Adults of Sea Mats are so called as they create flat, dense colonies on seaweeds and rocks. Each individual secrets a tough "cell" in which the tiny creature lives, glued to its surrounding neighbours. They produce huge numbers of larvae (called cyphonautes) which are liberated into the plankton. 

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A selection of cyphonautes is below. They can be seen at most times of the year but some months, e.g. November and March, they can be especially abundant.