Transcript Lecture 06, Annelida 1 - Cal State LA

the clade of Bilaterian animals
excluding the acoels was
recently named Nephrozoa –
“animals with kidneys”
Protostomes
the Nephrozoan ancestor
- 1st animal with an excretory system
Deuterostomes
Nephrozoan animals are
divided into 2 major lineages
that are distinguishable by
features of their embryos:
Protostomes
Deuterostomes
Nephrozoa = coelomates,
animals with a true coelom (or
at least, their ancestor had one)
Protostomes
the coelomate ancestor
- 1st animal with a coelom
- all its descendants got a coelom,
unless it was lost
Deuterostomes
Platyhelminthes
(flatworms)
coelomate
ancestor
Protostomes
Annelid
worms
Molluscs
Nematodes
in some groups,
coelom is critical
to movement &
feeding ecology
Arthropods
Deuterostomes
Platyhelminthes
(flatworms)
coelomate
ancestor
Annelid
worms
Molluscs
Nematodes
Arthropods
in some groups,
coelom was lost
or reduced
Phylum Annelida – coelomate worms
~17,000
species
- 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
Annelida
Sipuncula
Echiura
Pogonophora Polychaeta
Clitellata
segmentation
Old view of
coelomate worm
phylogeny
chetae
Former Coelomate Worm “Phyla”
Segmented (now Family Sibloglinidae)
Pogonophora – deep-sea tube worms
Vestimentifera – giant vent worms
Non-segmented:
Sipuncula
Echiura – innkeeper worms
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
Pareurythoe
Potamilla
(2) Clitellata
subclass Oligochaeta– earthworms
subclass Hirudinoidea– leeches
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”
marine “polychaetes”
25 Orders, 87 Families
~8,000 spp.
- 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
polychaete cross-section
serially repeated segments
LM dorsal blood
epidermis
vessel
CM
LM
segment junction
CM
septum
gut
nephrostome
ventral
nerve cord
ventral blood
vessel
have a “belly-bone”
instead of our
backbone
nephridium
CM = circular muscle ring; contracts body
LM = longitudinal muscle; pull lengthwise
parapodium
Circular muscle
Longitudinal mus.
notopodium
Coelom
chetae
oblique
muscle
neuropodium
Asiculum
Parapodium in cross-section
Close-up of chetae
straight, slim
Notopodium
Neuropodium
short, hooked
Dorsal view
Adaptive diversification of parapodia
anchoring
in tubes
gills
parapodia in different body regions can be variously modified,
some serving as gills, others in locomotion, others in feeding
Circulatory system
of Nereis
- 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
intestine
dorsal vessel =
anterior flow
esophagus
nephridium
ventral vessel
lateral vessel
Nervous system
eyes
Forebrain enervates
palps, midbrain the eyes
and hindbrain the
nuchal organ (chemical)
Primitive ventral “ladder” gradually fused, evolved into one
central nerve chord
palps
Polychaete locomotion
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: 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
`
Nereis
Eunice
Gametes form in coelom;
released through gonoducts,
nephridiopores, or simple
tearing of the body wall itself
There are a range of larval forms, but most pass through a
trochophore larva stage early in development
Trochophore
locomotory
band of
cilia
Juvenile
worm
Growth zone
2-day old trochophore
of Spirobranchus giganteus
no
mouth
Later stage: segmented, or
chetigerous, larva w chetae
Lecithotrophic: no mouth
between prototroch and
metatroch bands of cilia
Trochophore larva
of a serpulid,
posterior view
Newly metamorphosed
serpulid (juvenile worm)
Late-stage segmented larvae
Terebellid
Polychaete families & their ecology
order
family
ecology
Phyllodocida
Nereidae
Glyceridae
Polynoidae
errant, predatory
Spionida
Chaetopteridae
mucous webs,
parchment tubes
Terebellida
Terebellidae
Pectinariidae
Sabellaridae
deposit feeders
sand tubes
Sabellida
Sabellidae
Serpulidae
Spirorbidae
suspension feeders
calcareous tubes
often commensal
Order Phyllodocida
Family Nereidae
- one pair of large curved
jaws, held inside body
until deployed to catch
prey
- bodies typically homonomous:
all segments are alike
Order Phyllodocida
Family Glyceridae
- predatory
- extensible proboscis with
4 teeth; used in burrowing
and hunting
Glycera americana
Order Phyllodocida
Family Polynoidae
- short and flattened bodies
“Scale worms”
- 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)
Order Spionida
Family Chaetopteridae
worm out
of tube
- 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
Order Terebellida
Family Terebellidae
Thelepus crispus
branchial
plume
- “medusa worm” has elongated
tentacles used in selective
deposit feeding from inside the
safety of its tube (which it builds)
modified
prostomial
appendages
Deposit Feeding
tentacles are
hollow
feeding tentacles extended to gather organic matter from surface
Order Terebellida
Family Pectinariidae
Pectinaria californiensis, “ice cream cone worm”
- selects sand grains of precise size for each region of tube
Order Sabellida
Family Serpulidae
Spirobranchus sp.
“Christmas tree
worm”
- build calcareous tubes
- often imbedded in rocks or coral heads
- compound eyes on tentacles; shadows trigger rapid withdrawal
Order Sabellida
Family Spirorbidae
Major fouling organism – rapidly colonize most marine surfaces
with their tiny calcareous tubes
tubes encrusting a chiton’s shell valves
have a large operculum,
or stopper, to seal the
opening of their tube
after they withdraw their
feeding tentacles