Mytilus-Venus - Dissection guide for Mytilus californianus...

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Dissection guide for Mytilus californianus and Venus merceanaria Each student (along with their partner) should accomplish the following during the lab: 1. Sketch the external anatomy of your animal (shell, ligament etc.) 2. Sketch the generalized internal anatomy of your animal (making sure to label all relevant features) 3. Sketch and compare the relative anatomy of the ctenidia 4. Expose and sketch the circulatory system in the region of the heart 5. Time permitting dissect and sketch the digestive system (stomach, style, intestine) Remember. .. Annotate, annotate, annotate! Introduction Your first reaction to this lab might be: "Ugh--bivalves. All they do is filter feed seawater". That's quite true--that's pretty much all they do most of the time. But the extreme adaptations to filter - feeding one sees in bivalves are part of what makes them such fascinating objects of study. And even though all bivalves utilize basically the same food source, they inhabit a variety of habitats. The forms you will study today--the mussels and the quahog clam -- inhabit places as different as night and day: the mussel, the wave swept mid - tidal zone: the quahog, the sand or mud of quiet bays. As you go through this lab, keep comparing/ contrasting the two animals in the light of their different habitats and lifestyles, but don't lose sight of the fact that they are built on the same basic plan. Once you identify the elements in this plan, it will be easier for you to get a handle in the modifications each form has undergone. A Little Background In bivalves, or pelecypods ("knife-foot" in Latin) the mantle has become greatly enlarged, and covers the head. The gills are highly modified for filter feeding; because the food particles they eat are so small, bivalves have no need for the scraping radula and muscular buccal apparatus seen in most other mollusks. Today you will be looking at typical representatives of the two largest bivalve groups: the Pteriomorpha, which have adapted themselves primarily to living attached to a substrate, and the Hterodonta, which are mainly burrowers in mud or sand. Like many of its pteriomorph relatives, the mussel ( Mytilus californianus ) has the comparatively primitive "lamellibranch" or fillibranch ctenidia, in which the individual filaments are not bound together. The quahog clam ( Venus mercenaria ), a typical heterodont, has the more complex eulamellibranch ctenidia, with cross linked filaments. In addition to this, pteriomorphs have a comparatively weak hinge area, without true teeth, and they draw sea water in and out through a simple opening in a fused region of the mantle rather than trough true inhalant and exhalant siphons, as heterodonts do.
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Life Histories Unlike its relatives, the oysters and rock scallops, which attach their lower shell valve to the substrate, Mytilus attaches itself with elastic byssal threads. You can see these threads protruding from the valves of your specimens. Like most bivalves,
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This lab report was uploaded on 04/16/2008 for the course BIO 120 taught by Professor Idk during the Winter '04 term at UCSC.

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Mytilus-Venus - Dissection guide for Mytilus californianus...

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