CHAPTER 22. Echinoderms 22-1

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1 CHAPTER 22 Echinoderms 22-1

2 Phylum Echinodermata: Diversity and Characteristics Characteristics All members have a calcareous skeleton Spiny endoskeleton consists of plates Unique water-vascular system Possess pedicellariae and dermal branchiae Pentaradial symmetry in adults 22-2

Phylum Echinodermata: Diversity and Characteristics Diversity Asteroids or sea stars Mostly predators Ophiuroids or brittle stars Move by bending their jointed muscular arms May be scavengers,

3 Phylum Echinodermata: Diversity and Characteristics Diversity Asteroids or sea stars Mostly predators Ophiuroids or brittle stars Move by bending their jointed muscular arms May be scavengers, browsers, or commensal Holothurians or sea cucumbers Mostly suspension or deposit feeders Echinoids or sea urchins Found on hard bottoms while sand dollars prefer sand substrate Feed on detritus 22-3

Form and Function External Features Have a central disc with tapering arms extending outward Body is flattened and flexible, with a pigmented and ciliated epidermis Mouth is on the underside or oral

4 Form and Function External Features Have a central disc with tapering arms extending outward Body is flattened and flexible, with a pigmented and ciliated epidermis Mouth is on the underside or oral surface Ambulacrum runs from the mouth to the tip of each arm Usually there are 5 arms but there may be more Ambulacral groove bordered by rows of tube feet Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22-4

Radial nerve located in center of each ambulacral groove Ossicles or other dermal tissue covers these structures Aboral surface is spiny At base of spines are groups of pincer-like pedicellariae Keep

5 Radial nerve located in center of each ambulacral groove Ossicles or other dermal tissue covers these structures Aboral surface is spiny At base of spines are groups of pincer-like pedicellariae Keep the body surface free of debris Papulae (dermal branchiae or skin gills) are soft projections lined with peritoneum Function in respiration On the aboral side is a circular madreporite leading to the water-vascular system. 22-5

6 Endoskeleton Under the epidermis is the mesodermal endoskeleton Small calcareous plates or ossicles Bound together by an unusual form of mutable (change) collagen termed catch collagen Muscles in the body wall move rays and partially close ambulacral grooves 22-6

7 Coelom, Excretion, and Respiration Spacious body coelom filled with fluid Ciliated peritoneal lining of coelom circulates fluid around the cavity and into papulae Respiratory gases and ammonia diffuse across the papulae and tube feet Some wastes are picked up by coelomocytes, which migrate to exterior Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22-7

8 Water-Vascular System This system is another coelomic compartment and is unique to echinoderms Consists of system of canals, tube feet, and dermal ossicles Functions in locomotion, foodgathering, respiration, and excretion Opens to outside at madreporite on aboral side Madreporite leads to stone canal, which joins ring canal that encircles the mouth Radial canals diverge from ring canal and extend into each ray 4 or 5 pairs of Tiedemann s Bodies attach to ring canal and may produce coelomocytes 22-8

9 Polian vesicles may also be attached Function in fluid storage and regulation of internal pressure of water vascular system Inner end of each tube foot called an ampulla Lies within the coelom Outer end of each tube foot bears a sucker Water-vascular system operates hydraulically Muscles in ampulla contract forcing fluid into and extending the podium Contraction of longitudinal muscles in tube foot retracts it, forcing fluid back into the ampulla 22-9

10 Feeding and Digestive System Mouth leads through a short esophagus to large central stomach Lower cardiac part of stomach can be everted through the mouth during feeding Upper stomach is smaller and connected by ducts to a pair of pyloric ceca in each arm Anus is inconspicuous 22-10

11 Hemal System System of tissue strands enclosing unlined sinuses System itself enclosed in perihemal channels Hemal system may play a role in distributing nutrients 22-11

each ray Tactile organs are scattered over the surface and an ocellus is at tip of each

12 Nervous System The oral system of a nerve ring and radial nerves coordinate the tube feet Hyponeural system aboral to oral system forms ring around anus and extends into roof of each ray Tactile organs are scattered over the surface and an ocellus is at tip of each arm React to touch, temperature, chemicals, and light intensity Mainly active at night 22-12

water in early summer Regenerate lost parts Cast off injured arms and regenerate new

13 Reproductive System & Regeneration Sexes separate in most sexes Pair of gonads in each interradial space Fertilization is external Eggs and sperm are shed into the water in early summer Regenerate lost parts Cast off injured arms and regenerate new ones An arm can regenerate a new sea star if at least onefifth of central disc is present 22-13

Brachiolaria attaches to substrate and undergoes metamorphosis into a radial

14 Free-swimming larva, bipinnaria, has cilia arranged in bands Larva grows adhesive arms and a sucker at the anterior Now called a brachiolaria Brachiolaria attaches to substrate and undergoes metamorphosis into a radial juvenile Arms and tube feet appear, animal detaches from stalk and becomes a young sea star 22-14

slender and distinct from the central disc Lack pedicellariae or papulae Madreporite is on the oral surface Tube feet lack suckers and

15 Form and Function Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Ophiuroidea Brittle stars are secretive and live on hard or sandy bottoms where little light penetrates Arms of brittle stars are slender and distinct from the central disc Lack pedicellariae or papulae Madreporite is on the oral surface Tube feet lack suckers and ampullae Arms are moved in pairs for locomotion Five movable plates act as jaws and surround mouth No anus Skin is leathery and surface cilia are mostly lacking 22-15

Class Echinoidea Diversity Sea urchins lack

Most sea urchins have a hemispherical shape

dollars and (irregular echinoids) have become

move by tube feet Irregular urchins move by

16 Class Echinoidea Diversity Sea urchins lack arms but their tests show five-part symmetry Most sea urchins have a hemispherical shape with radial symmetry and long spines Sand dollars and (irregular echinoids) have become bilateral with short spines Regular urchins move by tube feet Irregular urchins move by their spines Echinoids occur from intertidal regions to deep ocean 22-16

Class Holothuroidea Sea cucumbers are greatly elongated in the oral-aboral axis Ossicles are

17 Diversity Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Holothuroidea Sea cucumbers are greatly elongated in the oral-aboral axis Ossicles are greatly reduced and has leathery body Some species crawl on the ocean bottom, others are found under rocks or burrow Cast out part of viscera when irritated Must regenerate these tissues 22-17

Chapter 22. Phylum Echnodermata 4/13/2009. Characteristics. Diversity. Group Diversity. Ecology, Economics, and Research.

Chapter 22. Phylum Echnodermata 4/13/2009. Characteristics. Diversity. Group Diversity. Ecology, Economics, and Research. Characteristics Chapter 22 All members of the phylum have a calcareous skeleton. The spiny endoskeleton consists of plates. They have a unique water vascular system. They possess pedicellariae and dermal