Back to Chapter 7

Back to Chapter 7The Marine Worms

So far, this chapter…

• Marine animals without a backbone• Vertebrates vs. invertebrates– Vertebrates have a backbone (a row of bones

called vertebrae)• 97% of all animal species are invertebrates• Animals – Multicellular– Cannot manufacture own food

Porifera - Sponges

• Sessile• Filter feeders• No true tissues or organs• Suspension feeders(eat food

particles suspended in water)

• Filter feeders )actively filter food particles

Types of Symmetry (Body Types)

Cnidarians: Radial symmetry

• Phylum Cnidaria• Also called coelenterates• Oral surface and aboral surface• Nematocysts (stinging structures

found in cnidocysts)• Two forms: polyp and medusa• Two layers of cell form a body wall– Epidermis external– gastrodermis lines gut

• with gelatinous mesoglea in between

Types of Cnidarians

• Hydrozoans –sessile, feathery or bushy colonies of tiny polyps

• Siphonophores – hydrozoans that form drifting colonies of polyps

• Scyphozoans – larger jellyfish– Large bell, swim with rhythmic

contractions of the bell• Anthozoans –lack a medusa stage– Sea anemones, corals, gorgonians

Ctenophora

• Comb jellies• Radial symmetry• Eight rows of ciliary

combs• Capture prey using two

long tentacles– Sticky cells named

colloblasts

Worms, Worms, Worms!

What are worms?

• Commonly, animals with long, thin bodies and no legs

• Bilaterally symmetrical invertebrates

Why bilateral symmetry?

• Allows animals to be more active– To capture prey– To develop sophisticated behaviors

• Implies development of an anterior end with a head, brain, and eyes.

Main groups of marine worms:• Flatworms• Ribbon worms• Nematodes - roundworms• Segmented worms :

• Annelids• Polychaetes• Oligochaetes• Leeches

• Peanut worms• Echiurans• Arrow worms – chaetognaths• Acorn worms

Flatworms: Platyhelminthes

• Dorsoventrally flattened• Simplest animal with

tissues organized into real organs and organ systems

• Brain and central nervous system

• Only one opening to gut• No body cavity

Flatworms

Flatworms

• Flukes or trematodes– All are parasitic– In fish, seabirds, whales

• Tapeworms or cestodes– Body in repeated units– Lack a mouth or gut– Found in sperm

whales,fish

Parasites in local fish

http://www.dfg.ca.gov/marine/parasites.asp

Ribbon worms: Nemertea

• More complex than flatworms

• Complete digestive tract– Gut with mouth and anus

• Closed circulatory system• Proboscis– Used to entangle prey– Secretes toxins, may have a

spine• 5mm- 30 m in length!

Nematodes• Roundworms• Pseudocoelem

– Tube-within-a-tube body plan

• In sediments • Some parasitic

– Seals, dolphins– Risk in sashimi, ceviche

• Small, slender, cylindrical bodies

• Gut, ends in anus– Lies within a body cavity

• Hydrostatic skeleton

Roundworm life cycle

Body cavity development

Flatworms

Roundworms

True coelom

• Segmented worms • Humans

• Gut lies in the coelom

Segmented worms: Annelida• Earthworms and marine worms• Body consists of similar segments• Gut goes through all segments• Gut lies in coelom• Hydrostatic skeleton• Longitudinal and circular muscles

– Efficient crawlers and burrowers– Longitudinal muscles lengthen and shorten segments– Circular muscles increase or decrease diameter.

• Closed circulatory system• Respiration by diffusion

bristleworm

Polychaetes• All marine annelids are polychaetes• Each body extension has a pair of parapodia– Flattened extensions– May be stiff, sharp bristles or setae

Annelida, Christmas tree worm

Polychaete variety

• May burrow• May crawl• May live in tubes • May be planktonic– Palolo worm

• Swarming• Timed by moon cycle• Bottom half of body breaks off and swims to surface to

spawn.

• Trochophore – planktonic larval stage

Leeches

• Blood sucking parasites that attach to marine fish and invertebrates

NOT Worms?

• Larval stages: grubs, caterpillars, maggots• Legless amphibians and reptiles• Insects • Centipedes

Anguis, or slow worm

Grubs: beetle larvae centipede

Marine Worms• Annelida (segmented worms) • Chaetognatha (arrow worms) • Gnathostomulid (jaw worms) • Hemichordata (acorn/tongue worms) • Nematoda (roundworms) • Nematomorpha (horsehair worms) • Nemertea (ribbonworms) • Onychophora (velvet worms) • Phoronida (horseshoe worms) • Platyhelminthes (flatworms) • Priapulida (phallus worms) • Sipuncula (peanut worms)

Sipuncula – peanut worms

•Some burrow in mud or rock•Some live in crevices•Shaped like a peanut•Unsegmented. •Intestine forms a loop•Retractable forward section, called the introvert•No circulatory or respiratory systems•1-35 cm long

EchiuraSoft, unsegmented, sausage-likeLike sipunculans, except for a non-retractable, spoon-like or forked proboscisDeposit feedersProboscis gathers organic material

The “fat innkeeper” lives in mud in a U-shaped tube.

Arrow worms - Chaetognatha•All marine.•Planktonic.•Transparent.•Fish-like tail and fins.•Head with eyes, grasping spines and teeth.•4mm-10cm in length.•Hermaphrodites.•Remain motionless and then dart rapidly toward prey.

Acorn worms - Hemichordata•Evolutionary link between Echinoderms and Chordata•Dorsal, hollow nerve cord•Openings along the anterior of the gut, gill slits,•Body in three parts•Worm-like deposit feeders•Live free or in U-shaped tubes•Use a thick, muscular proboscis to collect organic material from sediment

• Sea worm is a general term that may refer to a number of phyla of animals, or may refer specifically to:• Acanthocephala, parasitic worm • Annelida, segmented worms • Chaetognatha, arrow worms • Cycliophora, lobster worms • Entoprocta • Echiura, spoon worms • Gastrotricha, microscopic • Gnathostomulida, microscopic • Hemichordata • Kinorhyncha • Loricifera • Micrognathozoa, microscopic • Nematoda, round worms • Nematomorpha, parasitic worms • Nemertea, ribbon worms • Phoronida, horseshoe worms • Platyhelminthea, flatworms • Priapulida • Sipuncula, peanut worms • Xenoturbellida

Summary of distinguishing features

Annelida[3]Recently merged into Annelida[5] Closely-related Similar-looking phyla

Echiura[16] Sipuncula[17] Nemertea[18] Arthropoda[19] Onychophora[20]

External segmentation Yes no no Only in a few

species Yes, except in mites no

Repetition of internal organs Yes no no Yes In primitive forms Yes

Septa between segments In most species no no No No No

Cuticle material collagen collagen collagen none α-chitin α-chitin

Molting

Generally no;[13] but some polychaetes molt their jaws, and leeches molt their skins[21]

no[22] no[22] no[22] Yes[15] Yes

Body cavity

Coelom; but this is reduced or missing in many leeches and some small polychaetes[13]

2 coeloms, main and in proboscis

2 coeloms, main and in tentacles

Coelom only in proboscis Hemocoel Hemocoel

Circulatory system Closed in most species

Open outflow, return via branched vein

Open Closed Open Open