Question

A major finding of recent molecular studies is that a. the presence or absence of the mesoderm is not important in phylogeny. b. all animals do not share a single common ancestor. c. body symmetry, whether radial or bilateral, is not an important determinant in phylogeny. d. the echinoderms are not included in the deuterostome clade. e. the presence or absence of a coelom is not important for classification.

Short answer

The question is flawed as none of the given answers are correct.

Step-by-step solution

Understanding Key Terms

First, familiarize yourself with the key terms used in the options. For example, mesoderm is a primary tissue layer in animals, body symmetry refers to how an organism's body parts are arranged around a point or an axis, echinoderms are marine animals characterized by radially symmetric bodies, deuterostome clade includes all animals that share a common characteristic of development, and a coelom is a body cavity.

Applying Knowledge to Each Option

Apply your knowledge of these concepts to each option. a. The mesoderm is indeed important in phylogeny because the presence or absence of this tissue layer differentiates major animal groups. b. It's generally accepted that all animals do share a single common ancestor, making this statement incorrect. c. Body symmetry is an important determinant in phylogeny since it distinguishes between major animal groups. d. The echinoderms are included in the deuterostome clade, so this statement is incorrect. e. The presence or absence of a coelom is an important factor in the classification of animals, making this statement incorrect.

Choosing the Correct Option

From the analysis of each option, we can see that none of them are correct. Thus, there is a mistake in the question or it aims to test your knowledge about these terms and their implications on phylogeny and classification.

Key concepts

Phylogeny

Phylogeny is a crucial concept in understanding the evolutionary history and relationships among species. This field of biology assesses how organisms are connected through common ancestry. Researchers construct phylogenetic trees, which are like family trees for species, showing how they have diverged from common ancestors over millions of years.
Phylogeny is significant because it helps scientists classify organisms not just based on physical characteristics, but also genetic similarities and evolutionary history. This approach is refined by modern techniques like molecular phylogenetics, which uses DNA sequences to reveal the genetic relationships among species. The molecular studies constantly refine our understanding of the tree of life and often overturn previous assumptions about animal classification.

Mesoderm

The mesoderm is one of the three primary germ layers in early embryonic development, along with ectoderm and endoderm. It plays a pivotal role in differentiating between major groups of animals. Animals with a mesoderm are classified as triploblastic, meaning they have three germ layers.

• It gives rise to various systems such as the circulatory, muscular, and skeletal systems.
• The presence or absence of mesoderm changes how animals' body plans are structured and function, impacting their evolutionary lineage.

This differentiation is crucial in phylogeny because it impacts how organisms develop and evolve into more complex structures. Understanding the role of the mesoderm helps clarify why certain species group together and how their evolutionary pathways have diverged.

Body Symmetry

Body symmetry refers to how an animal's body parts are arranged around a central point or axis. There are two primary types of symmetry in animals: radial and bilateral.

• Radial symmetry means body parts are arranged around a central axis, like in jellyfish or starfish. Such animals often have a top and bottom but no left or right sides.
• Bilateral symmetry means that the body can be divided into mirrored halves along one plane. Humans and most animals fall into this category.

Body symmetry is important in classification because it reveals evolutionary adaptation related to movement and habitat. Bilateral symmetry, for example, is associated with higher mobility and complex organ systems, reflecting an evolutionary step towards more sophisticated organisms.

Deuterostome Clade

The deuterostome clade includes a group of animals characterized by a specific sequence in their embryonic development. "Deuterostome" translates to "second mouth," which refers to how the anus forms before the mouth during development. This clade includes animals like echinoderms and chordates.
The inclusion of echinoderms in the deuterostome clade was historically controversial until molecular studies confirmed their development patterns align with chordates. This shared development characteristic forms a unique connection in the evolutionary tree. The deuterostome grouping aids in understanding key evolutionary events and the diversity of life forms connected to these mechanisms.

Coelom

A coelom is a fluid-filled body cavity lined with mesoderm. It is a critical feature in animal classification, setting apart coelomates from acoelomates and pseudocoelomates.

• Coelomates have a true coelom, which provides space for organs and a circulatory system, allowing more complex body structures.
• Acoelomates lack a coelom, leading to a more compact body structure, like in flatworms.
• Pseudocoelomates have a body cavity not fully lined with mesoderm, seen in roundworms.

The presence, absence, or type of coelom reflects evolutionary adaptations to different environments and biological needs, offering insights into the evolutionary history and the functionality of body plans.