the “lophophorates” phylum bryozoa phylum phoronida phylum brachiopoda once upon a time, there...
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The “Lophophorates”
Phylum Bryozoa
Phylum Phoronida
Phylum Brachiopoda
Once upon a time, there were 3 phyla that had an apparent synapomorphy: the lophophore, a horseshoe-shaped ring of ciliated tentacles surrounding mouth, used in filter feeding
- 2 shell valves; large
- worm-like, tube-dwelling; large
- colonies made of microscopic zooids
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Lophophorates on the Tree of LifeLophophorates were 1st placed in the Deuterostomes, as:
- their early embryonic cleavage is radial & indeterminate
- body forms with 3 regions and a 3-part coelom
However, they also share some Protostome characteristics:
- mouth develops from blastopore in one group, Phoronids
- larvae of some look like modified trochophores
- they can make chitin, a building material not found in Deuterostomes
Where does molecular analysis of DNA + protein sequence data place them...?
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DeuterostomesEchinoderms
Chordates
Protostomes
Lophophorates
Chaetognaths
Nematodes
Annelids
Arthropods
Molluscs
Platyhelminthes
OLDSCHOOL(WRONG)
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DNA analysis: Lopho’s are protostomes
Halanych et al. 1995
Comparison of the highly-conserved 18S rRNA gene sequence showed that all 3 lophophorates grouped with protostomes, not with the deuterostomes
Proposed clade within protostomes: the Lophotrochozoa
- lophophorates, molluscs + annelids; excludes arthropods + nematodes
- no synapomorphy; either have a lophophore, or a trochophore larva (not really legit for naming)
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Deuterostomes
Echinoderms
Chordates
Nematodes
Arthropods
ProtostomesPhoronids
Chaetognaths
Spiralia
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Deuterostomes
Echinoderms
Chordates
Nematodes
Arthropods
Phoronids
Chaetognaths
Spiralia – spiral cleavage of embryos
Ecdysozoa –molting phyla
Lophotrochozoa
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Phoronids
Chaetognaths
Platyhelminthes
Rotifera
Brachipoda
Nemertea
Mollusca
Annelida
Lophotrochozoa
Trochozoa
phyla with atrochophorelarval stage
Spiralia
Platyzoa
Bryozoans
Entoprocts
Cycliophorans
Polyzoa
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Phoronids
Chaetognaths
Brachipoda
Nemertea
Mollusca
Annelida
Spiralia
The former“lophophorates”are scatteredamong all themajor clades
they are not a monophyletic group !!
Platyhelminthes
Rotifera
Bryozoans
Entoprocts
Cycliophorans
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All recent molecular studies support this version of protostomes
Spiralia: animals with spiral cleavage of their embryosPlatyzoa: flatworms, rotifers Polyzoa: bryozoans, entoprocts, cycliophorans
Trochozoa: animals with a trochophore stage annelids, molluscs, nemerteans, brachiopods
Ecdysozoa: animals with an external cuticle, that molt to grow nematodes, arthropods, minor phyla
PhoronidsChaetognaths
placement uncertain; phoronids are probably trochozoans
Note: all of these group names are names of clades, but do not correspond to phylum, class, order ranks
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Body divided in 3 parts, each with its own coelomic space:
This 3-part body/coelom structure is typical of deuterostomes like us... probably an ancestral feature kept by deuterostomes and lophophorates, which changed in the Spiralians
Lophophorate characteristics
Anterior Coelomic space Body regionProtocoel Prosome
Mesocoel Mesosome
Posterior Metacoel Metasome
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3 phyla have a lophophore, a circle of tentacles used in suspension feeding
Ciliated growth of tentacles arising from mesosome (middle coelomic compartment)
- tentacles contain fingers of coelom
- surround mouth, but not anus
The Lophophore
Is not a synapomorphy; evolved independently 2-3 times (= homoplasy)
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Cilia on lophophore tentacles generate a feeding current
- cilia catch particles, bounce them back and forth to mouth
Lophophore Function
- each tentacle has 1 row of frontal cilia and 2 rows of lateral cilia
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5,000 spp.
