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Lophophorates – a clade, or not? 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 Phylum Bryozoa - colonies made of microscopic zooids Phylum Phoronida - worm-like, tube-dwelling; large Phylum Brachiopoda - 2 shell valves; large Lophophorates on the Tree of Life Lophophorates were 1st placed in the Deuterostomia, 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 Deuterostomia Where does molecular analysis of DNA + protein sequence data place them...? Tree #1: early 1990s Annelids OLD SCHOOL PHYLOGENY Arthropods Molluscs (wrong) Protostomes Nematodes Platyhelminthes Lophophorates Deuterostomes Tree #2: 1995 DNA analysis: Lophos = protostomes 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; either have a lophophore, or a trochophore larva (no real synapomorphy; not legit for a name) Halanych et al. 1995 arthropods + nematodes are in a separate clade, Ecdysozoa Protostomes Lophotrochozoa Two distinct clades within protostomes... but in which do the lophophorates belong? Nematodes Arthropods Ecdysozoa – molting phyla Deuterostomes Phoronids Lophotrochozoa Chaetognaths Brachipoda Nemertea Mollusca Annelida Platyhelminthes Trochozoa phyla with a trochophore larval stage Platyzoa Rotifera Bryozoans Tree #3: 2009 Entoprocts Cycliophorans - analysis of 1,487 genes Polyzoa Phoronids Chaetognaths Brachipoda Nemertea Mollusca Annelida The former “lophophorates” are scattered among all the major clades so... not a monophyletic group (in 2009) Platyhelminthes Rotifera Bryozoans Entoprocts Tree #3 Cycliophorans - analysis of 1,487 genes; Hejnol et al. 2009, Proc Roy Soc B Phoronids Chaetognaths Brachipoda Nemertea Mollusca Annelida The former “lophophorates” are scattered among all the major clades implies that the lophophore evolved multiple times Platyhelminthes Rotifera Bryozoans Entoprocts Tree #3 Cycliophorans - analysis of 1,487 genes; Hejnol et al. 2009, Proc Roy Soc B Tree #4 - analysis of >72,000 amino acid positions Platyhelminthes Mollusca Annelida Nemertea (ribbon worms) new Lophophorata? suggests the lophophore really is a synapomorphy and Lophophorata is monophyletic!.. ..if you now include the entoprocts Brachiopoda Phoronida Bryozoa Entoprocta Laumer et al. 2015, Current Biology Polyzoa Lophophorate characteristics Body divided in 3 parts, each with its own coelomic space: Anterior Posterior Coelomic space Protocoel Body region Prosome Mesocoel Mesosome Metacoel Metasome This 3-part body/coelom structure is typical of deuterostomes like us... probably an ancestral feature kept by deuterostomes and lophophorates, which changed in other trochozoans like molluscs and annelids The Lophophore 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 Lophophore Function Cilia on lophophore tentacles generate a feeding current - cilia catch particles, bounce them back and forth to mouth - each tentacle has 1 row of frontal cilia and 2 rows of lateral cilia Phylum Bryozoa 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 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? 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 swimming larva colony of inter-connected zooids ancestrula asexual reproduction - Colony starts as a metamorphosed larva, which grows into one original zooid, the ancestrula - ancestrula then clones itself to form whole colony, asexually Bryozoan Groups Class Stenolaemata (tubular; mostly extinct) 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 Class Gymnolaemata Order Ctenostomata - cylindrical zooids - flexible, chitinous exoskeleton - zooids sprout from a horizontal runner called the stolon (at some distance from each other) Funiculus = coelomic connection between zooids (may even link stomachs) funiculus 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 collapses over - collar folds over withdrawn tentacles tentacles compare and contrast feeding in this group with sipunculan worms! Class Gymnolaemata Order Cheilostomata - polymorphic zooids - exoskeleton made of chitin + calcium carbonate - non-stoloniferous growth: walls of the zooids are attached to each other colony grows as a continuous sheet, all zooids fused together 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 Schizoporella unicornis showing orange opercula covering zooids Eurystomella bilabiata, only food of the “Hopkin’s Rose” sea slug lophophores extended Bugula neritina - common fouling organism, worldwide 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 Bryozoans may be sister to a clade composed of 1 or 2 phyla that was not historically considered “lophophorates” Bryozoa Cycliophora Entoprocta - based on molecular analysis of protein sequences Polyzoa Phylum Entoprocta 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 water moves through the ring of ciliated tentacles in the opposite direction of lophophore flow bryozoan water water entoproct Phylum Entoprocta developing larvae may be found attached to inside of calyx family Pedicellinidae Barentsia benedeni calyx, with fringe of tentacles stalk may have up to 12 joints on older individuals Phylum Cycliophora ~5 species Close-up of mouthparts of Norwegian lobster, showing… Symbion pandora Phylum Cycliophora First reported in 1995 Entire phyla are still waiting to be discovered used to stick to lobster mouth Phylum Phoronida 2 genera 14 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 - 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? Phoronis vancouverensis Few species = not evolutionarily successful Can be very ecologically important, however; tubes can form dense aggregations on local mudflats, creating habitat Phoronis australis commensals that attach to the tubes made by cerianthids, a group of tube-building anemones that live in soft-sediments Actinotroch larvae - distinctive flattened head, body ringed with fat tentacles - ring of cilia at base of body Phylum Brachiopoda 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 valves house lophophore inside mantle cavity Brachiopod Filter Feeding ciliary motion water flow - 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 Class Inarticulata Class Articulata - shells may be equal, especially in burrowers - shells usually unequal - valves not hinged; attached by muscles - valves hinged: ventral teeth lock into dorsal socket - lophophore w/out skeleton - lophophore w/ skeleton - anus present - no anus Articulate Brachiopod - 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 Brachiopod vs. Bivalve umbo is dorsal top valve is dorsal ventral ventral dorsal ventral Brachiopod vs. Bivalve evolutionary loser 350 living spp. evolutionary winner 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