Looking back

1. Sea spiders: I had to wait for a large order from MBL to order enough to be able to ask for sea spiders. You have seen pictures, now observe the real animal. Describe the overall anatomy of the spider. Estimate the length of the body to that of the long legs. Note that the "body" is not that much thicker than the legs, although terming the central cylinder a body is somewhat misleading as part of the GI tract + extend into the legs.

Dorsal surface showing proboscis, eyes and chelifores (appendages used

to tear bits of food).

Ventral surface showing oviger (used by males to carry eggs0 and gonopores or opening to reproductive organs.

Describe locomotion in these animals. Obtain a photograph showing the Oviger.

Looking ahead

Next week we will be surveying different Cnidaria. I would like you to observe the two different hydroids we have in lab.

You can obtain a bit of the fern looking colony of hydroids. This is a group that contains Hydra. Note how the polyps resemble hydra although individual are connected by a stolon into a colony.

Take a picture of one of the polyps. You may find some with long tentacles at their base, which are feeding polps and those only with very short tentacles that appear to be filled with some thing. These may be reproductive individuals producing eggs or sperm.

Most marine hydroid colonies produce medusae, which are small and sometimes go unnoticed. Our colony is not at a stage to produce medusea but hopefully some the colonies we get next week will have them.

Think about what you would have to measure to compare this colony to other hydroid colonies. Would you note whether the polyps appear singularly or in bunches on branches? Would the inter polyp distance vary among species. Would the appearance in terms of tiers of tentacles or length of tentacles vary. Your picture today will allow you to compare next week, several hydroids to thisspecimen.

Your teaching instructor on her computer can or she may volunteer a table to obtain images of a very different type of polyp that superficially looks like a hydroid but actually in a clade with anemones and true coral. We only have one specimen of this gorgonian but you should easily see how different the polyps are. They actually look more like little anemones sitting in crevices in their colony. Note the colony has a barnacle , called a whip barnacle that lives embedded in the colony. How many arms or tentacles can you count per polyp.

3. The innkeeper worm. Cheetopterus spp. is about the best group in which to see extreme specialization of segments in an annelid.

Chaetopterus is an annelid worm, related to earthworms. It lives in a tube buried underwater in the sand. The worm pumps water through its tube to obtain food. The segments in the posterior part of the body are packed with eggs or sperm (depending on the sex of the worm).

The body is divided into 3 distinct regions, the short anterior end with an inconspicuous head, a mid region with highly specialized feeding structures, and a longer, regularly segmented hind end with repeating appendages.

The worms pump water, filtering out organic particles with a mucus bag that acts as a sieve. Nodopodial paddles or or fan parapodium create the water current through the tube, while other segments bear suckers to help anchor the worm in position. The wing or Aliformparapodium help with the food cup hold the mucous net in place. When the mucus bag becomes clogged with particles, it is rolled into a ball, passed to the mouth by a ciliary tract and ingested, then a new bag is produced.

Observe the Chaetopterus specimens available in laboratory. Unfortunately their season will be over before our annelid lab. This is about the last week they can be connected in the wild, so we will have to jump ahead for this specimens and make some observations you can use later in the annelid lab.

Try to identify the different types of segments.

Most species have male and female individuals. Males and females are labeled for you so you can tell the difference. Note the gametes are developed on the latter unspecialized parapodia. Be able to compare males to females and comment on the specialized segments in your lab journal.

Commensal crabs and scaleworm

Two species of filter-feeding crustaceans from different families may make their homes in the Chaetopterus tube, Polyonyxgibbesi and Pinnixachaetopterana . The crustaceans may live most of their lives in the tubes, leaving in the case of disturbance by exiting through the chimneys at either ends or, when the chimneys are too narrow, by biting through the parchment tube. Various worms including a scale worms also live as commensals in Chaetopterus tubes.

The crabs were placed with the male worms and the one scale worm found with the female Chaetopterus.

IF you have time………………………….

You can if time permits obtain eggs and sperm by removing a segment from a female and male worm and opening them in a dish of sea water. The eggs and sperm will be kept separate until use.

Approximately 5 min after sperm addition, you can view the fertilization process under a light microscope.

After 45-60 min, place your beaker on the dissecting microscope at your table and focus on the bottom of the beaker where the eggs will have settled. Note whether or not they have achieved a slightly elongated shape (as in B or C below). If your eggs have been fertilized, they will appear elongated and you may see a "polar lobe" forming.

/ A. early stage of fertilization (zygote looks the same as an unfertilized egg)
B. fertile egg has elongated
C. a polar lobe is forming at one end of the egg
The polar lobe contains cytoplasmic determinates that are required for normal development.

Aproximately 60-75 min and 90 min after fertilization, cell division takes place. .

/ D. 2-cell stage (note the polar lobe
attached to one cell)
E. 4-cell stage (note the small polar lobe
attached to one cell)

As the zygote divides, the material within the polar lobe is segregated into one of the 4 cells. This uneven distribution of cytoplasmic determinants allows the cells to follow different developmental pathways. 4.

Development of the embryo proceeds rapidly and will reach the larval stage within 24 hours.

I fertilized some eggs last night. Check the culture for the presence of a living trochophore larvae. Trochophore larvae are early larvae and hatch at an earlier stage than Nauplius larvae.

/ The trochophore larval form is found in the development of most annelids and molluscs.