Lecture Notes 7: Annelida

Scolecida
- Echiura
Clitellata
- Oligochaeta (paraphyletic)
- Hirudinea
Palpata
- Aciculata
- Canalipalpata
- Siboglinidae
Odd families – several
?Sipuncula
?Nemertea
Metameric, spiralian, schizocoelous, protostomes
ANNELIDA
Large phylum, the "most complex" worms. 2 traditional classes: polychaetes & clitellates (oligochaetes & leeches)
– though new work shows polychaetes paraphyletic to clitellates, while oligochaetes are paraphyletic to leeches

- grooved feeding palps – only in Canalipalpata; tend to be U shaped, with ciliated path in groove serving to
transport food. Grooved palps dorsal and attached at prostomial-peristomial junction. Include paired spionid
palps, multiple terebellid tentacles (arise from prostomium), radioles of sabellids, buccal tentacles (again
multiple – e.g. Pectinariidae)
Segments: each w/ own separate, paired coelomic compartments; separated by septa & mesenteries.
Body wall:
Cuticle (collagenous, may contain scleroprotein),
Epidermis, circular, longitudinal muscle, peritoneum.
Circular muscle as sheet, long muscle in 4 bands in almost all (Rouse & Fauchald 1997)
Parapodia:
Notopodium, neuropodium, if loose one always loose notopodium.
Nereid type advanced, primitively low, brasing structures, without aciculas, little musculature, noto- and neuropodia
separate.
In evolution may become more muscular and gain aciculae (in Aciculata) and gain strong intrinsic musculature for
chaetae & whole paddle; for swimming, etc. Or reduced to chaetae only (clitellates). Dorsal and ventral cirri –
fleshy extensions; funky chaetae – aphroditids; scale of polynoids; specialized gills
Parapodial muscles evolve from circular musculature
Dorsal and ventral cirrus – outgrowths of body wall – mainly in Aciculata
Aciculae – in Aciculata only. Fully internalized chaetae, with strong muscles that help support and move large
parapodia. Neuropodia have it, notopodial aciculae also in many Eunicida and Phyllodocida
Neuropodia reduced to low welts = tori in many Scolecida & Canalipalpata
Chaetae: Chitinous, produced by chaetoblasts, has dynamic microvilli w/ start & stop activities, make complex
morphologies as a result. Variety of chaetal types, hooks, capillaries, uncini, compound. Chitin restricted to
protostomes. Setae - term for arthropod cuticle-coated structure w/ core of cells -- chaetae solid, secreted str.s.
Body cavity: Coelom, lined by peritoneum; prd. cavities in each segment, each of independent schizocoelous
origin; no coelom in unsegments. Peritoneum surrounds guts, blood vessels & nerves in middle in retroperitoneal
spaces. Septa = double peritoneum. Excretory organs & gonads associated w/ coelom. Advantages
include greater possibilities for locomotion, localization of injuries. Some polychaetes loose septa between
some segments and create larger, confluent coelomic spaces. Some (especially small, interstitial worms) loose
segmentation and coelom altogether.
Locomotion:
Circular & long. muscles together w/ hydrostatic skeleton for peristaltic locomotion - a segment at a time. A major
advantage of segmentation, is in locomotion: localized coelomic fluid, together with local contraction of
segmental muscles, allows the local widening or elongation of segments. Septa - give local control of
movement. Peristaltic wave like this passing down animal, allowing burrowing motion, crawling motion.
Also undulatory swimming, paddling w/ parapodia, both by alternate contractions of longitudinal muscles.
Several groups with large pharynxes lose septa at anterior end of their body and use large, resulting coelomic cavity
to power eversion of their pharynx – e.g. glycerids
Circ.: Both by coelom and by BVS. Most w/ closed BVS. Vessels of blastocoel, myoepithelial, their contraction
drives blood through bug. Dorsal vessel to head; ventral vessel to tail; dorsal especially contractile. Blood
vessels to gills -- respiration; to nephridial canal -- resorption. Variety of blood pigments: hemoglobin,
chlorocruorin (Fe), hemerythrin (Fe).
Circulatory system lost in some, e.g. "blood worms", glycerids, also capitellids, some terebellids – some loose septa
as well (e.g. to house proboscis in glycerids) so coelom takes over circulation and can hold blood pigments
(hence name).

