phylum mollusca homework and study guide

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5.5: Phylum Mollusca

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• Keene State College Students, BIO 381 Tropical Marine Biology
• Keene State College

The phylum Mollusca is defined by several special characteristics. These defining characteristics include a mantle with a mantle cavity, a shell (except where lost), visceral mass , foot , and radula . The odontophore is in the mouth of most mollusks and it supports the radula (a ribbon of teeth). In many molluscs, it moves forward while the radula contacts the food, allowing the mollusc to feed. Mollusca can be found in freshwater, marine and terrestrial habitats. More features of molluscs include bilateral symmetry, soft or unsegmented bodies, respiration via ctenidium , ganglia/nerve comprised nervous system , haemocoel body cavity, etc. [1].

Although when most people think of a mollusc they imagine a typical clam or snail with the shell on the exterior of the organism, there are actually variations of these characteristics. One example of this is the Flamingo Tongue . The Flamingo Tongue is a small marine snail. It is a fascinating organism, in that their mantle, when they are at rest, covers the outer shell on the exterior of the organism. When threatened the Flamingo Tongue will retract all of the exposed tissue back into the shell in a very interesting manner.

Polyplacophorans

Chitons are the common name for species in the Class Polyplacophora . Chitons are considered more primitive in relation to other groups within the phylum such as bivalves or cephalopods. There are 8 dorsal plates lining the dorsal surface of these organisms. There are many primitive species of the class Polyplacophora that are still extant. However, only a few species of Monoplacophorans still exist in the world today.

Gastropoda is a very diverse class of molluscs. The subclass Prosobranchia , are often identified by their coiled, cone shaped or tubular shells [1]. The mantel cavity is typically located on the anterior of the organism. Important distinctions of these organisms are the variations or the absence of radula. These organisms utilize Nephridia for excretion of nitrogenous waste. One characteristic of gastropods is the presence of a calcareous operculum . This structure acts as a shielded plate that protects the organism by covering the opening when it is retracted into its shell.

In the photo below, the dark oval in the center is the operculum. They are calciferous and rough to the touch, protecting the opening to the shell like a man-hole cover.

Nudibranchs

Nudibranchs are typically categorized as sea snails which lack shells. Often they are richly colored and captivating to the eye. Their magnificent beauty is the result of aposematism which is the bright coloration exhibited by these organisms that warns predators that they are toxic, distasteful or dangerous. The toxicity of these organisms differentiates from species to species, with some being exponentially more dangerous than others. Their toxicity is usually contingent upon their evolutionary specialization and their genus’s specific niche.

Class Bivalvia consists of molluscs that have two connected shells such as Oysters, Clams, Mussels, Scallops and many more. Most bivalves are enjoyed as delicacies, despite the fact that they are benthic level filter-feeders. As others in the phylum Mollusca, bivalves have a shell that is made up of deposits of Calcium Carbonate. These deposits are derived from substances in the water and harden over-time.

Visible among the many aspects of an open clam are the posterior and anterior adductor muscles. The function of these muscles is to hold the shell closed as a defense from predators. The strength of these muscles given their relative size is immense. The mantle is a layer of tissue that overlays the visceral mass of these organisms and is directly connected to the shell. The foot of the bivalve is directly responsible for its movement. The muscular foot will emerge when the shell is opened and pushes the organism along or into the benthos or substrate.

Cephalopods

Cephalopods exhibit several similarities but also distinguishable differences from other molluscs. They sometimes exhibit a calcium carbonate shell. Squids and Octopus lack this feature, but the more primitive Nautilus does have this feature. Species in the Class Cephalopoda contain a large closed circulatory system and prehensile arms/tentacles that encompass a mouth, complete with a beak and radula. One of the most important evolutionary aspects of these organisms are their large complex eyes. These eyes are specialized for improved sight at depths where little ambient light reaches. The mantle of these organisms forms a sizable ventral cavity containing ctenidia. A portion of the mantle also forms a muscular funnel. Water is taken up and forced through these chambers under pressure creating a unique form of jet propulsion. There are over 900 living species of cephalopods that inhabit the world today.

• Brusca, Gary J., Brusca, Richard C. 2003, Invertebrates 2 nd ed. ISBN 0-87893-097-3

The information in this chapter in thanks to content contributions from Alana Olendorf and Jason Charbonneau

Phylum in Biology

Overview of phylum.

Phylum is a fundamental concept in biology , especially in the field of taxonomy and classification. It helps scientists and researchers to organize and categorize the vast diversity of animal species on Earth .

Characteristics of Phyla

• Body Plan: The body plan of organisms within a phylum often exhibits similarities in terms of symmetry, number of body segments, and overall structure.
• Embryonic Development: Phyla may be distinguished based on their embryonic development, including features such as the presence or absence of certain embryonic tissues or developmental patterns.
• Structural Features: Organisms within the same phylum may share specific structural features, such as the presence of a notochord in chordates or the type of exoskeleton in arthropods .
• Evolutionary Relationships: Phylum classification also reflects evolutionary relationships among organisms , providing insights into their shared ancestry and evolutionary history .

