Annelids

Question 0

What are the 4 groups of convenience?

Answer 0

Acoelomates (no body cavity bar gut), Pseudocoelomates (“Aschelminthes”) Coelomates and others.

Question 1

What is a worm?

Answer 1

~18 Phyla of worm/worm-like organisms. 4 groups of convenience. All soft-bodied, bilaterally symmetrical, with veriform shape and at least 2-3x longer than wide.

Question 2

What are the notable evolutionary changes of the worms?

Answer 2

They moved from being diploblastic to triploblastic (+mesoderm).
The addition of the coelom, a space in the body which allows development of new organs that can function ‘indepenently’ of other processes. Cephalisation. Design by module - allows easy growth and specification.

Question 3

What are the relevant classes and subclasses of Phylum Annelida?

Answer 3

Classes: Polychaeta (bristle worms), Aeolosomata, and Clitellata (earthworms and leeches). Within Polychaeta there are the Errantia (free-moving) and Sedentaria (burrow or tube dwelling).

Question 4

What are the general features of class Polychaeta?

Answer 4

The body consists of many chaetigerous segments. The oldest segments are closest to the head. The prostomium contains the brain, the peristomium is the first true segment. The pygidium is the end of the end pf the gut track. The proliferation zone (segment blastema) is where the new segments are produced. The head may feature a palp (mouth parts) and tentacles.

Question 5

What are the main parts of the segments?

Answer 5

Septa: the divide between each segment. The first one from second & connective tissue.
Chetae: bristles.
Nephridium: kidney-like structure.
Nerve cord, blood vessels, muscles.

Question 6

What are the chaetae made of?

Answer 6

The acicula - a rod like structure that gives the chaetae structure and support. Made of protein.
As the worm ages the chaetae move from formative site to degenerative site. They are regenerated as they break.

Question 7

How do polychaetes feed?

Answer 7

Lugworms: make J/U shaped burrows, feed at bottom & defecate at top. Many spp have jaws as a substantial portion of the head - lots of muscle. Some are filter feeders, so selective. Some are suspension feeders, so non-selective Prospective feeders search, producing no mucous, and immediately ingest prey. Mucous nets are used by being thrown out, catching algae and then ingesting it.

Question 8

How do polychaetes move?

Answer 8

Swimming polychaetes use their chaetae to propel themselves. Peristaltic burrowers have less chaetae, usually if seen they’re actually gills.

Question 9

What is a specific technique of peristaltic burrowing?

Answer 9

The polychaete blows up its head, an elongating and forward movement.
This creates a gap in the sediment.
Chaetae prevent backward movement.
The polychaete move into the gap it’s made.

Question 10

What is polychaete worm reproduction like?

Answer 10

They are asexual - can bud off young through the proliferation zone.
Most reproduce sexually & are dioecious. Fertilisation occurs outside of the body.

Question 11

What is the life cycle of a polychaete?

Answer 11

Embryo -> trochophore -> metatrochophore -> nectochaete -> growing worm -> adult.

Question 12

What is Epitoky?

Answer 12

When individuals who are non-reproducing differentiate larger eyes and chaetae to swim up in the water column to reproduce, creating swarms of worms in the water column. The female can release pheromones to attract males.

Question 13

What is epitoky by epigamy?

Answer 13

The worm turns into an epitoke, reproduces and dies. Palolo worm swarms - very famous.

Question 14

What is epitoky by schizogamy?

Answer 14

Sexual forms are budded from the posterior ends of the organism, which enter the swarm, reproduce and then die. Asexual to sexual reproduction. Parent worm does NOT die.

Question 15

What are polychaete worms often used for?

Answer 15

Worm farming. They are good for sport fishing e.g. angling and also can be used as a disease free food for shrimp etc.

Question 16

What are the main features of class Aeolosomata?

Answer 16

They are mostly minute (<1cm) with around 25 spp.
There are freshwater and marine, living in interstitial spaces.
They are hermaphrodites but the ovaries and testes are in diff. segments.
Clitellum has ventral glands but they are residual and not homologous to clitellum of clitellata.
Simplified structure, relationship to other annelids not clear.
They feed on organic matter. Aeolosomata is an omnivore.

