No, that is not some weird fish. That is just an odd angle
view into the bell of a box jelly. What it shows really nicely
(besides the rhopalia and eyes
is the velarium, a ring of tissue
that extends around the bottom inside of the bell.
When the medusa contracts
during swimming, increased thrust is created because the velarium narrows
the opening at the bottom of the bell.
The velarium increases the efficiency of the jet propulsion.
Presumably, the velarium is
at least partly responsible for the great speeds with which cubozoans
are able to swim. In the close-up below, you
can see velarial canals. These canals are
extensions of the gut and they are very important in telling one
species of cubozoan from another.
Click on the buttons below to find out more about Cubozoa.