MFWB_A - Aquatic Invertebrates

porifera

sponges, no symmetry, sessile, filter feeding, metazoans (lack tissues and organs)

asconoid

single large chamber, lined with water feeding choanocytes

syconoid

larger differentiation of folding of mesohyl, therefore an increase in the amount of food

leuconoid

folding of pinococytes increase volume of mesohyl

cnidaria

primitive body plan, cnidocytes with nematocysts, diploblastic

jellyfish stingers

nematocysts

4 classes of cnidarians

hydrozoans, scyphozoans, cubozoans, anthozoans

Hydrozoa

dimorphic - medusa and polyp stages, multiple zooids (polyps), strong physiological integration (cannot survive independently), very small medusa stage

scyphozoa

true jellyfish, 200 species all marine, most dimorphic, seasonal at high latitudes (follow current of plankton), poly vestigial and atypical, medusa large and dominant - polyp can be planktonic or sessile, can reach up to 2 metres

cubozoa

box jellyfish, most dangerous of the aquatic venomous animals apart from sea snake, all 50 species are marine and hunters, sensory organelles allow them to avoid obstacles and capture prey, 4 tentacles - bunches of tentacles

anthozoa

sea anemones, corals, sea pens, 6000 species all marine, no medusa stage, contain cnidocytes - trigger mechanisms more advanced, can be tuned to capture prey more effectively

two stages of cnidarians

polyp - sessile stage - solitary or part of a colony, medusa - free living stage

cnidarian body plan

diploblastic, endoderm and epidermis, ectoderm and gastrodermis (lines digestive cavity), mesoglea fill in gaps

polyp/hydroid form

tentacles for feeding, in all classes however greatly reduced in Scyphozoa and cubozoa, colonies formed with divided labour (feeding (gastrozooid), reproduction (gonozooid), defence (dactylzooid)), can do asexual reproduction through budding

medusoid

all classes except anthozoa, water fills ‘balloon’, tetramous symmetry, exumbrella and subumbrella

cnidocysts

make nematocysts - triggered by mechanical stimulation of cnidocil, spirocysts and ptychocysts

spirocysts

found in anthozoa, ensnare or adhere to prey

ptychocysts

ceriantharians (tube-dwelling anemone), pleated

feeding in cnidarians

feeding tentacles capture prey, transport to mouth, small particles passed along tentacles/arms to mouth via cilia, ingested whole and expelled through mouth