Polyzoa and KryptozoaChapter 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.

• Cavity inside the lophophore is part of the coelom and filled with coelomic fluid.

• Thin ciliated walls act as respiratory surface for gas exchange.

• Lophophores normally extended but can be withdrawn for protection.

LophophoresThree 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.

Phylum Cycliophora• 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.

• 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 Cycliophora Feed by collecting bacteria or bits of food dropped

from their lobster host on a ring of compound cilia that surrounds the mouth.

Simple body plan where the mouth leads to U-shaped gut ending with an anus that opens outside the ciliated ring.

Acoelomate body Life cycle has sexual and asexual phases

Phylum EntoproctaAbout 150 species in

the phylum Entoprocta occur worldwide.Usually in marine

environments.

Less than 5 mm long and mostly microscopic, resembling hydroid cnidarians.

Phylum EntoproctaUrnatella gracilis is a common freshwater species in

North America.

Body or calyx is cup shaped and bears a circular crown of ciliated tentacles.

Attaches by a stalk with adhesive glands.

Phylum EntoproctaTentacles (3-30) and stalk are continuations of the

body wall.

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.

Phylum EntoproctaLong cilia on sides generate current bringing in

particles.

Short cilia on inner surfaces capture food and direct it to mouth.

Pair of protonephridia embedded in gelatinous parenchyma.

Well-developed nerve ganglion on the ventral side of stomach.

No circulatory or respiratory organs.

Phylum EntoproctaSome are monoecious, some dioecious, and

some first produce sperm and later eggs.

Fertilized eggs develop in a brood pouch.

Modified spiral cleavage leads to trochophore-like larva.

Phylum EctoproctaPhylum Ectoprocta

contains aquatic animals that often encrust hard surfaces (bryozoans).

Approximately 4500 living species.

Inhabit both shallow freshwater and marine habitats.

Phylum EctoproctaMost 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 EctoproctaCiliated 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 EctoproctaZooids feed by

extending lophophores into surrounding water to collect tiny particles

Zooids secrete exoskeleton in which they live in.

Phylum EctoproctaExoskeleton 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 EctoproctaTo 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.

Digestion begins extracellularly in the stomach and is completed intracellularly within the intestine.

Phylum EctoproctaRespiratory, vascular, and excretory organs

absent.

Gas exchange is through body surface.

Ganglionic mass and a nerve ring around the pharynx.

No sense organs.

Phylum EctoproctaReproduction - most hermaphroditic.

Some species shed eggs into seawater, but most brood their eggs.

Brooding occurs within coelom and some have an external chamber called an ovicell.

Sometimes embryos proliferate asexually from the initial embryo.

Cleavage is radial but mosaic.

Phylum EctoproctaLarva of brooding species do not feed and settle after a

brief free-swimming existence.

Attach to substratum by secretions from an adhesive sac, then metamorphose to adult form.

New colonies begin from this single metamorphosed primary zooid, called an ancestrula.Ancestrula undergoes asexual budding to produce

many zooids of a colony.

Phylum EctoproctaFreshwater

ectoprocts undergo budding that produces statoblasts.Hard, resistant

capsules containing a mass of germinative cells.

Phylum BrachiopodaBrachiopods 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 BrachiopodaCharacteristics 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 PhoronidaCharacteristics 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 Molecular characters have changed the phylogeny of

Lophophores and its associated groups. Developmental characters associated with spiral

cleavage are presumed to be ancestral to the clade. Spirally cleaving embryos have mosaic cleavage

patterns and mesoderm formation from particular endoderm cells.

But many members of the Lophophores do not follow these features and prevent clear placement into specific clades and groups.

Phylogeny and DiversificationPlacement 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 reversible proboscis in a unique coelomic cavity counters this original grouping.

Nemerteans coelomic cavity above the digestive tract sets them apart form other coelomate animals.