Pupae or seed?

Pupae or seed?

Observation - Pupae or seed? - UK and Ireland. Description: I keep finding these unusual disc shaped brown objects floating in the pond at the moment. They look a little like salami slices. I had assumed they were seeds, fallen into the pond. However, yesterday I squeezed one and the contents that sprayed out

I keep finding these unusual disc shaped brown objects floating in the pond at the moment. They look a little like salami slices.

I had assumed they were seeds, fallen into the pond. However, yesterday I squeezed one and the contents that sprayed out was yellow and milky, not thick like I would expected from a seed. I wondered whether this could be a pupae (that I had inadvertantly destroyed!).

The pond in which I find these is well-established, and supports good populations of a number of water beetles, and six caddisfly species too.