Examples of Major Phyla

• Characteristics: Presence of a notochord, dorsal nerve cord, and post-anal tail at some stage of development.
• Example Organisms : Humans , fish , birds , and reptiles .
• Characteristics: Segmented bodies, exoskeleton made of chitin, and jointed appendages.
• Example Organisms : Insects , spiders, crustaceans, and millipedes.
• Characteristics: Soft-bodied animals often protected by a hard shell, muscular foot, and mantle .
• Example Organisms : Snails , clams , octopuses , and squids .

Study Guide

Key concepts.

• Definition of Phylum: Understand the meaning and significance of phylum in the classification of organisms .
• Characteristics of Phyla: Familiarize yourself with the common characteristics that define and distinguish organisms within a particular phylum.
• Examples of Major Phyla: Study the key features and representative organisms of major animal phyla such as Chordata , Arthropoda, and Mollusca.

Study Questions

• What is the significance of phylum in biological classification?
• How do the characteristics of organisms within a phylum contribute to their classification?
• Give examples of major animal phyla and describe their distinguishing features.

Practice Activities

• Classification Activity: Create a chart or diagram that illustrates the classification of different organisms into their respective phyla based on key characteristics.
• Comparative Anatomy : Study the anatomical features of organisms from different phyla to identify similarities and differences in their body plans.

Additional Resources

• Textbook Readings: Review chapters or sections in biology textbooks that cover the classification of organisms into phyla.
• Online Tutorials: Explore online resources and tutorials that provide interactive lessons on animal phyla and classification.

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Phylum Mollusca Homework - Mollusks

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Description

Use this set of 2 printable or digital homework assignments or study guides on "The Phylum Mollusca" to provide your students with quality homework assignments for your invertebrate / mollusk units. This resource contains 7 student pages consisting of 115 questions. As I teach my unit on this phylum, I assign a portion of these questions for homework each night. The completed homework assignments provide a thorough study guide for the unit test. You can also use a few questions during class each day to check for student understanding of the concepts being taught.

This set of 2 homework assignments is perfect to use with my PowerPoint and Notes set: Phylum Mollusca PowerPoint and Notes Bundle. Click this link to view this set.

Both printable and digital versions of this resource are included. The student handouts can be printed or used in the paperless digital format in your Google Drive, Google Classroom, Microsoft OneDrive, or similar. This resource is perfect for traditional classroom settings, 1:1 schools, or for distance learning.

What is included in your download folder?

• Printable and Editable Homework Assignments / Study Guides (Set of 2)
• Digital paperless versions (not editable) for use in Google Drive, Google Classroom, and/or Microsoft OneDrive
• Teacher Guide and Answer Key
• Teacher Guide for Google Apps Versions

This set of 2 homework assignments can be used with the mollusk chapter of any biology textbook.

What material is covered by each assignment?

Homework 1:

• Characteristics of the Phylum Mollusca.
• Mollusks are coelomates: Includes the definition of “coelom”, the advantages of having a true coelom, and a list of animal phyla that have a true coelom. Differences between acoelomates, pseudocoelomates, and coelomates.
• The trochophore larva.
• Bilateral symmetry.
• The Mollusk Body Plan: Head, foot, visceral hump, mantle, shell, gills, radula.
• Three classes of mollusks: Class Gastropoda, Class Bivalvia, and Class Cephalopoda.
• Class Gastropoda: Characteristics of the members of this class, torsion, the open circulatory system, hemolymph, hemocoel, characteristics of snails, slugs, and nudibranchs.

Homework 2:

• Class Bivalvia: Characteristics of the members of this class, the parts of the bivalve shell, adductor muscles.
• External structures of the clam: Umbo, hinge, siphons, valves, growth rings, and foot.
• Internal structures of the clam: Mantle, foot, dorsal excurrent siphon, ventral incurrent siphon, palps, mouth, stomach, digestive gland, intestine, anus, anterior and posterior adductor muscles, heart, gills, and gonads.
• Class Bivalvia Body Systems: Movement, Food-getting and Digestion, Nervous system, Open Circulatory system, Reproductive system, Respiratory system.
• Class Cephalopoda: Characteristics of the members of this class, division of the foot into tentacles, predatory lifestyle, chromatophores.
• Cephalopod body systems: Closed Circulatory system, Nervous system, Reproductive system.
• Characteristics of squid, octopus, and chambered nautilus.
• The Ecology of the Mollusks: What roles do mollusks play in the ecosystem?

All answers are included in the very detailed 7 page teacher guide that is included with this resource.

This study guide is appropriate for any biology or life science class with students in grades 9 - 12.

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