Sponges

Cnidarians

acoelflatworms

Deuterostomes

Protostomes

the clade of Bilaterian animals excluding the acoels was recently named Nephrozoa –

“animals with kidneys”

the Nephrozoan ancestor

- 1st animal with an excretory system

Sponges

Cnidarians

acoelflatworms

Deuterostomes

Protostomes

Nephrozoan animals are divided into 2 major lineages that are distinguishable by features of their embryos:

Sponges

Cnidarians

acoelflatworms

Deuterostomes

Protostomes

Nephrozoa = coelomates, animals with a true coelom (or at least, their ancestor had one)

the coelomate ancestor

- 1st animal with a coelom - all its descendants got a coelom, unless it was lost

Deuterostomes

Echinoderms

Chordates

ProtostomesPlatyhelminthes(flatworms)

Annelidworms

Molluscs

Nematodes

Arthropods

coelomateancestor

in some groups,coelom is critical to movement &feeding ecology

Echinoderms

Chordates

Platyhelminthes(flatworms)

Annelidworms

Molluscs

Nematodes

Arthropods

coelomateancestor

in some groups, coelom was lost or reduced

Phylum Annelida – coelomate worms

- coelom acts as hydrostatic skeleton allowing worms to crawl (polychaetes), dig (earthworms), inflate body regions

- embryos develop through spiral cleavage, leading to a trochophore larval stage (shared with molluscs)

- segmented bodies divided into repeating blocks (metamerism)

- formed by teloblastic growth in larvae- blocks of segments are specialized for different functions

- complete digestive system; excretory system w/ metanephridia

- closed circulatory system; well-developed nervous system

- chetae: spines sticking out of epidermis for movement, defense

~17,000 species

Annelida

Sipuncula Echiura Pogonophora Polychaeta Clitellata

segmentation

Old view ofcoelomate wormphylogeny

chetae

Segmented (now Family Sibloglinidae)

Pogonophora – deep-sea tube worms

Vestimentifera – giant vent worms

Non-segmented:

Sipuncula

Echiura – innkeeper worms

Former Coelomate Worm “Phyla”

All are now just clades nested within Annelida !

Old system: 2 classes of annelids(1) Polychaeta– primarily marine worms

- errant (free-living)

- tube-dwelling

- burrowing

- interstitial

- planktonic

- pelagic

(2) Clitellata

subclass Oligochaeta– earthworms

subclass Hirudinoidea– leeches

Pareurythoe

Potamilla

recent evidence: Clitellata is a clade nested within polychaetes

Annelida

Sipuncula

Clitellata

Echiura

Siboglinidae

Used to be:

Sipuncula

Echiura

Pogonophoran

Annelida Polychaeta Clitellata

DNA data shows all these groups belong to one big clade, interspersed among different polychaete groups

Annelida

Problem: now, no group we can call “polychaetes”

– same as “Annelida” if you include these 4 clades in “Polychaeta”

– paraphyletic group if you exclude these 4 but keep using name “polychaete”

- parapodia (unjointed appendages) act as walking paddles or gills for respiration

- numerous chetae (bristles) on parapodia, each derived from a single epidermal cell

- reproductive structures may be simple or temporary

- foregut modified as eversible proboscis for feeding

- great habitat diversity (mostly marine)

- head elaborated into two regions: prostomium with tentacles and palps, and peristomium

marine “polychaetes”25 Orders, 87 Families ~8,000 spp.

ventral bloodvessel

ventralnerve cord

nephrostomegut

septum

CM

epidermis

LM dorsal blood vessel

CMLM

segment junction

nephridium

polychaete cross-section serially repeated segments

have a “belly-bone” instead of our backbone

CM = circular muscle ring; contracts bodyLM = longitudinal muscle; pull lengthwise

