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.

Echinopluteus

These pictures show an echinopluteus larva of the common Pacific coast species - the sea urchin Strongylocentrotus purpuratus (the purple sea urchin). I found this larva in a plankton sample collected off the docks in Charleston, OR on February 8th, 2012. All three pictures show the same specimen at the same developmental stage, but different focal planes, to emphasize different structures. The calcareous spicules making up the larval skeleton are clearly visible in the top photograph and appear rainbow-colored due to the use of polarized light. These spicules characterize the pluteus larva (found in echinoids and ophiuroids, a.k.a. sea urchins and brittle stars). The morphology of the larval skeleton is used to identify larval echinoids (sea urchins and sand dollars). The spicules support the larval arms (4 in this larva at this stage), which in turn support the ciliated band, used for feeding and locomotion. The longer the arms, the longer the ciliated band, the more efficient the larva can feed.

The middle photograph shows the mouth - the large oval shape at the anterior end of the larva (up) and a portion of the tri-partite gut, which characterizes all feeding echinoderm larvae. One can see the round stomach (in the center of the larva) and the esophagus (a short muscular tube that connects the mouth to the stomach). One can also see the two coelomic sacks (one on either side of the esophagus), which will form the body cavity and the water-vascular system of the adult urchin. The bottom photograph shows red pigment cells in the epidermis of the larva. These have been observed to function in wound healing in echinoid larvae: pigment cells in vicinity of the wound migrate to the damaged area and engulf cellular debris (George von Dassow, personal communication).

Encapsulated Mollusk Trochophore

This is a trochophore larva of an unidentified gastropod mollusk collected from the plankton on February 1st 2012 off a dock in Charleston. It swims about within its remarkable bilayered egg capsule. What appears as an opening at about one o’clock is most likely the micropyle (a remnant of the oocyte’s attachment to the ovary, which is also likely the site of sperm entry). The trochophore is characterized by the presence of the prototroch - a pre-oral ciliated band, which you can clearly see in this picture. Some mollusks with intracapsular development (as opposed to pelagic development) may have a reduced trochophore stage or no trochophore stage at all. Also, the stage at which the larva hatches out of its capsule can vary from species to species: some may hatch out as trochophores, while others hatch out as veligers, as this one did.

  Molluscan veliger larvae are characterized by the presence of a shell and a velum whose ciliated lobes are used for locomotion and food capture. The velum is derived from the prototroch. The picture on the left shows a large bilobed velum of a different gastropod veliger.

Unidentified polychaete metatrochophore

This is a metatrochophore larva of an unidentified polychaete annelid that I collected from a January 2012 plankton tow off the docks in Charleston. Its gut contains a large number of yolk droplets (of various color and size). Yolk droplets of this kind are often found in eggs of annelids with lecithotrophic larvae (meaning they do not feed and derive nutrition from maternal supplies), e.g. in larvae from the family Nereidae.  This suggests that this is likely a lecithotrophic larva.  One can also see two ciliary bands. The broad ciliary band just posterior to the ocelli (eyes) is called the prototroch. The narrow band near the posterior end is called the telotroch. These are used for locomotion. In planktotrophic (feeding) larvae the prototroch may also be used for collecting food particles. This larva has three setigers (segments that bear setae), which is how we know it is an annelid.

Micronereis nechtochaete larva

This polychaete nechtochaete larva was captured in a plankton sample taken off a dock in Charleston, OR on April 5, 2012. I identified it as belonging to Micronereis nanaimoensis (Fam. Nereidae) (Crumrine 2001). It has three setigers (body segments bearing chaete), and the chaete (or setae) are characteristically compound, i.e. composed of two  "segments". Nereid eggs are typically supplied with a large amount of yolk (in a form of large lipid droplets), and this larva clearly developed from such an egg. The "shiny marbles" in its gut are the lipid droplets. Nereid nechtochaetes, in general, have two anal cirri (leaf-like appendages at the posterior end), and large eyes. Micronereis is unusual among local nereids in that it does not have tentacular cirri (also known as prostomial antennae) decorating its prostomium (the segment anterior to the mouth, which bears eyes). 

On this photograph one can discern a pair of chitinous jaws inside the pharynx, a characteristic of all nereids. You can see the pharynx through the body wall - it is a large pear-shaped structure located just posterior to the eyes between the two anteriormost chaetal bundles and "bissected" by a longitudinal brownish line which corresponds to the lumen. The pharynx ends where the gut (filled with lipid droplets) begins.  The jaws are semi-transparent at this stage. If you look closely you will also notice three transverse ciliary bands (one per setiger) - the cilia are visible posterior to each chaetal bundle. The larva uses these ciliary bands to swim. These larvae do not feed until they exhaust their yolk reserves.

