Echinodermata (spiny skin)
Echinoderms include starfish, crinoids, blastoids, cystoids, and sea cucumbers. They are
entirely marine and are generally characterized by a symmetry that divides their body into five radial divisions. Echinoderms have a body cavity in which the gut is either straight, curved, or coiled. The mouth and anus are in various positions on the body. These positions change with the change of body symmetry.
Echinoderms are unique in
having a water-vascular system that carries on respiration, and also assists in movement as a sort of hydraulic system. Five grooves extend along the body of many echinoderms and transport food-bearing water to the mouth in many echinoderms. Plates and spines that support the body are formed in the mesoderm (middle layer of the body wall) and consist of the mineral calcite. The nervous system is highly organized.
existed in Early Cambrian times (ca. 520 million years ago) and survive today. Echinoderms are first cousins to humans and other vertebrate animals. This relationship of the phylum Echinodermata to the phylum Chordata is indicated by similarities in early larval development and by the presence of iron-based hemoglobin in the blood of both phyla. Most other invertebrates have a copper-based chemical used for oxygen transport in the blood.
Crinoidea (class) - Crinoids are sometimes called "sea lilies" for their plan t-like appearance. The most commonly found crinoid fossils are stalk and stalk fragments. These stalks are composed of radially symmetrical, disklike columnals stacked one on top of the other. An outer skin-like tissue covers this stalk in living crinoids; a canal with a blood vessel passes through the center of these columnals. The stalk is attached to the sea floor by a holdfast at the base of the stem. The calyx or "head" contains the mouth, grooves that carry food to the mouth, and the anus. Arms extend from the top of the calyx and act as food gatherers. Crinoids appeared in the Early Ordovician (ca. 480 million yea rs ago) and Jive today.
Blastoidea (class) - A blastoid calyx or head resembles a flower bud. This extinct echinoderm group is similar to crinoids, in many respects. The mouth of the blastoid is in the upper center of the calyx and is surrounded by five openings called spiracles. The function of these opening s is problematic. However, fossil blastoid eggs have been found in the spiracles. The water vascular system that carries on locomotion and respiration is located in the five depressed areas along the sides of the calyx. The columnals of the stem are similar to the crinoid columnals, but complete stems are seldom preserved. Blastoids lived from the Lower Ordovician (ca. 480 million years ago) to the end of the Permian (245 million years ago).
Cystoids (sack-like) "Cystoid" is an informal name applied to two extinct classes of stalked echinoderms that are related to blastoids. They are characterized by pores in the calyx that were the openings to respiratory structures. In the most advanced and complex cystoids, these pores are short, slit-like openings that extend across the edges of two adjacent calyx plates. Cystoids have a calyx that is egg-shaped to very flattened, a somewhat tapering stem that tends to be relatively shorter than in crinoids, and arms that are thicker than in blastoids. Caryocrinites is relatively common in the Middle Silurian (c. 430 million years ago) Rochester Shale in central and western New York. Cystoids appeared in the Late Cambrian (c. 493 million years ago) and went extinct in the Late Devonian (c. 375 million years ago). As other echinoderms, they are always found in marine deposits.
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