Phylum Annelida

Segmented Worms

Phylum Annelida

• Annelids are segmented worms.• They have bodies composed of a series of fused

rings.• Earthworms, leeches, clam worms.

Phylum Annelida• Old Traits

– Coelomate (body cavity)

– Closed circulatory system

– Cephalization (have a head)

• New Traits– Segmentation (body

divided in segments) – Setae (Bristles)

– Advanced nervous system

~ 40K species of annelids

Spirobranchus giganteusChristmas tree worm

Annelid Taxomony• Class Polychaeta (many segments)

• Class Oligochaeta (few segments)

• Class Hirudinea– Fixed # segments (34)– No bristles

Hirudo medicinalis

Class Polychaeta

• Polychaeta (many segments) is the largest, most diverse class. – May scavengers or

predators

– Live mostly in the benthic ocean .

Class Polychaeta

• Highly specialized head regions– Antennae– Sensory organs – Feeding appendages

• Paired extensions of body(parapodia)

• Often tube-dwelling

• Most have gills

sabellid worm

Class Polychaeta

• Polychaetes are mostly marine and mostly benthic.– May live under rocks,

burrow into sediment, or build their own tubes.

– Some are planktonic.

Class Polychaeta

• Sedentary and errant (free-moving) forms.– Filter or deposit

feeders.

Polychaete Reproduction

• Dioecious (separate sexes)

• Trochophore larvae

• Some species develop specialized segments containing gametes (epitoke)– Segments are released and

gametes burst out

Polychaete Asexual Reproduction

• Epitokes are essentially buds

• Clues to ancestral origin of segmentation

– Segmentation may have been derived from incomplete budding processes

Representative Polychaetes

• Fanworms or Featherduster worms – Unfurl tentacular

crowns to feed.

Representative Polychaetes

• Parchment Worms

– Lives in a U-shaped tube.

– Modified segments pump water through tube.

Giant tube worms (Vestimentifera)

Riftia pachyptila

trophosome

Beardworms

• Discovered in 1900.

• 150 species described.

• Giant beardworms that live in deepwater hydrothermal vents are 3 m long and 5 cm in diameter.

Oligochaetes

Class Oligochaeta

• Class Oligochaeta includes earthworms and many freshwater worms.

Earthworms - Nervous System and Sense Organs• Central nervous system and

peripheral nerves.• The brain secrete

neurohormones.– Regulate sex

characteristics, and regeneration.

• Lack eyes but have many photoreceptors in the epidermis.

• Sensitive to light, touch, moisture, chemicals, temperature, & vibrations

Earthworms - Feeding

– One way digestive system

– The lip digs through soil as earthworm feeds on organic matter (detritus)

– Food is stored in a sac like structure (crop.)

– Muscular gizzard

grinds food.

– Digestion and

absorption occur in

intestine.

Earthworms - Circulation and Respiration

• Blood transport food, wastes, and respiratory gases.

• Blood circulates in a closed system with five main trunks running along the body.

• Dorsal vessel contains valves and functions as a true heart.

Earthworms - Reproduction

• Earthworms are hermaphroditic – male and female organs in the same animal.

• When mating, two worms are held together by mucus secreted by the clitellum.

Earthworms Reproduction

The development is direct without any larval forms

Class Oligochaeta

• Darwin wrote about earthworms.

– He noted the beneficial activities of worms, aeration, moving nutrients up from subsoil, adding nitrogenous products, breakdown of organic matter in dead leaves etc.

– An earthworm can ingest its own weight in soil every 24 hours.

Annelid Body Plan

Setae

Oligochaete Anatomy

Seta: a.k.a. Bristles

Oligochaete Excretory System

Oligochaete Development

• For terrestrial oligochaetes, development is direct without any larval forms

• Some aquatic oligochaetes retain a trochophore-like larval stage

Common Terrestrial Oligocheates: Earthworms

• Octagonal-tail wormOctagonal-tail worm (Dendrobaena octaedra)• Red marsh wormRed marsh worm (Lumbricus rubellus)• Dew-worm or nightcrawlerDew-worm or nightcrawler (Lumbricus terrestris) • Pink soil wormPink soil worm (Aporrectodea rosea)• Canadian wormCanadian worm (Aporrectodea tuberculata)• Pasture wormPasture worm (Aporrectodea turgida) • Woodland white wormWoodland white worm (Octolasion tyrtaeum)• Redworm (Eisenia fetida )

Quick and Easy Earthworm Morphology Guide

Aporrectodea turgida Lumbricus rubellus

Morphology

Number & location of GTs and TPs, location & shape of clitellum

Ecology

Location of burrows

Aquatic Oligocheates

Class Hirudinea

Hirudo medicinalis

Phylum Sipuncula• ~250 species

• Trochophore larvae

Sipunculan Internal Structures

Phylum Echiura • ~140 species

• Closed circulatory system

• Trochophore larvae

Echiurus sp

Phylum Echiura

Bonellia viridis

Echiuran Anatomy

Oddities

• Sex determination & dimorphism in echiurans