- Prosome reduced/absent; mesosome fills lophophore + connects to metasome, which contains viscera (organs)
- Colonial, made up of individual zooids that bud asexually - zooids bilaterally symmetric, often polymorphic
- U-shaped gut, anus outside lophophore- No excretory or circulatory systems; whole body of an individual zooid may be reduced to “brown body” + excreted
- Hermaphrodites, as a colony; gonads simple, temporary
- Undergo radial cleavage (like deuterostomes); blastopore does not become mouth or anus (unique to them)
- Most produce lecithotrophic larvae that settle rapidly; important members of fouling communities
Phylum Bryozoa
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Polypide = soft tissue + lophophore
Zooid = exoskeleton + polypide
Autozooids = feeding
Heterozooids = no lophophore, do other functions for colony
Compare & contrast bryozoans with hydrozoans (Cnidaria) –
What convergent adaptations for colonial life do the 2 groups show?
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Heterozooids = no lophophore, do other functions for colony
Ovicells – incubators for developing embryos
- sperm taken up from seawater, used to fertilize eggs
- parental zooid degenerates, forming nutritive tissue chamber for fertilized eggs
Avicularia – giant claws used to defend colony
- polypide reduced to a few large muscles
- claw is modified operculum
- prevents fouling by larvae + spores of other organisms
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swimming larva ancestrula
asexualreproduction
colony of inter-connectedzooids
- Colony starts as a metamorphosed larva, which grows into one original zooid, the ancestrula
- ancestrula then clones itself to form whole colony, asexually
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Class Stenolaemata- most extinct- tubular, calcified exoskeleton
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Class Stenolaemata
Class Gymnolaemata - zooids connected by funiculus (a coelomic link)
Order Cheilostomata- openings covered by opercula- embryos usually brooded in ovicells- avicularia: claws function in defense
Order Ctenostomata- cylindrical zooids, attached by stolon- no operculum, ovicells or avicularia
Bryozoan Groups
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Funiculus = coelomic connection between zooids (may even link stomachs)
funiculus
Class Gymnolaemata Order Ctenostomata
- cylindrical zooids - flexible, chitinous exoskeleton
- zooids sprout from a horizontal runner called the stolon
(at some distance from each other)
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Class Gymnolaemata Order Ctenostomata
Extend lophophore by hydrostatic pressure: - parietal muscles contract, pressurizing coelom - fluid extends lophophore, expands tentacles
Retract lophophore by muscle action:- lophophore pulled in by retractor muscles- collar folds over withdrawn tentacles collapses over
tentacles
compare and contrast feeding in this group with sipunculan worms!
