What is the difference between echinoderms and other invertebrates

Fill in Table 3. Wherever possible, focus on similarities and differences of structure, function, and behavior. This document may be freely reproduced and distributed for non-profit educational purposes. Skip to main content. Search form Search. Join The Community Request new password. Main menu About this Site Table of Contents.

Activity: Comparing Echinoderms. A: Structure and Function LS1. Sea cucumbers feed by snaring plankton in the mucus coating on their tentacles. They bring the tentacles into the esophagus to wipe them clean, recoat them with mucus, and feed some more. They have a unique defensive mechanism. When threatened, they can evert sticky stinky hairs from their anus. Enough said Sea lilies are an ancient group, going back about mya. They were thought to be extinct until they were rediscovered growing on the ocean floor.

In sea lilies, the mouth and anus are both on the upper surface on a small disc, with the arms located along the edge of the disc. Crinoid tube feet are modified for filter feeding. How does the radial symmetry of echinoderms relate to their life style? Aren't all higher animals bilaterally symmetric? We now turn to the last phylum of animals, one that dominates the deuterostomes as thoroughly as arthropods dominate the protostomes, the Phylum Chordata 42, sp.

Chordates are eucoelomate deuterostomes , and probably share a common ancestor with echinoderms. Three important characteristics unite the Phylum Chordata. At some point in their life cycle, all chordates have a notochord , a dorsal hollow nerve cord , and pharyngeal gill slits.

A notochord is a flexible supporting rod of cartilage, although in most adult chordates the notochord is replaced by a vertebral column. The dorsal hollow nerve cord ultimately forms the spinal cord and the brain. The pharyngeal gill slits appear in all chordate embryos, an echo of our distant origin in the sea, but are usually lost in the early development of the organism.

Primitive chordates evolved small slits opening into the pharynx. By contracting the pharynx, the animal could draw water into its body and over the gill slits. These slits originally functioned in aiding respiration and capturing food by filter feeding. Smaller, more primitive vertebrates could rely on diffusion for gas exchange, but larger and more active forms required more surface area to allow rapid exchange of gases. Chordates evolved gills , sheets of highly folded tissue in the spaces between the gill slits, tissues with a very rich blood supply to exchange gases.

Gill arches were reinforced with cartilage to help hold them open. Over time, the area between the gills, or the gill arches, became ossified turned harder and migrated slightly forward to form the first primitive vertebrate jaw. Vertebrates could now bite and chew their prey, and were no longer limited to filter feeding as a way of life. Class Mammalia - placental humans , marsupial kangaroo , monotremes egg layers - platypus. Phylum Chaetognatha - sp.

I doubt if anyone here has ever noticed one of these worms while swimming in the ocean. These tiny little predators are only cm. But they are incredibly abundant. They are the most abundant carnivore in the ocean. They are the tiger sharks of the plankton. The tiny moveable hooks that surround the mouth, and give these creatures their name, are used to capture prey. Prey are injected with a tiny jolt of tetrodotoxin , the same paralytic poison found in some Japanese puffer fish.

They lack circulatory, respiratory and excretory organs, relying entirely on diffusion. They are living fossils, going back essentially unchanged for about my. They represent a very early branch on the chordate tree. These marine worms are another ancient group, evolving about mya.

They may be the first deuterostomes on Earth. They range in size from 2 cm to 1. They share some of the fundamental characteristics of the chordates, which we'll review later, such as a dorsal hollow nerve cord and gill slits. We used to think they also had a notochord, another chordate trademark, but closer study revealed this hypothesis to be wishful thinking.

They live in U-shaped burrows in the ocean floor. Notice the slits in the side of the pharynx. These pharyngeal gill slits are used for gas exchange and feeding. This obscure little structure will eventually give rise to the vertebrate jaw, a marvelous example of evolutionary constraint - evolution is constrained to run in certain channels.

All subsequent evolution has to start with what's already there. They share a common ancestor with echinoderms, a fact we deduce from their similar larval forms dipleurula larvae and other developmental similarities. This larval form, incidentally looks strikingly similar to the trochophore larvae of annelids and molluscs. Tunicates are sessile, marine organisms.

They are covered with a cellulose cloak, or tunic, which gives this group its name. They exchange gases and filter feed by means of their pharyngeal gill slits. They rely on two prominent siphons, an incurrent and excurrent siphon, to pull water through their bodies. The pharynx is lined with cilia, which draw water in.

The suspended organic particles stick to a layer of mucus in the pharynx, and are later eaten. These siphons are convergent with mollusc siphons. Tunicates look a bit like molluscs, and a bit like a transparent sponge, and may even function like these organisms, but these similarities are entirely superficial, and the three groups are not directly related. Although these curious animals don't especially look like us, they are very derived from their presumably bilateral and motile ancestors.

The larvae of tunicates looks very much like a little tadpole. One of the strongest theories of vertebrate origins suggests that vertebrates arose from tunicate larvae by a process called neoteny. In neoteny, the juvenile form becomes capable of sexual reproduction, and the adult stage is completely bypassed. Lancelets are very common in shallow water. They are usually hard to see because they bury themselves in the sand, with only the head end sticking out, so they can filter feed by means of the gill slits in their pharynx.

As you might expect of a sedentary filter feeder, their cephalization is greatly reduced. Above all, the main difference between echinoderms and chordates is their skeletal system. The echinoderms have a dermal skeleton made up of ossicles while chordates have an internal skeleton made up of bones and cartilages. Moreover, echinoderms have a tube feet for their locomotion while chordates use legs, fins or wings for locomotion.

Echinoderms are a phylum of animals with radial symmetry. They are non-chordates and they do not have a notochord or a central nervous system and their nervous system is made up of a nerve net. On the other hand, chordates are another phylum of animals including vertebrates. They develop a notochord and an internal skeleton made up of bones and cartilages. However, both echinoderms and chordates are deuterostomes and they show bilateral symmetry in any stage of their life cycle.

However, the main difference between echinoderms and chordates is the notochord and body symmetry. Bhavya, S. Figure 1: Brittle Star. View all posts. Birds are considered tetrapods because they evolved from tetrapod ancestors. The post-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 balance, locomotion, courting, and signaling when danger is near. In many species, the tail is absent or reduced; for example, in apes, including humans, it is present in the embryo, but reduced in size and nonfunctional in adults. Which of the following statements about common features of chordates is true? In addition to the vertebrates, the phylum Chordata contains two clades of invertebrates: Urochordata tunicates and Cephalochordata lancelets.

Members of these groups possess the four distinctive features of chordates at some point during their development. The tunicates [Figure 4 ] are also called sea squirts. The name tunicate derives from the cellulose-like carbohydrate material, called the tunic, which covers the outer body.

Although tunicates are classified as chordates, the adult forms are much modified in body plan and do not have a notochord, a dorsal hollow nerve cord, or a post-anal tail, although they do have pharyngeal slits. The larval form possesses all four structures. Most tunicates are hermaphrodites.

After hatching, a tunicate larva swims for a few days until it finds a suitable surface on which it can attach, usually in a dark or shaded location. It then attaches by the head to the substrate and undergoes metamorphosis into the adult form, at which point the notochord, nerve cord, and tail disappear. Most tunicates live a sessile existence in shallow ocean waters and are suspension feeders.

The primary foods of tunicates are plankton and detritus. Suspended material is filtered out of this water by 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 water. Lancelets possess a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail in the adult stage [Figure 5]. The notochord extends into the head, which gives the subphylum its name Cephalochordata.

Extinct fossils of this subphylum date to the middle of the Cambrian period — mya. The living forms, the lancelets, are named for their blade-like shape.