Posts Tagged ‘Family Corduliidae (Emeralds)’

Dark and moody

November 19, 2021

I spotted an emergent Uhler’s Sundragon (Helocordulia uhleri) during a photowalk along a mid-size stream at an undisclosed location in Prince William County, Virginia USA. The following photograph shows the exuvia from which the teneral adult emerged.

13 APR 2021 | PNC. Wm. County, VA | Uhler’s Sundragon | exuvia (ventral)

In the opinion of the author, larvae (nymphs)/exuviae from Family Corduliidae (Emeralds) and Family Libellulidae (Skimmers) can be challenging to differentiate and identify to the family level.

One way to differentiate Emerald from Skimmer larvae/exuvia is to look for a “ventromedial groove” in the prementum: it’s probably Corduliidae (Emeralds) if there is a ventromedial groove; it’s probably Libellulidae if there isn’t.

Look closely at a version of the preceding photo that was reformatted, rotated, and cropped to show an enlarged view of the prementum. You should notice a ventromedial groove on the basal half of the prementum, indicating this specimen is a member of Family Corduliidae (Emeralds).

13 APR 2021 | PNC. Wm. County, VA | Uhler’s Sundragon | exuvia (ventral)

Three raised structures on the underside of the prementum remind me of the hood ornament on a 1949 Lincoln automobile. (No, I wasn’t alive in 1949!)

Related Resources

Tech Tips

One reason I underexposed the photo is to add definition to the ventromedial groove and avoid overexposing the black background.

I prefer a white background for photographing odonate exuviae. Using a black background proved to be more challenging than I expected. More later in a follow-up blog post.

Copyright © 2021 Walter Sanford. All rights reserved.

Post update: What is it — emerald or skimmer?

November 5, 2021

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

The presence of a ventromedial groove in the prementum suggests this specimen is a member of Family Corduliidae (Emeralds) and in fact it is.

Congratulations to Douglas Mills, who correctly identified the family of this specimen.

Going with corduliidae for the groove. It’s got impressive crenulations — I had to double check they weren’t jagged and this was a trick question 🙂 Source Credit: Douglas Mills.

Douglas successfully avoided the trap that was set when I chose to use a specimen that features deeply-scalloped crenulations along the margins of the palpal lobes. According to Kevin Hemeon, member of the “Odonate Larvae and Exuviae” Facebook group, crenulations like these are a characteristic field mark for Genus Neurocordulia (Shadowdragons) in the Family Corduliidae (Emeralds).

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Relative length of cerci versus paraprocts

October 19, 2021

A quote from my last blog post sets the stage for this post …

One way to differentiate Emerald from Skimmer larvae/exuvia is to examine the anal pyramid: it’s probably Corduliidae (Emeralds) if the cerci are at least half as long as the paraprocts; it’s probably Libellulidae (Skimmers) if the cerci are less than half the length of the paraprocts. More about this in a follow-up blog post. Source Credit: Ventromedial groove, by Walter Sanford.

Here are two examples that illustrate when the method works to confirm exuviae are from Family Libellulidae (Skimmers).

Eastern Amberwing (Perithemis tenera)

Look closely at the full-size version of the following annotated image of an exuvia from an Eastern Amberwing dragonfly (Perithemis tenera).

Notice the cerci are slightly less than half the length of the paraprocts, indicating this specimen is from Family Libellulidae (Skimmers).

Carolina Saddlebags (Tramea carolina)

The next specimen is an exuvia from a Carolina Saddlebags dragonfly (Tramea carolina).

Notice the cerci are slightly less than half the length of the paraprocts, indicating this specimen also is from Family Libellulidae (Skimmers).


Finally, here’s an example that illustrates when the method doesn’t work.

Spot-winged Glider (Pantala hymenaea)

The last specimen is an exuvia from a Spot-winged Glider dragonfly (Pantala hymenaea). Spot-winged Glider is a member of Family Libellulidae (Skimmers).

