Question

Which of the following statements about the anatomy of a mollusk is false? a. Mollusks have a radula for scraping food. b. Mollusks have ventral nerve cords. C. The tissue beneath the shell is called the mantle. d. The mantle cavity contains hemolymph.

Short answer

The false statement is: d. The mantle cavity contains hemolymph.

Step-by-step solution

Review the anatomy of a mollusk

Before we start identifying the false statement, let's review some key structures of a mollusk's anatomy. Mollusks are invertebrates that often have a shell, a muscular "foot," a mantle, and a radula, which is a unique structure for feeding. They also have an open circulatory system with a fluid called hemolymph that serves a similar function to blood.

Evaluate statement a

Statement a mentions that "Mollusks have a radula for scraping food." This is true. Radula is a unique and characteristic feeding organ found in most mollusks. It is used for scraping food, mainly algae, from surfaces.

Evaluate statement b

Statement b states that "Mollusks have ventral nerve cords." This is also true. Mollusks have a well-developed nervous system, which consists of ganglion cells connected by nerve cords running through their bodies. The nerve cords are usually found on the ventral side of the body.

Evaluate statement c

Statement c claims that "The tissue beneath the shell is called the mantle." This statement is true. The mantle is an important tissue in mollusks that lines the outer portion of their body, forming a cavity called the mantle cavity. The mantle also secretes substances necessary to form the shell in mollusks with shells.

Evaluate statement d

Statement d says that "The mantle cavity contains hemolymph." This statement is false. While the mantle cavity is a critical part of the anatomy of a mollusk, it is not where the hemolymph is stored or circulated. Hemolymph is found within the open circulatory system of a mollusk, acting much like blood by delivering nutrients and oxygen while removing waste. The mantle cavity, on the other hand, is involved in respiration, reproduction, and waste disposal. So, the false statement is: d. The mantle cavity contains hemolymph.

Key concepts

Radula

The radula is a fascinating and unique anatomical feature found in many mollusks. It plays a crucial role in their feeding habits. Essentially, the radula is a tooth-covered, ribbon-like organ. It functions much like a tongue but with the added ability to scrape food from surfaces.

This organ is vital for mollusks that feed on algae and plant material, allowing them to efficiently gather their food. The microscopic teeth on a radula can vary slightly among different mollusk species, adapting to their specific dietary needs. This adaptability makes the radula an excellent example of evolutionary specialization in mollusks.

Mantle

The mantle is another essential component of mollusk anatomy. It is a layer of tissue that acts as a protective covering over the mollusk's internal organs. One of the distinguishing functions of the mantle is to secrete calcium carbonate, which forms the hard shell seen in many mollusks, such as snails and clams.

The mantle also plays several vital roles in the mollusk's life processes. It forms the mantle cavity, a space that houses gills or lungs for respiration. This cavity is key in facilitating gas exchange with the environment. Additionally, the mantle cavity often serves as an exit for waste products and as a chamber for reproductive activities.

Open Circulatory System

Mollusks typically have an open circulatory system, which is quite different from the closed circulatory system found in vertebrates. In this setup, the heart pumps hemolymph into the body cavity, where it bathes the organs directly. Hemolymph serves a similar purpose to blood, transporting nutrients and oxygen while removing waste products.

This type of circulatory system is efficient for many mollusks because of their relatively low metabolic rate. However, as hemolymph is not contained exclusively within vessels, it offers less control over the movement of blood compared to closed systems. Nevertheless, this simplicity is well-suited to the lifestyle and anatomy of mollusks.

Nervous System

Mollusks have a well-developed nervous system that varies in complexity from simple to more sophisticated arrangements. They possess ventral nerve cords, which are the main pathways for transmitting signals throughout the body.

The nervous system includes conglomerations of nerve cells called ganglia. These ganglia are often located in different parts of the body to control various functions such as locomotion, feeding, and sensory responses. In more advanced mollusks like octopuses, the nervous system is highly complex, allowing for intricate behaviors and learning capabilities. Despite these differences, the basic structure and function of the mollusk nervous system enable them to interact efficiently with their environment.