Zoology Chapter 11 - Annelids

What Characteristics of Phylum Annelida distinguish it from other phyla?

Segmentation, Metamerism, Parapodia, a Closed circulatory system, and a nervous system

How are members of Clitellata distinguished from other annelids?

They contain an oligochaete body plan, (earthworms and leeches) and have a clitellum (involved in reproduction)

Describe the annelid body plan, including body wall, segments, coelom and its compartments and coelom lining

body wall comprises 3 layers: Ectodermal Epidermis, mesodermal muscle layer and peritoneum, and the endodermal gut lining. The body is segmented both externally and internally, with grooves and septa diving the body into repeating units. The coelom is a fluid-filled cavity and serves as a hydrostatic skeleton, lined by peritoneum and divided into compartments by septa. The peritoneum, derived by the mesoderm, lines the coelom

Explain how the hydrostatic skeleton helps them burrow. How is burrowing efficiency increased by metamerism

The hydrostatic skeleton allows the longitudinal and circular muscles to shorten and lengthen the body of the worm in a shortened motion, helping the worm grip the sides of the tunnel and push it forward. Burrowing is more efficient with metamerism because it allows for specialization within segments, and each segment can move independently.

Describe 3 ways that various errantiate annelids obtain food and contrast these with food gathering in Sedentaria

Three ways annelids gather food are Carnivorous Predation, Deposit Feeding, and Filter Feeding. While Sedentaria mostly feeds through tube-dwelling filter feeding.

Define Each: Prostomium, Peristomuim, Radioles, parapodium, setea

Prostoumium: First body segment in an Annelid, anterior to the mouth, and usually without setae or parapodia.

Peristomium: Body segment in an Annelid that immediately follows the prostomium.

Radioles: Soft, fleshy, often colored protrusions that extend from the parapodia of Annelids.

Parapodium: Paired, lateral, fleshy protrusions on each segment of certain Annelids.

Setae: Bristle-like structures on the exterior of Annelids, used for traction.

Explain the Function of Each: Crop, Gizzard, typhosole, chloragogen cells

Crop: Thin-walled pouch near the junction of the esophagus and the gizzard, used for storing food temporarily.

Gizard: A thick-walled muscular pouch that grinds and breaks down food particles with the help of ingested stones or grit.

Typhlosole: A longitudinal infolding of the intestine wall that increases surface area for nutrient absorption.

Chloragogen Cells: Cells in the chloragogen tissue of some invertebrates, involved in the production, of coelomic fluid and excretion.

Which group of Annelids has the best-developed sensory structure?

Errantiate Polychaetes.

Sensory Structures -

Eyes, Antennae and Palps, Chemoreceptors, Lifestyle.

Describe the functions of clitellum and the cocoon

Clitellum

Mucus Secretion: Helps worms stick together during mating.

Cocoon Formation: Creates a protective casing for eggs after mating.

Nutrient Supply: Provides nutrients to developing eggs.

Cocoon

Protection: Shields fertilized eggs from harm.

Moisture Retention: Keeps the eggs moist for development.

Nutrient Supply: Contains nutrients for growing embryos.

Freshwater Clitellates

Habitat: Live in water (ponds, streams).

Body Structure: More elongated and streamlined.

Respiration: Absorb oxygen through the skin in water.

Reproduction: Varied cocoon structure, different egg-laying.

Locomotion: Swim and crawl using cilia or contractions.

Describe how leeches obtain food

Suction Feeding: Use suckers to attach to hosts (like fish).

Saliva with Anticoagulants: Inject saliva to prevent blood clotting.

Blood Feeding: Feed on the host's blood, swelling after a meal.

Other Sources: Some eat small invertebrates or decaying matter.

Digest blood over time, absorbing nutrients.

Describe the ways in which reproduction and development changed as alledlids colonized freshwater and terrestrial habitats. Why might selection have favored certain features such as monoecious reproduction and the use of the cocoon?

Monoecious Reproduction:

What It Is: Many annelids have both male and female parts.

Why It Matters: This helps them find mates more easily, especially in low populations.

Cocoon Formation:

What It Is: They create a protective cocoon for their eggs.

Why It Matters: The cocoon keeps eggs safe from drying out and predators, which is important on land.

Direct Development:

What It Is: Young look like mini adults instead of going through a larval stage.

Why It Matters: This helps them survive better in their environment.

Reasons for These Features

Changing Environments: These adaptations help them reproduce successfully even when conditions vary.

Finding Mates: Having both reproductive parts increases the chances of mating.

Protecting Offspring: The cocoon ensures that the young are safe, increasing survival rates.

Using Resources Efficiently: Direct development allows young to adapt quickly to their environment.

What is the largest siboglinid known? Where is it found, how is it nourished?

The largest known siboglinid is Osedax mucofloris.

primarily located in deep-sea

bone-eating worm that feeds on the lipids and nutrients found in the bones of dead marine animals.

What features of echiurans are shared with other annelids

Segmentation: Both have segmented bodies, though echiurans are less pronounced.

Body Plan: Similar structure with a head (proboscis) and trunk.

Coelom: Both have a body cavity (coelom) that holds organs.

Muscular System: They have muscles that help with movement.

Circulatory System: Both have a closed circulatory system with blood vessels.

Reproductive System: Similar reproductive strategies, including sexual and asexual reproduction.

Nervous System: Simple nervous system with a nerve cord and ganglia.

Where does a sipunculan live, and how does it collect food?

Peanut worms primarily live in marine environments, and sometimes in shallow waters or coral reefs.

retractable, tentacle-like structure called a proboscis.The proboscis is extended. The food collected by the tentacles is then brought to the mouth, where it is ingested and passed through the digestive system for nutrient absorption.

Siboglinid Worms (e.g., Osedax, Riftia)

Habitat: Found in deep-sea hydrothermal vents and cold seeps.

Nutrition: They have symbiotic bacteria that convert hydrogen sulfide or methane into organic compounds, which the worms use for nourishment.

Sedentary Polychaetes

Body Structure: Compact, less segmented, with a defined head and smaller side appendages (parapodia).

Movement: Mostly stay in one place (like burrows or tubes).

Feeding: Use tentacles to filter or collect food from the water or sediment.

Habitat: Live in stable environments where they can access food easily

Errantiate Polychaetes

Body Structure: Longer, more segmented, with larger, well-developed parapodia and bristles.

Movement: Highly mobile; can swim or crawl actively.

Feeding: Predators or scavengers with strong jaws to catch prey.

Habitat: Found in various environments where they can move to find food.

Echiurans:

Habitat: Some species live in marine sediments.

Nutrition: Certain echiurans also host symbiotic bacteria that help them digest organic matter.

Polychaetes (e.g., Lumbrineris, Hesionidae):

Habitat: Various marine environments.

Nutrition: Some polychaete worms have symbiotic relationships with bacteria that assist in breaking down food.

Earthworms

Habitat: Live in soil.

Body Structure: Thicker, segmented body for burrowing.

Respiration: Absorb oxygen through the skin (needs moisture).

Reproduction: Defined clitellum for cocoon formation, few cocoons.

Locomotion: Move by contracting and expanding body segments.