Invertebrate Zoology

The prefix "cephalo-" means "head." This can be seen in words like "cephalopod" (a type of marine mollusk with a head and tentacles) and "encephalitis" (inflammation of the brain). The other prefixes listed do not have a direct association with the meaning of "head."

Arthropoda is the correct answer because it is the largest phylum in terms of species diversity on Earth. Arthropods include insects, spiders, crustaceans, and other organisms, and they are found in a wide range of habitats. They have adapted to various environments and occupy diverse ecological niches, contributing to their high species numbers. This phylum includes over a million known species, making it the largest and most diverse group of organisms on the planet.

Echinodermata is the correct answer because it is the only phylum in the given options that is characterized by pentameral symmetry. Pentameral symmetry refers to a radial symmetry with five parts or segments arranged around a central axis. Echinoderms, such as starfish and sea urchins, exhibit this type of symmetry in their body structure. Mollusca, Ctenophora, and Chaetognatha do not have pentameral symmetry, making Echinodermata the correct choice.

Sponges are multicellular organisms that lack true tissues and organs. They have a simple body structure with no definite symmetry. Unlike the other options, sponges do not exhibit bilateral symmetry, meaning they cannot be divided into two equal halves along a single plane. Instead, they have irregular shapes and lack a distinct front or back. Therefore, sponges are the only organism listed that is not bilaterally symmetrical.

Phylogenetics is the study of relationships between groups of organisms. It involves analyzing genetic and morphological data to determine the evolutionary history and relatedness of different species. By examining similarities and differences in DNA sequences, scientists can construct phylogenetic trees that show the evolutionary relationships between organisms. This field of study helps in understanding the evolutionary processes, identifying common ancestors, and classifying organisms into different taxonomic groups based on their shared characteristics.

Porifera is the correct answer because this phylum is characterized by choanocytes, which are specialized cells that create a current to pull in food. Choanocytes have a collar of microvilli surrounding a flagellum, and their beating motion creates the necessary water flow for filter feeding. This unique feature is not found in the other phyla mentioned. Cnidaria, Urochordata, and Platyhelminthes have different feeding mechanisms and do not possess choanocytes.

Setae are bristle-like structures found on the body of an earthworm. These structures help the earthworm to anchor itself and move through the soil. They also aid in locomotion by providing traction. Sea stars do not have setae, as they have tube feet for movement. Flatworms also lack setae, and they use cilia for locomotion. Horseshoe crabs have a hard exoskeleton but do not possess setae. Therefore, the correct answer is earthworm.

A calcified spinal cord is not required to be a chordate. Chordates are characterized by the presence of a notochord, a dorsal hollow nerve cord, and a postanal tail. The notochord provides support and structure, the dorsal hollow nerve cord develops into the central nervous system, and the postanal tail aids in locomotion. However, a calcified spinal cord is not a characteristic feature of chordates.

Cnidae are specialized stinging cells found in cnidarians, which include coral polyps. These cells are used for capturing prey and defense. Comb jellies do not possess cnidae, as they belong to a different phylum called Ctenophora. Sponges and brittle stars also do not have cnidae, as they belong to different animal groups. Therefore, the correct answer is coral polyp, as cnidae are found in this organism.

Nematoda is the correct answer because this phylum of worms has a tough outer cuticle that undergoes ecdysis, which is the process of shedding and replacing the outer layer of the cuticle. This allows the worms to grow and adapt to their environment. Annelida, Platyhelminthes, and Nemertea do not have a tough outer cuticle that undergoes ecdysis.

The class Hydrozoa has members with a mutualistic relationship with zooxanthellae. Zooxanthellae are photosynthetic algae that live within the tissues of certain marine organisms, providing them with nutrients through photosynthesis. In return, the host organism provides the zooxanthellae with a protected environment and access to sunlight. This mutualistic relationship benefits both parties involved, as the host organism receives energy from the photosynthetic activity of the zooxanthellae, while the zooxanthellae receive a stable habitat and nutrients from the host organism.

Holothuroidea, also known as sea cucumbers, have the ability to eviscerate their internal organs as a defense mechanism. When threatened by predators, they can expel their internal organs through their anus, which distracts and deters the predator. The expelled organs can then regenerate over time, allowing the sea cucumber to survive the encounter. This unique ability is a survival strategy that helps Holothuroidea escape from predators and increase their chances of survival.

Ophiuroid is not an arthropod because it belongs to the phylum Echinodermata, whereas arthropods belong to the phylum Arthropoda. Echinoderms, like ophiuroids, have a radial symmetry and a water vascular system, while arthropods have a segmented body, jointed appendages, and an exoskeleton. Therefore, ophiuroids are not classified as arthropods.

Bryozoa is the correct answer because this phylum includes colonial and clonal organisms that encrust on surfaces. Bryozoa, also known as moss animals, are small aquatic invertebrates that form colonies and attach themselves to various substrates such as rocks, shells, and seaweed. These colonies can form encrusting structures that resemble moss or branching structures. They are filter feeders and use tentacle-like structures called lophophores to capture food particles from the water.

Broadcast spawning is the correct answer because it refers to the reproductive process in which both males and females release their gametes (eggs and sperm) into the water, allowing them to meet and fertilize externally in the water column. This method is commonly observed in marine organisms, such as corals and many fish species, where the eggs and sperm are released simultaneously during spawning events. It is an efficient strategy for reproduction in aquatic environments where the dispersal of gametes through water currents increases the chances of successful fertilization.