Resp.: Varied gill structures, though absent in small or narrow bugs; SA/V issues. Gills probably evolved many
times. Extensions of body wall, w/ or w/o coelom, usually in association w/ parapodia, usually heavily
vascularized.
w/ parapodia: arenicolids - bushy, cirratulids - threads
separate: terebellids - on dorsum of ant. segments.
chamber: polynoids & aphroditids
feeding appendages: sabellids, serpulids, spionids, etc
Resp. movements - may irrigate burrows
Excr.:
Paired nephridia / sgm in polychaetes = segmental organs.
- separate gonoduct and metanephridium – e.g. Capitellidae
- separate funnels for gono- and nephr., but become confluent so one exit – e.g. Hesionidae
- single main duct with nephrostome head for gametes + protonephridial head – e.g. Phyllodocidae
- single funnel system serves all – most families
- single funnel used for excretion; gametes exit through rupture of body wall – e.g., Nereididae
Dig.: Tripartite - stomodaeum, midgut, proctodaeum.
Stomodaeum may include eversible pharynx, either axial, all-around eversible, all ventral eversible pad; often w/
jaws.
Cuticle lining of stomodaeum can form jaws – many Eunicida and Phyllodocida
Ventral, eversible pad pharynx = ventral buccal organ & ventral muscular proboscis of Rouse & Pleijel (2001) –
only ventral part of pharynx everted.
Axial pharynx = simple axial proboscis and muscular axial proboscis of R&P - all around eversible
Midgut - ant. portion secretes dig. enzymes; undifferentiated in errants, differentiated in sedentaries into esoph., flat
stomach (dig. enzymes), thinner intestine - absorption. Salivary glands may occur. Proctodaeum -- rectum, for
fecal pellet fm., anus terminal, usually slightly dorsal on pygidium.
Nerv.: Brain in prostomium at least in part, though may penetrate back up to 5th/6th sgm. though even then within
prostomial space (septa bent to make room for it); never truly prd. as not segmental str., primitively not prd..
Circumesophageal ring in peristomiumto subesophageal ganglion in peristomium + 1-5 sgm? Though some
segmental ganglia may be moved up even into posterior end of brain. Ventral nerve cord prim. prd., may
become fused. Single or prd. ganglia per segment (sometimes only remnants of segmentation). Giant fibers -
1-5 prs. used for startle response in some sedentaries.
Sens.: General sensory cells over body, esp. dorsal cirri.
- Proprioceptors - respond to deformation or stress: 1) parapodial stretch receptors, 2) notopodial flap receptors, 3)
dorsal cirri receptors, 4) chaetae receptors.
- Statocysts in some, often w/ sandgrains, some make own lith, usually assoc. w/ ant. parapodia.
- Chemoreceptors - nuchal organs - 1 pr. at line between pro- and peristomium, ciliated sensory cells (+ciliated
supportive cells) covered by bizarre waxy cuticle.
- Photoreceptors as simple eye spots, only 2 cell / ocellus to great alciopid eyes, which can judge distance in open
water (stereoptical). Some eyes can form images. Few eyes ciliary, most rhabdomeric. Eyes on brachioles of
sabellids – shadow response (w/ giant nerve)
- Antennae, palps
Repr.:
Asexual reproduction common.
- budding as clonal propagation. Syllids can have either axial or lateral budding. Dodecaceria breaks up; single
segments will form whole worm – build large “colonies” really clonal aggregations with confluent tubes, but
separate bodies.

