Overview Of Invertebrates Chapter 27

An organ is a collection of different tissues that work together as a unit to perform a particular function. Organs are composed of multiple types of tissues, such as muscle, epithelial, and connective tissues, that collaborate to carry out specific tasks in the body. Each organ has a unique structure and function that contributes to the overall functioning of the organism.

Bilaterally symmetric animals have evolved a definite head end through a process called cephalization. This means that over time, these animals have developed a distinct concentration of sensory organs, such as eyes, ears, and a brain, at one end of their body. This allows them to have better control and coordination of their movements and to interact with their environment more effectively. Therefore, the statement is true.

Sponges are the exception because they lack true tissues. Unlike cnidarians, flatworms, and roundworms, sponges do not have specialized cells organized into distinct tissue types. Instead, their cells are loosely arranged and can perform various functions independently. This makes sponges unique among animals, as they do not exhibit the level of tissue organization seen in other animal groups.

Arthropods, such as insects, spiders, and crustaceans, do indeed have an exoskeleton made of chitin. This exoskeleton provides support and protection for the arthropod's body, as well as serving as a site for muscle attachment. The chitin exoskeleton is rigid and provides structural integrity to the arthropod, allowing it to maintain its shape and protect its internal organs. Therefore, the statement "Arthropods have an exoskeleton, a rigid external shell made of a substance called chitin" is true.

Sponges are the simplest multicellular animals and they lack any kind of symmetry. Unlike most other animals that have bilateral or radial symmetry, sponges have bodies that are asymmetrical. This means that their body parts cannot be divided into equal halves or exhibit any regular pattern. Instead, sponges have irregular shapes and structures, with various openings and canals for water flow. Therefore, the statement that the bodies of sponges completely lack symmetry is true.

Echinoderms were the first animals to develop an endoskeleton. This means that they have an internal skeleton made of calcified plates or ossicles. This characteristic sets them apart from other animals that have exoskeletons or no skeleton at all. The development of an endoskeleton provided echinoderms with structural support and protection, allowing for more complex body plans and evolutionary adaptations. Therefore, the statement is true.

Mollusks do not have segmented bodies. They have soft, unsegmented bodies that are typically covered by a hard shell. Segmentation is a characteristic of annelids, such as earthworms, where the body is divided into repeating segments. Mollusks, on the other hand, have a more simple body plan with distinct regions like the head, foot, and mantle, but they lack true segmentation.

Annelids, which include earthworms and leeches, do indeed have a well-developed cerebral ganglion, or brain, located in one of their anterior segments. This brain structure allows them to process sensory information and coordinate complex behaviors. Therefore, the statement "Annelids have a well-developed cerebral ganglion, or brain, in one of their anterior segments" is true.

Animals that have their body parts arranged around a central point are said to be radially symmetric. This means that their body can be divided into multiple similar parts that radiate out from a central axis, like the spokes of a wheel. Examples of radially symmetric animals include jellyfish and sea anemones. This type of symmetry allows them to interact with their environment from all directions equally.

Arthropods were the first animals with jointed appendages. Jointed appendages are specialized structures that allow for movement and manipulation of the limbs. Mollusks, annelids, and chordates do not possess jointed appendages. Arthropods, on the other hand, have a wide variety of jointed appendages such as legs, antennae, and mouthparts, which provide them with a great range of mobility and functionality. This unique characteristic sets arthropods apart from other animal groups and is one of the key features that define them.

The statement "Most animals reproduce asexually" is false. Asexual reproduction is a method of reproduction where offspring are produced without the involvement of gametes or the fusion of genetic material from two parents. While some animals, such as bacteria and certain invertebrates, can reproduce asexually, the majority of animals reproduce sexually. Sexual reproduction involves the fusion of gametes from two parents, resulting in genetic diversity and the creation of offspring with a combination of traits from both parents. This is the most common method of reproduction in the animal kingdom.

The statement "All animals have tissues" is false. While it is true that most animals have tissues, there are a few exceptions. For example, sponges are considered animals but they lack true tissues. Instead, they have specialized cells that perform different functions. Therefore, not all animals have tissues.

A pseudocoelum is a body cavity that is located between the endoderm and the mesoderm. This means that it is not completely lined by mesoderm, unlike a true coelom. The presence of a pseudocoelum allows for space and movement of organs within the body. Therefore, the statement that a pseudocoelum is located between the endoderm and the mesoderm is true.

Choanocytes are unique flagellated cells that line the internal body cavity of the sponge. These cells have a collar-like structure with a flagellum protruding from it. The flagellum helps in creating water currents that bring in food particles and oxygen, while the collar filters out the particles and directs them towards the cell for ingestion. Choanocytes also play a role in reproduction by producing sperm cells. Overall, choanocytes are essential for the feeding and reproductive processes of sponges.