Notice the cerci are longer than half the length of the paraprocts, suggesting this specimen is from Family Corduliidae (Emeralds). But the exuvia isn’t an Emerald — it’s a Skimmer!

As it turns out, for genus Pantala it’s more important to look at the relative length of the superior abdominal appendage (epiproct) versus the inferior abdominal appendages (paraprocts). Who knew?

What the take-aways?

Although I haven’t identified (with certainty) many species of exuviae from Family Libellulidae (Skimmers), it didn’t take long to find an exception to the rule of thumb for differentiating Emeralds and Skimmers by examining the relative length of cerci versus paraprocts.

In contrast, the rule of thumb that looks at the presence or absence of a ventromedial groove seems to work every time, with the caveat that some species in other families feature a ventromedial groove. In those cases, the family to which the specimen belongs is fairly obvious.

I think it’s good to have more than one arrow in your quiver, so you should be familiar with both methods for differentiating Emeralds and Skimmers. That said, I recommend starting the process of identification by looking for a ventromedial groove.

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Ventromedial groove

October 15, 2021

In North America (restricted to Canada and the United States of America) there are seven families of dragonflies in the suborder Anisoptera.

Identification of dragonfly larvae (nymphs)/exuviae to the Family Level is fairly straightforward for five of the seven families.

Flat labium

Three families feature a flat labium and are easy to differentiate: Aeshnidae (Darners); Gomphidae (Clubtails); and Petaluridae (Petaltails).

Darner larvae (nymphs)/exuviae have long, thin antennae; Clubtail larvae/exuviae have short, thick antennae. Petaltail larvae/exuviae feature several distinctive field marks that are easy to recognize.

Mask-like labium

Four families feature a mask-like labium: Cordulegastridae (Spiketails); Corduliidae (Emeralds); Libellulidae (Skimmers); and Macromiidae (Cruisers).

Two of these four families are easy to recognize. The distinctive jagged crenulations on the face mask of Spiketails are unmistakeable! Cruisers feature a prominent “horn” on the face-head.

In the opinion of the author, larvae/exuviae from Emeralds and Skimmers can be challenging to differentiate and identify to the family level.

Anal pyramid

One way to differentiate Emerald from Skimmer larvae/exuvia is to examine the anal pyramid: it’s probably Corduliidae (Emeralds) if the cerci are at least half as long as the paraprocts; it’s probably Libellulidae (Skimmers) if the cerci are less than half the length of the paraprocts. More about this in a follow-up blog post.

Ventromedial groove

Another way to differentiate Emerald from Skimmer larvae/exuvia is to look for a “ventromedial groove” in the prementum: it’s probably Corduliidae (Emeralds) if there is a ventromedial groove; it’s probably Libellulidae if there isn’t.

For example, look at the full-size version of the following annotated image of a Common Baskettail dragonfly (Epitheca cynosura) exuvia. Notice the groove down the middle of the prementum, oriented vertically in the photo — that’s a “ventromedial groove” (a compound word derived from “ventral” and “medial/midline”) — indicating this specimen probably is from Family Corduliidae (Emeralds).

… the groove is developed on the basal half of the prementum … Source Credit: K. J. Tennessen, Dragonfly Nymphs of North America, https://doi.org/10.1007/978-3-319-97776-8_11, p. 346.

Here’s another example showing a ventromedial groove in the prementum of a Prince Baskettail dragonfly (Epitheca princeps) exuvia.

In contrast, look closely at the full-size version of the following photo of a Spot-winged Glider dragonfly (Pantala hymenaea) exuvia. Notice there is no ventromedial groove in the prementum, indicating this specimen probably is from Family Libellulidae (Skimmers).

