Modification of Fig 2 from Wolfe et al 2021. As described below, but with the names of genera featured in the A-Z month listed next to their phylogenetic position. Living species in plain text, fossils in italics. Gross morphology in the convergent evolution of representative true crabs (Brachyura), porcelain crabs (Porcellanidae), hairystone crabs (Lomisidae), and king crabs (Lithodoidea). Losses (open circles) observed in frog crabs (Raninoidea). Topology simplified from our previous papers.

With the end of the month, #CrabAZ is truly over. I hope they helped distract you. As @upulie.bsky.social requested a megathread, I made a carcinization tracker, labeling featured genera (living in plaintext, fossil in italic).

Megathread follows, now back to your irregularly scheduled crabs! 🦀🧪🦑

Dammit my hashtag that I created was wrong, it's #CrabAZ singular. Scroll up if that's how you found this post

Zebra Urchin Crab (Zebrida adamsii) Zebra Urchin Crab from Hairball II on July 23, 2020 by Dan Schofield

Z is for Zebrida, completing the alphabet of #CrabAZ!

This pretty little guy rides around on fire urchins, which are venomous to us. But the crab nibbles its tube feet! Its body shape and colors both match and contrast with the urchin.

But it's not over yet! Come back tomorrow for a bonus post 🦀🧪🦑

Y is for Yaldwynopsis.

Like Dicranodromia, has small back legs that could carry items. But we don't know what they hold.

Early fossils of Yaldwynopsis' family, Homolidae, are known from 150 million years ago. Stegosaurus could have met them (if it was in the deep sea)!

#CrabAZ 🦀🧪🦑

Xylopagurus rectus, MCZ 52033. From 195-215 m depth. My photo of the specimen partially inside the wood, with the carapace and most legs visible. Next to it is the specimen number label, and a scale showing the specimen is about 6 cm long. We also have the type material of this species, but it was too delicate for me to remove.

Xylopagurus rectus, drawing Henri Filhol. Drawing or perhaps etching, of the crab inside a piece of wood. Clearly shows how the 6th and final segment of the abdomen forms a hard plug. https://en.wikipedia.org/wiki/Xylopaguridae#/media/File:FMIB_46952_Xylopagurus_rectus_(A_M-Eds).jpeg

Xylopagurus cf. philippinensis. Photo SJADES 2018. Cutaway of the slender twig dwelling hermit crab with a straight body inside its sunken wood. 12-15cm long, depth 375m. https://www.straitstimes.com/singapore/singapore-indonesia-deep-sea-expedition-discoveries

X is for Xylopagurus.

This hermit crab, found at depths of 170-475m, is WEIRD!

Instead of a shell, they tunnel a hole into fallen bits of wood (how did it get down there?).

Then they plug the end with their own butt (6th abdominal segment that is heavily calcified).

#CrabAZ 🦀🧪🦑

Line drawing of female holotype of Waldotheres mccainae. By Raymond Manning. She has a round/hexagonlike carapace, and the big fat pleon is open (even in this dorsal view) because there are eggs.

Line drawing of male Waldotheres mccainae by Raymond Manning. Carapace similar shape to the female, but you see no pleon, as it's completely under the body. The legs are hairy.

Since no photos exist for Waldotheres, this is of a similar species, Zaops. The photo is a person's hand holding an opened oyster, inside which are 5 round pea crabs. They look like weird orange peas with legs. https://www.inaturalist.org/observations/478370

W is the hardest letter of #CrabAZ, and it's for Waldotheres.

Zero photos of them exist! The 1993 description has drawings of #1 female and #2 male types from Rep. Congo. We know they are parasitic inside Donax clams, similar to others in the family (photo of the oyster pea crab)

#CrabAZ 🦀🧪🦑

It's the #CrabAZ that @franzanth.bsky.social has been waiting for: V is for Velolambrus...

or DORITO CRAB!!!

It's not "the" species he called a dorito, but I think these are even more dorito shaped. They are cryptic under rocks, mud, or seagrasses.

🦀🧪🦑

U is for Uca, the fiddler crabs!

A group so cool, @mrosenberg.bsky.social created an entire #FiddlerCrabBracket about their fascinating behaviors like courtship dances, fights, and tunneling!

Entire bracket details here, and ADORABLE winner below:

docs.google.com/document/d/1...

#CrabAZ 🦀🧪🦑

T is for Trizopagurus, the only "normal" (snail shell wearing) hermit crab of #CrabAZ.

The better known Halloween hermits (quoted) were in this genus until 1995, but they differ in ornamentation of legs and claws.

