Water Vascular System In Echinoderms

20.5: Echinoderms and Chordates

Last updated
Save as PDF

Folio ID: 65697

Deuterostomes include the phyla Echinodermata and Chordata (which includes the vertebrates) and two smaller phyla. Deuterostomes share similar patterns of early development.

Echinoderms

Echinodermata are named for their spiny pare (from the Greek "echinos" meaning "spiny" and "dermos" meaning "skin"). The phylum includes about 7,000^¹ described living species, such as sea stars, ocean cucumbers, sea urchins, sand dollars, and brittle stars. Echinodermata are exclusively marine.

Adult echinoderms exhibit pentaradial symmetry and have a calcareous endoskeleton made of ossicles (Figure \(\PageIndex{1}\)), although the early larval stages of all echinoderms take bilateral symmetry. The endoskeleton is developed past epidermal cells, which may likewise possess pigment cells, giving vivid colors to these animals, likewise as cells laden with toxins. These animals accept a truthful coelom, a portion of which is modified into a unique circulatory system called a h2o vascular system. An interesting characteristic of these animals is their power to regenerate, fifty-fifty when over 75 per centum of their trunk mass is lost.

Physiological Processes of Echinoderms

Echinoderms have a unique system for gas exchange, food apportionment, and locomotion called the water vascular organisation. The arrangement consists of a central ring culvert and radial canals extending forth each arm. Water circulates through these structures allowing for gas, nutrient, and waste exchange. A structure on tiptop of the body, called the madreporite, regulates the amount of water in the h2o vascular organization. "Tube feet," which protrude through openings in the endoskeleton, may be expanded or contracted using the hydrostatic pressure in the arrangement. The arrangement allows for slow motion, just a great deal of power, as witnessed when the tube feet latch on to opposite halves of a bivalve mollusk, like a clam, and slowly, but surely pull the shells apart, exposing the mankind within.

The illustration shows a sea star, which has a mouth on the bottom and an anus on top, both in the middle of the star. The disk-shaped stomach is sandwiched between the mouth and anus. Two tubes radiate from the stomach to each arm, and many small digestive glands connect to these tubes. Beneath the stomach is a central ring canal that also connects to tubes that extend into each arm. Tube feet are attached to these tubes. Each tube foot resembles a medicine dropper, with a bulb-shaped ampulla at the top and an extension called a podium at the bottom. The bottom of the podium protrudes from the bottom of the starfish. There are many podia along the length of each arm, which allow the sea star to latch onto objects and walk. A structure called a madreporite connects to the central ring and protrudes from the upper surface of the sea star, next to the anus. — **Figure \(\PageIndex{one}\):** This diagram shows the anatomy of a sea star.

The echinoderm nervous system has a nerve band at the center and five radial nerves extending outward along the arms. There is no centralized nervous control. Echinoderms have dissever sexes and release their gametes into the water where fertilization takes identify. Echinoderms may likewise reproduce asexually through regeneration from body parts.

Echinoderm Diversity

This phylum is divided into five classes: Asteroidea (sea stars), Ophiuroidea (brittle stars), Echinoidea (body of water urchins and sand dollars), Crinoidea (sea lilies or feather stars), and Holothuroidea (sea cucumbers) (Effigy \(\PageIndex{two}\)).

Maybe the best-known echinoderms are members of the class Asteroidea, or sea stars. They come up in a large variety of shapes, colors, and sizes, with more than ane,800 species known. The characteristics of sea stars that set them apart from other echinoderm classes include thick artillery that extend from a fundamental disk where organs penetrate into the artillery. Sea stars utilise their tube anxiety non just for gripping surfaces but besides for grasping prey. Sea stars have two stomachs, one of which they can evert through their mouths to secrete digestive juices into or onto prey before ingestion. This process can essentially liquefy the prey and make digestion easier.

CONCEPT IN ACTION

View this video to explore a sea star's body programme up close, lookout i move across the sea flooring, and run across it devour a mussel.

Brittle stars have long, thin arms that do not incorporate any organs. Sea urchins and sand dollars do not take arms only are hemispherical or flattened with five rows of tube feet, which assist them in slow movement. Sea lilies and plumage stars are stalked suspension feeders. Sea cucumbers are soft-bodied and elongate with five rows of tube feet and a series of tube feet around the oral cavity that are modified into tentacles used in feeding.

The sea star in photo a is red and white, with a thick squat body and protruding spikes. The brittle star in part b is brown with a flat, pentagon-shaped body. Thin striped legs extend from each point of the pentagon. Photo c shows a sea urchin with a round, black body and very long, thin, black spines. Photo d shows a sea lily that has appendages resembling branches of a spruce tree. Photo e shows a log-shaped sea cucumber with spikes extending from its body. — **Effigy \(\PageIndex{ii}\):** Different members of Echinodermata include the (a) sea star in form Asteroidea, (b) the brittle star in class Ophiuroidea, (c) the sea urchins of class Echinoidea, (d) the sea lilies belonging to grade Crinoidea, and (east) sea cucumbers representing form Holothuroidea. (credit a: modification of work past Adrian Pingstone; credit b: modification of work by Joshua Ganderson; credit c: modification of work by Samuel Chow; credit d: modification of work by Sarah Depper; credit e: modification of work by Ed Bierman)

Chordates

The majority of species in the phylum Chordata are found in the subphylum Vertebrata, which include many species with which we are familiar. The vertebrates incorporate more than sixty,000 described species, divided into major groupings of the lampreys, fishes, amphibians, reptiles, birds, and mammals.

