Identification of Isopoda Through Photos and Videos

By Oonagh Degenhardt

As more people are developing an interest in Isopoda as a whole they are also looking to identify the species they find. Posting photos of isopods on websites such as iNaturalist is a great way to get an identification, but photos without the proper identifying features could lead to the misidentification of species.

Here we show examples of what should be photographed and techniques to get photos of isopods for proper identification of species.

General Identifying Features of Isopoda

Ventral Photos

Ventral (underside) photos of isopods can be the hardest to get but they are very often the most important photo for identification. Here we will show examples of how to get ventral shots for identification.

Lungs (or lack thereof)

The number of lungs or analogous structures on an isopod is one of the most useful identifying features. Families like Trachelipodidae and Porcellionidae on some occasions can only be distinguished by the number of gill spots they have. (Trachelipodidae having five pairs of gill spots and Porcellionidae having two)

Troglodillo sp.

Shape of Uropods

The shape of the uropods, while often a minor identifying feature, can be very helpful in some cases, such as with Ligia occidentalis and Ligia pallasii. Ligia occidentalis having a much more elongated uropod than Ligia pallasii which has a much shorter uropod as seen below.

Uropod

Exopod

Protopod

Endopod

Drawings of male Porcellio scaber

Uropod

Protopod

Exopod

Endopod

Drawings of Ligia occidentalis

Female and male Ligia pallasii

Ligia occidentalis

This identifying feature is more useful with females as male Ligia pallasii are very distinct.

Dorsal Photos

Dorsal photos, while much easier to take should show certain angles in order to properly identify isopods. Here we will show the angles that should be shown.

Porcellio dilatatus

Telson Shape

The telson shape is yet another very useful feature for identifying isopods. Species like Porcellio scaber and Porcellio dilatatus, which in some cases can be hard to distinguish, have differently shaped telson as seen below. Porcellio dilatatus having a more elongated telson that's rounded at the tip and porcellio scaber having a shorter telson with a pointed tip.

Porcellio dilatatus

Porcellio scaber

Shape of Head Segment and Anterolateral Lobe

The shape of the head segment and anterolateral lobe can be quite useful for the identification of some species. For example in Porcellio scaber they have a fairly short and rounded anterolateral lobe, while in Porcellio dilatatus they have a large, slightly elongated and rounded anterolateral lobe as seen below.

Head segment

Anterolateral lobe

Drawings of male Porcellio expansus from two different angles

Porcellio dilatatus

Porcellio scaber

Troglodillo sp.

Ocelli/Ommatidia Count and Position

Ocelli count and position, while minor in most situations, can be very helpful to aid in the identification of some species, such as species in the genus Eluma, Ligia occidentalis, and Ligia pallasii.

Eluma is distinct among most isopods due to the fact that it only has one pair of ocellus as seen below. It is one of the most reliable identifying features for the genus.

Ligia pallasii and Ligia occidentalis can be distinguished by the position of their compound eye; Ligia pallasii has smaller and further apart compound eyes and Ligia occidentalis having much larger and closer together compound eyes making it superficially resemble the mainstream depiction of an alien.

Eluma caelata

Armadillidium vulgare

Ligia pallasii

Ligia occidentalis

Eluma caelata

General Anatomy/Habitus

A photo of the entire isopod along with your ventral shots and other angles is always very useful for identification. while the telson, head, gill spots etc... are useful for narrowing down the species a full body photo is almost always needed along side them for a proper identification.

Porcellio scaber

Porcellio dilatatus

Note the much rougher appearance of Porcellio scaber vs Porcellio dilatatus this is also an identifying feature of the two species.

Methodology

Ventral Photos

Porcellio scaber

Method one

Method one is easiest to do on larger species and can easily be done out in the field.

Gently pinch the sides of the isopod and pick it up and you're done!

Armadillidium maculatum

Method Two

Method two is easiest to do with isopods that conglobate (roll up) It requires a flat surface.

Place a conglobated isopod on a flat (preferably smooth) surface and wait for it to unroll and take a photo!

Trachelipus rathkii

Method Three

Method three works with most if not all isopods. It requires a plastic bag.

Place an isopod in a plastic bag, flip over the bag and take a photo!

Armadillidium maculatum

Method Four

Method four works with most isopods. It requires two deli cups and a sponge.

Place isopod in the first deli (you may need to wait for it to unroll). Once in the deli and standing, place your soft sponge on the isopod. Gently press on the sponge and pick up the deli then flip over and carefully put it sponge side down on other deli cup.

Photography with a phone

Intimidated by the photography aspect? here we will show simple and cheap ways of getting clean macro shots with a phone camera!

Method One: Magnifying Glass

This method is fairly simple and just requires a magnifying glass and a phone camera.

Hold the magnifying glass in front of your phone camera and zoom in with your camera. You may need to adjust how close your phone camera is to the magnifying glass or how close the magnifying glass is to the subject to get the subject in focus.

Method Two: Clip on Macro lens

Clip on macros can be very useful. While they do sometimes have warping around the edges of the photo this is minor and they tend to work very well regardless.

Method Three: Handheld Digital Microscope

While it can sometimes be hard to focus on something like an isopod with a handheld microscope they often result in the clearest photos out of these three options. They can get pricey but I've never had issues with the cheap ones.

Photography tips and tricks

Lighting

Lighting is a very important part of photography and can often make the difference between an unidentifiable photo of an animal to a photo you can easily take to the species level. Make sure (especially while photographing small animals) that you have bright unobstructed light either natural or artificial.

Photo of P. scaber taken in good lighting conditions.

Photo of P. scaber taken in poor lighting conditions