Question

Which phylum does not have at least some members with a closed circulatory system? a. Lophophorata b. Arthopoda c. Annelida d. Mollusca e. All of the above phyla have some members with a closed circulatory system.

Short answer

a. Lophophorata

Step-by-step solution

Understanding the Different Phyla

Firstly, it's important to know each of the phyla mentioned: Lophophorata, Arthopoda, Annelida, and Mollusca. In these phyla, many of the species have a closed circulatory system, meaning their blood flows in a system of vessels separate from the interstitial fluid of the body. However, some do not have any members with such a circulatory system.

Evaluate Each Option

The second step is to go through each option and apply the knowledge about these phyla to determine which ones have members with a closed circulatory system. It is known that Arthropoda, Annelida, and Mollusca have members with closed circulatory systems.

Identify the Correct Option

Once it's determined that Arthopoda, Annelida, and Mollusca do have members with a closed circulatory system, it implies that the phyla that doesn't have any members with a closed circulatory system must be Lophophorata. Hence, the correct answer is 'a. Lophophorata'.

Key concepts

Understanding Lophophorata

When exploring the diversity of life, the phylum Lophophorata often captures the interest of biologists due to its unique characteristics. Unlike some other phyla, Lophophorata, which includes Brachiopoda (lamp shells), Phoronida (horseshoe worms), and Bryozoa (moss animals), does not possess a closed circulatory system.

The members of this phylum are mostly aquatic organisms characterized by a lophophore, a crown-shaped structure used for feeding and respiration. Despite their aquatic habitat, where closed circulatory systems are common, Lophophorates rely on a more primitive open circulatory system or a simple diffusion process for the distribution of nutrients and oxygen. This absence of specialized vascular systems makes them particularly fascinating as it represents a divergence from the more complex systems seen in other aquatic invertebrates.

Differences Among Phyla

Biodiversity is strikingly evident when we examine the differences among various animal phyla. Notably, the presence or absence of a closed circulatory system is a key distinguishing feature. While organisms in the phyla Arthropoda, Annelida, and Mollusca have evolved this type of more advanced circulatory system in at least some of their members, Lophophorata stands out for not having a closed system at all.

The closed circulatory system, as seen in annelids such as earthworms, molluscs like squids, and even some arthropods (e.g., spiders), allows for efficient distribution of oxygen and nutrients through blood vessels. In phyla with organisms lacking this system, such as Lophophorata, there may be other adaptations that accommodate their specific ecological niches and metabolic needs. It's these evolutionary variations that contribute to the fascinating tapestry of life.

Circulatory System Types

Circulatory systems can generally be classified into two main types: open and closed. In an open circulatory system, blood is not entirely confined to vessels and can flow freely within cavities, coming into direct contact with tissues and organs. Insects and most molluscs are examples of organisms with this type.

Conversely, a closed circulatory system is one where blood circulates within a network of vessels that form a loop, separating it from the body’s interstitial fluid. This system allows for more efficient transport of oxygen and nutrients at higher pressures and speeds. Vertebrates, including humans, along with some invertebrates like octopuses and earthworms, possess this type of system.

Deciphering these systems sheds light on the intricate ways different organisms have adapted to their environments. A firm grasp of the differences between open and closed circulatory systems can enhance a student’s understanding of comparative physiology and evolutionary biology.