worms

Question 1

Nemertea

Answer 1

-Ribbon or Bootlace worms
-Unsegmented, often flattened
-Carnivorous predators
-Proboscis – characteristic/unique organ (dorsal to
gut)
-Osmoregulation/excretion – flame cells
-Outer surface ciliated – also moves by muscular
action
-Closed circulatory system and no specialised gas
exchange surfaces

Question 2

Platyhelminthes

Answer 2

-Commonly known as flatworms (platy = flat and
helminth = worm)
~30,000 described species
-Some free living, most parasitic
-Model organisms for understanding regeneration
-Considered a ‘basal’ bilaterian > important for
understanding evolution

Question 3

Platyhelminthes – characteristics

Answer 3

-Bilateral symmetry, dorso-ventrally flattened
-One gut opening
-Only feed on animal tissues (predator-scavengerparasite)
-Most hermaphrodites
-Moves by ciliary gliding/muscular contractions
-Well developed regenerative capacity

Question 4

Platyhelminthes – penis fencing

Answer 4

-Direct copulation where sperm is transferred to
another individual via the female reproductive organ
-Dermal impregnation where spermatophores are
deposited onto the surface of another individual
-Hypodermic insemination where one animal injects
sperm through any part of the epidermis of another
individual using an armed penis

Question 5

Priapulidae : the penis worms

Answer 5

• Priapulids (penis worms) are a small phylum of
  exclusively bottom‐dwelling marine worms
• There are only 19 described species; despite their
  low species number (one of the smallest of any
  phylum), they are ecologically diverse
• Priapulids occur in both warm tropical and cold
  arctic waters, from depths ranging between the
  intertidal to several thousand metres, and range in
  size from 1 mm to 40 cm

Question 6

Priapulids - anatomy

Answer 6

• The body consists of two parts: the prosoma, or
  introvert, is basically the mouth, and this structure is
  bulbous, covered in rows of spines and can also
  withdrawn into the rest of the body.
  -The second part of the body is the muscular trunk,
  which is covered in a thin, chitinous cuticle which
  has to be moulted as the Penis Worm grows.
  -Penis worms burrow through sediments by
  extending their prosoma, gripping the mud with
  their spines, and then dragging their whole body
  forward by withdrawing the prosoma into the trunk.

Question 7

Polychaetes (phylum annelida)

Answer 7

-Polychaete worms are more commonly called
segmented worms
-Over 17,000 species
-Extremely abundant
-Benthic polychaetes can be broadly categorised into
two groups;
-errant polychaetes which are motile and can
actively move,
-and sedentary polychaetes which are sedentary
and usually housed in tubes