Animals in the phylum Chordata share iv key features that appear at some stage of their development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail (Effigy \(\PageIndex{3}\)). In certain groups, some of these traits are nowadays only during embryonic development.

The chordates are named for the notochord, which is a flexible, rod-shaped structure that is establish in the embryonic stage of all chordates and in the adult stage of some chordate species. Information technology is located between the digestive tube and the nervus string, and provides skeletal back up through the length of the body. In some chordates, the notochord acts every bit the primary axial support of the body throughout the animal'southward lifetime. In vertebrates, the notochord is nowadays during embryonic development, at which fourth dimension it induces the development of the neural tube and serves as a back up for the developing embryonic body. The notochord, however, is not found in the postnatal stage of vertebrates; at this point, it has been replaced by the vertebral column (the spine).

The dorsal hollow nerve string is derived from ectoderm that sinks beneath the surface of the skin and rolls into a hollow tube during development. In chordates, it is located dorsally to the notochord. In contrast, other animal phyla possess solid nerve cords that are located either ventrally or laterally. The nervus cord found in about chordate embryos develops into the brain and spinal string, which compose the key nervous system.

Pharyngeal slits are openings in the pharynx, the region just posterior to the rima oris, that extend to the outside environs. In organisms that alive in aquatic environments, pharyngeal slits allow for the get out of water that enters the mouth during feeding. Some invertebrate chordates use the pharyngeal slits to filter food from the water that enters the oral cavity. In fishes, the pharyngeal slits are modified into gill supports, and in jawed fishes, jaw supports. In tetrapods, the slits are further modified into components of the ear and tonsils, since there is no longer whatsoever need for gill supports in these air-breathing animals. Tetrapod ways "four-footed," and this group includes amphibians, reptiles, birds, and mammals. (Birds are considered tetrapods because they evolved from tetrapod ancestors.)

The mail-anal tail is a posterior elongation of the body extending beyond the anus. The tail contains skeletal elements and muscles, which provide a source of locomotion in aquatic species, such as fishes. In some terrestrial vertebrates, the tail may also function in residuum, locomotion, courting, and signaling when danger is near. In many species, the tail is absent or reduced; for example, in apes, including humans, information technology is present in the embryo, merely reduced in size and nonfunctional in adults.

Fine art Connexion

The illustration shows a fish-shaped chordate. A long, thin dorsal hollow nerve cord runs the length of the chordate, along the top. Immediately beneath the nerve cord is a notochord that also runs the length of the organism. Beneath the notochord, pharyngeal slits cut diagonally into tissue toward the front of the organism. A post-anal tail occurs at the rear. — **Figure \(\PageIndex{3}\):** In chordates, iv common features appear at some betoken in development: a notochord, a dorsal hollow nerve string, pharyngeal slits, and a postal service-anal tail. The beefcake of a cephalochordate shown here illustrates all of these features.

Which of the following statements about common features of chordates is true?

The dorsal hollow nervus cord is function of the chordate key nervous system.
In vertebrate fishes, the pharyngeal slits become the gills.
Humans are not chordates because humans do non have a tail.
Vertebrates exercise non have a notochord at whatever point in their development; instead, they have a vertebral column.

Invertebrate Chordates

In addition to the vertebrates, the phylum Chordata contains two clades of invertebrates: Urochordata (tunicates) and Cephalochordata (lancelets). Members of these groups possess the 4 distinctive features of chordates at some betoken during their development.

The tunicates (Figure \(\PageIndex{4}\)) are also called sea squirts. The name tunicate derives from the cellulose-like carbohydrate fabric, called the tunic, which covers the outer body. Although tunicates are classified equally chordates, the developed forms are much modified in body plan and do non accept a notochord, a dorsal hollow nerve string, or a mail-anal tail, although they do have pharyngeal slits. The larval class possesses all four structures. Most tunicates are hermaphrodites. Tunicate larvae hatch from eggs within the developed tunicate's torso. Later hatching, a tunicate larva swims for a few days until it finds a suitable surface on which it tin can attach, usually in a dark or shaded location. Information technology then attaches by the head to the substrate and undergoes metamorphosis into the developed form, at which signal the notochord, nerve string, and tail disappear.

