Phylum Annelida

Phylum Annelida

Terrestrial, marine, freshwater.

Repeating segments.Triploblastic.

True coelomates – complete gut.

Closed circulatory system. Well developed nervous

system.Respiratory organs.

Protostome development.Metamerism (unspecialized)

segmentation.One or more pairs of setae.

Phylum Annelida• Ancestral Traits

– Coelomate

– Lophotrochozoan- non-molting protostomes

– Protostome

– Closed circulatory system

– Cephalization

• Derived Traits– Segmentation

• Metamerism

• Septa

– Setae• Bristles

– Myelinated neurons~ 40K species of annelids

Spirobranchus giganteusChristmas tree worm

Systems

• IntegumentIntegument- epidermis is one cell layer with mucous gland that secrete a moist cuticle.

• SkeletalSkeletal -hydrostatic (using coelom)• MuscleMuscle- longitudinal and circular muscles Each segments

muscles are independent of the other segments.• DigestiveDigestive- complete, complex, with absorption and

digestive glands and excretory cells.

Systems (continue)

• ExcretoryExcretory- a pair of nephridia per segment.• RespiratoryRespiratory -through skin, some through parapodia; tubeworms

have gills.• CirculatoryCirculatory- closed system, use hemoglobin as oxygen carrier.• NervousNervous- dorsal brain; ventral, double, solid nerve cord, with

ganglia in each segment.• EndocrineEndocrine- hormones secreted by nervous system.• ReproductiveReproductive-

– Dioecious in Polychaeta; no special organs, posterior end becomes gonads.– Monoecious in Oligochaeta and Hirudinea; Clitellium.

Annelid Taxonomy

• Phylum Annelida (an-nel-i-da)– Class Polychaeta (poly-key-ta)

• Nereis, Aphrodita, Chaetopterus, Arenicola, Amphitrite– Class Clitellata– Subclass Oligochaeta (ol-e-go-key-ta)

• Lumbricus, Tubifex– Subclass Hirudinea (hi-ru-din-e-a)

• Hirudo, leech

• Earthworm dissection

Annelid Taxomony

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

Hermodice Hermodice crunculatacrunculata

Annelid Taxomony

• Class Polychaeta

• Class Clitellata– Subclass Oligochaeta (few bristles)

• Freshwater, marine & terrestrial

Lumbricus terrestris

Annelid Taxomony• Class Polychaeta

• Class Clitellata– Subclass Oligochaeta– Subclass 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

Spirobrancheus giganteus

Polychaete Anatomy

http://www.telegraph.co.uk/news/picturegalleries/picturesoftheday/9093134/Pictures-of-the-day-20-February-2012.html

Parapodia with setae

Polychaete Anatomy (cross section)

PolychaetaAmphitrite

Polychaeta

Lugworm (Arenicola sp)

Polychaeta

Polychaeta

Parchement worm

Clade-Siboglinidae

Ridgea sp Riftia pachyptila

Giant tube worms (Vestimentifera)

Riftia pachyptila

trophosome

http://www.bbc.co.uk/nature/life/Polychaete/by/rank/all

Polychaete Reproduction

• Most are dioecious-few monoecious

• Some asexually but sexually more common

• 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

Typosyllis nipponica

Samoan palolo worm Palola viridis

Class Oligochaeta

Phylum Annelida27

Class Oligochaeta

• Defining characteristics– Pronounced cylindrical

glandular region of the body = clitellum

• Second largest class in the phylum Annelida

• Most spp. are earthworms, very few are marine

Phylum Annelida28

Polychaetes and Oligochaetes

• Oligochaetes differ from polychaetes in several ways:– No parapods, fewer setae (if

at all)

– Hermaphroditic with sex cells produced in a separate section

– No larval stages

Giant Gippsland earthworm

Oligochaete Anatomy

Oligochaete Anatomy

Setae: a.k.a. Bristles

Oligochaete Reproduction

Oligochaete Development

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

• Some aquatic oligochaetes retain a trochophore-like larval stage

http://www.naturewatch.ca/english/wormwatch/resources/anatomy.html

Site for earthworm anatomy:

Quick and Easy Earthworm Morphology Guide

Aporrectodea turgida Lumbricus rubellus

-Earthworms can be classified by size, burrowing habits, and color

-Number, location and pattern of genital tumescences (GT) and tubercular pubertatis (TP)

-Location & shape of clitellum

Common Terrestrial Oligochaetes: Earthworms

Eisenia foetidaRedworm

Octagonal Tail WormOctagonal Tail WormDendrobaena octaedra

http://www.earthlife.net/inverts/oligochaeta.htmlThis link shows diversity of Oligochaetes!

Earthworm Dissection

Return to taxonomy

Cross section

Aquatic Oligocheates

Phylum Annelida38

Subclass Hirudinea• Defining characteristics

– Posterior sucker• Predominately freshwater,

but do occur in all seas and moist soil

• Leeches do not burrow, lack parapods and setae

• Clitellum only visible during breeding

Horse leech-actually feeds on small worms Haemopis sanguisuga

Great Amazon Leech

Haementaria ghiliani

Subclass Hirudinea

Phylum Annelida41

Leech Anatomy• Anterior sucker is small

and contains the mouth– Anterior sucker

creates a wound with saw like jaws

• Leeches drink other animals’ blood, usually vertebrates– Can be carnivores, or

scavengers; leeches are not set in their feeding habits

Hirudo medicinalis

More leech info:http://www.earthlife.net/inverts/hirundinae.html

Phylum Annelida44

Leech Reproduction

• Leeches are simultaneous hermaphrodites that lack a free-living larvae stage

• Fertilization is internal through copulation

• Development occurs in a cocoon similar to the Oligochaetes