zooids are located.  The embryos undergo cleavage and gastrulation within the ovicell, developing into a lecithotrophic coronate larva that is eventually released into plankton and swims briefly before settling and undergoing metamorphosis.  The seasonal timing of larval release is largely dependent upon whether the colony is over-wintering or nascent (Strathmann 1987).  

The second picture shows three ovicells with embryos that I dissected from the colony using a pair of sharp forceps.  With care and practice one can gently crack the ovicell and extract the embryo. 

The bottom picture shows an embryo I was able to dissect out of the ovicell intact.  The embryo is enclosed by a transparent egg envelope, or chorion.  This particular embryo is at a relatively early stage of development, and one can clearly see the outlines of individual cells (blastomeres).  This picture illustrates the biradial cleavage pattern characteristic of bryozoans in general.

Strathmann, Megumi F.  Reproduction and Development of Marine Invertebrates of the Northern Pacific Coast.  United States: University of Washington Press (1987): pp. 505.  Print.