Exercise 7_Molluscs II_Remote

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Exercise 7 – Molluscs II: Cephalopoda and Gastropoda Subclass: Nautiloidea Nautilus : https://skfb.ly/6AJID . This genus includes the only living cephalopods with external shells. (See Clarkson figure 8.21) A. On the image label : a. body cavity (living chamber) b. septal neck c. septum d. siphonal tube e. non-living chambers

B. Examine the straight-shelled nautiloids ( https://skfb.ly/6AFst and https://skfb.ly/6RsRE ) . Long, straight-shelled nautiloids are especially common in the Ordovician. Look for the siphuncle, siphuncular opening, septa, and camerae. Describe the characteristics that allow you to identify this specimen as a nautiloid (as opposed to some other chambered mollusc). - Banded chambers - Larger siphuncle opening - Long septa Sublcass: Coleoidea C. Examine the belemnites ( https://skfb.ly/6AvTC and https://skfb.ly/6AwGV ) and locate the following features: rostrum (or guard), phragmocone, siphuncle, septa. D. Which morphological features will you use to differentiate an orthocone nautiloid and a belemnite? Be certain that these are features you can observe. - - Belemnite has an elongated rostrum - - Belemnite septa are larger You can find images and descriptions of living members of coleoidea here: https://www.uwlax.edu/biology/zoo-lab/lab-6--molluscs/ Subclass Ammonoidea Suture patterns are useful for identification at the species level. The average complexity of sutures also increased over the evolutionary history of the Ammonoidea. For each of the specimens, identify the type of suture pattern. See Clarkson Figure 8.26. Specimen Suture type (goniatitic, ceratitic, ammonitic) https://skfb.ly/6AyI8 Oxynoticeras oxynotum https://skfb.ly/6RoIo Neoglyphioceras https://skfb.ly/6zZMr Meekoceras

H. This pyritized specimen preserves the siphuncle (circled in green), which is visible due to a gap in the exterior of the fossil. Describe the position of the siphuncle with respect to the rest of the shell. - Straight through the center to the opening I. Which morphological features will you use to differentiate a nautiloid and an ammonoid? - The siphuncle runs through the center of the septa and camerae

Class Gastropod Anatomy Examine the gastropods at your station and find the following features on each. a. Aperture b. Apex c. Youngest Whorl d. Oldest Whorl If you have broken or sectioned gastropods, you should also be able to see the internal columella. J. Label the images on the right with the aperture, apex, youngest whorl, oldest whorl and columella. K. The specimen below (and this one here: https://skfb.ly/6ABqF ) has its operculum in place. What is the function of the operculum? - To protect the organisms form the exposed soft parts of it’s body. Acts as a lid

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