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Polyzoa and Kryptozoa Chapter 15
Lophophores • Phylogenetic evidence indicates that lophophores evolved more than once. • Lophophores have a crown of ciliated tentacles that are used in food capture and respiration. • Thin ciliated walls act as respiratory surface for gas exchange. Lophophores normally extended but can be withdrawn for protection.
Lophophores Three major phyla were previously lumped under lophophores: Phoronida, Ectoprocta, Brachiopoda. Lophophores and animals with trochophore larvae features are merged to form a new group called Lophotrochozoans. Ectoprocta is now placed in a clade called Polyzoa with Cycliophora and Entoprocta where all three taxa share ciliated tentacles. Brachipoda and Phoronida are placed in the clade Brachiozoa.
Clade Polyzoa • Phylogenetic studies using multiple genes have supported the clade Polyzoa that unites the cycliophorans, entoprocts and ectoprocts. • Members of the three groups have fascinating body plans and life cycles.
Phylum Cycliophora • Cycliophorans live exclusively on mouthparts of marine decapod crustaceans in northern hemisphere. • Attach to bristles with an adhesive disc on the end of an acellular stalk.
Phylum Entoprocta About 150 species in the phylum Entoprocta occur worldwide. Usually in marine environments. Less than 5 mm long and mostly microscopic, resembling hydroid cnidarians.
Phylum Entoprocta Body or calyx is cup shaped and bears a circular crown of ciliated tentacles. Tentacles on lateral and inner surfaces can roll inward but cannot be retracted into the calyx. Gut is U-shaped with both mouth and anus opening within the circle of tentacles. Attaches by a stalk with adhesive glands. Modified spiral cleavage leads to trochophore-like larva.
Phylum Ectoprocta contains aquatic animals that often encrust hard surfaces (bryozoans). Approximately 4500 living species. Inhabit both shallow freshwater and marine habitats.
Phylum Ectoprocta Most are sessile, some slide slowly, and others crawl actively across surfaces. Mostly colony builders. Each member is less than 0. 5 mm in length and is called a zooid.
Phylum Ectoprocta Ciliated tentacles are also a respiratory device permitting gas exchange between surrounding water and internal coelomic fluid. Gut is U-shaped: Mouth opens inside the lophophore ring, and the anus opens outside the ring.
Phylum Ectoprocta Zooids feed by extending lophophores into surrounding water to collect tiny particles Zooids secrete exoskeleton in which they live in.
Phylum Ectoprocta Exoskeleton may be gelatinous, chitinous, or stiffened with calcium and possibly impregnated with sand. Shape may be boxlike, vaselike, oval, or tubular. Some colonies form limy encrustations on seaweed, shells, and rocks. Others form fuzzy or shrubby growths or erect branching colonies. Freshwater colonies may form mosslike colonies on stems of plants or on rocks.
Phylum Ectoprocta To feed, the lophophore is extended and tentacles spread out into a funnel. Cilia on tentacles draw water into funnel. Food particles caught by cilia in the funnel are drawn into the mouth.
Phylum Ectoprocta Freshwater ectoprocts undergo budding that produces statoblasts. Hard, resistant capsules containing a mass of germinative cells.
Phylum Brachiopoda Brachiopods appear similar to bivalve molluscs because they have two calcareous shell valves secreted by a mantle. Dorsal/ventral instead of left/right. Pedicel – a fleshy stalk used for attachment.
Phylum Brachiopoda Brachiopods are an ancient group they were prolific during the Paleozoic and Mesozoic eras. One living species, Lingula, is considered to be a living fossil since it has changed little since the Ordovician (505 mya).
Phylum Brachiopoda Characteristics of both protostomes & deuterostomes: Cleavage is radial (deuterostome) Coelom formation enterocoelous at least in some brachiopods. (deuterostome) The relationship of the blastopore to the mouth is uncertain.
Phylum Phoronida Species in the phylum Phoronida are small wormlike animals. Secrete tubes to live in. Tentacles of the lophophore are extended for feeding. U-shaped digestive tract.
Phylum Phoronida Characteristics of both protostomes & deuterostomes: Blastopore becomes mouth (protostome). Cleavage is radial (deuterostome). Coelom formation – highly modified enterocoelous (deuterostome).
Phylum Nemertea Ribbon worms, phylum Nemertea, use a proboscis to capture prey. Almost completely marine. Active predators. General body plan similar to turbellarians.
Phylum Nemertea An anus is present providing these worms with a complete digestive system. Nermeteans are the simplest animals to have a closed loop blood-vascular system.
Phylogeny and Diversification n Molecular characters have changed the phylogeny of Lophophores and its associated groups. n Developmental characters associated with spiral cleavage are presumed to be ancestral to the clade. n Spirally cleaving embryos have mosaic cleavage patterns and mesoderm formation from particular endoderm cells. n But many members of the Lophophores do not follow these features and prevent clear placement into specific clades and groups.
Phylogeny and Diversification Placement of Nemerteans are contentious and highly debatable. Nemerteans used to be with Platyhelminthes due to flame cells and cilated epidermis but the presence of complete digestive tract and eversible proboscis in a unique coelomic cavity counters this original grouping. Nemerteans coelomic cavity above the digestive tract sets them apart form other coelomate animals.