Echinoderms

By | September 9, 2016

The starfish and sea urchins we see at the beach belong to an ancient group of sea-dwelling animals known as echinoderms (“ee-KYE-no derms”). Echinoderms have round or star-shaped bodies and feet like tiny suckers, but no heads or brains. Fossils reveal that echinoderms of the distant past were much like those we see today.

FAMILY FACT FILE

Key features

■ Body divided into five equal parts arranged in a circle around a central disk

■ Rows of small, suckerlike feet on base

■ No front or back and no head or brain

When

Echinoderms first appeared at the start of the Cambrian Period, about 530 million years ago. Over 7,000 species are found in oceans across

the world today.

Encrinus (EN-crine-us)

 encrinus-1


Encrinus trapped food with its sticky arms. The arms could close tightly for protection from predators.


When: 235–215 million years ago (Middle Triassic)

Fossil location: Europe

Habitat: Shallow seas

Size: Cup 1.1/2–2.1/4 in (4–6 cm) long

Attached to the seafloor by a stalk, Encrinus used a ring of 10 feathery arms to catch tiny organisms floating past. The organisms, trapped in a sticky fluid, were then swept by tiny hairs toward a central mouth. Encrinus belonged to a class of echinoderms known as crinoids or sea lilies that still exists today.

Clypeus (CLY-pee-us)

clypeus

Clypeus found food by burrowing and eating its way through the mud on the seafloor.

 


When: 176–135 million years ago

(Middle to Late Jurassic)

Fossil location: Europe, Africa

Habitat: Burrows on the seafloor

Size: 2–4.1/2 in (5–12 cm) across

Clypeus was a type of sea urchin. Like a modern sea urchin, it had a hard, rounded shell made up of five parts arranged in a star pattern. The shell was covered by spines, but unlike the stiff, pointed spines of many sea urchins, these were soft and hairlike.

Pentasteria (PEN-ta-STEER-ee-a)

pentasteria


When: 203–100 million years ago (Early Jurassic to Early Cretaceous)

Fossil location: Europe

Habitat: Sand beds

Size: Up to 4.1/2 in (12 cm) across

Pentasteria was a starfish that lived during the age of the dinosaurs. It was much like a modern starfish, with five arms, a mouth in the middle of its underside, and two rows of tubelike feet along each arm. Unlike modern starfish, however, it couldn’t use its feet as suckers to prize open shells.

Hemicidaris (HEM-ee-sid-AR-is)

hemicidaris


When: 176–65 million years ago (Middle Jurassic to Late Cretaceous)

Fossil location: England

Habitat: Rocky seabeds

Size: Including spines 8 in (20 cm) diameter. Without spines 3/4-1.1/2 in (2–4 cm)

Fossils of Hemicidaris are covered with bumps where its vicious, 3 in (8 cm) long spines were attached. These were flexible, allowing Hemicidaris to move its spines with muscles. It lived on firm seabeds and used its sticky feet to creep around.

Pentacrinites (PEN-ta-CRINE-ee-tees)

pentacrinites


When: 208–135 million years ago (Jurassic)

Fossil location: Europe

Habitat: Open seas

Size: Arms up to 31 in (80 cm) long

Pentacrinites was a crinoid (sea lily) as tall as a man and lived rooted to one spot by a stalk, catching food in its feathery arms. Its hundreds of densely packed arms made it look more like a beautiful plant than an animal.

Its fossils are often found with fossilized wood, suggesting that the creature may sometimes have attached itself to floating driftwood.

LIVING RELATIVE

 sea-urchins

Sea urchins are small, ball-shaped creatures that often have prickly, even poisonous spines for protection. They creep slowly across the seafloor using dozens of tiny sticky feet.

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