{"id":755,"date":"2021-03-09T19:10:15","date_gmt":"2021-03-10T00:10:15","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/earthhistorylab\/?post_type=chapter&p=755"},"modified":"2021-03-15T11:32:01","modified_gmt":"2021-03-15T15:32:01","slug":"fossils-of-the-paleozoic-phylum-mollusca-the-bivalves-gastropods","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/earthhistorylab\/chapter\/fossils-of-the-paleozoic-phylum-mollusca-the-bivalves-gastropods\/","title":{"raw":"Fossils of the Paleozoic: Phylum Mollusca (The Bivalves & Gastropods)","rendered":"Fossils of the Paleozoic: Phylum Mollusca (The Bivalves & Gastropods)"},"content":{"raw":"Phylum Mollusca includes several different types of animals with very different life habits and functions in the ecosystem. Being able to distinguish these different types is important, and so we will be examining three major classes of Phylum Mollusca: Class Bivalvia (the bivalves), Class Gastropoda (the gastropods, or snails) and Class Cephalopoda (cephalopods, including squid, octopi, nautilus and the extinct ammonites).\r\n\r\nMembers of Class Cephalopoda are very different from the slow-moving members of Class Bivalvia and Class Gastropoda; these alert, aggressive predators are strong swimmers with keen eyesight, and able to compete with marine vertebrates. As a class they attained the largest physical size of all the invertebrates. We will learn more about them in Lab 8. In today\u2019s lab we will focus on Classes Bivalvia and Gastropoda.\r\n

Class Bivalvia (Includes Clams & Oysters)<\/h1>\r\nClass Bivalvia ranges from Lower Cambrian to today, and peaked in the Cenozoic. Bivalve animals are typically encased in two shells\u2014also called valves\u2014hence the name bivalve. The shells have bilateral symmetry from top to bottom (the two shells look the same), rather than the side-to-side symmetry of the brachiopods (Figure 7.10).\r\n\r\n \r\n\r\n[caption id=\"attachment_762\" align=\"aligncenter\" width=\"650\"]\"\"<\/a> Figure 7.10 |<\/strong> Examples of Class Bivalvia.[\/caption]\r\n\r\nBivalves feed by sweeping food out of the water column and drawing it through the shell; for most bivalves this food is phytoplankton. Unlike brachiopods, the animal uses powerful muscles to hold the shells together, so upon death the two valves usually fall apart and are most often preserved as separate shells.\r\n\r\nAnother difference between bivalves and brachiopods is that bivalves lack the small opening at the hinge for a pedicle. Instead, they move about by extending a \u201cfoot\u201d between their valves. Some bivalves attach themselves to the ocean bottom and may form large masses or banks. Others burrow into wood pilings or mud close to shore. Bivalve shells take many different forms that reflect the characteristics of the environment in which they lived, and they are easily preserved. This class is the most important index fossil for the Paleozoic, Late Mesozoic and most of the Cenozoic.\r\n\r\n \r\n
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Questions a & b<\/p>\r\n\r\n<\/header>\r\n

\r\n\r\na.\u00a0\u00a0 What energy would epifaunal bivalves experience in comparison to infaunal bivalves?\r\n\r\nb.\u00a0\u00a0 What effect might this have on shell characteristics of the two life habits?\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n

A. Sample 30<\/a>: Modern Clam Shells<\/h3>\r\nThis sample can be picked up but please treat it with care.<\/strong><\/span>\r\n\r\n \r\n\r\n[h5p id=\"89\"]\r\n\r\n \r\n
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Question c<\/p>\r\n\r\n<\/header>\r\n

c.\u00a0\u00a0 If you have access to Sample 30, draw a simple sketch of the sample from (1) the front, (2) the side and (3) the top, and indicate the plane of symmetry on your sketches. If you do not have access to the physical sample to view from all sides, click here<\/a> to view a 3D model of a clam shell. Note: The clam in this model is animated. Click the pause button on the bottom left just below the model (it's difficult to spot) to make it sit still for a portrait.<\/div>\r\n<\/div>\r\n

B. Sample FFA18<\/a>: Large Bivalve Shell<\/h3>\r\nThis sample can be picked up but please treat it with care.<\/strong><\/span>\r\n\r\n \r\n\r\n[h5p id=\"90\"]\r\n\r\n \r\n
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Questions d-g<\/p>\r\n\r\n<\/header>\r\n

\r\n\r\nd.\u00a0\u00a0 Identify the growth rings on the shell. What could these rings tell us about the environment in which this animal lived? Think about the environmental conditions that would make a clam happy versus what would stress the animal.\r\n\r\ne.\u00a0\u00a0 Describe the sedimentary rock that formed inside the shell. (See the last slide for a close-up view, or use a hand lens if you have access to the physical sample).\r\n\r\nf.\u00a0\u00a0 If the shell weathered away and this brown sedimentary material was left behind, what kind of fossil would this be? (Click here<\/a> to review information about types of fossils in Lab 5.)\r\n\r\ng.\u00a0\u00a0 How does this sample\u2019s symmetry differ from that of Samples 13, 9, and 15? Click here<\/a> to see these samples again.\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n

