Archaeocidaris sp. teste ossicle - a photo on Flickriver

            Age: 343–337 Ma
          Viséan
               Middle Mississippian Epoch
                        Carboniferous Period - Giant arthropods and amphibians, early reptiles, most plants fern or lycophyte-like, known for tropical forests and seas
                                            Paleozoic Era - pre-Dinosaurs

Location: Hurst Green (Stonyhurst)
          Hodder Place
          Stonyhurst Bathing Hut remains by the riverbanks of the Hodder

Rock Type: Among the Rad Brook Mudstone Member within the Pendleside Limestone Formation, however it pulled out in one large slab from near the top and I'm not entirely sure if it was from the bedrock here, or if it rested on top in a way that looked uniform with the shale, because this particular rock looked much more akin to the Clitheroe Limestone Formation's reef knoll rocks like at Salthill Quarry, so may be a rock washed downriver.

Archaeocidaris is an extinct genus of primitive sea urchins (echinoids) that lived from the Late Devonian through to the end of the Permian period. It belongs to the phylum Echinodermata, class Echinoidea, and is one of the earliest well-documented representatives of the echinoids (sea urchins). Members of the genus Archaeocidaris are characterised by their rigid, globular tests (skeletons) and long, robust spines, which make them distinctive in the fossil record. They also have many backwards-facing barbs along their spines that make them quite recognisable.

The genus was particularly widespread during the late Palaeozoic, with fossils found in marine limestones across Europe, North America, and Asia. Archaeocidaris was among the dominant echinoids, thriving in shallow, warm, carbonate-rich environments alongside crinoids, brachiopods, and corals. These habitats provided abundant surfaces for attachment and feeding opportunities within reefal and near-reefal ecosystems.

Morphologically, Archaeocidaris possessed a spherical to slightly flattened test constructed from tightly interlocking plates. The most striking feature of this genus is its spines, which could be very long relative to body size with backwards-facing barbs. These spines were likely used for defence against predators, as well as for stabilisation on soft substrates. Unlike many modern sea urchins, which exhibit varied modes of locomotion and feeding, Archaeocidaris is thought to have been primarily a grazer or detritivore, feeding on organic material and microbial films coating seafloor sediments.

As an early echinoid, Archaeocidaris retains primitive features compared to its later relatives. Its arrangement of plates and tubercles reflects a simpler structure, placing it within the order Cidaroida, a group often referred to as the “pencil urchins.” Remarkably, cidaroids are one of the few groups of echinoids to have persisted to the present day, with modern cidaroids still inhabiting tropical and subtropical seas.

Fossils of Archaeocidaris are often preserved as disarticulated plates and spines, which are commonly found in Carboniferous limestone deposits. Complete tests are much rarer. The durable spines are especially frequent in the fossil record and are sometimes mistaken for other skeletal elements.

In terms of evolutionary significance, Archaeocidaris illustrates the early diversification of echinoids during the Palaeozoic. Whereas other early echinoid groups went extinct, cidaroids successfully survived multiple mass extinction events, including the devastating Permian–Triassic extinction.
   

Taken in: UK / England / Ribble Valley District / Great Mitton (show map)

Taken on: August 17, 2025

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Archaeocidaris

echinoid

spine

fossilspine

echinoidspine

barbedspine

barbs

defensive

ossicle

test

plates

tubercles

globulartest

echinoidskeleton

marineinvertebrate

filterfeeder

grazer

detritivore

reefdweller

reefal

shallowmarine

carbonate

carbonateplatform

reefecosystem

stabilisation

fossilrecord

echinoidbarbs

echinodermata

animalia

cidaroida

cidaroid

seaurchin

fossil

fossilurchin

fossilseaurchin

primitiveechinoid

paleozoic

echinoidfossil

earlyechinoid

mississippian

visean

carboniferous « less

Sets appears in: • Lepidocidaris sp.

Camera: Olympus TG-6, f/5.0, 1/400 sec, 11.1mm, ISO 100 (more info) (hide info)

Camera:	Olympus TG-6
Aperture:	f/5.0
Exposure Time:	0.003 sec (1/400)
Focal Length:	11.1mm
ISO:	100
Exposure Bias:	-1.7 EV
Flash:	Off, Did not fire
Exposure Program:	Creative (Slow speed)
Exposure Mode:	Manual
Metering Mode:	Multi-segment
White Balance:	Manual
Light Source:	Cloudy
Color Space:	sRGB
Software:	Version 1.0
Show full info

Stats: 70 views

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