Post update: Cordulegastridae exuvia

In a recent blog post entitled Cordulegastridae exuvia, I was able to identify the specimen to the family level. Since then, I was able to identify the genus and species.

The dichotomous key for Cordulegastridae larvae that appears on p. 330 in Dragonflies of North America, Third Edition by Needham et al. was used to identify the exuvia.

dichotomous key: a key for the identification of organisms based on a series of choices between alternative characters. Source Credit: Merriam-Webster Dictionary.

The first couplet [1, 1′] is as follows.

1. No lateral spines on abdominal segments 8-9; western [2]
1’. Lateral spines present on segments 8-9; eastern [3]

No. 1 | Cordulegaster sp. | exuvia (ventral)

(See a full-size version of the original photo, without annotation.)

Since the preceding annotated image shows lateral spines on abdominal segments eight and nine (S8, S9), proceed to the third couplet [3, 3′].

3(1’). Palpal setae 4; usually 5 large and 5 small premental setae present; some setae on margin of frontal shelf spatulate (Fig. 391e) [erronea]
3’. Palpal setae 5-7; 5-9 large and 3-5 small premental setae present; all setae on frontal shelf slender, not spatulate (Fig. 391f) [4]

(See a full-size version of the original photo, without annotation.)

The preceding annotated image shows the inner side of the prementum. Four (4) palpal setae are present, plus five (5) large- and five (5) small premental setae. The premental setae on the lower-right side of the prementum seem to be more intact than the ones on the upper-left: the large premental setae are labeled using white numerals; the small premental setae are labeled using red numerals.

The setae on the frontal shelf are mostly missing, as shown below. It’s possible they were broken off either when the larva burrowed in stream sediment (personal correspondence, Sue Gregoire) or when I cleaned the specimen.

No. 3 | Cordulegaster sp. | exuvia (frontal shelf)

(See a full-size version of the original photo, without annotation.)

Genus and species

The number of palpal setae strongly indicates the specimen is an exuvia from a Tiger Spiketail dragonfly (Cordulegaster erronea). Further, the rudimentary ovipositor shown in Photo No. 1 indicates this individual is a female.

The face behind the mask

Do you remember the way the female exuvia looked with its mask-like labium in place? In my opinion, she looked exotically beautiful!

No. 4 | Cordulegaster sp. | exuvia (face-head)

(See a full-size version of the original photo, without annotation.)

Well, that was then and this now. The following photo shows the face and mouth of the exuvia after the face mask was pulled away from the face in order to count the setae on the inner side of the prementum. Look closely at the full-size version of the photo. Yikes, that’s the stuff of nightmares!

No. 5 | Cordulegaster sp. | exuvia (face and mouth)

Related Resource: Cordulegastridae exuvia, a blog post by Walter Sanford featuring an exuvia collected by Mike Boatwright.

Tech Tips

The following equipment was used to shoot macro Photo No. 2, 3 and 5: Canon EOS 5D Mark II digital camera, in manual mode; Canon MP-E 65mm Macro lens (set for 2x); and Canon MT-26EX-RT Macro Twin Lite. A Sunpak LED-160 Video Light (with a white translucent plastic filter) was used for some photos.

The following equipment was used to shoot macro Photo No. 1 and 4Fujifilm X-T1 digital camera; Fujifilm MCEX-11 extension tube; and Fujinon XF80mm macro lens. An off-camera Fujifilm EF-X500 external flash unit and Sunpak LED-160 Video Light (with a white translucent plastic filter) were used for Photo No. 4. A Raynox DCR-250 close-up filter and Canon MT-26EX-RT Macro Twin Lite was used for Photo No. 1.

Adobe Photoshop CC 2017 was used to annotate selected images.

Copyright © 2018 Walter Sanford. All rights reserved.

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8 Responses to “Post update: Cordulegastridae exuvia”

  1. Mike Powell Says:

    Great shots, Walter. The close-up details are amazing, as is your explanation of the choices you made as you worked through the key.

    • waltersanford Says:

      You’re too kind, Mike! I’m not 100% satisfied with the overall quality of my macro photos. I enjoy working to improve my skills, and feel like I’m making some progress.

  2. Arjan Kop Says:

    Hi Walter, just a tip for when you need to change the position of parts like mentums: you can apply a drop of water on the ‘hinge’ and let it do its work for at least 15 minutes. After that time, try to grab the palps with a pair of fine tweezers and start pulling. If the mentum doesn’t move, just repeat. In that way, you’ll keep your specimens in one piece 😉

    • waltersanford Says:

      Thanks for the tip, Arjan! There are two, maybe three “hinges” on the mentum. Would I need to apply a drop of water to all of the hinges? It would be GREAT to see a video demonstration of your technique. Are you feeling creative? 🙂

      • Arjan Kop Says:

        Making vids is definitely not my specialty, but I guess I could give it a go. For a study on European Cordulegaster larvae, I had to count hairs and measure several aspects of their mentums. I simply applied a large enough drop to ensure that both hinges got wet. After a while, I could start pulling- not at once, but gently flexing/deflexing it until it started to move. I simply cut off the prementum with a pair of surgeon’s scissors right behind the hinge, but if you only have a few specimens, that is not really a thing you’d like to do.
        Are you, by the way, interested in European exuviae? I often collect far more than I could keep even if I wanted to.

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