- budding as preamble to sexual reproduction: epitokes. Epitokes are morphologically-modified stages that are
budded off the rear of the vegetative worm. E.g. eunicids - palolo worms budded off parent, which stays in
substratum, hind end swims off. Swarms 7 th day after 1 st full moon following autumn equinox. Swarms so
large in Fiji / Samoa that they are harvested for food! Spaghetti nights on coral spawning nights!
- heteronereids – not epitokes – whole worm metamorphoses into swarmer. Body wall muscles change, gut
resorbed, parapodia and chaetae become modified for more effective swimming, especially toward posterior
end of worm. (pretty distinct posterior – anterior differentiation in Platynereis dumerilli and Nereis vexillosa,
but not much separation in Neanthes brandti).
- gonads: peritoneal, primitive metazoan condition. Gametes mature in coelom and released either through
gonoducts or by disintegration of worm (e.g. in nereids – body rupture).
Development:
Spiralian, schizocoelous protostomes.
Trochophores
Some brood – e.g. sabellid tube brooding
Ecology & Diversity:
Scolecida
Palpata
- Aciculata
- Canalipalpata
SCOLECIDA
- tend to have “simple axial buccal organs”, i.e., short, eversible, pad-like pharynxes used for deposit feeding,
eversion driven by coelomic pressure, thus tendency of families to have lost septa in anterior segment to allow
this, muscular retraction.
- mostly unselective, burrowing deposit feeders, without head appendages, free living (though some maldanids
make sandy tubes).
Arenicolidae
- J-shaped tube, surface dimple, eat organic rich accumulations; fecal casts
- burrow irrigation
Maldanidae
- tube-dwelling deposit feeders; live head down in tube, gobble sediment. Simple axial buccal organ like
arenicolids. Nor all have tubes, but local Axiothella does, tube of poorly agglutinated, thick layer of sediment.
Common in mid False Bay
Capitellidae
- burrowing, free-living sediment ingestors - earthworms of sea
PALPATA – ACICULATA
- well-defined clade with many synapomorphies, most strikingly the acicula, antennae, well developed parapodia
Onuphidae
- tube building omnivores
- sister to Eunicidae, very similar, except build parchment tube (which come carry around), and has ceratophores on
antennae and palps.
- palps antenniform, so with 3 antennae end up with 5 similar “tentacles” on head
- Diopatra lunge out at prey from parchment tube
- pair of peristomial cirri on peristomium behind prostomium – unique to Eunicidae-Onuphidae
- many with large, well developed dorsal gills in anterior segments (good for respiration in tube-confines)
Eunicidae

- palps antenniform, + 1-3 antennae = 3-5 similar tentacles on head
- pair of peristomial cirri on peristomium behind prostomium – unique to Eunicidae-Onuphidae
- rowing raptorial omnivores w/ jaws on ventral pad pharynx
Amphinomidae
- fire worms; calcified chaetae with venom
- caruncle
- rowing predators; especially striking in tropics
Polynoidae
- scale worms; elytra arising from dorsal side of alternate notopodia
- lack well developed dorsal cirri on scale-bearing segments; though not clear homology between cirri and elytrae
- rowing predators and symbionts
Glyceridae – carnivore, especially of crustaceans
- Glycera lives in burrow system with multiple entrances, sitting near base of branches, feeling for vibrations with 4
prostomial tentacles and also by chemoreception. Moves up into appropriate burrow to capture prey, via
eversible, pharynx armed with 4, hollow, venomous fangs. Venom glands. Especially crustacean predator
- lack septae in anterior ~20 segments to accommodate huge eversible pharynx
Nereididae
- prostomium with paired antennae, palps, peristomium reduced, first segment compound with multiple tentacular
cirri
- errant, temporary mucus tube, herbivorous, some carnivory, scavenging
- paired large jaws in large eversible pharynx look formidable, but mostly used for pulling algae into gut.
Platynereis farms Ulva, attaching it to tube, cutting off pieces and in turn attaching those to tube and grazing on
growth. In winter, when no Ulva, switches over to eating diatoms
PALPATA – CANALIPALPATA
Sabellidae
- prostomium largely transforms into radiolar crown, which developmentally is homologous to prostomial palps,
and seen as arising as such in larvae
- ciliary feeding, tentacles with three sets of channels: food, tube-building grains, reject channel
- thorax (usually 8 segments) and abdomen, with chaetal inversion
- dorsal thoracic and ventral abdominal fecal groove
Serpulidae
- like Sabellidae, but calc tube
- Spirobranchinae within it – tiny, spiral worms that brood, direct dev, ubiquitous
Chaetopteridae
- in parchment tubes, either U shaped or straight down
- some with paired feeding palps, some lost it
- major body tagmatization: arms to secrete mucus bag, cup to hold it, major notopodial paddles to drive current
- mucus bag feeding, can get tiny particles
Spionidae
- some of the most abundant polychaetes, enormous densities
- tube dwelling, tiny, paired feeding palps, can be used for deposit or suspension feeding or both
Terebellidae
- spaghetti worms – multiplied palps give spaghetti effect
- palps with ciliary track for carrying food; walk out with it upside down

