Page 404 - Introduction to Paleobiology and The Fossil Record

DEUTEROSTOMES: ECHINODERMS AND HEMICHORDATES 391

High-level epifaunal Crinoid

Blastoid
Low-level epifaunal

Edrioasteroids
Helicoplacoid
Holothurian
Calcichordate

Rhombiferan

Echinoid
Asteroid Ophiocistioid
Echinoid

Echinoid

Mobile infaunal and epifaunal
Mobile epifaunal
Figure 15.1 Life modes of the main echinoderm body plans. (Based on Sprinkle 1980.)

tains Late Silurian echinoderms within fi ne- most remarkable echinoderm Lagerstätte
grained turbidites, and the Lower Jurassic occurs in the Upper Ordovician succession of

Starfish Bed of South Dorset, England is dom- the Craighead inlier, north of the Girvan
inated by ophiuroids suddenly buried by a valley, southwest Scotland. Here, the Lady
thick layer of sandstone. However, one of the Burn Starfish Bed is one of several sandstone

Box 15.1 Echinoderm classifi cation

In broad terms, the Echinodermata may be divided into two main sister groups – the stalked pel-
matozoans and the mobile eleutherozoans. But there are a number of more bizarre Lower Paleozoic
forms, known from only a few specimens at single localities, which are difficult to classify at present.

The classification is based on a number of key features: the main body of the animal, enclosed by
plates (the theca or test), areas bearing tube feet (ambulacra) with perforations or holes (brachioles)
and, in the case of the pelmatozoans, the possession of a cup (calyx) and arms (brachia).

Subphylum PELMATOZOA
Class EOCRINOIDEA

• Globular or flat theca with 2–5 ambulacra bearing brachioles

• Cambrian (Lower) to Silurian
Continued