Polyzoa and Kryptrochozoa CHAPTER 15 Polyzoa and Kryptrochozoa Powerpoints revised by Franklyn Tan Te Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
Ectoprocts (Bugula neritina) and other animals fouling a boat bottom.
Evolutionary Experiments Greatest evolutionary “bang” the world has known occurred 570 million years ago called the Cambrian Explosion Fossil evidence indicate that all major phyla and most small phyla became established. Many phyla existed in the Paleozoic than today but have since disappeared due to several major extinction events that have led evolution to go through many “experimental models”.
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 Lophophores normally extended but can be withdrawn for protection.
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.
Figure 15.1 Proposed relationships among polyzoans and kryptrochozoans.
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
Figure 15.2 Symbion pandora, a cycliophoran living on setae on the mouthparts of lobsters.
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 Cellular epidermis surrounded by a cuticle Life cycle has sexual and asexual phases Feeding animals form internal buds called Pandora larvae
Phylum Cycliophora Pandora larvae become new feeding individuals upon release and cloned members occupy vacant areas on the lobster mouthparts In sexual reproduction, male larvae is released and settles atop another animal that houses a female larvae Male larvae produce secondary males with reproductive organs and internal fertilization occurs as secondary male mates with a female larva leaving the body of a feeding animal Once fertilization occurs, Chordoid larva develops inside the body of its mother and consuming it
Phylum Entoprocta Characteristics About 150 species occur worldwide Usually in marine environments Less than 5 mm long and mostly microscopic May be solitary or colonial, sessile and on stalks All ciliary feeders. Urnatella gracilis common freshwater species in North America while other species are marine.
Figure 15.3 A, Urnatella sp., a freshwater entoproct, forms small colonies of two or three stalks from a basal plate. B, Loxosomella sp., a solitary entoproct. Blue arrows indicate the direction of water movement. C, A live Loxosomella sp.
Phylum Entoprocta Form and Function Body or calyx is cup shaped and bears a circular crown of ciliated tentacles Attaches by a stalk with adhesive glands Body wall has a cuticle, cellular epidermis and longitudinal muscles Tentacles (3-30) and stalk are continuations of the body wall Tentacles are ciliated on the lateral and inner surfaces and can roll inward to protect the mouth and anus but cannot be retracted into the calyx
Phylum Entoprocta Gut is U-shaped with both mouth and anus opening within the circle of tentacles Long cilia on sides generate current bringing in particles Short cilia on inner surfaces capture food and direct it to mouth Digestion and absorption occur in stomach and intestines Pseudocoel is fluid filled with gelatinous parenchyma with flame bulb protonephridia and ducts that unite and empty into mouth
Phylum Entoprocta Well-developed nerve ganglion on the ventral side of stomach Body surface has sensory bristles No circulatory or respiratory organs Some are monoecious, some dioecious, and some produce sperm first and later eggs called protandrous hermaphrodites Fertilized eggs develop in a brood pouch between gonopore and anus Has modified spiral cleavage leads to trochophore-like larva
Phylum Ectoprocta Characteristics Contains aquatic animals that often encrust hard surfaces Most are sessile, some slide slowly, and others crawl actively across surfaces Mostly colony builders with each member less than 0.5 mm in length Colony members are called zooids that feed by extending lophophores into surrounding water to collect tiny particles Zooids also secrete exoskeleton in which they live in called zoecium
Figure 15.4 A, A colony of Membranipora, a marine encrusting bryozoan (Ectoprocta). B, Portion of a colony of an encrusting bryozoan with lophophores extended.
Phylum Ectoprocta Zoecium may be gelatinous, chitinous, or stiffened with calcium and possibly impregnated with sand that can be boxlike, vaselike, oval, or tubular in shape Approximately 4500 living species Inhabit both shallow freshwater and marine habitats Some marine colonies form limy encrustations on seaweed, shells, and rocks Others form fuzzy or shrubby growths or erect branching colonies Freshwater colonies may form moss-like colonies on stems of plants or on rocks
Figure 15. 5 Colonies of marine ectoprocts Figure 15.5 Colonies of marine ectoprocts. A, The zooids are encrusting in this lacy colony of Membranipora tuberculata. B, Bugula neritina has upright, branching colonies.
