#crustacea

[clawmarks]

Poissons - Félix Bracquemond - 1866 - via The British Museum

[snototter]

A shield shrimp (Triops australiensis) in Kimberley, Australia

by Ian Bool

[feliusdax]

[alphynix]

Strange Symmetries #13: The Hermit Crab Cycle

Hermit crabs are crustaceans that first appeared at the start of the Jurassic, about 201 million years ago. Despite their common name they aren't actually true crabs, instead being a classic example of convergently evolving a crab-like body plan via carcinization.

They also have noticeably asymmetric bodies, with abdomens that coil to one side and differently-sized front claws.

Pagurus bernhardus by Arnstein Rønning | CC BY 3.0

And while modern hermit crabs are famous for inhabiting scavenged snail shells, their fossil record suggests this wasn't always the case.

Originally, they seem to have lived in ammonite shells.

Palaeopagurus vandenengeli lived in what is now northern England during the Early Cretaceous, about 130 million years ago. Around 4-5cm long (~1.6-2"), it was found preserved inside the shell of the ammonite species Simbirskites gottschei.

Its left claw was much larger than its right, and together they would have been used to block the shell opening when it was hiding away inside. And while the exact shape of its abdomen isn't known, it probably asymmetrically coiled to the side to accomodate the spiralling shape of the host shell.

Hermit crabs seem to have switched over to using gastropod shells by the Late Cretaceous, around 90-80 million years ago, possibly due to marine snails developing much stronger sturdier shells during this period in response to the increasing prevalence of specialized shell-crushing predators. The more upright snail shells would also have been much easier to drag around the seafloor than ammonite shells – and meant that they were ultimately less affected by the total disappearance of ammonites during end-Cretaceous mass extinction.

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NixIllustration.com | Tumblr | Twitter | Patreon

[sina-man]

Spec evo terrestrial ostracods.

First one is a small detritivore hiding in mud, leaf litter and rotten wet wood.

Second one is a small predator that hunts other terrestrial ostracods, woodlice and insect larvae.

[creatureimages]

call this pink coralline alga the apple store circa 2009. the way it's got ipods in it

[rattyexplores]

Photos 1-2 - Specimen 1

Photos 3-4 - Specimen 2

Photos 5-6 - Specimen 3

D. senex hermit crabs residing in empty Moon Snail shells.

13/08/23 - Diogenes senex

QLD:WET - Flying Fish Point, low tide sandy bay

[eiders]

an exciting surprise!! my blonde duckies produced their first offspring!

[colorsoutofearth]

Sapphirina spp.

Photo by Solvin Zankl

[kararadaygum]

..

[clawmarks]

Lehrbuch der Zoologie : für höhere Lehranstalten, die Hand des Lehrers und für alle Freunde der Natur - Otto Schmeil - 1930 - via e-rara

[snototter]

A red reef lobster (Enoplometopus occidentalis) off the coast of Kona, Hawaii, USA

by Pierrette Wagner

[feliusdax]

Good Crab 🦀 13 pcs/pzs

[alphynix]

Strange Symmetries #20: The 16 Million Year Fiddler Crab Rave

Many decapod crustaceans have slightly asymmetrical pincers, often with one claw being chunkier and specialized for "crushing" while the other is more slender and used for "cutting".

But fiddler crabs take this sort of asymmetry to the extreme as part of their sexual dimorphism – males have one massively oversized claw, which is used for both visual display to potential mates and for physical fights against rivals.

Some of the earliest fiddler crabs are known from the Miocene of what is now northern Brazil. Although the fossils have been given several different taxonomic names since their discovery in the 1970s (including Uca maracoani antiqua, Uca antiqua, and Uca inaciobritoi) they're currently considered to be indistinguishable from the modern Brazilian fiddler crab, Uca maracoani, meaning that these crabs have remained externally unchanged for the last 16 million years.

Up to about 4cm in carapace width (~1.6"), modern Uca maracoani are found in coastal mangrove swamps and tidal mudflats around the northern and eastern coasts of South America – and some of these environments have also undergone little change since the Miocene. Males of the species can develop their enlarged pincer on either side of their bodies, with lefties and righties seeming to occur in equal numbers.

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NixIllustration.com | Tumblr | Twitter | Patreon

[sitting-on-me-bum]

Unidentified hermit crab from the Sea of Japan by Alexander Semenov Via Flickr: With Balanus barnacles on the shell