T. magnificus is so cute on its own though! Together they are spots & stripes!

🦀🦑🧪

Yellowline Arrow Crab (Stenorhynchus seticornis) Yellowline Arrow Crab from Guantánamo Bay, Guantánamo, CU on May 24, 2023 at 07:33 PM by Robin White. Molted

S is for Stenorhynchus.

The arrow crab might have the most alienesque shape of all. Found in the wild in the Caribbean, they can be a menace in the reef aquarium, but friendly to people.

Here's one with its own moult!

#CrabAZ 🦀🧪🦑

Dorsal view of Raninoides benedicti alone on black background. Photo by Arthur Anker. Very elongate, carapace at least 2x as long as wide, true crab. Small abdomen is sticking straight out the back. Claws look like wrenches and multiple distal segments of the legs look like spades. Crab is brown with orangeish mottling. Limbs have blue edges. https://www.crabdatabase.info/en/crabs/brachyura/podotremata/raninoidea/raninidae-4

Plate of colorful raninid crabs including the same image of Raninoides benedicti. Shows the variations within the "family" of frog crabs. Lyreididae. a, Lyreidus tridentatus; b, Lysirude channeri . Raninidae. c, Cosmonotus grayii; d, Flaberhina balabacensis; e, Notopus dorsipes; f, Ranilia muricata; g, Ranina ranina; h, Raninoides benedicti; i, Raninoides lamarcki; j, Symethis variolosa; k, Umalia misakiensis. Plate 39: https://www.publish.csiro.au/book/7895/

Psst: carcinization is not inevitable!

R is for Raninoides, one of the best examples of DEcarcinization. It's a true crab, but its body is elongated and the abdomen sticks out. The wrench and spadelike appendages, and torpedolike body, are good for burrowing (see video, next skeet)

#CrabAZ 🦀🧪🦑

Q is for Quadrella.

Members of the coral guard crab family defend their hosts against marauders, even snipping away crown of thorns stars (see quote!).

You might say the coral is under (protection of) Quadrella-ella-ella-a...

#CrabAZ 🦀🦑🧪

Holotype of Patagurus rex, dorsal view. Photos by Arthur Anker. This is a strange hermit crab, shown naked. Its carapace is shaped like 2 triangles stuck together, hardened with several lateral projections. Unlike other hermits that have a long, curved abdomen, this one is tiny, perhaps 1/3 the length of the carapace. The carapace is whitish/pinkish, claws red, walking legs red and white striped.

Dorsal view of the Patagurus holotype again (always the holotype because there are no other specimens). This time you see a small bivalve, the mussel Gregariella, covering the pleon in a sideways fashion.

Similar to the last photo, except the bivalve is popped off (but in the image) and the crab is seen slightly more anteriorly, so its mouthparts are visible

P is for Patagurus, a hermit crab known from only ONE SPECIMEN EVER!

Instead of a snail shell, it wears a bivalve to cover its tiny abdomen. Is this how hermit crabs gave up their houses in carcinization? 🤔 (see king & coconut crabs, ALSO hermits)

#CrabAZ 🦀🧪🦑

www.biotaxa.org/Zootaxa/arti...

Dorsal view of Ommatocarcinus pulcher specimen. Photo by chekiangense_longpotamon. It has eyestalks longer than the carapace width, and a pentagon shaped carapace. The claws and carapace have red dots. One leg is missing. https://www.inaturalist.org/observations/213167907

Goneplax rhomboides in the mud, photo by Emil @bergylta. There isn't an in situ photo of any Ommatocarcinus that I could find. The angular crab is seen rearing up with its legs still buried. Long claws 2x the body are both outstretched in a threat display. The long eyestalks (a biy smaller than Ommatocarcinus) give it a funny rather than scary look. https://www.inaturalist.org/observations/99962774

O is for Ommatocarcinus.

What's up with this crab other than having extremely long eyestalks? It can make sounds, by rubbing a claw against its...face!?

Like the relative Goneplax, pic by @bergylta.bsky.social, they bury themselves in soft mud, waiting to meet friend or foe.

#CrabAZ 🦀🧪🦑

Genus Neodorippe Neodorippe from 6 Changi Village Rd, Changi Point Coastal Walk, Singapore 509907 on May 9, 2024 at 04:54 AM by budak

N is for Neodorippe, the leaf porter crab, who offers...a mangrove leaf...for Valentine's Day!

By day: crab buried in mud, leaf on top.

By night: crab swims underneath leaf, near the surface.

At all times, crab is hidden. But its love is not! 💕

#CrabAZ 🦀🧪🦑

Meme of Japanese spider crab. It's a red crab with cartoonishly long claws on a black background. Text: "This Tuesday has been exceptionally long. Please send thoughts, prayers, and treats to a very tired Reginald "

#CrabAZ never ignores memes. M is for Macrocheira.

