THE ECHINODERMATA starfish, sea urchins, sand dollars, crinoids, blastoids

Phylum Echinodermata The phylum Echinodermata consists of several types of complex organisms which show a general pentameral symmetry and have a well developed water vascular system. Echinoderms are also characterized by their mesodermal skeleton. Echinoderms occur in a variety of morphologies including free-living forms such as starfish and sand dollars as well stalked forms such as sea lilies which are attached to the sea floor.

Pelmatozoans Exclusively marine and live in a variety of habitats of normal salinity. They are all filter-feeders. Pelmatozoans have been quite abundant in the geologic past especially the Paleozoic, yet since the close of the Mesozoic they have mainly relegated to deep-water, cryptic environments. Free-living echinoderms all have a mesodermal skeleton comprised of calcite plates and a complex water- vascular system including tube-feed. Unlike the pelmatozoans, the groups of this lab are quite abundant in the modern seas, occupying a large number environments by an equally large number of life-habits.

PELMATOZOAN GENERAL MORPHOLOGY Pelmatozoan skeleton can be dived into two main parts: The stem and the calyx. The stalk or stem is composed of numerous disks called columnals. Stems are often secured to the substrate by means of a holdfast or root system. The calyx (sometimes called theca), is cup-like structure, which may or may not support a variety of arms. The calyx is usually composed of a number of different kinds of plates, grooves, and pores; some of which are quite specialized

SUBPHYLUM CRINOZOA Crinoids are animals which resemble flowers - they consist of a calyx with arms, which is attached to the sea floor by a stem of calcite disks called columnals. Some living crinoids are swimmers, and not attached

CLASS BLASTOIDEA Blastoids were attached by a stem to their substrate. The calyx of most species consists of 13 main plates: 5 deltoids, 5 radials, and 3 basals. Pores are restricted to the 5 ambulacral areas covered by lancet plates. The mouth is centrally located on the top of the calyx

SUBPHYLUM ASTEROZOA CLASS ASTEROIDEA (starfish) –The Asteroids, or starfish, have thick, hollow arms with prominent ambulacral grooves extending to the tips of the arms on the ventral side. –In life, the grooves were lined with the tube feet. –The mouth is located on the ventral (under) side, and the anus, when present, is located on the ventral side next to the madreporite. CLASS OPHIUROIDEA –The Ophiuroids, or brittle stars, are characterized by whip-like arms made of articulated plates. –The plates resemble tiny vertebrae. –Ophiuroids have a mouth centrally located on the ventral surface but lack an anus.

SUBPHYLUM ECHINOZOA The echinozoans: echinoids, holothurians, and edioasteroids. Echinozoans occupy a variety of infaunal and epifaunal environments, yet like their pelmatozoan relatives, they are stenohyaline and require normal marine salinities

CLASS ECHINOIDEA Echinoids, including sea urchins and sand dollars, generally have skeletons which are sub-spherical, or disk-shaped. Like the crinoid calyx, they are composed of a mosaic of plates; unlike the crinoids, they are covered by spines. These are tiny bristles in some, but can be quite large in others. The spines generally detach from the main skeleton after death, because they are held to it only by non- mineralized ligaments. There are no arms, and the ambulacral areas (where the perforated plates are found) stretch from pole to pole. Echinoids can be divided into two groups regular and irregular

Regular Echinoids Regular echinoids have five-fold radial symmetry Mouth and periproct at opposite poles. Regular echinoids are mostly epifaunal mobile grazers that sometimes occur in rocky subtidal and intertidal environments

Irregular Echinoids Irregular echinoids have bilateral symmetry; Mouth toward anterior on ventral side, and periproct in posterior interambulacral area. Irregular echinoids occur primarily in infaunal environments. The depths at which individuals lived can sometimes be deduced by their external morphology

PHYLUM HEMICHORDATA Hemichordates form a small phylum (only a few hundred species). Their importance for the study of vertebrate evolution, however, cannot be underestimated. The fossil record of one group of hemichordates, the graptolites, is very well known and is often used to correlate rocks. Hemichordates are distinguished by a tripartite (threefold) division of the body. The name "hemichordate" means "half chordate," and hemichordates share some (but not all) of the typical chordate characteristics. There are branchial openings, or "gill slits," that open into the pharynx; there is a rudimentary structure in the collar region, the stomochord, that is similar to a notochord; and there is a dorsal nerve cord, in addition to a smaller ventral nerve cord. However, hemichordates are not classified as true chordates, although they are quite closely related.

Hemichordates Of the three classes of hemichordates, the most familiar living ones are the Enteropneusta, the acorn worms. Acorn worms also have multiple branchial openings, as many as 200 in some species. They are slow burrowers, using the proboscis to burrow through sediment, and may either deposit feed (consume sediment and digest the organic matter) or suspension feed (collect suspended particles from the water). Some of these worms may be very large; one species may reach a length of 2.5 meters (almost eight feet), although most are much smaller.

Hemichordates The second living class is the Pterobranchia, an obscure group with only about 20 living species. Pterobranchs as very different from acorn worms; they form colonies in which the individuals are interconnected by stems, or stolons. Individuals, or zooids, are often less than 1 millimeter long. The proboscis is not elongated, as it is in acorn worms, but shield-shaped

CLASS GRAPTOLITHINA Unlike their pterobranch kin, which typically live encrusting rocks and shells, most graptolites are thought to have been planktonic, floating or slowly sinking through the water. The spiral shape of some was probably an adaptation to slow sinking. Other graptolites may have been connected to gas-filled sacs, keeping them buoyant

GRAPTOLITES