Oligochaeta
3100 spp. (Barnes); most land & FW, 200 marine; primitively FW, secondarily to land and sea. Generally
scavenger / deposit feeder, some FW carnivores. In FW usually burrow in bottom sediments, good indicators
of pollution. Earthworms - feed on decomposing matter; aerate and mix soil greatly; very beneficial. Darwin -
on vegetable mounds and earthworms. Giant australian earthworms to 1+m.
Externally simpler than polychaetes: no parapodia; few chaetae - hence name; no head appendages (in a few
genera prostomium drawn out into tentacle); small eversible pharynx in some FW forms; sucking pharynx in
earthworms. Chaetae in 2 prd. bundles / sgm. presumed to be homologous to noto- & neuropodia.
In earthworms middorsal coelomic pores w/ sphincters to wet skin in burrowing.
Around intestine - chloragogen tissue - glycogen & fat synthesis & storage; fm. of NH4, urea, also has waste
concretions (silicates...).
Excr. by metanephridia - highly convoluted ducts to regain water - hyperosmotic urine, urea; many empty
nephridia into gut to have more chance at water reabsorption.
Resp.: The largest terrestrial animals w/o specialized respiratory structures are giant earthworms - complex
capillaries under epidermis though.
Asex. repr. very common. All hermaphroditic, w/ distinct gonads, few repr. sgm., clitellum. 1-2 male sgm., then 1
female sgm. following it, ea. w/ prd. distinct gonad; release developing gametes into coelom, where held in
specialized septal pockets: seminal vesicles and ovisacs. Then funnel w/ sperm duct, traverses several sgm.
before emptying, unite if 2 testicular segments. Funnel w/ oviduct, opens into immediately posterior segment.
Ant. to female sgm. are 1-many sgm. having blind ending seminal receptacles. Clitellum 2-60 sgm, 6-7 in
Lumbricus; lies post. to genital sgm.s. Sgm. w/ greatly swollen epidermis, w/ abundant gland cells - which
produce mucus for copulation, secrete cocoon wall & albumin for eggs. Copulation, places sperm in seminal
receptacle. Few days later - tough cocoon secreted by clitellum, passed forward, first eggs, then sperm into it,
then sealed as gets off worm.
Hirudinea
Q&D, Barnes
Leeches, 500 spp., SW, FW, land; primitively FW. Derived from oligochaetes. 1-40cm.
Protandric hermaphrodites, lack parapodia, chaetae, head appendages, similar repr. - clitellum.

Dorso-ventrally flattened; Ant. and post. suckers modified from sgm.s. Suckers used in inch-worming locomotion;
elongate by contracting circ. muscles, reach out and attach. Fixed number of 34 sgm., though obscured by
secondary annulations. As expected for such fixety, no asex. repr. or regeneration.
Coelom-circ.: Well developed connective tissue and loss of distinct coelom; perhaps related to no need for it in
locomotion; or swimming - undulations. Acanthobdella retains 5 prd. coeloms anteriorly (& these sgm.s bear
chaetae); otherwise no septae, coelomic cavity reduced to interconnecting coelomic sinuses and channels -
developed into a new BVS. Original oligochaete BVS retained in some (Rhynchobdellida), but lost in many.
Coelomic fluid propelled by muscular contractions (unlike expected from Ruppert & Carle's division).
Dig.: 1/4 of spp. predacious on invert.s (but frog w/ me) and swallow prey whole, or some suck host dry (literally),
3/4 blood-sucking ectoparasites - mostly on vert.s, some on inverts; may associate w/ host temporarily or
permanently. Have either an eversible, muscular, sucking proboscis (Rhynchobdellida) which is trust into host
tissue; or a sucking pharynx w/ 3 jaws within the ant. sucker (Gnathobdellida) and a muscular pumping
pharynx. Pharyngobdellida, as Gnathobdellida but muscular folds instead of jaws. Great gut bacterial flora to
aid in digestion. Esophagus, stomach (=crop), intestine, rectum; stomach in most w/ 1-11 prs. of caeca;
intestine may also have 4 caeca.
Hirudo - still used in medicine, eats 2-5X body weight in blood infrequently, then piss blood-water out. hirudin =
anticoagulant
Nerv.: Brain, connectives, subesophageal ganglion + several segmental ganglia all en mass in sgm.s X-XII., prd. V.
cords w/ fused sgm.'l ganglia posteriorad. Neurons large – neurophysiologist’s toy.
Repr.: Sperm transfer by penis or hypodermic impregnation; internal fertilization - directly into female system
(unlike earthworms). Clitellum forms cocoon & albumin into it.