Posts Tagged ‘Neurocordulia yamaskanensis’

Neurocordulia yamaskanensis exuvia

April 13, 2020

A Stygian Shadowdragon dragonfly (Neurocordulia yamaskanensis) exuvia was collected by Freda van den Broek on 10 June 2019 along the St. Croix River in Interstate Park, Polk County, Wisconsin USA.

A two-step process was used to verify the genus and species of the exuvia.

  1. Determine the family.
  2. Determine the genus and species.

Step 1. Family

First, determine the family of the specimen. For reference, watch the excellent Vimeo video, Identifying dragonfly larva to family (8:06). Here’s the decision tree used to identify the exuvia as a member of the Family Corduliidae (Emeralds).

  • The specimen has a mask-like labium (prementum) that covers the face, as shown in Image No. 1, characteristic of four families of odonates: Cordulegastridae (Spiketails); Corduliidae (Emeralds); Libellulidae (Skimmers); and Macromiidae (Cruisers).
  • There is no horn on the face-head, characteristic of Macromiidae, so it’s not a cruiser.
  • Cordulegastridae has angular, jagged crenulations on its labium, so it’s not a spiketail. The crenulations for Corduliidae and Libellulidae can look similar.
  • Look at the anal pyramid to differentiate Corduliidae and Libellulidae: It’s probably Corduliidae if the cerci are at least half as long as the paraprocts. [Editor’s Note: It’s probably Libellulidae if the cerci are less than half the length of the paraprocts.]

In summary, the exuvia has a mask-like labium, and no horn on its face-head. The deeply-scalloped crenulations along the margins of the palpal lobes are a characteristic field mark for Genus Neurocordulia (Shadowdragons) in the Family Corduliidae (Emeralds), according to Kevin Hemeon, member of the “Odonate Larvae and Exuviae” Facebook group.

Although the anal pyramid isn’t shown clearly in any of the photos in this field guide, careful examination of photos of the teneral adult that emerged from the exuvia (see The Backstory, below) confirmed the dragonfly is a Stygian Shadowdragon. Stygian is the only species of Neurocordulia (Shadowdragons) within range of Wisconsin.

A face-head view of the exuvia is shown in Image No. 1, magnified approximately two and one-half times life size (~2.5x). Notice the mask-like labium that covers the face of the exuvia, including deeply-scalloped crenulations with bundles of bristles (setae) located along the margins of the palpal lobes.

No. 1 | Neurocordulia yamaskanensis | exuvia (face-head)

Step 2. Genus and species

Dichotomous keys from Identification Keys to Northeastern Anisoptera Larvae, compiled by Ken Soltesz, were used to verify the genus and species of the exuvia. Field marks that match this specimen are highlighted in boldface green text.

Key to the Genera of the Family Corduliidae, p. 28.

1a. Pair of small tubercles on top of head; Lateral lobe of labium with 4 or 5 setae (except sometimes 6 or 7 in Neurocordulia). (2)

2a. Strong lateral spines of abdominal segment 8 very divergent and as strong as parallel spines of [S]9. (Neurocordulia)

Alternate Key to the Genera of the Family Corduliidae, p. 29.

1a. Dorsal hooks present and well developed on some of the abdominal segments. (2)

2a. Lateral spines present on segment 8. (3)

3a. Crenulations on distal margin of labial palpi nearly semicircular or even more deeply cut; Lateral spines on segment 8 divergent. (Neurocordulia)

Key to the Species of the Genus Neurocordulia, p. 31.

1b. Lateral spines of 9 about 30 to 50 percent of the length of segment 9, not extending beyond the tips of the caudal appendages; Dorsal hooks of segments 7 to 9 reduced to scarcely more than a short ridge; Length 22 – 24.5 mm. (yamaskanensis)

The following annotated focus-stacked composite images illustrate key field marks described in Soltesz’s dichotomous keys.