Class Gastropoda (Snails)<\/h1>\r\nClass Gastropoda ranges from the Cambrian to today (no peak). Many marine gastropods move across the ocean floor and scrape algae off the sediments or rocks. Others are sediment deposit feeders and some are carnivores.\r\n\r\nGastropods share some similarities with clams, but they are more advanced. They have a distinct head with eyes, feelers, and a mouth with a rasp-like tongue.\r\n\r\nIn most gastropod species the shell is coiled and consists of only one unchambered valve (Figure 7.11), but some have uncoiled valves. Others, like the garden slug, that have no valve at all. Gastropods can have shells with conispiral or planispiral coils, but in this course we examine only on gastropods with conispiral coiled shells (Click here<\/a> to review coiling from Lab 5).\r\n\r\n \r\n\r\n[caption id=\"attachment_771\" align=\"aligncenter\" width=\"650\"]\"\"<\/a> Figure 7.11 |<\/strong> Examples of Class Gastropoda with coiled shells.[\/caption]\r\n\r\nGastropods are common index fossils for the Late Mesozoic and most of the Cenozoic because they are abundant in the fossil record, have varied and easily identifiable forms, and their shell characteristics reflect their living environment.\r\n
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Question h<\/p>\r\n\r\n<\/header>\r\n

h.\u00a0\u00a0 In what environmental range do gastropods live?<\/div>\r\n<\/div>\r\n \r\n

C. Sample 1: Modern Gastropod Shells<\/h3>\r\nThese samples can be picked up but please treat them with care.<\/strong><\/span>\r\n\r\n \r\n\r\n\"\"<\/a>\r\n\r\n \r\n
\r\n

Question i<\/p>\r\n\r\n<\/header>\r\n

i.\u00a0\u00a0 What type of preservation is displayed in Sample 1? Explain your reasoning.<\/div>\r\n<\/div>\r\n \r\n

D. Sample FL3<\/a>: Pleistocene Gastropod Shells (within the last 1.8 MY)<\/h3>\r\nThese samples can be picked up but please treat them with care.<\/strong><\/span>\r\n\r\n\u00a0<\/strong>\r\n\r\n[h5p id=\"93\"]\r\n\r\n \r\n
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Questions j & k<\/p>\r\n\r\n<\/header>\r\n

\r\n\r\nj.\u00a0\u00a0 What type of coiling do these samples demonstrate?\r\n\r\nk.\u00a0\u00a0 Parts of the outer shells of Sample FL3 have been eroded away and the infilled sediment is visible. Are these shells chambered?\r\n\r\n<\/div>\r\n<\/div>\r\n

E. Sample 21<\/a>: Gastropod Shells<\/h3>\r\nThese samples can be picked up but please treat them with care.<\/strong><\/span>\r\n\r\n \r\n\r\n[h5p id=\"94\"]\r\n\r\n \r\n
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Question l<\/p>\r\n\r\n<\/header>\r\n

l.\u00a0\u00a0 Describe the shell characteristics of Sample 21, then look back<\/a> at the three brachiopods samples (Samples 13, 9, and 15).\u00a0 Based on shell characteristics, do you think this gastropod lived in a high or low energy environment? Explain your reasoning.<\/div>\r\n<\/div>\r\n ","rendered":"

Phylum Mollusca includes several different types of animals with very different life habits and functions in the ecosystem. Being able to distinguish these different types is important, and so we will be examining three major classes of Phylum Mollusca: Class Bivalvia (the bivalves), Class Gastropoda (the gastropods, or snails) and Class Cephalopoda (cephalopods, including squid, octopi, nautilus and the extinct ammonites).<\/p>\n

Members of Class Cephalopoda are very different from the slow-moving members of Class Bivalvia and Class Gastropoda; these alert, aggressive predators are strong swimmers with keen eyesight, and able to compete with marine vertebrates. As a class they attained the largest physical size of all the invertebrates. We will learn more about them in Lab 8. In today\u2019s lab we will focus on Classes Bivalvia and Gastropoda.<\/p>\n

Class Bivalvia (Includes Clams & Oysters)<\/h1>\n

Class Bivalvia ranges from Lower Cambrian to today, and peaked in the Cenozoic. Bivalve animals are typically encased in two shells\u2014also called valves\u2014hence the name bivalve. The shells have bilateral symmetry from top to bottom (the two shells look the same), rather than the side-to-side symmetry of the brachiopods (Figure 7.10).<\/p>\n

 <\/p>\n

\"\"<\/a>
Figure 7.10 |<\/strong> Examples of Class Bivalvia.<\/figcaption><\/figure>\n

Bivalves feed by sweeping food out of the water column and drawing it through the shell; for most bivalves this food is phytoplankton. Unlike brachiopods, the animal uses powerful muscles to hold the shells together, so upon death the two valves usually fall apart and are most often preserved as separate shells.<\/p>\n

Another difference between bivalves and brachiopods is that bivalves lack the small opening at the hinge for a pedicle. Instead, they move about by extending a \u201cfoot\u201d between their valves. Some bivalves attach themselves to the ocean bottom and may form large masses or banks. Others burrow into wood pilings or mud close to shore. Bivalve shells take many different forms that reflect the characteristics of the environment in which they lived, and they are easily preserved. This class is the most important index fossil for the Paleozoic, Late Mesozoic and most of the Cenozoic.<\/p>\n

 <\/p>\n

\n
\n

Questions a & b<\/p>\n<\/header>\n

\n

a.\u00a0\u00a0 What energy would epifaunal bivalves experience in comparison to infaunal bivalves?<\/p>\n

b.\u00a0\u00a0 What effect might this have on shell characteristics of the two life habits?<\/p>\n<\/div>\n<\/div>\n

 <\/p>\n

A. Sample 30<\/a>: Modern Clam Shells<\/h3>\n

This sample can be picked up but please treat it with care.<\/strong><\/span><\/p>\n

 <\/p>\n

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