what do you guys think... arthropod or slug?

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Home » Guide » Arthropods (Arthropoda) » Crustaceans (Crustacea) » Malacostracans (Malacostraca) » Marsupial Crustaceans (Peracarida) » Isopods (Isopoda) » Scutocoxifera » Valve-tailed Isopods (Valvifera) » Idoteidae

Photo#483153

Copyright © 2011 Chris Mallory

what do you guys think... arthropod or slug?

Crystal Cove, Orange County, California, USA
December 30, 2010
Size: about 25mm

Dorsal image

Found this individual in the low tide zone clinging to sea grass. Surprisingly efficient swimmer. I had assumed this to be a mollusc, but as I look at the photos, especially the ventral image, it appears to be segmented: in particular, I count 7 body segments, a head, and a tail segment (pleoteleson perhaps?), while the antennae appear to be segmented as well (4 large segments + many smaller terminal segments). All of these characters are consistent with the isopod clade Valvifera (compare with plates here). But, it is much different than the other valviferan I shot that day (1). Behaviorally it was different as well.

The problem here is that I can't really distinguish any legs or facial features. I've been looking at isopods all week so it could be that everything I look at now appears isopodiform, so I seek a second opinion. Thanks!

Images of this individual: tag all

what do you guys think... arthropod or slug?

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Contributed by Chris Mallory on 4 January, 2011 - 2:17pm
Last updated 25 July, 2015 - 4:41pm

Moved

Moved from Peracarida (Amphipods and Isopods).

… Aaron Hunt, 25 July, 2015 - 4:41pm

Moved

Moved from Malacostracans. I'd agree with Valvifera. Moving it here for now.

… Aaron Hunt, 20 June, 2015 - 4:00pm

Another useful link I found for this suborder

For those who are interested, Here is another key I found to Valvifera, containing also a glossary of terms and a few live images. The site also has keys for several other groups of pacific coast crustacea.

… Chris Mallory, 8 January, 2011 - 12:54pm

Book

I don't know if you have a copy, but you might consider picking up "The Marine Isopod Crustaceans" by George A. Schultz. It is part of the "How to Know - Pictured Key Nature Series". As with any book, the taxonomy is probably out of date, but I think you will probably find it useful if you are going to continue your tide pool research.

… John R. Maxwell, 8 January, 2011 - 9:37am

thanks for the reccomendation john

I found a copy for cheap on ebay so I impulsively placed an order on the book. I'm sure it will prove to be helpful even if a little old, as there is not much isopod literature readily available on the internet. Thanks.

… Chris Mallory, 8 January, 2011 - 11:47am

Moved

Moved from ID Request.

… Chris Mallory, 5 January, 2011 - 1:23pm

wondering if these images are worth keeping...

If it is Valvifera, with these images I can only key it into family Idoteidae (seven free pereonites, head not fused with first pereonite), and I can't key it any further without being able to see how many pleonites the pleon is composed of. In intertidal california there are twenty species in five genera in this family that are possible, and for most of these species there are no live images available on the web, so I have nothing to go by except for these plates. Looking only at the elongate species with antennae with multiarticulate flagellum, that still leaves quite a few possibilities. As is, I think my other Valviferan image stands a better chance of getting an ID than this ever will, and if they are the same species as I expect then this one should probably be trashed in favor of the other one.

For now though, I guess it won't hurt to move it to Malacostraca with my other isopods.

… Chris Mallory, 5 January, 2011 - 1:23pm

So was this in salt water then?

Is crystal cove in the ocean? Because not many insects can live in that type of environment, and it usually more brackish than actually marine. But Ephydridae are known to live on coastlines, and there is one typical Ephydra that does kinda look like this, and someone commented on your other pic that they thought thats what it might be.

… Natalie Hernandez, 4 January, 2011 - 4:14pm

Salt water, yes.

Should have mentioned that earlier. Are there any images of these Ephydra larva? I can't find similar images on the guide or google.

… Chris Mallory, 4 January, 2011 - 4:23pm

I was looking at the nearctic manual of diptera.

Their siphons are a little different though, they have one tube, then two tubes come out of that. After looking at the link you posted though I'm wondering if it is an isopod.

If you're interested, free download of the dipteran manuals are here:

http://www.esc-sec.ca/aafcmono.html

… Natalie Hernandez, 4 January, 2011 - 4:27pm

Excellent resource, thanks for the link!

Pretty cool that the ECS provides so many free guides including these, thanks for sharing.

Upon looking up Epydra larvae, I can certainly see the similarity. The only major difference that I can readily discerne is that the antenna of my individual have a multiarticulate flagellum while the antennae (are these even antennae? I don't know much about fly larva morphology) of the image in the guide are not.

… Chris Mallory, 4 January, 2011 - 4:50pm

Not antennae, but spiracles.

If this were a fly larva, then the end with the tubes would be the butt end, and they would be posterior spiracles. The antennae are often just small little nubbins on the head, or not really visible at all.

Many fly larvae adapt them into long siphons like that, and I believe it is to obtain oxygen while underwater, by reaching out of the water. Although some I think it is to obtain oxygen while being buried under debris or sand, and some may just be to increase surface area to allow more gas exchange.

… Natalie Hernandez, 4 January, 2011 - 4:56pm

Learn something new everday

I had not known this before. But with this new info, I think it makes it easier to rule out fly larvae, for the following reasons:
1) If you look on the ventral image, if we assume it is an isopod and the end with "antennae" is the head, you can make out two black eyes on the side of the head, consistant with valviferan morphology.
2) Although circumstantial, I will testify that the creature swam and crawled antennae-end first (though I suppose some flies might swim backwards, I have no idea in that regard).

… Chris Mallory, 4 January, 2011 - 5:05pm

Oooooh that makes so much more sense!

Yeah I didn't realize that other image was ventral, but now that I look at it I agree, we can rule out fly larva.

Flies normally still walk head first, so they would not be going in the direction of the tubes, which I am now sure are antennae and not posterior spiracles.

… Natalie Hernandez, 4 January, 2011 - 5:07pm

No idea

but agree that it looks segmented and not at all slug like to me. I don't know anything about this animals but looking through the drawings you've provided in the link, it looks to me maybe like 83. Idotea resecata. To me the "tail end" looks a little indented + the over all shape. ???

… Livan, 4 January, 2011 - 3:47pm

Thanks for the input

I. resecata does look close, but I wonder if the posterior margin of the pleotelson is not concave enough in my individual to be that species (which is the defining characteristic of the species in the key I am using).

After examining the full size originals extremely carefully, I think I can definitely make out what appear to be seven pairs of legs, eyes, and a mouth on the ventral image. I compared these to some images of my other Valviferan, and it does appear that they are capable of almost completely obscuring their legs under the body segments. Unfortunately, the defining characters I would need to key this out (ie the pleon and the mouthparts) I cannot determine in any photo under any magnification. I suspect this might even be the same species as the other Valviferan I posted, despite the huge color difference.

… Chris Mallory, 4 January, 2011 - 4:20pm

Not an ID

but looking through the book (not enough detail in the images so I made some guesses and did some "picture matching"), but Idotea does seem to make the most sense (so far).

… John R. Maxwell, 8 January, 2011 - 11:24am

The clincher

for Idotea is if we could tell from the image that the pleon is composed of two complete pleonites and one incomplete pleonite. But like you said, there's not enough detail in this image so I appreciate you looking through the book for matches.

… Chris Mallory, 8 January, 2011 - 11:59am

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