Coelom

obliquemuscle

Circular muscle

Longitudinal mus.notopodium

chetae

neuropodium

parapodium

Asiculum

Parapodium in cross-section

Notopodium

Neuropodium

Close-up of chetae

straight, slim

short, hooked

Dorsal view

anchoring in tubes

Adaptive diversification of parapodia

parapodia in different body regions can be variously modified,some serving as gills, others in locomotion, others in feeding

gills

Circulatory systemof Nereis

dorsal vessel = anterior flow

esophagus

nephridium

ventral vessellateral vessel

intestine

- No hearts; contractions of dorsal vessel & body wall controls blood flow

- In species w/ incomplete septa, blood cells flow through continuous coelom

- hemoglobins & other respiratory pigments

Nervous system

palps

eyes

Primitive ventral “ladder” gradually fused, evolved into one central nerve chord

Forebrain enervates palps, midbrain the eyes and hindbrain the nuchal organ (chemical)

Parapodia move out of phase lateral undulations.

Chetae contact the substrate, push off with each stroke

Coelomic cavities in each segment are hydraulically isolated from each other, allowing independent movement of segments

Polychaete locomotion

Polychaete locomotion: Variable speed

Polychaete locomotion: Burrowing

If septa between coelomic spaces are absent, contraction of 1 area produces extension of another region (fluid is continuous)

Circular muscles make movements possible that aren’t available to nematodes, which have only longitudinal muscles

Polychaete reproduction

Benthic polychaetes form epitokes, which swim to the surface & spawn

Reproductive structures are simple, often temporary

Gametes form in coelom; ` released through gonoducts, nephridiopores, or simple tearing of the body wall itself

Nereis Eunice

There are a range of larval forms, but most pass through atrochophore larva stage early in development

Trochophore

locomotoryband ofcilia

Growth zone

Juvenile worm

2-day old trochophore of Spirobranchus giganteus

Later stage: segmented, orchetigerous, larva w chetae

Lecithotrophic: no mouth between prototroch and metatroch bands of cilia

nomouth

Newly metamorphosed serpulid (juvenile worm)

Trochophore larvaof a serpulid,

posterior view

Terebellid

Late-stage segmented larvae

Polychaete families & their ecology

order family ecologyPhyllodocida Nereidae errant, predatory

Glyceridae Polynoidae often commensal

Spionida Chaetopteridae mucous webs,parchment tubes

Terebellida Terebellidae deposit feedersPectinariidae sand tubesSabellaridae

Sabellida Sabellidae suspension feedersSerpulidae calcareous tubesSpirorbidae

Order PhyllodocidaFamily Nereidae

- one pair of large curved jaws, held inside body until deployed to catch prey

- bodies typically homonomous: all segments are alike

- predatory

- extensible proboscis with

4 teeth; used in burrowing and hunting

Order PhyllodocidaFamily Glyceridae

Glycera americana

Order PhyllodocidaFamily Polynoidae

- short and flattened bodies

- homonomous; few segments of fixed number

- dorsum covered by scales called elytrae

- 1 pair of jaws

- often commensal on other invertebrates: live on them, neither hurt (parasite) nor help (mutualist)

“Scale worms”

Order SpionidaFamily Chaetopteridae

- adult body is highly tagmatic: front and back ends are very different (heteronomous) - trap suspended particles by pulling water through a mucous web - web is balled up, consumed, re-spun every 18 minutes - parchment tube is home to many commensal organisms

tube, often in U-shape

worm out of tube

Thelepus crispusOrder TerebellidaFamily Terebellidae

branchial plume

- “medusa worm” has elongated tentacles used in selective deposit feeding from inside the safety of its tube (which it builds)

feeding tentacles extended to gather organic matter from surface

Deposit Feedingmodifiedprostomialappendages tentacles are

hollow

Order TerebellidaFamily Pectinariidae

Pectinaria californiensis, “ice cream cone worm”

- selects sand grains of precise size for each region of tube

Order SabellidaFamily Serpulidae

Spirobranchus sp.

“Christmas tree worm”

- build calcareous tubes

- often imbedded in rocks or coral heads

- compound eyes on tentacles; shadows trigger rapid withdrawal

tubes encrusting a chiton’s shell valves

Order SabellidaFamily Spirorbidae

Major fouling organism – rapidly colonize most marine surfaces with their tiny calcareous tubes

have a large operculum, or stopper, to seal the opening of their tube after they withdraw their feeding tentacles