“Sea Urchins Feed through Their Bottoms”. True or false?

"Sea urchins feed through their bottoms"... I have heard several times, including a similar remark from the film, Johnny English [DVD](upon hearing this, in a sushi bar, Rowan Atkinson's character then proceeds to spit out the sea urchin dish, in disgust).

This myth stems from the remarkably different anatomy, or body plan, of sea urchins (echinoids).

Sea urchins consist of a somewhat spherical body, covered in spines.  In most species, the mouth is on the lower or 'bottom' surface (known as the 'oral surface') — whereas its ‘true’ bottom or anus is on the opposite side of the organism, on its upper surface (‘aboral surface’).

Thus, sea urchins feed through their ‘bottom’ surface, but this includes their mouth, not their anus. So Rowan Atkinson’s character need not be so disgusted…

This unusual body plan (at least compared to our anatomy) appears to be an adaptation of the sea urchin to living on the ocean floor, so that its mouth is in contact with the substrate, allowing it to feed on algae or detritus.  As the anus is situated on its upper surface, waste does not therefore become mixed up in its food.

Read more about sea urchins...

Peacock Caterpillars in September?

These strange alien-looking black creatures are, believe it or not, caterpillars of the butterfly species, the Peacock (Inachis io).  They can be seen here (Sevenoaks, UK) eating their favourite food, the unpopular stinging nettle (Urtica dioica).  They shelter, here, underneath their communal web built of silk — an organic, wispy tent also incorporating their droppings and the skin which they periodically shed in order to grow. Note the spines, which provide these caterpillars with a source of protection from predators, particularly when they wriggle their body from side to side, or roll up in a ball.

However, the most unusual fact about the sighting, is that they were spotted in September — several months after the single brood of caterpillars normally emerges.

Typically, the adult female normally leaves 200 or more small eggs in May, on the leaves of nettles.  The caterpillars normally emerge 2 to 4 weeks later in late May or June and form their chrysalis in early July.  In late July and August, the adults emerge and begin to stock up on nectar for their hibernation during the cold British winter.

So, then Peacock caterpillars in September?  This must be a second brood, a rare occurrence for the species but occurs during 'good years' .  And, indeed, this year we've had a good, warm summer.  The Big Butterfly Count, run by the charity Butterfly Conservation, has recorded four times as many butterflies this year, compared to 2012 — a real surge — with an increase in Peacocks of 3,500%! Read more... 

However, will this second batch survive?  By the time they have transformed into adults, later in the autumn, they will face much greater difficulties surviving the cold (being reliant on the heat of the sun for temperature regulation) and also gathering nectar from fewer sources around. Read more about butterflies...

 

Below: an adult Peacock feeding in August on a buddleia