Arenicola brasiliensis is a large annelid worm that lives sub-tidally in a j-shaped sand burrow. It deposits its eggs in a big mucous mass anchored in the sand. We collected one of these egg masses weeks ago, and baby worms have begun hatching out!
A picture of the egg mass, courtesy of one of our favorite websites: Sea Net, run by James Watanabe.
The juvenile worms move by two types of motion: they beat their cilia, and move with muscles as well. In this video you can see the cilia beating, with especially long ones near the head and butt.
In this video you can see the two red eye spots at the anterior of the juvenile, the segmentation of the body, and the juvenile's muscle's flexing to move the animals "chaeta"(pronounced see-tee, the sharp and clubbed bristles protruding from the segments).
Just a quick update on our little Hermissenda friends:
We are now 7 days into the veliger stage, and unfortunately a good chunk of our population has died (likely due to overcrowding). The good news is that those that are left are going strong, and should begin to metamorphose in 27-51 days. When I have the opportunity to go collecting, I will introduce some thecate hydroids to their bowl in an attempt to induce earlier metamorphosis.
In the mean time, here are some of our remaining veligers having fun. See if you can find the eye spots behind the velum (the ciliated, figure-eight-shaped foot protruding from the shell):
The medusae's tentacles are beginning to lengthen. Right now they only seem to have one pair on opposite "corners," but eventually they will have up to 150 on the fully grown animal. The tentacles can be contracted closely towards the body.
A. victoria moves with strong muscular contractions of the bell. Here you can see one moving its manubrium around. The manubrium of a jellyfish bears the mouth at its tip.
Several different species of adult Colonial Ascidians.
Below are tadpoles fertilized around 15:00 4/23/13. Spawned from adults above. Spawning Colonial Ascidians release sperm and ova. Pictures below taken around 18:30 same day. They attach to a substrate and metamorphose rapidly. In the first picture the notochord is clearly visible.
Below are pictures of Nematostella vectensis (starlet sea anemone) eggs and planula. The life cycle of N. vectensis is egg-->gastrula-->planula-->primary polyp-->adult polyp. They are in the same phylum as jellies and the same class as corals. All these creatures have a polyp phase but, like corals, anemones don't have a medusa phase which is that classic jelly fish image.
These egg pictures show the fertilized eggs encased in jelly. The sperm penetrates the jelly and it remains until the planula larvae break out of it about 36-48 hours after fertilization (Uhlinger, 1997). The cell masses surrounding the eggs are 'nematosomes' which are made up of nematocytes and flagellated cells (Uhlinger, 1997). These eggs were fertilized 4/18/13 at 13:30 and the photos were taken a few hours later.
Below is a video of a planula that was fertilized on 4/16/13 at 15:00 and was taken on 4/23/13. This looks like a 'late' planula, the Oral-Aboral (OA) axis is elongated. The aboral pole is the end where we see the long apical tuft (lines coming off the planula to the left in the video). The opposite end is the oral pole. The aboral pole is where the apical tuft is and is where the anemone polyp will attach to a substrate and the oral pole is where the tentacles will form around the mouth. Also note the cilia pulsating all around the planula.
1. Uhlinger, Kevin R.(1997). Sexual Reproduction and Early Development in the Estuarine Sea Anemone, Nematostella vectensis Stephenson, 1935. UC San Diego: California Sea Grant College Program. Retrieved from: http://www.escholarship.org/uc/item/6cq8h6f3
Today we are going to be looking at ascidian development. These animals belong to our own phylum and are representatives of the group of invertebrates most closely related to us.
This embryos is surrounded by follicle cells which are involved in fertilization, block to polyspermy, and in some species, secrete sperm attractants.
Saturday, April 20, 2013
Take a look in the sea water table at the adult Pleurobrachia, the look at this video of the Cydippid larva. There's a small jar of these larvae with about 7-10 of them next to the adults. They are pretty tiny, but you can see them under the scope by their tentacles being cast.