Crumrine, L. 2001. Polychaeta. In: An identification guide to larval marine invertebrates of the Pacific Northwest. Edited by A. L. Shanks. Oregon State University Press. Corvallis.  

Two-tentacled actinula of narcomedusa Solmundella

This is a picture of an unusual hydrozoan larva, a two-tentacled actinula of the narcomedusa Solmundella (Woltereck 1905). We found several of these in a near-surface plankton sample taken about 2 miles off shore and 5 miles south of the mouth of Coos Bay, Oregon on December 9, 2011. The anterior of the actinula larva (to the right on these pictures) is somewhat pointed, the posterior may be rounded, truncated or bell-shaped. The arms are solid and supported by what looks like a single row of neatly stacked clear endodermal cells.

These larvae can retract their arms, so they look like short bumps (left), or stretch them out so they are several times the body length (not shown). They can also flex their arms, so they are pointed forward, spread out like a "T", or folded back.

One of these larvae metamorphosed overnight into a young medusa (shown on the left). The medusa of Solmundella has only two tentacles, which arise from the bell, rather then its margin. Narcomedusae are part of the order Trachylina (class Hydrozoa), which characteristically lacks polyp generation. As you can see here, the larva of Solmundella directly develops into a medusa, so a benthic stage is lacking from the life cycle entirely. In other Hydrozoans (e.g. order Hydroida) the larva (typically, non-tentaculate planula) settles and develops into a benthic polyp, which may form a colony of interconnected zooids and bud off medusae (which develop gonads, and release eggs, which develop into planulae, and so on). See a post by Ashley Choi on the life cycle of the hydrozoan Obelia - which includes both the polyp and the medusa generations.

Woltereck, R. 1905. Entwicklung der Narcomedusen. Deut. Zool. Gesell. Verhandl. 15.

Brachiolar arms in late-stage asteroid larvae

This is the brachiolaria larva of a starfish, Pisaster ochraceous,that I raised during the Embryology class. Larval anterior end is up, and you are looking at the ventral side. The brachiolaria is characterized by the presence of brachiolar arms and an adhesive disk, and the bottom image shows a close up of the pre-oral protuberance of the frontal lobe that bears these structures. The brachiolaria larva follows the bipinnaria larval stage in the forcipulates, a group of starfish.

The brachiolaria is the last larval stage in these asteroids. It is characterized by three brachiolar arms (the three stubby arm buds near the top of the larva in the first image and zoomed in on in the second image) which surround a central adhesive disk (the brown spot between the lower two brachiolar arms in both images). These appendages have sticky cells and are used to make contact with the substratum when the larva is competent to settle. Some other asteroids, that have lecithotrophic, or non-feeding development, skip the bipinnaria stage, and directly produce large yolky brachiolaria with three brachiolar arms and an adhesive disk also used for settlement and attachment.

Spermatophore of Phoronopsis harmeri

The first image shows the spermatophore of a phoronid worm Phoronopsis harmeri. A spermatophore is a package that contains multiple sperm. Sperm is produced by males inside the body coelom, then released through the nephridiopores at the anterior end, and shaped into these packages by the special spermatophoral gland located inside the crown of tentacles (called the lophophore) which surrounds the mouth. The spermatophores of this species are round, about 300 micron in diameter, and equipped with a cork-screw shaped transparent “sail”. The sail is easily dislodged from the capsule.

The second picture shows two spermatozoa (or sperm). The sperm in this species is unusual in that it is V-shaped. The nucleus is in one arm of the “V”, and the flagellum forms the other arm, the acrosome is at the apex of the “V”. After the spermatophore is released it floats in the water and lands on the lophophore of a female. Once there, the spermatophore somehow makes its way into the tentacular coelom of the female, and eventually into the body coelom where internal fertilization occurs. Typically development is arrested until the female releases the fertilized eggs into the water. Occasionally development is initiated inside the female coelom, and one can find gastrulae or even more advanced developmental stages. See a post by Phillip Warner showing a 6-day old actinotroch larva of this species reared in the lab, and a post by Svetlana Maslakova showing an advanced actinotroch of this species collected from plankton.

Polar lobe in Nassarius fossatus

Nassarius fossatus is a marine snail. Snails, or gastropods, belong to the Spiralia - a large group of animals with spiral cleavage. Nassarius fossatus has unequal cleavage, which means that one of the cells at the two-cell and four-cell stage is larger than the others. The first four cells in a spiralian embryo are denoted as A, B, C and D. The D cell is the largest in unequal spiral cleavage. There are several mechanisms by which unequal cleavage can be accomplished. Nassarius does this via the so-called polar lobe, which is shown in these pictures. A polar lobe is an anucleated protuberance which forms at the vegetal pole during first, second, and sometimes subsequent cell divisions. It then fuses with one of the cells, making it larger than the others.

