Ctenophores

ctenophores

• carnivorous, gelatinous marine organisms

• about 150 described species

• major part of the planktonic biomass in many parts of the world

• can reach concentrations of several hundred per cubic meter in costal waters

• can be major predators on plankton including larvae of commercially important organisms

How do ctenophores become invasive species?

Some have been carried in the ballast water of ships to coasts where they are not native, becoming invasive species with an impact on costal ecosystems

ctenophore phylogenetic position

Features present in both cnidaria and ctenophores are likely to have been present in the ancestor of bilaterians 

in sponges, cnidarians and ctenophores, the future egg cell grows by

phagocytosis of other cells (nurse cells); simple way to make a nutrient rich egg, may have been how eggs were made in ancestor of animals

ctenophore movement

• move using 8 rows of combs made up of fused cilia

• cilia up to 200x length of those in other animals

ctenophore organization

• mouth at one end

• stomach and gastrovascular canals lined with endoderm (digestive epithelial cells)

• between ectoderm and endoderm is mesoglea

• within mesoglea, muscle cells and mobile amoeboid stem cells

• 2 anal pores to expel waste

• apical sense organ

mesoglea holds a lot of water

dry weight of many ctenophores is only about 4% of their wet weight

some ctenophores found in open ocean get much bigger than coastal species

• don’t have to survive wave action or sediment - are more fragile

• some species up to 3 feet across

ctenophore nervous system

network of neurons instead of a brain and nerve cords

apical sense organ

• controls balance, includes a statolith on 4 tufts of cilia

• each tuft connected to 2 comb rows

• when body tilts, statolith presses more on one tuft of cilia, stimulus causes two other of the comb rows to beat more to stay upright

ctenophores methods of getting prey

• tentacles

• colloblasts

colloblasts

• adhesive cells for holding prey, only found in ctenophores

• each one has a mass of adhesive granules attached to a contractile filament, come in clusters

Mnemiopsis leidyi feeding

• has oral lobes and short tentacles, both with colloblasts on them

• cilia produce a current carrying prey toward the oral lobes and tentacles

low mobility prey (larvae, fish eggs)

get carried into oral lobes, tentacles

larger mobile prey (copepods, fish larvae)

get carried in, don’t respond to ciliary current carrying them until they are engulfed by the oral lobes

Ctenophore embryonic development

• most planktonic ctenophores studied are hermaphroditic and able to fertilize their own eggs

• it only takes 1 of these ctenophores to make more ctenophores

• can start reproducing before they have grown to full size

• generation times are short and populations can increase quickly

cydippid larva

• looks basically like an adult

• may eat smaller prey than the adult, depending on the species

Diverse ctenophore morphologies

• Some ctenophores are flattened along the oral-aboral body axis

• Some of these live on surfaces and are colored, not transparent