echinoidssss

morphological features of the echinus.

* genital plates
* apical system
* ambulacra
* interambulacra
* occular plates
* madeporite
* pore pairs
* spinal bases

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Where does the mouth lie?

on the ventral (lower surface)

What does the apical disc consist of?

large genital plates each with a pore connected to the internal gonad.

how can you set apart the genital plates and madeporite?

the madeporite has fine perforations in addition to just the genital pore.

What is the structure of the ambulacral plates?

consist of a double column of elongated plates which meet along a central zig-zag suture.

What is the most common type of symmetry in echinoids?

Five-point symmetry

Whats the difference between regular and irregular echinoids?

regular echinoids have no front or back end and can move in any direction. Irregular echinoids have a definite front and back and move in a particular direction.

What function did the struts on shallow burrowers fufil?

It prevented the echinoid from being flattened by the sediment by holding the shell up.

What function did the lunules fufil?

They prevented the echinoid from being lifted out of the sediment by wave action.

Give 3 morphological features of deep burrowers

* elongated shell for deeper burrowing
* lunule for food harvesting
* thinner walls due to protection by sediment

What functions do tentacles serve in echinderms?

Used as a defense mechanism