“Comma shrimp, or cumaceans, are a group of little peracarid shellfishes with over 1,900 living types presently explained worldwide,”stated Dr. Javier Luque from the University of Cambridge and Dr. Sarah Gerken from the University of Alaska Anchorage.

“Despite their international circulation, their physiological variety, types richness, and abundance, the fossil record of cumaceans is among the poorest amongst marine arthropods.”

“This is perplexing due to the fact that they normally reside in fine-grained sediments with generally high fossilization capacity.”

“Such a sporadic fossil record is most likely due to their little size (1-35 mm); their fragile and gently biomineralized integument, which might decrease conservation in the fossil record; and substantial taxonomic predispositions due to their unknown anatomy.”

“These aspects make fossil cumaceans simple to misidentify, be puzzled with shellfish larvae of unidentified affinities, or be translated as pieces of other shellfishes.”

“In truth, living cumaceans were at first translated as possible larvae, and there was debate regarding what they were up until fully grown women bearing broods were found.”

The newly-described comma shrimp, Makrokylindrus itoilived around 2.5 million years earlier (Plio-Pleistocene).

The perfectly maintained specimen was discovered in the siltstones of the Hijikata Formation in Japan.

“The particular fossil is remarkably maintained, consisting of information of the carapace, cuticle, and some appendages,” the paleontologists stated.

“The holotype was a subadult male, determining 8.5 mm in length from the idea of the pseudorostral lobe to the posterior end of the pleon.”

“The carapace, pereon, and pleon were covered with a mix of big and little pits in a scale-like pattern.”

Makrokylindrus itoi represents the very first recognized fossil of the household Diastylidae and just the 4th fossil crown group comma shrimp understood to date.

The discovery shows that the fossil record of comma shrimp is more prevalent and varied than formerly understood.

“We recommend that the limited and sparsely understood fossil record of cumaceans most likely shows an absence of acknowledgment due to their little size and unknown anatomy, making fossil cumaceans simple to misidentify, be puzzled with shellfish larvae of unidentified affinities, or be analyzed as pieces of other shellfishes (taxonomic predisposition), instead of an absence of fossilization capacity (taphonomic predisposition),” the scientists stated.

Their paper appears in the journal Invertebrate Biology

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Javier Luque & & Sarah Gerken. A perfectly maintained comma shrimp (Pancrustacea: Peracarida) from the Plio-Pleistocene of Japan and the fossil record of crown Cumacea. Invertebrate Biologyreleased online September 10, 2024; doi: 10.1111/ ivb.12440