Chapter 17: Annelids and Allies

Annelids are what kind of organisms?

Coelomate Protostomes

- Meaning their coelom forms through schizocoely.

- Forms through Spiral Mosaic Cleavage

What are the three phylums in this chapter?

- Annelida

- Echiura

- Sipuncula

Where is the term "Annelida" derived from?

The Latin root annelus (little ring)

What does the Phylum Annelida consist of?

- Earthworms

- Leeches

- Polychaete worms

Annelids divide themselves into segments known as _______

Metameres

Annelids have rings known as what?

Annuli

What are Annuli?

Rings found in Annelids.

Some Annelids have chitinous bristles called what?

Setae

What habitats to Annelids inhabit?

Worldwide

- Nearly all habitats

What is characteristic about the heads in Annelids?

They have ancestral parapodia attached.

What type of symmetry do Annelids have?

Bilateral

What kind of organisms are Annelids (in terms of layers)?

Triploblastic Organisms

In Annelids, what does the epithelium secrete?

moist cuticle

How is the digestive system structured in Annelids?

It is complete instead of segmented.

How do Annelids reproduce?

They reproduce asexually through fission and fragmentation

Annelids typically have a pair of kidney-like organs per segment for waste removal. What are these organs?

Metanephridia

Do Annelids have an open or closed circulatory system?

Closed Circulatory System

How is the head of an Annelid structured?

Two-Part Head

- A Prostomium

- A Peristomium (behind the prostomium)

What is the terminal portion of an Annelid called?

The Pygidium (tail)

Where are newer segments located in an Annelid?

Just in front of the pygidium.

Where are older segments located in an Annelid?

At the front of the Annelid.

How is each segment of an Annelid structured?

Each segment typically has its own circulatory, respiratory, nervous, and excretory structures.

- With the EXCEPTION of Leeches

What about their internal structures makes leeches unique compared to other Annelids?

Coelom is filled with fluid

- Makes a hydrostatic skeleton

Where is the name Polychaeta derived from?

From the Greek roots polys (many) and chaite (long hair)

Are most Polychaetes marine, freshwater, or terrestrial?

Marine

- Can be up to 3m long

Where do polychaetes live?

Under rocks, in crevices, shells, in sediment, etc.

Members of the Class Polychaeta are a significant component of marine what?

Food chains

What is the general body plan of a Polychaete like?

Well differentiated head with good sense organs, paired parapodia on most segments.

Polychaetes have many __________

Setae

- Bristles present on the body of an organism that aid with attachment to a substrate.

Polychaetes are usually divided into what two forms?

Sedentary and mobile forms

What are characteristics of the prostomium of a Polychaete?

- Sometimes retractile

- Holds eyes, tentacles, and sensory palps

What are characteristics of the peristomium of a Polychaete?

- It surrounds the mouth

- Has setae, palps, & chitinous jaws in predatory forms

What are all the guts a Polychaete has?

Foregut, midgut, & hindgut

Mobile species of Polychaetes are usually _____________

Scavengers or Predators

Sedentary species of Polychaetes are usually ______________

Filter feeders

What body parts do Polychaetes utilize for gas exchange?

Parapodia and gills

Smaller species of Polychaetes use what?

Diffusion across the body wall

In Polychaetes, there are three different types of kidneys that are dependent on species. What are they?

1. Protonephridia

2. Metanephridia

3. A mix of both

How many kidneys can polychaetes have?

Up to three

What type of nerve cord do Polychaetes have?

Double Ventral Nerve Cord

Polychaetes possess eyes, statocysts, and __________

nuchal organs

Polychaetes possess eyes, ___________, and nuchal organs.

Statocysts

Polychaetes possess __________, statocysts, and nuchal organs

Eyes

- Anything from simple eyespots to eyes with good visual acuity & complicated structures (lens & cornea)

In polychaetes, what body parts are chemoreceptive?

The nuchal pits

In polychaetes there are usually no permanent ___________

Sex organs

- Gonads show up temporarily in the form of swelling.

- Gametes shed into the coelom

Is fertilization internal or external in polychaetes?

External

- Have trochophore larvae stage

What groups are representative of the Polychaetes in this chapter?

Genus Nereis

Scale Worms

Fire worms

Tube worms

Genus Nereis consists of what?

Clam/Sand Worms

Where do members of Nereis live?

Mucus-lined burrows in sediment

How do Nereis feed?

They come out at night to hunt.

- Feed on small animals, seize food with jaws, food swallowed as worm withdraws pharynx

How do Nereis move?

They creep along, but can swim quickly by undulation (wave-like up and down swimming)

What examples of Nereis did Roelke show us?

- Video of a Nereis

- Video tutorial on how to catch sand worms to use for bait

What is the body of a scale worm like?

Flattened

What type of feeding pattern do scale worms exhibit?

