Gnathiferans and Smaller Lophotrochozoans

Protostomia

Lophotrochozoa Ecdysozoa

Clade Protostomia divided into two subclades- Lophotrochozoa & Ecdysozoa

• most lophotrochozoans are acoelomate (e.g. Platyhelminthes)• some phyla we’ll discuss today are acoelomate, others pseudocoelomate

• RECALL: pseudocoelomate body has an internal cavity (pseudocoelom) surrounding the gut and is only partially lined with mesoderm

• The pseudocoelom provides a cavity within which digestive, excretory, & reproductive systems can be elaborated from mesoderm• The pseudocoelom may be filled with fluid or gelatinous material with mesenchyme cells.• It serves as a hydrostatic organ or permits circulation of body fluids.

Gnathifera

Four taxa in the Clade Gnathifera• characterized by complex cuticular jaws

• cuticle – tough, flexible non-mineral material; often provides protection• Phyla of the Clade Ganthifera

• Gnathostomulida

Gnathifera

Four taxa in the Clade Gnathifera• characterized by complex cuticular jaws

• cuticle – tough, flexible non-mineral material; often provides protection• Phyla of the Clade Ganthifera

• Gnathostomulida• Micrognathozoa

Gnathifera

Four taxa in the Clade Gnathifera• characterized by complex cuticular jaws

• cuticle – tough, flexible non-mineral material; often provides protection• Phyla of the Clade Ganthifera

• Gnathostomulida• Micrognathozoa• Rotifera

Gnathifera

Four taxa in the Clade Gnathifera• characterized by complex cuticular jaws

• cuticle – tough, flexible non-mineral material; often provides protection• Phyla of the Clade Ganthifera

• Gnathostomulida• Micrognathozoa• Rotifera• Acanthocephala

Four Lophotrochozoan Phyla of unknown relationship to members of the Clade Gnathifera• Cycliophora• Gastrotricha• Entoprocta• Ectoprocta

Gnathifera: Phylum Gnathostomulida

• called “jaw worms”• very small (< 2mm) members of the meiofauna

• small animals that live in the interstitial spaces between grains of sand

• ~ 80 species

Gnathifera: Phylum Gnathostomulida

• Form & Function:• Epidermis ciliated (each epidermal cell has a single cilium)• move by gliding or swimming in spirals or loops• Nervous system not well known• Feed by scraping bacteria from substrate using jaws on the pharynx• body is acoelomate & has blind gut• No circulatory system

•Excretion & gas exchange via diffusion

• Reproduction:• not well known• appear to be hermaphroditic & cross-fertilize

Gnathifera: Phylum Micrognathozoa

• Only 1 species known, described in 2000• Tiny animal of meiofauna (142 um)• body = two-part head, thorax, & abdomen• epidermis w/ dorsal plates, ventral w/out• locomotion by cilia, ventral adhesive pad• 3 pairs of complex jaws• complete gut, but anus opens only periodically• excretion through 2 pairs of protonephridia• Reproductive system not well known

• only female organs found• perhaps parthenogenetic

Head

Thorax

Abdomen

1 2 33 pairs of jaws

Gnathifera: Phylum Rotifera• ~ 2000 species

• 40 um to 3mm long

• found in many ecological conditions• Benthic, pelagic, aquatic vegetation, meiofauna, epizoic (on body of other animal), parasitic

• can endure long periods of desiccation• some have been dried for 4 years prior to reviving after addition of water• some can survive extreme temps. (-272 degrees C, -458 degrees F)

Gnathifera: Phylum RotiferaForm & Function:External Structure• ciliated head (corona), Trunk, Foot• body non-ciliated & covered w/ cuticle

• likely contributes to desiccation resistance• first appearance of cuticle (important skeletal component in nematodes & arthropods)

• Mouth located inside corona, cilia aid in feeding & locomotion• foot often has 2 to 4 toes• ringed cuticle on foot makes foot retractable• foot contains pedal glands that secrete adhesive material

Head

Trunk

Foot

Gnathifera: Phylum RotiferaForm & Function:Internal Structure• Digestive system complete with mouth and anus• pharynx (mastax) has hardened jaws (trophi) to grind food particles• salivary and gastric glands aid in extracellular digestion that occurs in stomach• Excretory system w/ 2 protonephridial tubules each with flame cells• Nervous system with bi-lobed brain

• sensory organs = eyespots (photoreception), sensory bristles & antennae in some

Gnathifera: Phylum RotiferaReproduction:• Dioecious & sexually dimorphic (females larger than males)• in some, males are entirely unknown; in others males only exist for a few weeks a year• In females repro system contains ovaries & yolk glands (germovitellaria)

• yolk supplied to developing embryo, rather than through special yolk cells (as in vitellaria of platyhelminths)

• in female-only groups repro is through parthenogenesis (diploid females produce diploid eggs that hatch into diploid females) – mature in a few days

Gnathifera: Phylum RotiferaReproduction in Class Monogonata very complex

2N

2N

2N

2N

2N

2N

2N

2N

2N

N

N

N

2N

DiploidParthenogenesis

SexualReproduction

Amicticfemale

Amicticfemale

Amicticfemale

Amicticfemale

Micticfemale

haploidegg

male

fertilization meiosis

Stimulus: crowding, diet, photoperiod

• During most of the year diploid females produce diploid amictic eggs (develop into diploid amictic females) – Diploid parthenogenesis

• amictic eggs are incapable of being fertilized

• Temporary habitats• Env. Factors cause amictic eggs to develop into diploid mictic females• mictic females produce haploid eggs• if not fertilized, develop into males• if fertilized, become thick-shelled mictic eggs that are dormant & survive winter• favorable conditions return, develop into amictic females

