BIOL172 Exam 2: Lophotrochozoa

Lophotrochozoa

Triploblastic

Bilaterally symmetrical

Beginning of cephalization

- evolution of a concentration of nervous tissues and sensory organs in the head of the organism

Protostomes: include acoelomate, pseudocoelomate, and eucoelomate

Most possess either a lophophore feeding apparatus or a trochophore larva

Platyhelminthes (flatworms), Rotifera (rotifers), Annelida (annelids), Mollusca (mollusks)

Lophophore

Crown of ciliated tentacles that functions in feeding

Trochophore

Free-swimming larval stage

What group of animals shows a flat body, flame cells as part of their excretory system, and are important human parasites?

Platyhelminthes / Flatworms

Flame cells

- specialized cells used for excretion and osmoregulation

- remove waste, regulate water balance

- use cilia to move fluid

- alternative to kidney

Platyhelminthes

Flatworms

Acoelomate organisms

Free living and parasitic forms (Trematodes and Cestodes)

Lophophore and trochophore larvae are absent

- Polycladida larvae are considered to be homologous to trochophore larvae

Spiral cleavage

Uncertain phylogeny

Monophyletic clade:

- Monogenea (fish ectoparasites), Trematoda (flukes), Cestoda (tapeworms)

Monophyletic lineages:

- Catenulida (chain worms): budding reproduction, offspring not fully detached

- Rhabditophora (rhabdite bearers): rod-like structures discharged in the mucus produced by some free-living flatworms

Absent circulatory and respiratory systems

- gas and nutrient exchange dependent on diffusion and cell-to-cell junctions

Most monoecious, internal fertilization

Asexual reproduction by fission

Ciliate ventral part (free-living species)

Cerebral ganglia (concentrations of nerve cell bodies)

Platyhelminthes: Cestodes

Tapeworms

Lack a mouth and a gastrovascular cavity

Embryos penetrate intestinal wall and circulate to musculature

Rotifera

Wheel-bearer

Corona: feeding structure, appear to rotate under microscopic light

Mastax: muscular pharynx with toothy law-like structures

Microscopic aquatic organisms (mostly freshwater)

Filter-feeders

Usually free-swimming or planktonic organisms (the foot can secrete an adhesive substance)

Pseudocoelomates

Dioecious (male and female reproductive parts on seperate individuals) with sexual dimorphism (males and females look different)

Nemertea

Ribbon worms or proboscis worms

Marine (predominantly benthic), freshwater, damp habitats

Carnivores, predators (worms, clams, crustaceans)

Commensalism with mollusks

1cm to several m

Bilateral symmetry

Proboscis (long eversible / can shoot out tube, captures prey and defense) and Rhynchocoel (fluid filled internal cavity that houses the proboscis)

Contractile properties

Coelomic, but sometimes classified as acoelomates

Protonephridia: excretory tubules for osmoregulation

Dioecious or monoecious

Fragmentation is common

External fertilization (eggs and sperm are released in water)

Mollusca

Snails, slugs, squids, octopi, clams, oysters...

Soft body

Marine, freshwater, terrestrial

Bilaterally symmetrical

Cephalized

Triploblastic

Schizocoelous coelomates (body cavity COMPLETELY LINED by mesoderm)

- schizocoely: forms a coelom by a split in a solid mass of mesoderm

Gulls in aquatic species, lungs in terrestrial species

Molluscan Body Regions

Pallium: secretes a calcium-carbonate-hardened shell (most)

Foot: muscular, locomotion and anchorage (arms and tentacles in cephalopods)

Crop: storage pouch

Radula: abrasive tongue-like structure (except bivalves)

Gonad: reproductive system

Gill: respiratory structures

Classes of Mollusca

Caudofoveata and Solenogastres

- lack calcareous shell, worm-like, benthic marine habitats, eyeless, no tentacles, or nephridia

Monoplacophora

- bearing 1 plate

- posses a single, cap like shell that covers the dorsal body

Polypacophora

- bearing many plants

- chitons

Gastropod

Cephalopoda

Bivalvia

Scaphopoda

- boat feet, tusk shells or tooth shells

- 8 plates

- Hemocoel (open circulation system)

Mollusca: Gastropoda

Stomach foot

50% of aquatic and 100% of terrestrial

Asymmetrical with coiled shells

Embryonic development of torsion (counterclockwise rotation)

Mollusca: Bivalvia

2 valves

Flattened body, no conspicuous head or mouth, filter feeders, absent radula, nacreous substance

Mollusca: Cephalopoda

Carnivores, predators (beak-like jaw + radula)

Chambers with gas or water for buoyancy

Rapid color changing

Sepia or dark ink (melanin)

Dioecious, lays eggs after mating, no larvae formation

Chambered nautiluses are the only living cephalopods with an external shell

Annelida

annulus: little rings

Segmented worms (metamerism = true segmentation)

Marine, terrestrial, and freshwater habitats (humidity is necessary)

Polychaetes: marine annelids with multiple appendages, dioecious

Oligochaetes: earthworms and leeches, monoecious

Subclass Hirudinea: no bristles, suckers at both ends, seasonal clitellum

Chaetae / Setae: bristles made of chitin, forms parapodia

Parapodia: respiratory organs

Clitellum: reproductive-aid structure: mucus, cocoon

Teloblastic growth (growth behind the head)

Collagenous external cuticule

Lack a well developed respiratory system

- gas exchange occurs across moist body or via parapodia

Well-developed and complete digestive system

- filter feeders, blood feeders, predators, etc

How do polychaetes differ from oligochaetes in terms of structure and lifestyle?

Polychaetes

- many bristles / chaetes per segment

- have parapodia (paired paddlelike appendages used for movement and gas exchange)

- well developed head

- marine

- predators or filter feeders

- free swimming

Oligochaetes

- few chaete per segment

- no parapodia

- reduced / simple head

- soil or freshwater

- decaying organic matter

- slow moving