Phylum Annelida

Phylum Annelida• Ancestral Traits

– Coelomate

– Lophotrochozoan

– Protostome

– Closed circulatory system

– Cephalization

• Derived Traits– Segmentation

• Metamerism

• Septa

– Setae• Bristles

– Myelinated neurons

~ 40K species of annelids

Spirobranchus giganteusChristmas tree worm

Annelid Taxomony

• Class Polychaeta (many bristles)– most numerous # species– marine

Hermodice Hermodice crunculatacrunculata

Annelid Taxomony

• Class Polychaeta

• Class Oligochaeta (few bristles)– Freshwater, marine & terrestrial

Lumbricus terrestris

Annelid Taxomony• Class Polychaeta

• Class Oligochaeta

• Class Hirudinea– Fixed # segments (34)– Setae absent

Hirudo medicinalis

Annelid Phylogeny

Annelid Body Plan

Setae

Class Polychaeta

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

• Paired extensions of body(parapodia)

• Often tube-dwelling

– Burrow into substrate and secrete mucus/CO3 materials

Bispira bunneasabellid worm

Polychaete Anatomy

Polychaete Anatomy (cross section)

Polychaeta

Amphitrite

Polychaeta

Lugworm (Arenicola sp)

Polychaeta

Polychaeta

Clade Siboglinidae (Phylum Pogonophora)

Ridgea sp Riftia pachyptila

Giant tube worms (Vestimentifera)

Riftia pachyptila

trophosome

Polychaete Reproduction

• Dioecious

• Trochophore larvae

• Some species develop specialized segments containing gametes– Epitokes– 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

Class Oligochaeta

Oligochaete Anatomy

Oligochaete Anatomy

Seta: a.k.a. Bristles

Oligochaete Excretory System

Oligochaete Nervous System

Oligochaete Nerve Cord

Oligochaete Reproduction

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