BSC2010L Invertebrate Dissection Quiz

Earthworms and Crayfish

Dorsal Side (Light or Dark?)

Dark

Ventral Side (Light or Dark?)

Light

How do you identify the tail (posterior) end?

Farthest from the clitellum

How do you identify the head (anterior) end?

Closest to the clitellum

Clitellum (function AND appearance)

Light band; secretes sacs to form the egg’s cocoon, where fertilization and embryo development occur

Setae (function AND appearance)

On ventral side (belly); bristles that help grab soil to move worm forward, anchor the body, and burrow

Aortic arches

Hearts, pumping blood (dorsal to ventral direction) through blood vessels

Crop

Posterior end of esophagus; temporary food storage

Gizzard

Grinds food using muscles and swallowed sand or grit

Nephridia

Excretory organ; removes metabolic wastes; regulates water and salt balance

Nephridiopores

Fluid and wastes from nephridia leave the body through external openings

Seminal vesicles

Store worm’s sperm (produced in the testes) for maturation

Seminal receptacles

Receive and store sperm from another worm during mating

Seminal receptacles versus Seminal vesicles

Seminal receptacles receive sperm from another worm during mating; seminal vesicles store the worm’s own sperm

Suprapharyngeal (cerebral) ganglia

Simple brain, coordinating sensory information, movement, and responses to stimuli

What is peristalsis?

Muscular contractions that shorten or lengthen a worm’s body

How do earthworms reproduce?

Earthworms are hermaphroditic (monoecious), which means they have both male and female reproductive parts. They do not self fertilize, so they reproduce by joining and fertilizing each other’s eggs. Later, a tube of mucus is secreted by the clitellum (a raised band), which secretes a sac (tube of mucus), forming an egg case that slips off the worm’s body. This is where the eggs develop. Then, young worms hatch out into the soil.

Carapace (location)

Protects the internal organs like cephalothorax and underlying structures, including the gills

Rostrum (location)

Protects the anterior region around the eyes and pointed projection to the head

Swimmerets (location)

Appendages and the first pair can be used to determine sex

Periopods (location AND function)

Used for walking or cleaning or handling food (legs)

Uropods/telson (location AND function)

Form part of the tail fan used for rapid backward swimming; telson middle piece of tail fan, uropods are the two side pieces on each side (four total; five including telson)

Chelipeds (location AND function)

Structures used to capture and hold prey and provide defense (claws)

Antennae

Chemoreceptor

Digestive glands

Secrete enzymes into stomach for chemical digestion; primary site for nutrient absorption and energy storage

Gastric mill

Grinding in the cardiac stomach; chitinous teeth; breaks down and grinds food particles before passing into digestive tract

Green glands

Primary excretory organs; waste excreted through pores near the base of the antennae

Mandibles/maxillipeds

Appendages for feeding and food processing: Mandibles (jaws) and Maxillipeds (leg-like mouthparts for sense, touch, taste, tear, and manipulation of food toward mandibles

How do you determine the sex of a crayfish?

Males have enlarged swimmerets (gonopods)

Compare and contrast reproduction in earthworms and crayfish

Earthworms have both male and female sex organs, while crayfish have separate male and female individuals. Earthworms have mutual sperm exchange, while crayfish males transfer sperm packets to females using swimmerets. Earthworm young have direct development, while crayfish hatchlings stay attached to the mother for a short time