An important caveat

Beware: Some larvae/exuviae in other families of dragonflies, such as Tiger Spiketail dragonfly (Cordulegaster erronea), feature a ventromedial groove in the prementum. Therefore the take-away from this post is the presence of a ventromedial groove is not a single definitive morphological character for Emeralds, rather it should be used in combination with other field marks.

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Beware of look-alikes!

September 28, 2021

Some species of dragonfly larvae/exuviae look similar to other species. Here are a couple of look-alikes from two different families that might fool you.

One species of Corduliidae in our region [North America], Epitheca princeps, resembles the macromiid general body shape and is nearly as large, but the legs are short compared to its body dimensions and it lacks a triangular frontal projection. Source Credit: K. J. Tennessen, Dragonfly Nymphs of North America, https://doi.org/10.1007/978-3-319-97776-8_10, Macromiidae, p. 329.

The first annotated image shows a ventral view of a Prince Baskettail (Epitheca princeps) exuvia. E. princeps is a member of Family Corduliidae (Emeralds).

Notice the appearance of the E. princeps exuvia is quite similar to the Stream Cruiser (Didymops transversa) exuvia shown below. D. transversa is a member of Family Macromiidae (Cruisers).

The E. princeps exuvia features lateral spines and well-developed mid-dorsal hooks on some abdominal segments. Notably “it lacks a triangular frontal projection” (K. J. Tennessen), or stated more simply, there isn’t a “horn” on its face-head.

The D. transversa exuvia also features lateral spines and mid-dorsal hooks, as shown below. Notice the mid-dorsal hooks aren’t as cultriform as E. princeps. In contrast to the E. princeps exuvia, notice the prominent “horn” on the face of the D. transversa exuvia. It’s all about the “horn.”

A “horn” on the face-head is a characteristic field mark for odonate larvae/exuviae in the Family Macromiidae (Cruisers).

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Previews of Coming Attractions – Fall Species of Odonates

August 31, 2021

There is an annual cycle of odonate activity that can be subdivided into three broad categories: Early Season (spring); Mid-season (summver); and Late Season (fall).

As we endure the “Dog Days of Summer,” waiting for the calendar to turn to fall, it’s time to begin looking for the Late Season (fall) species of odonates.

This blog post provides a photo sampler of some of the fall species of odonates that can be seen during September, October, and November in the Commonwealth of Virginia. This post is not intended to be a comprehensive field guide that features every odonate species that can be seen during the same time period.

Full Disclosure

Some fall species are easier to find than others. And some species are flyers rather than perchers, making it almost essential to capture them in flight using an insect net. That being said, it’s richly rewarding to find any of the rare to uncommon species so do your homework and be persistent. Good luck and happy hunting!


Editor’s Notes

Click on the date listed in the caption for each photo to see the original blog post for that image; click on the odonate name to see all of my blog posts related to that species.

Sincere thanks to Michael Boatwright, founder and administrator of the Virginia Odonata Facebook group, for providing photographs of many of the rare to uncommon fall species of odonates featured in this photo sampler. Click on the word “Photo” in the caption for each of Mike’s photographs to see his original Facebook post for that image.

Every species features the following information: common name; scientific name; early-date/late-date; abundance; and habitat. All information is excerpted from “CHECKLIST OF THE DRAGONFLIES AND DAMSELFLIES OF VIRGINIA, April 2017 and April 2020 updates” by Dr. Steve Roble, Staff Zoologist at the Virginia Department of Conservation and Recreation, Division of Natural Heritage.


Dragonflies (Order Anisoptera)

Family Aeshnidae (Darners)

Black-tipped Darner (Aeshna tuberculifera)

Adult flight period: JUN 30 – OCT 29. Rare to uncommon. Habitat: Montane ponds.

Photo used with written permission from Michael Boatwright.

Common Green Darner (Anax junius)

Adult flight period: FEB 27 – DEC 30. Common. Habitat: Ponds.

Fawn Darner (Boyeria vinosa)

Adult flight period: JUN 03 – NOV 07. Common. Habitat: Streams, rivers.

