Echinoids
Some Echinoids are hard to tell apart since they look similar.
The spines are more commonly found than the shell.
The reproductive plate is so delicate it doesn't always fossilise.
Most echinoids have five Ambulacral plate sections.
Conulus (also known as Offaster)
LOWER CRETACEOUS TO UPPER CRETACEOUS. 135-68 MYA.
Conulus is recognised by it's unique inability to be preserved with its spines. Unlike most Echinoids, we may never know whether it had spines or not, as no Conulus with spines has been found. 2 inches is a decent size for a Conulus.
The Interambulacral plates do not have a Mamelon; the plate shape is like a sqashed Hexagon.
The Interambulacral plates do not have a Mamelon; the plate shape is like a sqashed Hexagon.
Diademopsis
LOWER TRIASSIC TO LOWER JURASSIC. 230-180 MYA.
Diademopsis is recognised by it's unique Pentagonal doughnut shape. 5 inches is a decent size for a Diademopsis.
The Interambulacral sections plate pattern comprises 2 rows of small Memelons (plates) centered, then within these two rows, are two rows of larger Mamelons (plates). It is shaped like a Pentagonal doughnut and the Reproductive plate is so delicate it doesn't fossilise, this causes a Pentagonal shape in the center.
The Interambulacral sections plate pattern comprises 2 rows of small Memelons (plates) centered, then within these two rows, are two rows of larger Mamelons (plates). It is shaped like a Pentagonal doughnut and the Reproductive plate is so delicate it doesn't fossilise, this causes a Pentagonal shape in the center.
Hirudocidaris
MIDDLE CRETACEOUS TO UPPER CRETACEOUS. 100-70 MYA.
Hirudocidaris is recognised by it's unique thin wavey Interambulacral plates. 6.5 inches is a decent size for a Hirudocidaris.
It has 2 rows of different size pentagonal plates on the Interambulacral section. The Ambulacral section looks like a wavey line.
It has 2 rows of different size pentagonal plates on the Interambulacral section. The Ambulacral section looks like a wavey line.
Micraster
MIDDLE CRETACEOUS TO LOWER TERTIARY. 90-60 MYA.
Micraster is recognised by it's unique heart shaped shell. 3.5 inches is a decent size for a Micraster.
Unlike most Echinoids, we may never know whether it had spines or not, as no Micraster with spines has been found. The Ambulacral plates have a slight indentation. It's Interambulacral plates are hexagonal shaped, however it has no Mamelon.
Unlike most Echinoids, we may never know whether it had spines or not, as no Micraster with spines has been found. The Ambulacral plates have a slight indentation. It's Interambulacral plates are hexagonal shaped, however it has no Mamelon.
Phalacrocidaris
MIDDLE CRETACEOUS TO UPPER UPPER TERTIARY. 90-0 MYA.
Phalacrocidaris is recognised by it's unique widely spaced Interambulacral plates.
5.5 inches is a decent size for a Phalacrocidaris.
It has 2 rows of different size pentagonal plates on the Interambulacral section; they are wider apart than usual.
5.5 inches is a decent size for a Phalacrocidaris.
It has 2 rows of different size pentagonal plates on the Interambulacral section; they are wider apart than usual.
Phymosoma
MIDDLE JURASSIC TO LOWER TERTIARY. 165-60 MYA.
Phymosoma is recognised by it's unique high number of Ambulacral plates.
4 inches is a decent size for a Phymosoma.
It has two rows of hexagonal plates on each Interambulacral section. It has many Ambulacral sections (approximately 10-15).
4 inches is a decent size for a Phymosoma.
It has two rows of hexagonal plates on each Interambulacral section. It has many Ambulacral sections (approximately 10-15).
Tylocidaris
MIDDLE CRETACEOUS. 100-90 MYA.
Tylocidaris is recognised by it's unique bulging spines.
4.5 inches is a decent size for a Tylocidaris.
It has 2 rows of hexagonal Interambulacral sections.
Around the Mamelon there is a distinctive ring, known as a boss. The spines are unusually large and they have plates themselves; their pattern is just long lines.
4.5 inches is a decent size for a Tylocidaris.
It has 2 rows of hexagonal Interambulacral sections.
Around the Mamelon there is a distinctive ring, known as a boss. The spines are unusually large and they have plates themselves; their pattern is just long lines.