CL
Last week, we collected a pair of Hermissenda crassicornis on the San Carlos Beach breakwater. Even though individuals of this species are simultaneous hermaphrodites (each individual contains both male and female gametes at any given time), current evidence suggests that they reproduce exclusively via allogamy (the sperm from one individual must fertilize an ovum from another individual; self-fertilization is either not possible or not common). This meant that we had to encourage our specimens to mate before we could observe any embryonic development:
Several days after excretion, developing veligers (free-swimming nudibranch larvae) became active within their rapidly-dissolving egg capsules. The tubes around the capsules kept the fertilized eggs in a spaghetti-like mass until they were ready to hatch.
Several egg capsules broke free during collection, and provided an excellent view of developing veligers. Close inspection reveals the embryonic shell (looks like a snail shell) that will disappear later in the organism's development.
Hatched veligers are fast swimmers, but the putting them in the correct dish corrals them long enough to make basic observations about their body plan. Shortly before the following videos were taken, we fed these larvae red microalgae. As a result, their gut compartments have a distinctive pink glow:
We now have some Aeqorea victoria (Crystal jellies) from the Monterey Bay Aquarium. These hydromedusae are found off the North American west coast of the Pacific ocean, from the Bering Sea to southern California. Crystal jellies are bioluminescent and emit blue-green light from their outer bells. One of the proteins they use to produce this light, a green fluorescent protein (GFP), is often used in experiments as a biological marker. The scientists who isolated GFP from A. victoria won a Nobel Prize in 2008.
Little medusae swimming around. The manubrium (stalk-like structure dangling from the center of the jelly) can move back and forth. We are feeding them brine shrimp and rotifers right now.
Thanks to Wyatt Patry of the Monterey Bay Aquarium we now have Cnidaria including Cephea cephea! These Cephea cephea or Crown jellies are from Japan. The aquarium's page on Crown jellies can be seen here.
This is a page from my sketchbook of some more info about Cephea cephea.
Below is a video of some polyps. Freya believes that the lighter color one is in the Scyphoistoma stage and the darker color one may be in the Strobila stage closer to strobilating. Notice that the ephyra seen in the next video is also a darker color. Cephea cephea undergo monodisc strobilation so only one ephyra and medusa will result from each polyp as opposed to polydisc strobilation where many ephyra result from one polyp.
This is the only Cephea cephea ephyra we currently have. Hopefully more are to come!
These larvae were reared in Texas for a month by Paul Gonzalez and Chris Cameron - we are lucky to be able to see these critters close up. Some of the most beautiful larvae !
These are "bipinnarian" larvae of the bat star Patiria miniata. They look a lot like the sea cucumber "auricularia" larvae from the last post, but you can tell the difference between starfish and sea cucumber larvae by looking at the ciliated band on the oral hood, which in starfish is separate from the ciliated band that outlines the larval body. These larvae have been eating red algae, which stained their stomachs pink. If you look closely, you may see to thin sacks on the sides of the larval gut. These are the larval "coeloms"--pouches of mesoderm that line the body walls of many complex animals. One of the larval coeloms will ultimately contribute to the water vascular system of the adult starfish.
Our sea cucumber larvae have been developing beautifully.
Gastrulation is the process of forming an animals tissue layers. It is usually the first noticeable sign of an animal forming it's body axes. This is the early "gastrula" of a warty sea cucumber. The tube in the middle of the larva is the larval gut, and the place that the tube contacts the outside will be the larval anus.
This is a later gastrula. The tube on the short bottom of the larva is the forming gut, and the divot on the long side of the larva is where the top of the gut tube will contact the outside layer of the larva and the mouth will form.
These warty sea cucumber larvae are old enough to feed. Each larva has an oral hood (shaped like a star trek badge) and a lobe on the posterior (shaped like a keyhole). The flickering you may see in the thickenings around the margins of the animal and the oral hood are cilia in the ciliary band, which the larva uses to swim and capture algae to eat. Below the upside-down tear-drop shaped mouth (partially under the oral hood) you will see a tube (the esophagus) leading to a bulb shaped stomach. The anus opens on the posterior lobe, making the whole gut curved.