Flatworms are the only animals in the given options that have a gut with only one opening. This opening serves as both the mouth and the anus. Roundworms, snails, and leeches all have separate openings for ingestion and excretion. Therefore, the correct answer is flatworm.

The circulatory system is a network of vessels that carries fluids, such as blood, to all parts of the body. It includes the heart, blood vessels, and blood, and is responsible for transporting oxygen, nutrients, hormones, and waste products throughout the body. The circulatory system plays a vital role in maintaining the body's overall function and homeostasis.

A protostome is an animal whose mouth develops from the blastopore. In protostomes, the blastopore eventually becomes the mouth during embryonic development. This is in contrast to deuterostomes, where the blastopore develops into the anus and the mouth forms later. Cephalostome and pseudocoelom are not relevant to the development of the mouth from the blastopore.

Chordates are a group of animals that possess a dorsal hollow nerve cord, a notochord, and pharyngeal slits. These characteristics are defining features of chordates and are present in all members of this group. However, a water vascular system is not a characteristic of chordates. Instead, it is a unique feature found in echinoderms, such as starfish and sea urchins. This system is used for locomotion, respiration, and feeding in echinoderms, but it is not present in chordates.

In deuterostomes, the mouth does not develop from or near the blastopore. Instead, the anus develops from the blastopore, and the mouth forms later in a different region. This is a key characteristic that distinguishes deuterostomes from protostomes, where the mouth does develop from the blastopore.

Leeches have a well-developed gut that includes a food storage area called a crop. This crop allows leeches to store and digest their food efficiently. It acts as a reservoir where they can store blood or other nutrients for a longer period of time. The crop also aids in the digestion process by breaking down the stored food gradually, ensuring a steady supply of nutrients for the leech. Overall, the presence of a crop in the leech's gut is an adaptation that allows them to survive in their environment.

All animals other than sponges are known as eumetazoans. This means that sponges are not considered eumetazoans. Eumetazoans are a group of animals that have true tissues and organs, while sponges lack these characteristics. Therefore, sponges are excluded from the category of eumetazoans.

Roundworms do have muscle tissues and a gut, but they have two openings - one for the mouth and another for the anus. This allows them to have a complete digestive system where food enters through the mouth and waste is expelled through the anus. Therefore, the statement that roundworms have only one opening in their gut is false.

Each segment of an annelid has a pair of excretory organs called nephridia. Nephridia are tubular structures found in each segment of an annelid's body. They function as excretory organs, removing waste products from the body. Nephridia filter waste from the coelomic fluid and release it through small pores called nephrostomes. This helps maintain the osmotic balance and remove metabolic waste from the annelid's body.

Cnidarians digest their food extracellularly in a digestive cavity. This means that their food is broken down and digested outside of their body, in a specialized cavity. This allows for the efficient breakdown of food and absorption of nutrients.

Sponges digest their food intracellularly, meaning the digestion process occurs within their cells. This is different from extracellular digestion, where digestion takes place outside the body. Intracellular digestion involves the breakdown of food particles within specialized cells, allowing the sponge to absorb the nutrients directly. This method is efficient for sponges, as they lack a true digestive system and rely on individual cells to carry out digestion.

Annelids are animals whose basic body plan can be described as "a tube within a tube". This means that their bodies have an outer tube-like structure called the body wall, and an inner tube-like structure called the digestive tract. This arrangement allows for efficient digestion and movement. Mollusks, flatworms, and roundworms do not have this specific body plan, making annelids the correct answer.

An animal in which the gut is completely surrounded by tissues and organs is called an acoelomate. In acoelomates, there is no body cavity between the gut and the body wall, meaning that the organs are in direct contact with the body wall. This lack of a body cavity allows for more direct interaction between the organs and body wall, but it also limits the complexity and organization of the internal organs. Examples of acoelomates include flatworms and tapeworms.

Both cnidarians and ctenophores have a radially symmetric body structure. This means that their bodies are symmetrical around a central axis, similar to the spokes of a wheel. This symmetry allows them to have multiple identical body parts arranged around this axis, such as tentacles or rows of cilia. This adaptation is advantageous for these organisms as it helps them to efficiently capture prey and navigate their environment in all directions.

The development of a coelom occurred first in mollusks. Coelom is a body cavity that is lined with mesoderm and provides a space for the organs to develop and function. Mollusks are a diverse group of invertebrates that include snails, clams, and squids. They have a well-developed coelom, which allows for efficient organ function and movement. Chordates, arthropods, and annelids also have a coelom, but the development of this body cavity occurred earlier in mollusks.