Juvenile Echinoderm

Juvenile Echinoderm

Observation - Juvenile Echinoderm. Description: I noticed this creature on the glass of my marine aquarium this morning. There was another on a rock. It is 1mm across (hence image quality!). I have in this aquarium Cushion Stars (Asterina gibbosa), Brittle Stars (prob Ophiothrix fragilis), and Shore Se

I noticed this creature on the glass of my marine aquarium this morning. There was another on a rock. It is 1mm across (hence image quality!). I have in this aquarium Cushion Stars (Asterina gibbosa), Brittle Stars (prob Ophiothrix fragilis), and Shore Sea Urchin (Psammechinus miliaris). This is highly likely to be a home-grown juvenile of one of these. But which?