This is both the largest arthropod alive (3.8 m or 12 ft leg span, only males are this extreme) and the only living species in its family. Mainly found in Japanese waters up to 600 m depth.

(Yes we know it's Thursday, sorry)

🦀🧪🦑

L is for Lomis!

On #DarwinDay, it's fitting that the #CrabAZ species is MY FAVORITE, and I saw it in Tasmania, where the Beagle also visited. It's camouflaged in the intertidal (except the blue antennae!)

BTW, the crab feed is >300 likes, join and post your favorite! bsky.app/profile/luci...

🦀🧪🦑

Kiwa hirsuta, photo Alexis Fifis. Elongated white squat lobster, seen dorsally. Most notable feature is hairy legs (hirsuta = hairy) and exceptionally hairy claws. The proximal parts of the claws are more than 2x the length of the carapace

@thefuzzyslug artwork of a group of 15+ white Kiwa tyleri, all overlapping each other and taking up nearly the entire frame. This is true to their real life behavior. Some colored anemones are in the corners. Bottom of this image says polarlightszine.itch.io

K is for Kiwa.

In hydrothermal vents and methane seeps >1000m, exotic locales like Antarctica and the Galapagos, yeti crabs (of octonauts fame) thrive. Divorced from sunlight, they farm chemosynthetic bacteria on their own claws, waving them around!

Art @thefuzzyslug.bsky.social

#CrabAZ 🦀🧪🦑

Clipperton Land Crab (Johngarthia oceanica) Clipperton Land Crab from Tecomán, MX-CL, MX on April 16, 2018 at 12:39 PM by J.R. Kuethe. Ninja crabs

J is for Johngarthia.

Land crabs are awesome! This genus eats small birds(!) and their eggs, and traverses up to 1000m above sea level on isolated islands. This species can't swim, but can tolerate immersion in freshwater - some other land crabs will drown if fully immersed.

#CrabAZ 🦀🧪🦑

Insulaplax inermis (Takeda & Miyake, 1971), female (2.4 × 1.9 mm) (ZRC 2019.0483), Palau. Photos by Peter Ng. A, overall dorsal view (missing 2 legs on the right side); B, frontal margin and underlying proepistomal tooth; C, frontal margin showing entire anterior carapace rim and underlying proepistomal tooth. https://brill.com/view/journals/cr/92/8/article-p979_6.xml

The unidentified hymenosomatid I found in a tidepool in a parking lot Tasmania, seen in my hand. Since this wasn't Palau, it's not Insulaplax and is probably a Halicarcinus species (that doesn't match any key). Dark brown in a sort of pentagon shape. Missing a leg.

Halicarcinus quoyi, photo Lisa Kean. Also in Tasmania, illustrates the flat fuckery. Frontal view of the crab, which is dark brown, and looks like its top half is cut off. Because it is FLAT. Around the crab is what might be brown algae - flexible tubes of something. https://www.inaturalist.org/observations/146030488

I is for Insulaplax.

A member of my favorite, FLAT FUCK, true crab family. This species is endemic to streams in Palau, but other Hymenosomatidae live in marine, intertidal, brackish, and fresh waters. Why I care: I had one in my hand, didn't recognize it, and didn't collect it. FAIL 🤣

#CrabAZ 🦀🦑🧪

Huenia heraldica, photo Lynn Biscop. Some bright green algae looking thing on black sand. But wait! It has legs! As you look closer, you see the side of the carapace and even the eye. Edges of the carapace are scalloped to mimic the shape of the algae. It's attached a hilarious large bit of algae to the top of its head. https://www.inaturalist.org/observations/155593497

Hoplophrys oatesii, aka the candy crab, photo Steve Smith. A white background crab with stripes and many pink spiky protrusions, standing in a pink and white coral that it looks exactly like. Its legs and eyes look like polyps. Actual polyps of the same coral are attached on the head. https://www.inaturalist.org/observations/195416615

H is for Huenia, and Hoplophrys.

What these crabs (yes, they are) have in common is ✨fashion✨!

Their bodies imitate their environment (algae, soft coral) and use little hooked setae to wear pieces of their home as camouflage.

They love you and help fight the horrors with silliness.

#CrabAZ 🦀🧪🦑

G. dennerle, photo Chris Lukhaup A purple crab, darker body and legs and bright claws, with bright yellow eyes with pseudopupils. On the "cheeks" are lattice like setae that help keep them wet when they go on land. It's viewed from the front on gravel in an aquarium.

