NOTES FOR 3/15-3/19

LAST WEEKS LAB

Body cavities -

Acoelomate - no body cavity, just a gastrovascular tube running through the body Pseudocoelomate - a fluid filled body cavity surrounding the gastrovascular tube that houses the organs Celomate - a bounded body cavity separated from the gastrovascular tube and mesoderm by a peritoneum.

Phylum Platyhelminthes were acoelomates, Phylum Nematode were pseudocoelomates.

An incomplete digestive system is in two directions, in and out. The complete digestive system is one way moving in through the mouth and out through the anus. The advantage, as we may note this week is that areas of the tract can become specialized to one way movement, where in two way movement, the tract must remain generalized.

Muscles - longitudinal, circular/diagonal. Hydrostatic skeletons or fluid-filled cavities are incompressible. When muscles around them contract, the fluid moves to another part of the cavity facilitating movement.

The Platyhelminthes head moved from side to side and the head followed. According to your book, their movement is facilitated by gliding over surfaces powered by broad layers of cilia. I would also like to point out that the book questions the idea that flatworms are protostomes and considers their characteristics to be derived and not ancestral.

The Nematodes have only longitudinal muscles that operate with the hydrostatic skeleton of the pseudocoel to produce a characteristic flipping and bending movement.

The epicuticle was composed of proteins and lipids and was excreted in the Class Trematoda. There were several functions from aid in respiration, absorption, and resistance to digestive enzymes as well as host chemical attacks. The cuticle in the Phylum Nematode was more chemically complex, but its function was similar.

WE WERE NOT LOOKING FOR EARTHWORMS - WE WERE LOOKING FOR NEMATODES - BE SURE YOU UNDERSTAND THE DIFFERENCE THIS WEEK.

THIS WEEKS LAB

This lab covers protostome coelomates with complex systems of organs and compartments. They have well developed systems of nerves, circulation, excretion, reproduction and digestion.

Phylum Mollusca - Class Polyplacophora, Gastropoda, Bivalvia, and Cephalopoda

The mantle is a specialized layer of epidermal cells that secretes a shell. Not all mollusks have shells though. The coelom is reduced to a small chamber around the heart. They have open circulatory systems with no small vessels or capillaries, only a few large vessels and a heart.

The visceral mass refers to the organ systems and sensory structures. The foot is muscular and used for locomotion. The mantle secretes a shell (in some) and may aid in respiration and locomotion. Some mollusks have a differentiated head. The radulas are tooth structures in the mouth.

Class Polyplacophora (many moving plates) - chitons, marine animals with a primitive mollusk structure.

Class Gastropoda (stomach foot) - snails Slugs are snails that do not produce a shell. They may be marine, fresh water or terrestrial.

Class Bivalvia (two shells) - clams, oysters, scallops and mussels Water is pumped through the shell in from the ventral incurrent siphon and out through the excurrent siphon. The water passes over the gills and food is collected and moved to the mouth by cilia. The space between the shell and the visceral mass is called the mantle cavity. Be sure you can identify the parts and functions here.

Class Cephalopoda (head foot) - squid, octopuses, nautilus and cuttlefish The foot is modified into tentacles. The cuttlebone is an internal shell in the cuttlefish. The squid have eyes - the largest in the kingdom animalia belonging to the giant squid. The eyes resemble mammal eyes, but are not ancestrally related.

Phylum Annelida - Class Polychaeta, Oligochaeta, and Hirudinea

All members of this phylum have characteristic segmentation. The segments are divided by septa, and each segment contains parts of the circulatory, digestive, nervous, and excretory systems. Annelids have a closed circulatory system and setae, which are bristle-like appendages, found usually in pairs along the lateral and ventral surfaces. The setal development is distinctive for each class.

Class Polychaeta (many setae) Each segment bears a pair of parapodia or fleshy appendages for movement and respiration. The setae protrude from the parapodia. Some may be filled with poison or help filter food.

Class Oligochateta (few setae) The most common member here is the earthworm. The movement is not by undulation, but by extension, anchoring and contraction using an alternation of circular and longitudinal muscles against hydrostatic pressure within each segment. They lack parapodia and have few setae. They are hermaphroditic producing both eggs and sperm. The clitellum is the series of swollen segments associated with reproductive function.

The seminal vesicles transport the sperm that exit through the male gonopore in segment 15. The seminal receptacles on either side of segment 10 store the sperm. After a few days, the eggs are transported by a mucous band from the female gonopore to the seminal receptacles. The fertilized eggs are released as a cocoon.

We find complex internal developments here. A pharynx for ingestion, esophagus for transport, a crop for storage, a gizzard for maceration, and intestines for absorption. This specialization along the gastrovascular cavity was possible because of a complete digestive tract with one way movement. There is the development of a rudimentary brain, ventral nerve cord and excretory system made up of nephridia, nephrostomes, and nephridiopores.

Class Hirudinea (non-distinctive segments and no seta) This is the class of leeches, resembling our flatworms except in complexity. They are hermaphroditic and an interesting reproductive system. The sperm packet called a spermatophore can be deposited into the female gonopore, or can be injected through the epidermis through the use of tissue-dissolving enzymes. In this case the sperm enter the coelomic cavity and make their way to the ovaries.