nightfly's picture

Idotea granulosa

Observed: 14th March 2013 By: nightflynightfly’s reputation in Invertebratesnightfly’s reputation in Invertebratesnightfly’s reputation in Invertebratesnightfly’s reputation in Invertebratesnightfly’s reputation in Invertebrates
14 Mar 13 (52)
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A very good lilkeness for the other Idotea in this observation here:-

Species interactions

No interactions present.


ChrisMcA's picture

It's quite a pain trying to

It's quite a pain trying to separate I.granulosa & I. neglecta but yours seems pretty clear thanks to the pics; however the example given, though the right shape, & though I agreed to it, I now feel sure is I. neglecta. eg all sources give granulosa size to 20mm, highlandteucher reckoned his 45mm, but pics showed it 2fingers wide (=40mm on my lge hands but neglecta's up to 30mm).Species-identification shows all 8 Idoteas (I.metallica occasionally gets here from N.America on seaweed), & for 4 illustr's both male & female. Its' descriptions also include verbatim those of 'Synopses of the British Fauna no.3' which by googling the same you can surprisingly download/view on the net as a pdf (4Mb & 90 pages). There's also remarkably good pics of isopods at Nature22, but it's a site Mcafee hasnt tested yet.
The Synopsis 3 also shows how telson shape changes with age so ID of young ones is tricky.

nightfly's picture

The shape of this one when

The shape of this one when viewed from above, is very like that of the first large picture of Idotea neglecta in the linked site Chris- the swell in the width in mid section. The only apparent inconsistent feature seems to be the pitched roof shape of the pleotelson in the linked example. My one above doesnt seem to have that roofed pleotelson but that doesnt necessarily mean it isnt neglecta.

I dont think I have seen an image yet of granulosa with the swollen width in the middle as above, you may well be right that this is neglecta. If you are confiden that it is go ahead and add a revised ID? Up to you, I dont know these things well, I'd probably need to do some more familiarising.


ChrisMcA's picture

No I meant yours was

No I meant yours was Granulosa.These sp's have head, body of 7 plates, & tail,& on either side of the 7 plates side plates called coxal plates.I was going on species-identification's description of neglecta's (& especially the illustration), at , as against granulosa's illustration etc at .
Also size in the flagellum (=whippy bit) of 2nd (=large)antenna; In Neglecta it's 1/4 to 1/5 of body length & in Granulosa less than 1/5.I checked species-identificn's illustrns & they fitted, & yours fits granulosa & the other neglecta. But I'll have another look at photos

ChrisMcA's picture

I havent found any pics of

I havent found any pics of granulosa as wide (in propn to body lgth) as yours; but also none of either with same shape for above (sudden widening 1/2 way) or the side (1st 5 segmts coxal plates slim/invisible);but even odder are the no. of body segments, well seen in side view;(see which shows the 7 plates of the pereon of an [presumably all] isopoda + diagram of Idotea) But in yours after the head there's 8, then the "2complete pleon segments & an incmplete suture" then telson. It's also short of the 7 pairs of legs on the underside. As all the other Idoteas in, eg species-identfcn or Collins (or the 10 californians on tolweb) it seems to be a genetic aberration.

nightfly's picture

Thanks for all the feedback

Thanks for all the feedback Chris, sorry I misunderstood you earlier about neglecta. Posted another here that I'd appreciate your opinion on please:


ChrisMcA's picture

Sorry, I was looking at the

Sorry, I was looking at the 1st photo & taking the front bit as head (you can't see the real head's eyes), so there's 7 after all (& it may after all be neglecta).

dejayM's picture


It's true it is a bittie fat (N Irish food!). But I believe the ID is correct.
See mine here
And note they seem to take on the background habitat colour.