Hemiaster bowerbanki
Hemiaster bowerbanki
View age-specific evidence and explanation
There are no currently eligible, unambiguously age-indexed published Occurrences for this Species. This does not indicate absence or rarity.
These counts describe published LBPS Occurrence records with directly assigned, unambiguous geological-unit mappings—not specimen abundance. Records at restricted Localities and ambiguous or unsupported ages are excluded. Species-level age labels are not used as proof of an age-specific Occurrence.
Specimen-based rarity requires comparable, correctly identified physical fossils, geological provenance and publication permissions. It does not estimate your chance of finding a fossil or collecting access.
Quick Identification
Look for:
- A sea-urchin test with a distinct front and back, often broadly heart-shaped or oval rather than evenly circular.
- Paired, petal-shaped pore zones on the upper surface of the test.
- A front depression or groove, where the front of the shell is preserved.
Useful check
- Look down onto the upper surface and, if possible, view it from the side: compare the petal-like areas with the shell immediately beside them, rather than judging its outline alone.
How to tell it apart
- Gregory (1891) contrasted H. prestwichi, whose paired petal-shaped areas lie almost level with the surrounding test, with H. bowerbanki. The comparison needs sufficiently intact upper plating.
Be careful
- Compression can change the apparent depth of the petal-shaped areas. A loose spine, single plate or flattened fragment is not enough for a confident species identification.
Summary
Imagine a sea urchin with a flower-like pattern across its upper shell, yet not a single petal. Hemiaster bowerbanki lived in the early Eocene sea whose sediments formed the London Clay. Unlike a round sea urchin, this heart urchin had a definite front and back, and its hard, calcite-plated shell carried paired, petal-shaped rows of tiny pores. Through these openings, tube feet once emerged.
In living heart urchins, comparable tube feet on the upper surface help with breathing, while bristling spines can move the animal through seabed sediment. This offers a way to picture a possible life for H. bowerbanki, but its particular feeding habits, burrowing depth and movements are not known. The shell, or test, is the evidence that survives; it can be crushed, worn or broken after burial, obscuring the animal’s original form.
Those fragile fossils puzzled even nineteenth-century specialists. In 1891, J. Walter Gregory called Britain’s Eocene heart urchins rare and very badly preserved, although H. bowerbanki was among the better-known examples. He pointed to a subtle difference from Hemiaster prestwichi: in that species, the petal-shaped parts of the upper shell lie almost flush with its surface. A small detail preserved in stone could therefore help distinguish two animals, showing how much the faint outlines of a fossil sea urchin can reveal about the ancient life of the London Clay.
Diagnostic Features
- Test: irregular echinoid with bilateral symmetry and distinct anterior/posterior orientation; broadly heart-shaped to ovate where preserved.
- Paired petaloid ambulacra: petal-like pore-bearing zones on the aboral surface; their position relative to the adjacent test surface is important for comparison.
- Anterior sulcus: an anterior groove or depression may be observable on an appropriately preserved test, but can be reduced or obscured by damage.
- Comparative diagnosis: Gregory (1891, p. 22) distinguished H. prestwichi from H. bowerbanki because its paired petaloid areas are almost flush with the test; judge this character only when the relevant plating retains its original relief.
- Historical taxonomic caution: Gregory (1891, p. 21) did not regard the number of genital pores as adequate for separating Hemiaster from Ditremaster, or as independently diagnostic of these species.
- Identification limit: test shape, single plates or isolated spines are insufficient for secure species-level attribution; the diagnostic upper-test morphology must be preserved together.
Fossil Details
Recorded Fossil Sites
No fossil-site occurrences have yet been recorded for this species.
Diagnostic Sources
Forbes (1852), pp. 24–25, pl. III fig. 6 (excluding fig. 6e in Gregory’s 1891 synonymy), is the original species account. Gregory (1891), pp. 21–23, records the species from the London Clay at Sheppey and from historical basement-bed localities in the Reading area; these literature statements do not create LBPS Species Occurrences. He described British Eocene spatangoids as rare and badly preserved, retained H. bowerbanki in Hemiaster rather than Ditremaster, and on p. 22 distinguished H. prestwichi by its paired petals lying almost flush with the test. Differences discussed on p. 23 with H. forbesi concern anterior groove, lateral ambulacra and posterior shape; the 20 × 18 × 13 mm dimensions there refer to H. forbesi, NOT H. bowerbanki. No defensible typical-size range or species-specific diet, burrowing depth or locomotor behaviour has been established. Comparisons with living heart-urchin respiratory tube feet and sediment movement in the Summary are explicitly broader-group analogies (Smithsonian NMNH, Living and Fossil Sea Urchins; British Geological Survey, Echinoids), not observations of this fossil species. Hemiaster prestwichi is named as a literature comparator in Quick Identification; its canonical LBPS Species ID has not been verified, so do not silently add a Similar Species relationship.
- Forbes, E. (1852). Monograph of the Echinodermata of the British Tertiaries. Palaeontographical Society Monograph View reference
- Gregory, J. W. (1891). A revision of the British fossil Cainozoic Echinoidea. Proceedings of the Geologists' Association, 12(1–2), 16–60. Geologists' Association View reference
References
- Forbes, E. (1852). Monograph of the Echinodermata of the British Tertiaries. Palaeontographical Society Monograph View reference
- Gregory, J. W. (1891). A revision of the British fossil Cainozoic Echinoidea. Proceedings of the Geologists' Association, 12(1–2), 16–60. Geologists' Association View reference