Notice the specimen has stubby mid-dorsal hooks along the length of its abdomen, as shown in Image No. 2.

Lateral spines are present on abdominal segments eight and nine (S8-S9): the lateral spines on S8 are divergent; the ones on S9 are parallel.

The exuvia is ~2.4 cm (~0.95 in) in length — the longest shadowdragon larva/exuvia in the genus Neurocordulia. Notice the lateral spines on abdominal segment nine (S9) don’t extend beyond the tips of the caudal appendages (terminal appendages), as shown below.

The Backstory

The following narrative was provided by Freda van den Broeck.

On the last morning of the Wisconsin Dragonfly Society Annual Meeting weekend — Sunday, June 10th 2019 — I made my way to the boat landing in Interstate Park, St. Croix Falls, Wisconsin USA.

The previous morning I’d photographed Mustached Clubtail emerging there (with Alon Coppens). We also saw several teneral Rapids Clubtails. One didn’t have to look hard to find exuviae — they were most easily seen on the rocks, just a couple of feet above the water line. I was really hoping to find a Snaketail emerging, but had no such luck.

Photo of St. Croix river used with permission from Freda van den Broek.

Just as I was about to head back to the car, I spotted a teneral, that had crawled up the rock face higher than I would have expected. At that point, I thought it was “just another baskettail” — we’d seen many of them on Friday afternoon and Saturday. But it was pretty and shiny, so I had to take a few pictures, even though I was late for breakfast. (It was around 8:20 am.)

It was several days later before I realized that it wasn’t a baskettail, but a Shadowdragon, and that a few of the exuviae I’d collected there were Stygian Shadowdragons. Source Credit: Freda van den Broek.

Photo used with permission from Freda van den Broek.

Tenerals are usually tough to identify, but you’ll notice in both photos that the [small yellow] spot on [side of] the thorax is clearly visible. Source Credit: Freda van den Broek.

Photo used with permission from Freda van den Broek.

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – N. yamaskanensis exuvia (face-head)

April 10, 2020

The following annotated focus-stacked composite image shows a Stygian Shadowdragon dragonfly (Neurocordulia yamaskanensis) exuvia collected by Freda van den Broek on 10 June 2019 along the St. Croix River in Interstate Park, Polk County, Wisconsin USA.

10 JUN 2019 | Polk County, WI | Stygian Shadowdragon (exuvia)

Notice the unusual shape of the crenulations between the palpal lobes of its mask-like labium. Is this field mark unique to N. yamaskanensis or common to all species of the genus Neurocordulia (Shadowdragons)? Enquiring minds want to know!

Tech Tips

Laowa 25mm Ultra Macro lens, set for 2.5x magnification, and Canon EOS 5D Mark II DSPLR was used to photograph the subject against a pure white background (255, 255, 255) following the “Meet Your Neighbours” (MYN) technique.

24 photos were used to create the composite image, including 23 photos taken using an aperture of f/5.6 and one photo taken at f/16.

If you look closely at the full-size version of the image, then you will notice some areas that indicate the final image is a few layers short of a perfect focus stack. But hey, not bad for a new lens and a manual focus rail that I used for the first time!

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – N. yamaskanensis exuvia (dorsal, ventral)

April 8, 2020

A Stygian Shadowdragon dragonfly (Neurocordulia yamaskanensis) exuvia was collected by Freda van den Broek on 10 June 2019 along the St. Croix River in Interstate Park, Polk County, Wisconsin USA.

Dorsal

The first dorsal view is a square crop of the full-size version of a focus-stacked composite image of the subject. Notice the specimen has stubby mid-dorsal hooks along the length of its abdomen and lateral spines on abdominal segments eight (S8) and nine (S9).

10 JUN 2019 | Polk County, WI | Stygian Shadowdragon (exuvia)

The original full-size image, shown below, was straightened and cropped slightly.