Gnathifera: Phylum Acanthocephala

• called spiny-headed worms

• ~ 1100 species

• most endoparasitic in intestines of fish, birds, & mammals (rarely humans)

• intermediate host = arthropods (crustaceans & insects)

• range in size from 2mm to >1m

• sexually dimorphic (females larger than males)

Gnathifera: Phylum Acanthocephala

Form & Function• body surface covered in crypts

• has extensible proboscis with many recurved hooks

• no resp. or digest. system

• excretory system w/ protonephridia & flame cells

crypts

Gnathifera: Phylum Acanthocephala

Reproduction:• dioecious• female repro. System has uterine bell that sorts eggs prior to passing them to the uterus• fully developed eggs = long & slender

• immatures sorted and retained for further development

• eggs discharged in host feces• hatch when eaten by intermediate host

Additional Lophotrochozoan PhylaPhylum Cycliophora:

• first discovered in 1995• only 3 species known• tiny animals (< ½ mm)• very specialized habitat – They live on the mouthparts of lobsters!• attach to mouthparts using adhesive disc• feed using ring of cilia around mouth• acoelomate with complete gut• epidermis surrounded by cuticle

Adhesive disc

Additional Lophotrochozoan PhylaPhylum Cycliophora:

Life Cycle:• complex (sexual & asexual repro)• male and female larvae produced by budding• male larva released from feeding individual & settles on top of individual containing female larva• male larva produces a new male w/ repro organs that mates with the female larva• fertilized egg develops inside mother and consumes it• newly developed larva swims to new lobster host & produces new feeding animals via budding

Adhesive disc

Additional Lophotrochozoan PhylaPhylum Gastrotricha:• ~450 species• found in fresh & brackish water & marine

• body generally elongated w/ bristles, spines, or scales on the surface• tail elongated & forked into adhesive tubes

Additional Lophotrochozoan PhylaPhylum Gastrotricha:

• Adhesive tubes have dual-gland system for attachment & release (similar to Turbellarians)• no specialized respiratory or circulatory structures• acoelomate w/ complete digestive system

• Mouth, pharynx, stomach-intestine, anus• feed on algae, protozoa, & bacteria; use cilia on head• digestion appears extracellular, but details unknown• excretion through protonephridia, but rather than flame cells they have cylindrical solenocytes with a single flagellum

Additional Lophotrochozoan PhylaPhylum Gastrotricha:

Reproduction:• generally hermaphroditic (monoecious)• in those with separate sexes, males so rudimentary they are effectively parthenogenetic females• similar to rotifers, have rapidly developing thin-shelled eggs & thick-shelled dormant eggs• juveniles mature in a few days

Additional Lophotrochozoan PhylaPhylum Entoprocta:• ~150 species• tiny (< 5mm), sessile & resemble hydra-like cnidarians• tentacles ciliated• solitary or colonial• All but one marine

Additional Lophotrochozoan PhylaPhylum Entoprocta:Form & Function• body called the calyx which has a crown of tentacles• attaches to substrate by stalk w/ adhesive disc• gut is U-shaped, mouth & anus open inside circle of tentacles

• Entoprocta actually means “anus within”• cilia generate water currents for feeding• Digestion extracellular• Excretion by protonephridia & flame cells• circulatory & respiratory systems absent

Calyx

Stalk

Adhesive disc

Reproduction• some dioecious• some monoecious• most protandrous hermaphrodites

• first produces sperm and then eggs

Additional Lophotrochozoan PhylaPhylum Ectoprocta (also called Bryzoans – moss animals):• Representative of group of animals characterized by feeding structure called lophophore (unique arrangement of ciliated tentacles attached to body wall) •~4500 species• sessile & colonial• both freshwater & marine

Additional Lophotrochozoan PhylaPhylum Ectoprocta (also called Bryzoans – moss animals):Form & Function:• each individual of a colony is a zooid• zooids live in chamber called zoecium (secreted by epiderm.)

• gelatinous, chitin, or calcium (can be fibrous & flexible or quite hard)

• body = polypide & cystid• polypide includes feeding structures, digestive tract, & muscles• cystid includes body wall & secreted exoskeleton (zoecium)

zooids

Additional Lophotrochozoan PhylaPhylum Ectoprocta (also called Bryzoans – moss animals):Form & Function:• live a type of “jack in the box” existence

• Pop up to feed, can quickly retract when disturbed

• zoecium has small “trap-door” called an operculum• cilia on tentacles for feeding• complete U-shaped gut, anus open outside of feeding tentacles (hence the name)• Digestion extracellular in stomach, intracellular in intestine• no resp., circ., or excretory organs• no specialized sense organs

Additional Lophotrochozoan PhylaPhylum Ectoprocta (also called Bryzoans – moss animals):Reproduction:• Most hermaphroditic• Each colony begins with a single zooid that settles & develops into an adult called an ancestrula• ancestrula buds asexually producing a colony of zooids

Figure 9_10b

Statoblast from freshwater ectoproct Cristatella

http://www.youtube.com/watch?v=utPtyceR_YY

http://www.youtube.com/watch?v=g1H3e0Iynso&feature=related

Fluid-filled space within the mesoderm

Fluid-filled space within the mesoderm

Importance:• Mesodermal lining of coelom provided attachment-points for organs (mesentaries)• ideal locations for vessel networks• suspended alimentary canal allowed greater specialization of organ systems• allowed evolution of larger, more complex animals