Annelida 🪱

ZO 350 - Animal Phylogeny & Diversity Spring 2024

Human Interactions

fish food, agriculture support, medicinal leeches, research, ecosystems, darwin’s brilliance

Body Plan

spiral/mosaic, protostome, triploblast, true coelem;

bilateral symmetry, segmentation & limbs, hydroskeleton

Anatomy

head, segmentation, tail (pygidium)

segments (metameres) appear next to pygidium

Segmentation

repeated units w/repeated organs

in annelids = allows for efficient burrowing and movement

Parapodia

respiratory organ, dorsal & ventral parts, used for crawling, swimming, anchoring

Polychaetes Nutrition

Mobile = predators

sedentary = filter feeders

Oligochaetes Nutrition

detritus

Hirudinians Nutrition

parasites

Transport

circulation: closed system

respiration: across skin + parapodia

Excretion

nephridia in each segment; funnel pulls water in, tubules reabsorb water, empties out nephridiopore

Nervous System

cerebral ganglia connects to ventral nerve cord; giant axons increase signal speed

Sense Organs

eyes and statocysts

palps and antennae

Parapodia

for movement or anchors

Peristalsis

circular & longitudinal muscles, setae anchors

Undulation

longitudinal muscles move to create wave-like motions

Reproduction

Asexual: budding (polychaetes)

Sexual: external fertilization; hermaphroditic

Early larvae = trocophore

Class Clitellata

Oligochaetes (earthworms) & Hirudinea (leeches)

Oligochaetes Basic Info

~5000 species, moist habitats, setae, less developed head structures, hermaphroditic,

Class Clitellata; clitellum = makes cocoon for development

Oligochaetes Digestion

detrivores; crop stores food, gizzard grinds, intestine absorbs

Setae

bristles moved by tiny muscles, used as anchors

longitudinal muscles contract + segments widen = setae moves

Oligochaetes Reproduction

1. align in opposite directions, ventral surfaces together

2. exchange sperm

3. after, clitellum secretes cocoon

4. cocoon passes forward w/eggs + sperm poured in

5. external fertilization in cocoon that is shed

6. young worms emerge (no trochophore)

Hirudinea Basic Info

Class Clitellata, leeches

no setae, anterior + posterior suckers, freshwater, clitellum only during reproduction

Hirudinea Nutrition

ectoparasites (blood), secretes anticoagulant in saliva

Hirudinea Reproduction

1. sperm transferred by penis/hypodermic impregnation

2. temporary clitellum; secretes cocoon then buried in mud

Tubifex Worms/Sludgeworms

oligochaetes; live in sludge and looks like sludge

Marine Polychaetes Basic Info

differentiated head & sense organs, parapodia (setae in bundles)

mobile/errant = predators

sedentary = ciliary feeders

scale worms

mobile/errant polychaetes; flattened bodies covered w/broad scales

clamworms

mobile/errant polychaetes; most abundant

fireworms

mobile/errant polychaetes; hollow, brittle setae w/poisonous neurotoxin (feels like fire), feed on cnidarians

tube worms

sedentary polychaetes; burrow, use cilia + mucus to feed, tubes stabilize ecosystem

fan worms

sedentary polychaetes; use cilia or tenties to feed

zombie (bone-eating) worms

sedentary polychaetes; found in whale falls, feeds on carcass

spoonworms

~140 species of marine worms, burrows in shells or rocky crevices, loss of segmentation, ciliated groove on proboscis, feeds on detritus

parchment worms

parchment-like tube, pulls water in and filter feeds

peanut worms

~250 species of benthic marine worms, sedentary, live in burrows/shells/coral, no segmentation or setae, retractable proboscis, trochophore larvae