10 JUN 2019 | Polk County, WI | Stygian Shadowdragon (exuvia)

Ventral

The first ventral view is a square crop of the full-size version of a focus-stacked composite image of the subject. Notice the compact size of the prementum, and its unusual shape.

10 JUN 2019 | Polk County, WI | Stygian Shadowdragon (exuvia)

The original full-size image, shown below, was cropped slightly.

10 JUN 2019 | Polk County, WI | Stygian Shadowdragon (exuvia)

Related Resources

Tech Tips

This subject was photographed against a pure white background (255, 255, 255) using the “Meet Your Neighbours” (MYN) technique.

Three (3) photos were used to create the dorsal composite image, including a single photo focused on the head/thorax, and two places along the abdomen (S5-S6 and S9).

13 photos were used to create the ventral composite image, including multiple photos focused on the prementum, thorax, and two places along the abdomen (S3-S4; S7-S8).

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – N. yamaskanensis exuvia (dorsal-lateral)

April 6, 2020

The following focus-stacked composite image shows a dorsallateral view of a Stygian Shadowdragon dragonfly (Neurocordulia yamaskanensis) exuvia collected by Freda van den Broek on 10 June 2019 along the St. Croix River in Interstate Park, Polk County, Wisconsin USA.

10 JUN 2019 | Polk County, WI | Stygian Shadowdragon (exuvia)

Notice the specimen has stubby mid-dorsal hooks along the length of its abdomen and lateral spines on abdominal segments eight (S8) and nine (S9).

Related Resources

Tech Tips

This subject was photographed against a pure white background (255, 255, 255) using the “Meet Your Neighbours” (MYN) technique.

Four (4) photos were used to create the composite image, including a single photo focused on the head, thorax, and two places along the abdomen (S6-S7 and S9-S10).

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – Focus-stacked composite image

April 3, 2020

The following focus-stacked composite image shows a Stygian Shadowdragon dragonfly (Neurocordulia yamaskanensisexuvia collected by Freda van den Broek on 10 June 2019 along the St. Croix River in Interstate Park, Polk County, Wisconsin USA.

10 JUN 2019 | Polk County, WI | Stygian Shadowdragon (exuvia)

Related Resources

Tech Tips

This subject was photographed against a pure white background (255, 255, 255) using the “Meet Your Neighbours” (MYN) technique.

24 photos were used to create the composite image, including 23 photos taken using an aperture of f/5.6 and one photo taken at f/16.

If you look closely at the full-size version of the image, then you will notice some areas that indicate the final image is a few layers short of a perfect focus stack. But hey, not bad for a new lens and a manual focus rail that I used for the first time!

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – Stygian Shadowdragon exuvia

March 30, 2020

A Stygian Shadowdragon dragonfly (Neurocordulia yamaskanensis) exuvia was collected by Freda van den Broek on 10 June 2019 along the St. Croix River in Interstate Park, Polk County, Wisconsin USA.

Stygian is the only species of Neurocordulia (Shadowdragons) within range of Wisconsin.

10 JUN 2019 | Polk County, WI | Stygian Shadowdragon (exuvia)

Notice the interesting crenulations on the labium (face mask) of the exuvia, including bundles of bristles (setae) along the margins of the palpal lobes.

Tech Tips

This subject was photographed against a pure white background (255, 255, 255) using the “Meet Your Neighbours” (MYN) technique.

I set the Laowa 25mm Ultra Macro lens for 2.5x magnification and an aperture of f/5.6, then took some test shots of the subject. Next I shot 23 photos for a focus-stacked composite image showing the face-head-dorsal view of this specimen.

Finally I shot a few photos at f/16, focused manually on the face mask. At the time of this writing, it was too late to create the focus stack so here’s one of the shots at f/16. An aperture of either f/5.6 or f/8 is the “sweet spot” for this lens, according to video reviews I watched. The net result — some image sharpness was sacrificed in favor of more depth of field.

Copyright © 2020 Walter Sanford. All rights reserved.


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