Phylum Ectoprocta Ectoprocts were also called Bryozoans (moss animals) and are differentiated from Entoprocta by the location of the anus on the outside of the tentacular ring around the mouth. Form and Function Zooids consists of a feeding polypide and a case-forming cystid Polypide includes the lophophore, digestive tract, muscles, and nerve centers Cystid includes the body wall of an animal, together with its secreted exoskeleton
Phylum Ectoprocta Polypides pop up to feed, but withdraw quickly at the slightest disturbance into its chamber with a trapdoor called operculum To extend tentacular crown, muscles contract and increases hydrostatic pressure within the body cavity that forces the lophophore out Other muscles contract to withdraw crown to safety back into the chamber with great speed. To feed, the lophophore is extended and tentacles spread out into a funnel Cilia on tentacles draw water into funnel and food particles caught by cilia are drawn into the mouth by the pumping action of the muscular pharynx and by the action of the cilia
Figure 15.6 A, Ciliated lophophore of Electra pilosa, a marine ectoproct. B, Plumatella repens, a freshwater bryozoan (phylum Ectoprocta).
Phylum Ectoprocta Marine ectoprocts have circular lophophore ridge while freshwater species have U-shaped lophophore with a protocoel and flap over the mouth called epistome Digestion begins extracellularly in the stomach and completed intracellularly in the intestine in a complete gut system. Respiratory, vascular, and excretory organs absent with gas exchange through body surface using coelomic fluid for transport Ganglionic mass and a nerve ring around the pharynx with no sense organs.
Phylum Ectoprocta Coelomocytes engulf and store waste materials within the coelomic fluid Ectoproct colonies usually contain feeding individuals but sometimes have non-feeding members called heterozooids Aviculariums are modified zooids that resemble bird beaks and can snap at small invading organisms that approach the colony Vibraculum have long bristles that sweep away foreign particles
Phylum Ectoprocta Ectoprocts are mostly 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 in a process called polyembryony Cleavage is radial but mosaic Larva of nonbrooding species have a functional gut and swim for a few months before settling Larva of brooding species do not feed and settle after a brief free-swimming existence
Phylum Ectoprocta Larvae attach to substratum by secretions from an adhesive sac, then metamorphose to become an 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 Freshwater ectoprocts undergo budding that produces statoblasts which are hard, resistant capsules containing a mass of germinative cells Statoblasts occur in the summer and fall that eventually give rise to polypides and later forming new colonies
Figure 15.7 Statoblast of a freshwater ectoproct Cristatella sp.
Phylum Brachiopoda Characteristics Ancient group that were called lamp shells Approximately 325 living species with fossil records of up to 12,000 species Generally attached, bottom-dwelling, marine forms that inhabit shallow water but are found nearly in all ocean depths Externally resemble bivalves but have dorsal and ventral valves instead of lateral valves in clams Attached to substrate directly or by fleshy stalk, called the pedicel
Figure 15.8 Brachiopods.
Phylum Brachiopoda Brachiopods have ventral valve (pedicel) that is slightly larger than dorsal valve (brachial) with an end projecting out like a beak. For many species, the pedicel valve is shaped like a classic oil lamp of ancient Greece hence the name “lamp shells” Shell valves distinguish the two classes of brachiopods Articulata have connecting hinge with an interlocking tooth-and-socket arrangement Inarticulata have no hinge and held together by muscles
Phylum Brachiopoda Body occupies only the posterior space between valves Extensions of the body wall form mantle lobes that line and secrete the shell Have large horseshoe-shaped lophophore in the anterior mantle Ciliated tentacles are involved in feeding and respiration with ciliary water currents carrying food between the valves. Tentacles catch food and move particles to mouth via lophophore which can also absorb dissolved nutrients.
Phylum Brachiopoda Three coelomic cavities like protocoel, mesocoel and metacoel are present Coelomocytes ingest wastes and are expelled by pair of nephridia that open into coelom and empty out to the mantle Have open circulatory system with contractile heart Nerve ring with small dorsal and large ventral ganglion Most have separate sexes and fertilization is external while some brood their young
Phylum Brachiopoda Cleavage is radial with coelom and mesoderm formation in some as being enterocoelic. In articulates, metamorphosis of larvae occurs after they are attached by pedicel In the inarticulates, juveniles resemble small brachiopods with coiled pedicel in the mantle cavity and no metamorphosis.
Figure 15. 9 Phylum Brachiopoda. A, An articulate brachiopod Figure 15.9 Phylum Brachiopoda. A, An articulate brachiopod. B, Feeding and respiratory currents. Blue arrows show water flow while black arrows indicate food movement.