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Class Gymnolaemata Order Cheilostomata
- polymorphic zooids
- exoskeleton made of chitin + calcium carbonate
- non-stoloniferous growth: walls of the zooids are attached to each other (grow in a sheet)
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Class Gymnolaemata Order Cheilostomata
- hard casing causes a problem: how to pressurize coelom? - solution: flexible frontal membrane on top
- muscles pull membrane down, pressurizing coelom
lophophore extends
In most successful group, membrane = the ascus
- internal, for protection; outer wall is solid
- pore lets seawater in when ascus is pulled down
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showing orange opercula covering zooids
Schizoporella unicornis
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lophophores extended
Eurystomella bilabiata,only food of the “Hopkin’s Rose”sea slug
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Bugulaneritina
Contains defensive compounds, the bryostatins
- made by a unique bacterial symbiont
- chemicals protect the large, lecithotrophic larvae from predation during their brief planktonic journey
- in clinical trials as an anti-cancer drug
- common fouling organism, worldwide
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Bryozoans are sister to a clade composed of 2 phyla that were never even grouped as “lophophorates”
Platyhelminthes
Rotifera
Bryozoa
Cycliophora
Entoprocta
Platyzoa
Polyzoa
- based on molecular analysis of protein sequences
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150 species
- solitary or colonial filter feeders
- feed with anterior ring of ciliated tentacles, but anus opens inside the ring (ento = within, procta = anus)
- no blood vessels, U-shaped gut
- spiral, determinate embryonic cleavage (typical protostome kind)
- some species have trochophore-like larvae
embryos + larvae are like other protostomes, adults are like bryozoans.. close relatives that develop quite differently
Phylum Entoprocta
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water moves through the ring of ciliated tentacles in the opposite direction of lophophore flow
Entoproct
Lophophoratewater
water
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Phylum Entoprocta
family Pedicellinidae
Barentsia benedeni
calyx, with fringe of tentacles
stalk may have up to 12 joints on older individuals
developing larvae may be found attached to inside of calyx
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Phylum Cycliophora
Symbionpandora
Close-up of mouthparts of Norwegian lobster, showing…
~5 species
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Phylum Cycliophora
First reported in 1995
Entire phyla are still waiting to be discovered
used to stick to lobster mouth
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2 genera14 species
- worm-like body inside a chitin tube - body has a flappy prosome, mesosome w/ lophophore, and an elongated trunk (metasome)
- U-shaped gut; mouth and anus very close together- 1 pair of metanephridia, closed circulatory system
- gonads simple, temporary; separate sexes or hermaphrodites
- blastopore becomes mouth (protostome character)- unique actinotroch larvae
Phylum Phoronida
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- lophophore is a double row of tentacles- each tentacle contains blood vessel for gas exchange, extension of coelom
- food particles brought into ring by current; then trapped in mucus lining food groove
- gametes proliferate in metacoel of trunk, released through nephridia, or ruptured out of tentacle ends
.. similar to many annelid worms; is this a synapomorphy or a case of convergent evolution?
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Phoronis vancouverensis
Few species = not evolutionarily successful
Can be very ecologically important, however; tubes can form dense aggregations on local mudflats, creating habitat
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commensals that attach to the tubes made by cerianthids, a group of tube-building anemones that live in soft-sediments
Phoronis australis
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Actinotroch larvae
- distinctive flattened head, body ringed with fat tentacles
- ring of cilia at base of body
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350 living species
30,000 fossil species
- body enclosed between 2 valves (dorsal + ventral)
- live cemented to bottom, or dig with ventral foot-like pedicle
- valves lined by mantle, creating mantle cavity (as in molluscs)
- U-shaped gut, with or without anus
- 1-2 pairs of metanephridia,
- open circulatory system
- separate sexes; temporary gonads
- blastopore closes;
mouth + anus form secondarily
Phylum Brachiopoda
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valves house lophophore inside mantle cavity
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Brachiopod Filter Feeding
- Water passes over lateral cilia bands, which send particles to frontal bands by localized beat reversal
- Frontal cilia then re-direct particles to food groove
ciliary motionwater flow
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Class Inarticulata Class Articulata - shells may be equal, - shells usually unequal especially in burrowers
- valves not hinged; - valves hinged: ventral teeth attached by muscles lock into dorsal socket
- lophophore w/out skeleton - lophophore w/ skeleton
- anus present - no anus
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- Ventral valve bears teeth that lock into dorsal valve socket
- Adductor muscles close valves; diductors open valves - contrast w/ bivalve, where springy ligament forces shell valves open if adductor muscles relax
Articulate Brachiopod
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Brachiopod vs. Bivalve
top valve is dorsal
ventral
umbo is dorsal
ventral
dorsal ventral
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Brachiopod vs. Bivalve
evolutionary loser evolutionary winner 350 living spp. 7,600 living spp.
Bivalves and brachiopods compete for the same resources; bivalves have been come dominant, while most brachiopods went extinct
Key bivalve innovation may have been the mantle fusing into a siphon for drawing water into the shell