Photo a shows tunicates, which are sponge-like in appearance and have a few holes along the surface. Illustration b shows the tunicate larval stage, which resembles a tadpole, with a post-anal tail at the narrow end. A dorsal hollow nerve cord runs along the upper back, and a notochord runs beneath the nerve cord. The digestive tract starts with the mouth at the front of the animal connected to a stomach. Above the stomach is the anus. The pharyngeal slits, which are located between the stomach and mouth, are connected to an atrial opening at the top of the body. Illustration c shows an adult tunicate, which resembles a tree stump anchored to the bottom. Water enters through the mouth at the top of the body and passes through the pharyngeal slits, where it is filtered. Water then exits through another opening at the side of the body. The heart, stomach, and gonad are tucked beneath the pharyngeal slits. — **Effigy \(\PageIndex{four}\):** (a) This photograph shows a colony of the tunicate Botrylloides violaceus. In the (b) larval stage, the tunicate can swim freely until information technology attaches to a substrate to become (c) an adult. (credit a: modification of work by Dr. Dwayne Meadows, NOAA/NMFS/OPR)

Most tunicates live a sessile existence in shallow sea waters and are intermission feeders. The primary foods of tunicates are plankton and detritus. Seawater enters the tunicate'southward body through its incurrent siphon. Suspended cloth is filtered out of this water past a mucus net (pharyngeal slits) and is passed into the intestine through the action of cilia. The anus empties into the excurrent siphon, which expels wastes and h2o.

Lancelets possess a notochord, dorsal hollow nervus string, pharyngeal slits, and a post-anal tail in the adult stage (Figure \(\PageIndex{5}\)). The notochord extends into the caput, which gives the subphylum its proper noun (Cephalochordata). Extinct fossils of this subphylum engagement to the centre of the Cambrian flow (540–488 mya).The living forms, the lancelets, are named for their blade-like shape. Lancelets are merely a few centimeters long and are usually found buried in sand at the bottom of warm temperate and tropical seas. Similar tunicates, they are suspension feeders.

The illustration shows a lancelet with the head protruding from the sand, and the rest of the body buried. On the head, tentacles surround the mouth. The mouth leads to the digestive tract. The anus is located just before the post-anal tail. The pharyngeal slits are next to the atrium, which empties into the atriopore. The body has segmented muscles running along it from top to bottom. — **Effigy \(\PageIndex{5}\):** Adult lancelets retain the four key features of chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a mail-anal tail.

Section Summary

Echinoderms are deuterostome marine organisms. This phylum of animals acquit a calcareous endoskeleton equanimous of ossicles covered past a spiny peel. Echinoderms possess a water-based circulatory system. The madreporite is the indicate of entry and exit for water for the water vascular arrangement.

The characteristic features of Chordata are a notochord, a dorsal hollow nerve string, pharyngeal slits, and a post-anal tail. Chordata contains two clades of invertebrates: Urochordata (tunicates) and Cephalochordata (lancelets), together with the vertebrates. Nigh tunicates live on the ocean floor and are break feeders. Lancelets are pause feeders that feed on phytoplankton and other microorganisms.

Art Connections

Figure \(\PageIndex{3}\): Which of the following statements about common features of chordates is true?

A. The dorsal hollow nerve cord is part of the chordate central nervous arrangement.
B. In vertebrate fishes, the pharyngeal slits become the gills.
C. Humans are not chordates because humans practice not have a tail.
D. Vertebrates practise non have a notochord at any bespeak in their development; instead, they have a vertebral cavalcade.

Respond: A

Glossary

Cephalochordata: a chordate clade whose members possess a notochord, dorsal hollow nervus string, pharyngeal slits, and a post-anal tail in the adult stage

Chordata: a phylum of animals distinguished by their possession of a notochord, a dorsal hollow nerve string, pharyngeal slits, and a post-anal tail at some bespeak during their development

dorsal hollow nervus cord: a hollow, tubular structure derived from ectoderm, which is located dorsal to the notochord in chordates

Echinodermata: a phylum of deuterostomes with spiny skin; exclusively marine organisms

lancelet: a member of Cephalochordata; named for its bract-similar shape

madreporite: a pore for regulating entry and exit of water into the water vascular organisation

notochord: a flexible, rod-shaped structure that is establish in the embryonic stage of all chordates and in the adult stage of some chordates

pharyngeal slit: an opening in the pharynx

mail service-anal tail: a muscular, posterior elongation of the body extending across the anus in chordates

tetrapod: a four-footed animal; includes amphibians, reptiles, birds, and mammals

tunicate: a sessile chordate that is a member of Urochordata

Urochordata: the clade equanimous of the tunicates

vertebral column: a series of dissever bones that surround the spinal cord in vertebrates

h2o vascular system: a organisation in echinoderms in which water is the circulatory fluid

Contributors and Attributions

Samantha Fowler (Clayton State University), Rebecca Roush (Sandhills Community College), James Wise (Hampton University). Original content by OpenStax (CC BY 4.0; Access for gratuitous at https://cnx.org/contents/b3c1e1d2-83...4-e119a8aafbdd).