G. notophorum, photo Oliver Mengedoht Close up on the carapace and face of an orange crab. Notably, she has over a dozen translucent BABY CRABS riding on top of the carapace. The baby crabs have eyes. Scale bar 5mm, the mom is maybe 15 mm and the babies about 1 mm

G. malayanum, photo Francesco Tomasinelli An adorable nepenthiphile crab which is mostly dark purple with claws tipped in red. It is peeking out from the rounded mouth of a carnivorous pitcher plant, which also has spiky leaves

G. bau, photo Lars Fehlandt Bright red crab with dark eyes, on a bright green fernlike leaf. Photo in the wild in Sarawak, Malaysian Borneo

G is for Geosesarma.

Popular pets, some species were/are exploited by the aquarium trade before being described. Each has a small range in SE Asia, traversing freshwater and land. They hatch as minicrabs instead of larvae, and the mom keeps them safe for a few weeks!

#CrabAZ 🦀🧪🦑

Fennerogalathea chani, photo Tin-Yam Chan (yes he photographed the species that is named for him) Dorsal view of an elongate squat lobster (Galatheidae), a form of false crab (Anomura). It looks like a skinnier lobster, with claws more than twice the length of the body. Mostly translucent, with red eyestalks and banding patterns on the claws.

These squat lobsters are galatheids but not identified to genus; I include the image to show you the lifestyle that Fennerogalathea apparently also has. A large antipatharian with associated galathaeid crabs from the Northwestern Hawaiian Ridge. Image: A. Baco FSU, E.B. Roark TAMU, NSF, with HURL Pilots T. Kerby and M. Cremer https://peerj.com/articles/16024/

F is for Fennerogalathea.

3 species of these squat lobsters, part of false crabs (Anomura), were described from 120-320m deep (some hanging out in corals) in the south Pacific. The genus is named for Fenner Chace, who collected crab specimens I've studied at MCZ!

(Paper next skeet) 🧪🦀🦑 #CrabAZ

Puget Sound King Crab (Echidnocerus cibarius) Puget Sound King Crab from Strathcona, BC, Canada on November 10, 2023 at 02:32 PM by Daniel Hershman

E is for Echidnocerus.

This is a cute and funny shallow water king crab, but it's not a true crab! Carcinization molded hermit crab ancestors into abandoning shells and developing these camouflaged tanks. Orange ones are juveniles - they become multicolored adults (see video next)

🦀🦑🧪 #CrabAZ

Dicranodromia doederleini, photo Tin-Yam Chan. It's a dorsal view of a crab specimen in color (light carapace, pink limbs). The carapace is elongated and the antennae are longer than most true crabs. The abdomen is partially visible instead of being more folded under. The back 2 pairs of legs are smaller (see next image for why)

Homolodromia sp, photo Teng-Wei Wang. Yes its not Dicranodromia, but there are only 2 genera in the family and no photo available. This is a ventral view of a similar looking specimen, except its legs are hairy (feature Dicranodromia doederleini would not have). The behavior is the same though, which is that you see it looks to be surrounded by a weird lattice helmet bigger than the crab itself. That's a sponge which it holds onto with the back 2 pairs of legs

In #CrabAZ we show obscure species too!

D is for Dicranodromia. One of the earliest diverging true crabs (thus why it's elongate). Normally found >400m depth, this species is shallower (200-300m). This is why we don't have enough DNA to know their spot in the tree of life.

Read the alt text!

🦀🧪🦑

Typical Box Crabs (Genus Calappa) Typical Box Crabs from Puri Jati, Bali, Indonesia on October 16, 2017 by uwkwaj

This month, fight the horrors with #CrabAZ.

C is for Calappa, the shamefaced crab, so called because they bury themselves in sand. They peel open snails with specialized, asymmetrical claws! You can see a bit of the can opener right hand here (click through to 3rd pic for mindblowing cuteness)

🦀🦑🧪

This month, fight the horrors with #CrabAZ.

B is for Birgus, the largest land invertebrate alive! It is a specialized hermit crab (they live in the ocean with shells when young). This one is about 15 years old, and will be released after 1 year in captivity - they can reach 60 years!

🦀🦑🧪

Aegla strinatii Aegla strinatii from Gruta do Rolado III on January 10, 2018 at 01:22 PM by Cave Naturalist. Gruta do Rolado III, crédito: Rabelo L.M.

Before *everything* I told @franzanth.bsky.social I would do a crab A-Z in Feb. Not sure if I still should, but:

A is for Aegla, the only genus in its family and the only fully freshwater false crabs. Endemic to S America, males fight with the palmar crests on their claws

🦀🧪🦑 #CrabAZ