andrewcowley's picture

Juvenile Trivia NOT Lacuna pallidula.

Observed: 11th September 2010 By: andrewcowleyandrewcowley’s reputation in Invertebratesandrewcowley’s reputation in Invertebrates

Near ELWST. I've included the larger photo with the Trivia for scale. I have to admit I didn't notice this until I looked at the photo and by then the tide had come in! L. pallidula has much deeper sutures between the whorls so I'm not convinced that's correct.
Added three more photos. This is juvenile T. monacha

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andrewcowley's picture

Thanks, Mike

I haven't had a chance to do much checking but the habitat seems wrong for Akera. It was in a gully near ELWST, on a moderately exposed (Ballantine 3) shore. Hayward and Ryland say "In and on soft fine mud in sheltered bays formerly favoured by Zostera". The cowrie was 8-10mm. I estimate, so maybe a little too big for Retusa obtusa.

Mike Kendall's picture

that make life a little more difficult

Even a tentative ID was always going to be something of an educated guess, particularly as we can't see the form of the aperture.

I agree these species like softer sediments so there is a potential problem with the ID

I suppose there was a body inside the shell and its simply not a wash-in to the gully? There is plenty of Zostera in the Camel Estuary.

Mike Kendall

andrewcowley's picture

Firm identity

I found three more of these in the same locality. All three have smooth shells and visible but very depressed spires as shown in picture. One had the beginnings of the adult ridged shell visible around the aperture. I have read Hayward and Ryland more carefully and this is typical of the juvenile form. T. monacha must reach almost full size as a juvenile , as two of these were much larger (7-9mm shell length) than many mature ones seen in drift (dead) shells from this locality.

JoC's picture

Juvenile Triva

Having looked at H& R, I am agreeing with Andy on this one. This site shows some juvenile Trivia from Scapa Flow if anyone is up that way...


dejayM's picture

Mistaken identity

I have just removed my agreement here. It seems very unlikely that Andy would have have mistaken a Trivia for anything else, so I do not understand, considering he added the "larger photo with the [adult] Trivia for scale"
It is also interesting to note that he wrote "..three have smooth shells and visible but very depressed spires" this does NOT describe a juvenileTrivia of the size we see - maybe 12-15mm - must be bigger than 10 mm surely. And note the translucence of the shell and the possible animal inside it.
And then there is the evidence, presented in Mike Kendal's (flawed) ID. I am pondering my opinion that he might be right about it being the shell of a Opisthobranch.

A few things then (only two of you will get flags) -
Where are the missing three pictures (Jo?) "Added three more photos. This is juvenile T. monacha" (Andrew)
Why (and perhaps when) did Andrew make the title Juvenile Trivia NOT Lacuna pallidula
Might we three have been mislead by the presence of trivia in the subject photo? I was!
Read (of juvenile trivia) "Under 7mm high the juvenile shell has a typical gastropod aperture and spire" in JoC's link and SEE those pictures here DO note the colour.

Andrew will not have had access to these see specialy picture7
I again commend Ian F Smith's pictures http:[email protected]/popular-interesting/

dejayM's picture


I have spent a while looking at these wonders of photography https:[email protected]/sets/72157662463937079/.
Somehow, I cannot imagine that Andrew might photograph something (anything) so closely and not handle it, or lift it to see the underside; however, it seems so.
One thing that convinces me that this might be an Opisthobranch shell, is the colour..
I accept that juvenile Trivia are (surprisingly!) almost conical with whorls at one end. But I am not convinced by the agreements here.
If anyone can find a picture of a 'transforming' sub-adult Trivia I'd like a link.

JoC's picture

A ressurection of an earlier post

and Andy is not available to comment.
I will return to this later, but as to size, Andy said the obvious cowrie was 8-10 mm, so I suggest the 'other' shell is less than 8mm.


JoC's picture


Trivia Andys post of juvenile
Photo 28, "3 month post-veliger juvenile' on IF Smith still looks just like Andy's post to me.
https:[email protected]/24063560262

Lacuna pallida is small, around 2mm. I don't know why this species was mentioned by Andy. There is no other trace in the post now.

At around 10mm maximum, it could be the internal shell of an Opisthobranch, but it would have to be an Aplysiidae or Pleurobranchidae because, according to H&R the other shelled species are too small.
We may never know.....