Shadow Darner (Aeshna umbrosa)

Adult flight period: JUN 08 – DEC 05. Common. Habitat: Ponds, streams.

Family Corduliidae (Emeralds)

Clamp-tipped Emerald (Somatochlora tenebrosa)

Adult flight period: JUN 08 – OCT 15. Common. Habitat: Ponds, small streams.

Photo used with written permission from Michael Boatwright.

Fine-lined Emerald (Somatochlora filosa)

Adult flight period: JUL 10 – OCT 15. Rare to uncommon. Habitat: Boggy streams, swamps, marshes.

18 SEP 2019 | PNC. Wm. County | Fine-lined Emerald (male)

Family Gomphidae (Clubtails)

Arrow Clubtail (Stylurus spiniceps)

Adult flight period: JUN 13 – OCT 19. Uncommon to common. Habitat: Rivers.

Photo used with written permission from Michael Boatwright.

Laura’s Clubtail (Stylurus laurae)

Adult flight period: JUN 20 – SEP 26. Rare to uncommon. Habitat: Streams, rivers.

Photo used with written permission from Michael Boatwright.

Russet-tipped Clubtail (Stylurus plagiatus)

Adult flight period: JUN 15 – NOV 06. Uncommon to common. Habitat: Streams, rivers.

Family Libellulidae (Skimmers)

Autumn Meadowhawk (Sympetrum vicinum)

Adult flight period: MAY 28 – JAN 03. Common. Habitat: Ponds.

Blue-faced Meadowhawk (Sympetrum ambiguum)

Adult flight period: MAY 22 – NOV 19. Uncommon. Habitat: Swamps, ponds.

Black Saddlebags (Tramea lacerata)

Adult flight period: APR 12 – OCT 30. Common. Habitat: Ponds.

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

Spot-winged Glider (Pantala hymenaea)

Adult flight period: MAY 08 – OCT 20. Common. Habitat: Ponds.

A Spot-winged Glider dragonfly (Pantala hymenaea) netted at Saint Louis Catholic School, Fairfax County, Virginia USA. This individual is a female.

20 JUL 2016 | Fairfax County, VA USA | Spot-winged Glider (female)

Wandering Glider (Pantala flavescens)

Adult flight period: MAY 02 – NOV 17. Common. Habitat: Ponds.

Damselflies (Order Zygoptera)

Family Lestidae (Spreadwings)

Great Spreadwing (Archilestes grandis)

Adult flight period: JUN 25 – NOV 11. Uncommon. Habitat: Streams, ponds.

Spotted Spreadwing (Lestes congener)

Adult flight period: JUN 10 – NOV 11. Uncommon. Habitat: Ponds.

Photo used with written permission from Michael Boatwright.

 


Classification of Fall Species into Sub-groups

Migratory Species

At least five major species of dragonflies known to be migratory in North America.

  • Black Saddlebags (Tramea lacerata)
  • Common Green Darner (Anax junius)
  • Spot-winged Glider (Pantala hymenaea)
  • Wandering Glider (Pantala flavescens)

Rare to Uncommon Species

  • Arrow Clubtail (Stylurus spiniceps)
  • Black-tipped Darner (Aeshna tuberculifera)
  • Blue-faced Meadowhawk (Sympetrum ambiguum)
  • Clamp-tipped Emerald (Somatochlora tenebrosa)
  • Fine-lined Emerald (Somatochlora filosa)
  • Laura’s Clubtail (Stylurus laurae)
  • Ocellated Darner (Boyeria grafiana)
  • Great Spreadwing (Archilestes grandis)
  • Spotted Spreadwing (Lestes congener)

Copyright © 2021 Walter Sanford. All rights reserved.

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.

Related Resources

Odonate Exuviae – a hyperlinked list of identification guides to many species of odonate exuviae from seven families of dragonflies and three families of damselflies.

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.


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