Pachymatisma johnstonia

Penny Martin pachymatisma johnstonia??

Bernard Picton It's a Didemnid, Didemnum maculosum perhaps, though I doubt if what we call D.maculosum is really all a single species. Didemnids are the most difficult sea squirts to identify, and often look like sponges.

Bernard Picton Perhaps Didemnum coriaceum if that's a valid species... http://www.habitas.org.uk/marinelife/species.asp?item=ZD860

Penny Martin Thank you for your help .... sorry I am so dim .... I am seeing loads but don't find it easy to ID ... is there a good book on sea squirts and sponges ??