1. 4. Bilaterally Symmetrical Worms

2. 4. Bilaterally Symmetrical Worms
Marine worms, and organisms hereafter, kick it up a notch exhibiting bilateral symmetry (just like humans).
Instead of addressing front and back, we will discuss anterior, posterior, dorsal and ventral.
Also pick up a CNS!
Bilateral symmetry, and all that goes with it, results in enhanced motion and sophisticated behaviors.

3. 4. Bilaterally Symmetrical Worms
Anterior – head with brain or accumulation of nerve cells and sensory organs like eyes
Posterior – bottom/backside
Dorsal – back
Ventral – Belly
Bilateral symmetry allows organisms to actively pursue prey and develop sophisticated behaviors

4. A. Flatworms: Phylum Platyhelminthes
Simplest flatworms – has CNS
Simple brain – aggregation of nerve cells
Several nerve cord running from brain through length of body
Nervous system coordinates movement of well-developed muscular system.

5. A. Flatworms: Phylum Platyhelminthes
Gut has an opening
Have a middle layer of tissues, in developing embryos it is called mesoderm
Mesoderm gives rise to muscles, reproductive system and other organs
20,000 known species
Turbellarians are the most common – striking color patterns
Live in or on oysters, crabs, and other invertebrates

6. A. Flatworms: Phylum Platyhelminthes
Flukes (trematodes)
Largest group (6,000 species)
All parasitic
Feed on tissues, blood, or intestinal contents
Adult flukes live in vertebrates
Larvae may inhabit invertebrates like snails and clams or vertebrates like fish
Larva must be eaten by a vertebrate
Common in fish, seabirds, and whales

8. A. Flatworms: Phylum Platyhelminthes
Tapeworms (cestodes)
Parasitic
Have long body with repeating units
Head attaches to walls of gut by suckers and hooks
Lack gut or mouth
Absorb nutrients from host across body wall
Found in invertebrates and vertebrates
Longest recorded in sperm whale was 50 feet!!

9. B. Ribbon Worms: Phylum Nemertea
More complex than flatworms
Complete digestive tract (mouth, gut, anus)
Have a circulatory system
Proboscis – long flesh tube to capture prey
Everted in cavity above mouth
Feed on worms and crustaceans
900 species, mostly marine
Found in all oceans, most common in shallow temperate waters

10. B. Ribbon Worms: Phylum Nemertea
Some nocturnal, some brightly colored found under rocks at low tides
Elastic, and proboscis may extend to a meter or more beyond body length
Longest invertebrate – reaches 100 ft!!

11. C. Nematodes: Phylum Nematoda
Roundworm numbers are staggering in the marine world, yet hardly ever seen
Many are parasitic and found in most marine organisms.
Adapted to live in sediment or tissues of other organisms

12. C. Nematodes: Phylum Nematoda
Typically pointed at both ends
Anus lies within body cavity filled with fluid that transports nutrients
Layer of muscle in the tough but flexible body pushes and squeezes against the fluid which acts as hydrostatic skeleton that provides support and aids in locomotion

13. C. Nematodes: Phylum Nematoda
10,000 to 25,000 species and estimates that half a million still undiscovered
Anisakis and few related inhabit seals and dolphins
Larvae found on flesh of many types of fish and may infect humans who eat raw or poorly cooked fish
Often larvae are vomited or coughed up without further complications
Sometimes penetrate into walls of stomach or intestine causing symptoms similar to ulcers

14. D. Segmented Worms (phylum Annelida)
20,000 spp. known as Annelids
First example of segmentation.
Gut through all segments and lies in cavity known as coelom
Coelom fluid filled and divided by partitions

15. D. Segmented Worms (phylum Annelida)
Segments acts as hydrostatic skeleton contracting in sequence by muscles in body
Efficient crawlers and burrowers

17. i. Polychaetes (class Polychaeta)
Body segments of most have a pair of flattened extensions or parapodia
Parapodia have stiff sharp bristles (setae)
Have closed circulatory system
Muscular contractions help circulation of blood
In small organisms, oxygen in water can easily move across body wall to all tissues
Large organisms have gills on parapodia
Parapodia - One of the fleshy paired appendages that function in locomotion and breathing
Gills - thin wall extensions of body that have capillaries where gas exchange takes place

18. Sandworm Nereis

19. i. Polychaetes (class Polychaeta)
Have planktonic larval stage – trochophore
Biologists compare larvae stage of polychaetes with other invertebrates to examine evolutionary relationships
Body 5-10cm
Many crawl and hide under rocks
Have several pairs of eyes and other sensory organs
Use proboscis with jaws to capture prey
Others are deposit feeder

20. i. Polychaetes (class Polychaeta)
Many live in temporary or permanent tubes made from mucus, proteins, bits of seaweed, cemented mud particles, sand grains, or tiny fragments of shells
Tube dwelling have reduced parapodia
Have tentacles which have cilia and mucus that catch organic particles and move them to their mouths
Some use feathery tentacles covered with cilia to capture, sort, and transport particles
Some of calcium carbonate tubes built on rocks and other surfaces

21. This feather-duster worm, Sabella melanostigma, is a perfect example
of beauty, form and function.

22. i. Polychaetes (class Polychaeta)
Some are ptanktonic and use flat parapodia to swim
The Palolo worm break off & posterior half swims up to surface to spawn
Timed with phases of the moon
Some places people with gather worms for food
Live on external surface of sea stars & sea urchins, in burrows of invertebrates, and shells of hermit crabs

23. Beard worms (pogonophorans)
Highly specialized lack gut and mouth
Tuft (thousands of long tentacles) absorb nutrients in dissolved water
Some have symbiotic relationship w/ bacteria
Bacteria use the nutrients to manufacture food for the worm
Mostly restricted to deep water
4-7 feet
Related vestimentiferans grow larger and found at hydrothermal vents

25. ii. Oligochaetes (subclass Oligochaeta)
Small and found in mud and sand feeding on detritus
Lack parapodia

26. iv. Leeches (class Hirudinea)
Blood sucking found attached to fish and other invertebrates
Distinguished by suckers and no parapodia

27. E. Peanut Worms (phylum Sipuncula)
Soft unsegmented bodies
Burrow in muddy bottoms, rocks, corals, and empty shells
All are marine living in shallow waters
Deposit feeders
Long anterior portion of body contains mouth and set of small lobes or branching tentacles
Tentacles can be pulled into remaining body, become compact
1-35 cm in length

28. F. Echiurans (phylum Echiura)
Soft segmented sausages buried in mud or in coral
Look like peanut w/out retractable spoon-like or forked proboscis
Deposit feeders that use proboscis to gather organic matter
Urechis caupo lives in U-shaped tubes in mud