Carnivorous feeding

How & where do most scale worms live?

Most exist in commensal relationships

- Live in burrows of other polychaetes or with cnidarians, mollusks, or echinoderms

What organisms have hollow & brittle setae that secrete venom?

Fire worms

What is unique about the setae of fire worms?

They puncture the attacker and break off in the wound, depositing venom.

What do fire worms feed on?

Cnidarians

How do tube worms feed?

Some are sedentary and are filter feeders, while others deposit feed by extending tentacles to find bigger food.

Featherdusters are what kind of organisms and have what for filter feeding?

- Tube worms

- Radioles

What class of organisms contains the Beard worms?

Class Siboglinidae

What did Class Siboglinidae (the beard worms) used to be called?

Pogonophora

- From the Greek root pogon (beard)

Why were Beard Worms (Class Siboglinidae) unknown before 1900?

Because they are almost exclusively associated with deep sea hydrothermal vents

How is the digestive system of a beard worm (Class Siboglinidae) structured?

They have no mouth or digestive tract

- Absorb nutrients from seawater

- Have mutualistic associations with chemoautotrophic bacteria, contained in an organ called a trophosome

Beard worms (Class Siboglinidae) have what kind of relationship with bacteria?

Mutualistic

Beard worms have mutualistic relationships with what?

Chemoautotrophic Bacteria

- Contained in an organ called a trophosome

Where do beard worms live?

In the mud on the ocean floor

- They secrete long, chitinous tubes

- They can only be obtained by dredging

How is the body of a beard worm structured?

They have long, cylindrical bodies covered with cuticle.

Structures:

- Forepart

- Trunk

- Small, segmented opisthosoma

Beard worms have a well-developed ______ circulatory system.

Closed

How are sexes organized in beard worms?

Sexes are separate

- A pair of gonads will be located in the trunk

What type of cleavage do beard worms exhibit?

Somewhat spiral, schizocoelic

- Weird and poorly known cleavage

The embryos of beard worms are what?

Worm-shaped, ciliated, and are carried by water currents.

What is included in the Clade Clitellata?

Worms, their close relatives, and leeches.

What unique characteristic categorizes organisms under the Clade Clitellata?

A unique reproductive structure called a clitellum.

- A ring of secretory cells in the epidermis (band on a worm)

When is the clitellum visible on leeches?

During reproductive season.

General Information about the Clade Clitellata

- They have no parapodia

- They are all monoecious

- Young develop in a cocoon, so larval stage is not visible (appear as miniature adults)

What organisms are included in the Class Oligochaeta?

Worms

How many species of oligochaetes are there?

3,000 +

- Most are terrestrial or marine, a few parasitic

Do oligochaetes have setae?

Yes, usually. However, they are less numerous than in polychaetes.

Which forms of oligochaetes usually have longer setae?

Aquatic forms

How are oligochaetes able to form and function?

by peristaltic movement

What is peristaltic movement?

Contract and relax the circular muscles while using a specific body point as an anchor by contracting longitudinal muscles

oligochaetes are scavengers

decaying vegetation and animal matter

oligochaetes food is drawn

in by muscular pharynx

• - food stored in crop

Oligochaetes digestive system

food is stored in a crop

moved to gizzard, where it is ground

digestion and absorption in intestine

• - folded into a typhosole

Oligochaetes have a yellowish chloragogen

tissue to synthesize glycogen and fat.  When cells are full they are released into coelom as eleocytes.

Oligochaetes have a double transport system

Coelomic fluid and circulatory fluid

How many blood trunks do Oligochaetes have

Five main blood trucks through body

Oligochaetes Dorsal vessel

above the alimentary canal from pharynx to anus

Oligochaetes Aortic arches

maintain steady blood pressure in dorsal vessel

Oligochaetes Single ventral vessel

serves as aorta

Oligochaetes Circulation and respiration

Blood contains hemoglobin to carry oxygen

Gas exchange occurs over moist skin

Almost all Oligochaetes have metanephridia

Each one occupies parts of two separate segments

Oligochaetes have a ciliated funnel called

•nephrostome leads to loops and then an opening called the nephridiophore, which acts as a bladder. 

Waste discharged to the outside through another nephridiophore.

Oligochaetes Aquatic species secrete waste as ammonia

terrestrial species sometimes use urea, but can use a combination of both

Salts and water can pass across integument

Oligochaetes pair of cerebral ganglia

act as brain

In Oligochaetes Neurosecretory cells in brain preform

endocrine functions

Oligochaetes possess “giant axons“ in nerve cord

• for very efficient signal transmission

have some learning ability

What is the reproductive system of oligochaetes?

Oligochaetes are monoecious and usually simultaneous hermaphrodites.

How many sets of gonads do oligochaetes have?

have multiple sets of gonads.