Hunt for Meridiastra mortenseni - A Cushion Star

I am sure we all know the New Zealand Common Cushion Star (Patiriella regularis) and have walked past them many times without taking too much notice - I know I have! However, there is also another common endemic cushion star that lurks in the same habitat as @clinton pointed out to me in this obs and we do not have it on NW yet.

The M.mortenseni is dark red or blue and looks smooth when wet whereas the common one is not. If you look at all of the common cushion star obs found you will be able to see quite clearly at a glance that they are not smooth.

Same as the New Zealand Common Cushion Star (Patiriella regularis).

What to photograph
Both the top and underside of the cushion star to help with ID.

Happy Hunting!

Posted on March 27, 2017 10:11 PM by tangatawhenua tangatawhenua


Yep, it's a tricky one! I haven't found that colour or smoothness is a particularly consistent character and have had to use the other identification characters (e.g. placement of spines on the under side) to differentiate between Patiriella regularis and Meridiastra mortenseni (which was originally described as Patiriella mortenseni). To see the spines you need a really good macro (or at least high def) photo of the underside. They definitely co-occur, but I'm not clear how widely :)

Posted by kaytee about 7 years ago

I really appreciate your input into this post @kaytee - I have spent about 6 hours wandering around where the Patiriella regularis live and had come to the conclusion that either (a) they are not common up here or (b) they have interbred because I can find lots of dark red and blue on individuals but none that are just dark red or just blue or (c) I may be going colourblind LOL

Do you know anywhere that there are photos online that show the spines of both these species so I can do a comparision and add them to this post? :)

And is the underside of this obs a good enough macro? If so, I can work on getting the focus better LOL

Posted by tangatawhenua about 7 years ago

The people that first separated P. regularis and P. mortenseni used several characters to differentiate between them. You should be able to see the paper if you click on the link below. Table 1 on page 708 summarises them. I'm often looking at preserved samples (which lose their colour) so the thing I look for on the underside is the presence or absence of a row of spines along the furrow (have a look at the pictures and the drawing on page 707). But (isn't there always a but!), some specimens have a partial row or only some of the other characters ... which is why I find them tricky to ID. I've never had the time to sit down and look at a whole lot of them and sort it out!

From the photo, your cute little square star (and I am assuming it was quite little?) seems to be P. regularis (has a bare row of plates behind the two rows of furrow spines, a rough appearance, prominent subadambulacral spines (that's the second row of spines from the furrow)). BUT it is red and seems to have some mid actinal (the triangular area between each arm) plates with two spines.

See what I mean? Sorry for all the confusing terminology - they have their own language :)

Posted by kaytee about 7 years ago

Much appreciated for all of the info @kaytee :)

Posted by tangatawhenua about 7 years ago is the new guide out for Echinoderms and has a good page on this - as well as lots of new additions :)

Posted by tangatawhenua about 7 years ago

I'd welcome any feedback on the refreshed guide too! :)


Posted by kaytee about 7 years ago

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