The top picture shows polar lobe formation during the first cell division. One can see two polar bodies. Polar bodies are the tiny sister cells of the oocyte which are produced during meiosis, contain discarded DNA and mark the animal pole of the embryo (up in the first three pictures). The opposite pole of the embryo is the vegetal pole. The two cells at the animal pole are the first two blastomeres. What looks like a third cell at the vegetal pole is the polar lobe, which at this stage is nearly completely cinched off from either blastomere. Subsequently the polar lobe fuses with one of the blastomeres (second picture from top), so that by the end of the first cell division one of the blastomeres (called CD) is noticeably larger than the AB cell (third picture from top). Polar lobe also forms at the second cell division (not shown). At the four-cell stage blastomere D is the largest, blastomere C is the second largest, while A and B cells are about the same size (bottom picture). The first three pictures are lateral views, while the bottom picture is a polar view. It is the first time I have heard of and observed unequal spiral cleavage, and I think it is remarkable. I also liked these eggs because the egg capsules they are laid in are very beautiful when viewed under the dissecting microscope (see picture by Janelle Urioste).

Gastropod Egg Masses

I was intrigued by the diversity of egg masses among marine gastropods (snails and slugs). In our Embryology class I observed three species with different habits of laying their eggs, namely, the snails Nucella emarginata, and Nassarius fossatus, and a nudibranch (or sea slug) called Diaulula sandiegensis. N. emarginata (also known as the “dog winkle”) and N. fossatus (also known as the “giant western dog whelk”) belong to the group of marine prosobranchs and produce egg capsules which are leathery or hard, and tend to be attached to various substrata in the environment. The top picture shows two egg capsules laid in our sea table by Nucella emarginata. These capsules are shaped like a wine goblet, and are opaque and hard, and each contains numerous eggs. The middle picture shows a single egg capsule of Nassarius. These are more or less transparent, so the eggs are easily visible through the wall of the capsule. When well fed, these scavenger snails will lay egg capsules attached to the walls of sea table, or the hose as close to the surface of the water as they can get. These egg capsules are beautifully sculptured. The bottom picture is of the egg mass laid in our sea table by the nudibranch Diaulula sandiegensis. Opisthobranchs, in general, lay their eggs in gelatinous ribbon-like masses. These masses are often loosely attached to the substratum, and tend to be only a few eggs thick.

Regeneration in bipinnaria II

In May I surgically bisected several bipinnaria larvae of the starfish Pisaster ochraceous. I made the cuts across the esophagus (anterior to the coeloms), separating the preoral lobe and the mouth from the rest of the larva (see pictures). I wanted to see if the fragments would indeed regenerate, as described in the literature.

The anterior and posterior fragments were cultured together and observed 13 days post-surgery. I observed two distinct morphotypes in the culturing vessel representing the anterior and posterior fragments. The first photo shows one of the posterior fragments 13 days after bisection. You can see that these fragments healed and regenerated the preoral lobe and the mouth. The fragments that I interpreted as being anterior, healed, but did not appear to regenerate 13 days after bisection (see bottom picture). This is surprising because bipinnaria larvae of the same species are apparently capable of regenerating their anterior ends under similar experimental conditions (Vickery et. al. 2002). I continued to monitor these fragments for several more weeks to see if the anterior ends would finally regenerate. As of six weeks post-surgery, I found two (out of original 15) anterior fragments that did not appear to regenerate.

Vickery, M. S., Vickery, M. C. L., McClintock, J. B. 2002. Morphogenesis and Organogenesis in the Regenerating Planktotrophic Larvae of Asteroids and Echinoids. Biol. Bull. 203: 121–133

Pseudocyphonautes of Flustrellidra

These pictures are of the bryozoan Flustrellidra coniculata and its pseudocyphonautes larva. The pseudocyphonautes resembles the planktotrophic cyphonautes larva of some bryozoans in that it has a bivalve shell. But it is lecithotrophic (non-feeding) and is brooded. The top picture shows the bean-shaped pseudocyphonautes larva using a dark-field technique. One can distinguish the cilia of the corona ciliata along one edge of the larva. One can also see a ridge on the opposite side which corresponds to the shell margin. The clear outer coating is the shell that protects the larva’s interior structures.

The middle picture shows a small section of the colony (with zooid lophophores retracted). The three white oval shapes out of focus are the larvae which I have dissected. Just beneath the surface of the colony one can see a few yellowish-white masses. These are the ovicells, specialized zooids for brooding eggs and larvae. I extracted the pseudocyphonautes larvae by puncturing the ovicells with a pair of fine forceps and squeezing gently to push them through the hole.

The bottom picture shows a complete Flustrellidra colony, with my palm for scale. This is the largest upright bryozoan colony I have ever seen. It does not look like a bryozoan at all. In the field I would have easily mistook this animal for some sort of alga or a sponge!