Minor Phyla

Question 0

What are the 4 classes of Platyhelminthes?

Answer 0

Turbellaria (have a head), Monogenea, Trematoda, Cestoda*

*=parasitic.

Question 1

What are the Platyhelminthes?

Answer 1

The flatworms. They are hermaphrodites. Approk 250k spp distributed between 4 classes. They are bilaterally symmetrical and don’t like the light.

Question 2

What is the body plan of the Platyhelminthes?

Answer 2

They are bilaterally symmetrical. Three layers of tissue - outer epidermis, inner muscle layer, mesoderm parenchyma. No body cavity except for a blind-ended gut.

Question 3

What is the nervous system of a Platyhelminthes like?

Answer 3

Smaller, simpler forms have a nerve net but large more active spp have circum-oesophageal ring, with a pair of cerebro-pleural ganglia connected to a pair of ventral solid nerve cords. Most also have chemoreceptors to find food. Primitive light sensing organs and other basic sensory structures. Beginnings of cephalisation. Capable of complex behaviour.

Question 4

What is the Platyhelminthes excretory system like?

Answer 4

They have protonephridum (flame cell) singularly or in pairs down the body. There are excretory pores down the sides.

Question 5

What are the Nemertea?

Answer 5

They have a similar body plan to the Platyhelminthes but with a through gut and a rhynchocoel (cavity holding proboscis). Range from 5mm to reportedly 60m.

Question 6

What is the rhychocoel?

Answer 6

An extendable proboscis of nemerteans. It’s a fluid filled sack.

Question 7

What are the Nematoda?

Answer 7

The greatest metazoan radiation ever. Found at tops of Mt. Everest to hadal depths. Means ‘threadlike.’ 1mm-5cm.
V. important component of marine meiofaunal communities, e.g. temperate marine coastal sediments contain 4.5 million m-2

Question 8

What is the body plan of the Nematoda?

Answer 8

Bilateral symmetry, 2 cell layers - tissues & organs.
Outer layer - cuticle complex structure - important in resisting internal hydrostatic pressure and host antibody recognition in parasites.
Through gut, excretion by renette cells.

Question 9

How do the Nematoda reproduce?

Answer 9

Most spp dioecious - have males and females. Male cirrus has shape unique to each species. Evidence of complex mating behaviour - females of some spp produce attractant pheromones.

Question 10

What are the Sipuncula?

Answer 10

Means ‘little pipe’. Often called peanut worms. 320 spp, all marine, living in muddy sediments, shells, & boring into rock. Size range 2-720mm.

Question 11

What is the body plan of the Sipuncula?

Answer 11

Bilaterally symmetrical, but divided into a trunk and movable introvert/proboscis. Lack a circulatory system but have RBCs based on copper. Have a ‘brain’ - bi-lobed. Dioecious.
Several cell layers, outer layers contain cellulose fibres.
Complex organ systems, e.g. fused nerve cord and cpg (central pattern generator?) form single brain.
Respiratory pigments found in some spp (Cu based haemocyanin.)

Question 12

How do the Sipuncula reproduce?

Answer 12

Dioecious eggs and sperm formed internally shed into the coelom and eventually pass out via the nephridiopore. External fertilisation producing a pelagic trochophore larva.

Question 13

What are the general trends of the minor phyla?

Answer 13

Increasing cephalisation coupled with increasing sophistication os sense organs and rise of the cpg ‘brain.’
Development of organs and integrated organ systems.

Question 14

What are the Rotifera?

Answer 14

Means ‘wheel bearer’. 1.8k spp in FW and SW. Meiofaunal in size - max 5mm. Live at sediment-water interface and in water column.

Question 15

What is the body plan of the Rotifera?

Answer 15

Bilateral symmetry. 2 layers but with well defined exoskeleton. Organs complex and reduced in number, moving towards systems. Dioecious but in many spp males small or absent so parthenogenesis is common. Bdelloids can withstand desiccation & disperse in wind. When sexual repro takes place females have no genital opening so male stabs female with dagger-like penis. Larvae released by female bursting.

Question 16

What are the Echiura?

Answer 16

Means viper tail. Spoon worms. 135 marine species shallow water to hadal trenches. Strong annelid affinities. Soft bodied, muscular trunk, highly extendable proboscis. Noxious mucous as protection. Complex organ systems - circulatory and respiratory. Dioecious but dwarf males found in many spp to overcome prob. of mating encounters. trochophore larvae.

Question 17

What are the gastrotrichs?

Answer 17

Hairy stomachs. 400 spp. meiofauna. Detritivores, important in material recycling in benthic food webs. Bilaterally symmetrical. No body cavity, 2 cell layers. Through gut. Not internal circulatory/gaseous exchange. basic nerve systems of cpg & ganglionated nerve cords. Hermaphrodites but many spp parthenogenic.

Question 18

What are the Kinorhyncha?

Answer 18

Moving snout. Exclusively marine phylum 150 meiofaunal spp in muddy sediment. Bilateral symmetry, body divided into 13-14 zonites. Through gut. 2 cell layers of tissues and organs. Ptrotonephridia on zonite 11. Basic Nervous system. Ganglia along ventral cords. Dioecious.