Question

Which of the following organisms are considered cyclostomes? a. tunicates b. hagfish c. lampreys d. both a and b e. both b and c

Short answer

The correct answer is option e: both b (hagfish) and c (lampreys) are considered cyclostomes.

Step-by-step solution

Understanding Cyclostomes

Cyclostomes are a group of agnathans, which means these are jawless fish. They are characterized by having round mouths, like a cycle, which is where their name 'cyclostomes' comes from. There are two main types of cyclostomes known in the kingdom Animalia, which are hagfish and lampreys.

Identify the Cyclostomes in the given options

Now, look at the given options. Tunicates (option a) are a type of invertebrate animal, a subphylum of the phylum Chordata, thus they are not cyclostomes. Hagfish (option b) and lampreys (option c) are indeed both types of cyclostomes. Therefore, both option b and c are correct.

Final Answer

Considering the options that contain both b and c, only option e is correct. So, the cyclostomes in the given options are both b (hagfish) and c (lampreys), making option e (both b and c) the correct answer.

Key concepts

Agnathans

Agnathans are a fascinating group of creatures that hold a significant place in the evolutionary history of vertebrates. They are aptly named as they lack jaws, a feature that distinguishes them from other fish. This group is comprised of cyclostomes, which we will explore as jawless fish.
Agnathans have some unique characteristics:

• They possess a cartilaginous skeleton.
• They have eel-like bodies.
• Their mouths are circular and adapted for suction, rather than biting.

Agnathans are important for studying the evolutionary transition to more complex vertebrates, as they represent some of the earliest forms of fish life. Though they lack jaws, they have adapted in various ways to survive in their environments.

Jawless Fish

Jawless fish are an intriguing evolutionary group that includes cyclostomes such as hagfish and lampreys. These fish provide insight into the primitive states of vertebrate evolution.
Key features of jawless fish include:

• A distinct lack of jaw structures.
• A cartilaginous internal skeleton, much softer than bone.
• A lack of paired fins, which are common in more advanced fish.

Despite their simplicity, jawless fish have adapted unique feeding methods, like filter-feeding or suction, that allow them to survive in diverse aquatic environments. Understanding jawless fish helps scientists paint a broader picture of vertebrate evolution.

Hagfish

Hagfish are a peculiar group of jawless fish known for their extraordinary ability to produce slime. They occupy a critical role both ecologically and scientifically.
Hagfish characteristics include:

• Soft, elongated bodies that lack scales.
• Slimy excretion that aids in deterring predators.
• Absence of vertebrae, although classified under vertebrates due to their primitive characteristics.

Their diet mainly consists of marine carcasses, which they consume by burrowing into them. Such unique features make hagfish a subject of interest in studies of vertebrate development and evolution.

Lampreys

Lampreys are another vital group of jawless fish that, like hagfish, are part of the agnathan clade. They display a different set of characteristics and ecological behaviors.
In terms of features:

• Lampreys have a sucker-like mouth filled with rows of teeth.
• They are often parasitic, attaching to other fish to feed on their blood.
• They undergo a complex metamorphosis from larvae to adults.

Lampreys inhabit both freshwater and saltwater environments. Their life cycle and feeding strategies make them a remarkable example of evolution and adaptation within the environment.

Tunicates

Although tunicates might seem related due to being part of the phylum Chordata, they are not classification-wise agnathans or cyclostomes. Instead, they are invertebrates with some fascinating qualities.
Tunicates are known for:

• Their sac-like bodies which are covered by a tough outer "tunic."
• Being sessile, often attaching to submerged surfaces.
• Filter-feeding mechanism that allows them to extract nutrients from water.

They are remarkable for their life cycle that includes a mobile larval stage with a notochord and a nerve cord, highlighting their transitional characteristics within the chordate phylum. While not directly related to jawless fish, they offer valuable insights into the chordate lineage.