Phylum Phoronida Characteristics Contains about 20 species of small, wormlike animals that range from few mm to 30 cm Most live on substrate of shallow coastal waters, especially in temperate seas Each worm secretes a leathery or chitinous tube in which it lies free, but never leaves the tube Tubes may be anchored singly or in a tangled mass on rocks, shells, or pilings or buried in sand
Figure 15.10 Internal structure of Phoronis (phylum Phoronida).
Phylum Phoronida Phoronids thrust out tentacles on lophophore for feeding but withdraw into the tube when disturbed Lophophore has two parallel ridges curved in a horseshoe shape with mouth in between the two ridges Cilia in tentacles direct water currents toward groove between two ridges Plankton and detritus caught in current become entangled in mucus and are carried by cilia to mouth
Phylum Phoronida Anus lies dorsal to mouth outside of lophophore next to nephridiopore Water leaving the lophophore passes over the anus and nephridiopores to remove wastes Cilia in stomach of the U-shaped gut aid in food movement Body wall consists of cuticle, epidermis, and both longitudinal and circular muscles Protocoel is present as small cavity in epistome Septum separates mesocoel and metacoel
Phylum Phoronida Extensive system of contractile blood vessels in functionally closed circulatory system but no heart Blood contains hemoglobin within nucleated cells Nerve ring sends nerves to tentacles and body wall with a diffuse system that lacks distinct ganglion or brain Has giant motor fiber in the epidermis and epidermal nerve plexus supplies the whole body
Phylum Phoronida Have monoecious and dioecious species with one species reproducing asexually Fertilization may be internal or external Cleavage is radial and coelom formation is highly modified enterocoelous form with the blastophore forming the mouth Free swimming ciliated larvae called actinotroch will sink into the sea floor and metamorphoses to an adult that secretes a tube and remain sessile
Phylum Nemertea Characteristics Often called ribbon worms that are thread shaped or ribbon-shaped bilaterally symmetrical triploblastic worms Have a long muscular tube, the proboscis used to grab prey Over 1000 species and most are less than 20 cm long but some get to several meters Nearly all marine with some brightly colored while others are dull and live in secreted gelatinous tubes.
Figure 15.11 Ribbon worm Amphiporus bimaculatus (phylum Nemertea)
Phylum Nemertea Epidermis is ciliated with many gland cells Excretory system has flames cells; several have rhabdites Mostly dioecious with ciliated larvae resembling trochophores Adult has an anus, producing a complete digestive system that is more efficient with ingestion and defecation occurring at the same time. Simplest animals with a blood-vascular system Mostly active predators; some scavengers
Figure 15.12 A, Structure of female nemertean worm Amphiporus sp. B, Amphiporus, with proboscis extended to catch prey.
Figure 15.13 Baseodiscus is a genus of nemerteans whose members typically measure several meters in length.
Phylum Nemertea Form and Function Slender and fragile with body wall that has ciliated columnar cells and layers of circular and longitudinal muscles Move by gliding over slime track or by undulatory swimming Mouth is anterior and ventral with complete digestive tract extending along body and ends in the anus Digestion is extracellular in the gut lumen with cilia moving food along intestines
Figure 15. 14 A, Cross section of female nemertean worm Figure 15.14 A, Cross section of female nemertean worm. B, Excretory and circulatory systems of nemertean worm.
Phylum Nemertea Some species detect prey when physically near and use proboscis hiding in a cavity called the rhynchocoel to seize it. Proboscis is long, blind muscular tube that opens at anterior end called proboscis pore which is above the mouth Muscular pressure on fluid in the rhynchocoel causes the proboscis to be everted rapidly through the proboscis pore and exposes a sharp barb called a stylet that stabs prey Stylet release toxins into prey and sticky slime covered proboscis coils around it and moves to mouth for swallowing
Phylum Nemertea Nemerteans have true circulatory system and blood flow is irregular due to contraction of vessels and general body movements Flame bulb protonephridia associated with circulatory system to achieve true excretory role of removing wastes Have nerve ganglia with one or more pairs of longitudinal nerve cords Reproduce via fragmentation and regeneration plus a wide range of sexual reproductive strategies
Phylum Nemertea Nemerteans are mostly dioecious and fertilization is often external but some are hermaphroditic and may have internal fertilization A few species have ovoviviparous development that has egg develop into live young before being release by the parent Phylogeny of Nemerteans is still debatable due to larval development patterns and coelom formation issues
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 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 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