Question 17

What is the basic layout of Aeolosomata?

Answer 17

Similar to that of the polychaetes. Prostomium, mouth, peristomium. Chaetae on the segments.

Question 18

What are the defining features of class clitellata subclass oligochaeta?

Answer 18

No parapodia - adapted for burrowing so chaetae unneeded. Similar to proto-annelids. 5000spp, feed on detritus, 100-200 segments.

Question 19

What is the difference between megadriles and microdriles?

Answer 19

Microdriles are usually water based, whereas megadriles. Both require water for respiration and live in clay soils.

Question 20

What is the global distribution of oligochaetes?

Answer 20

1/3 of 5000spp are aquatic. They are predominantly terrestrial. Microdriles fully aquatic, megadriles both. 1100 freshwater spp, mostly freshwater.

Question 21

What is the external anatomy of an oligochaete?

Answer 21

They are segmented. The chaetae are found along the ventral side of the worm. Chaetae are produced by the chaetal sack.

Question 22

What are the pores in oligachaeta & what are they used for?

Answer 22

Dorsal or cebmic pores, and nephridial pores which are used for kidney like functions.

Question 23

What is the internal anatomy of the earthworm?

Answer 23

The oligochaete has 5 hearts. A ventral nerve cord and blood vessels run the length of the organism. The oligochaetes have all undergone cephilisation - the movement of sensory organs to the head. There are no eyes but pigments that are able to sense light and dark.

Question 24

How do oligochates reproduce?

Answer 24

Through asexual reproduction: it divides itself in half. All oligochates are hermaphrodites. The clitellum is critical in reproduction. They breed semi-continuously. They become covered in mucous & are held together by genital chaetae. There is no larval stage, they move from eggs to small adults.

Question 25

What is the clitellum and what is its use?

Answer 25

A band of tissue either around the entire worm (annular) or half of it (saddle, can be flared or non flared). In aquatic species it’s usually 2 segments, in terrestrial species 6-60 segments. It secretes mucous & albumin that is used in reproduction.

Question 26

What is subclass Branchiobdellida?

Answer 26

An ectoparasite. 100spp, <1cm but usually 2-3. Parasite on many f/water crayfish. Live on gills/carapace. Similar to oligochaetes and leeches.

Question 27

What is branchiobedillida anatomy like?

Answer 27

The head is a fusion of 4 segments - anterior. The mouth is replaced by a sucker, which contains the buccal cavity and 2 teeth. Sometimes the posterior also has a sucker. There are NO chaetae. The anus is midway down the organism. They are all hermaphrodites with internal fertilisation.

Question 28

Are branchiobdellids parasitic or commensal?

Answer 28

At low densities they have a cleaning function. At high densities they are parasitic. They become parasitic when there is not enough food due to overpopulation. Their net effect depends on the environment.

Question 29

What is subclass Hirudinea and what are their general features?

Answer 29

The leeches. 500spp, some drink blood but the majority do not. Most specialised annelid forms. Lack parapodia. Hermaphrodites. Have clitellum and lack a larval stage.

Question 30

What is the external anatomy of class Hirudinea?

Answer 30

They are dorsoventrally patterned. Their posterior and anterior ends are modified to suckers. The anterior sucker surrounds the mouth. There are an average of 33 segments, 1-4 are the mouth.

Question 31

What is the internal anatomy of class Hirudinea?

Answer 31

They have a thick fibrous cuticle resulting in a smaller caelum. The loose tissue (Botryoidal tissue) is used for secretory, storage and structural purposes. They have a ventral nerve cord and blood vessels. Muscles run longitudinally, circularly and obliquely. There is a nephridium in each segment.

Question 32

How do class Hirudinea move?

Answer 32

They use a longitudinal contraction, extending their body, attaching the anterior sucker to the ground, and then contracting muscles to shorten the body and move forward.

Question 33

How do class Hirudinea reproduce?

Answer 33

No asexual reproduction/generation of lost parts. They are protandric hermaphrodites, males first and then females. Hypodermic impregnation transports spermatophore from male -> female. Eggs laid between 2 days/months after fertilisation.

Question 34

What is the role that Hirudinea play in medicine?

Answer 34

Their saliva contains anticoagulants and prevent platelets from combining.