Echinoderms: Study with Video Lessons, Practice Problems & Examples

Echinoderms, including starfish, sea urchins, and sea cucumbers, are unique deuterostome animals characterized by bilateral symmetry and an endoskeleton made of plates. They possess a water vascular system for locomotion and feeding, utilizing tube feet for movement and prey capture. Echinoderms can reproduce sexually or asexually, with distinct sexes in sexual reproduction. Their spiny skin gives them their name, and they play vital roles in marine ecosystems, showcasing adaptations that enhance their survival and ecological interactions.

Echinoderms

Hi. In this video, we're going to be talking about echinoderms, which are animals like starfish, sea urchins, sea cucumbers, and sand dollars. And in these images here, you can actually see a couple of examples. We have a starfish right here. This is a sea cucumber in the middle, kind of looks like a slug. And over here behind my head, we have a sand dollar. Now, echinoderms are deuterostome animals, and unlike however their appearance might make you think that they're actually some type of protostome. They're deuterostomes. However, they're not chordates. In fact, they're the only deuterostome animals we're really going to look at that are not chordates. They are considered bilateral, which is probably easier to see in some organisms rather than others. However, their symmetry is bilateral. If it helps, you know, you can draw a line through the starfish like that. Maybe that makes the symmetry more clear. And their name actually comes from the spiny skin seen in some species. You see they have this endoskeleton, meaning internal skeleton, and it's made up of these plates that, in some cases fuse together, in others are connected by tissues, and they actually look similar to like a knight's armor or something, and how the plates are stacked together. Now, they have skin that grows over these plates, however, you can still kind of see their form, for example, in this starfish. Now, echinoderms can reproduce sexually, though some also reproduce asexually. And, it should be noted that there are individuals with separate sexes in the case of sexual reproduction. They have a couple of unique features that I want to talk about. One is this water vascular system, which is basically a series of tubes around the body that are fluid-filled and are used for internal transport and respiration, similar to like our own vascular system. However, what's cool and unique about theirs is that they also use it for locomotion. So by circulating the water around, they can actually cause motion. And you can see an outline here of the water vascular system, all these little tube structures that radiate around the body. Now, these echinoderms also have what are called tube feet. They're actually extensions to the water vascular system. You can see them right here. And they use those tube feet, in order to move and feed. So that's what they're actually moving fluid around through to cause locomotion, and they also can trap prey in these tube feet and use them for feeding. Alright. That's all I have for this video. I'll see you guys next time.

Here’s what students ask on this topic:

What are the main characteristics of echinoderms?

Echinoderms are marine animals that include starfish, sea urchins, sea cucumbers, and sand dollars. They are deuterostomes, meaning their embryonic development is similar to that of chordates, but they are not chordates themselves. Echinoderms exhibit bilateral symmetry, which can be seen more clearly in some species than others. They possess an endoskeleton made of calcareous plates, often covered by spiny skin. A unique feature of echinoderms is their water vascular system, a network of fluid-filled tubes used for locomotion, feeding, and respiration. They can reproduce both sexually and asexually, with distinct sexes in sexual reproduction. Their tube feet, extensions of the water vascular system, aid in movement and prey capture.

How does the water vascular system function in echinoderms?

The water vascular system in echinoderms is a network of fluid-filled canals that play a crucial role in locomotion, feeding, and respiration. It consists of a central ring canal and radial canals that extend into each arm or body segment. Water enters the system through a sieve-like structure called the madreporite. The water is then circulated through the canals, extending into tube feet, which are small, flexible appendages. By contracting and relaxing muscles around these canals, echinoderms can control the movement of water, allowing the tube feet to extend and retract. This hydraulic mechanism enables them to move, capture prey, and exchange gases for respiration.

What is the role of tube feet in echinoderms?

Tube feet are small, flexible appendages that extend from the water vascular system in echinoderms. They play a vital role in locomotion, feeding, and respiration. Each tube foot consists of an ampulla (a bulb-like structure) and a podium (a tube-like extension). By contracting the ampulla, water is forced into the podium, causing it to extend. This allows the echinoderm to adhere to surfaces and move. Tube feet also aid in capturing prey by trapping and holding food items. Additionally, they facilitate gas exchange, contributing to the respiratory process. Overall, tube feet are essential for the survival and ecological interactions of echinoderms.

How do echinoderms reproduce?

Echinoderms can reproduce both sexually and asexually. In sexual reproduction, most echinoderms have distinct sexes, with separate male and female individuals. They release their gametes (sperm and eggs) into the water column, where external fertilization occurs. The fertilized eggs develop into free-swimming larvae, which eventually settle and transform into adult forms. Some echinoderms also reproduce asexually through processes like fragmentation and regeneration. For example, a starfish can regenerate a new individual from a severed arm, provided a portion of the central disc is attached. This ability to reproduce asexually enhances their capacity for survival and population maintenance.

What is the ecological importance of echinoderms?

Echinoderms play significant roles in marine ecosystems. As predators, scavengers, and herbivores, they contribute to the balance of marine food webs. For instance, starfish are known to control the population of bivalves, such as mussels, preventing their overgrowth. Sea urchins graze on algae, helping to maintain the health of coral reefs and preventing algal overgrowth. Additionally, echinoderms contribute to nutrient cycling by breaking down organic matter and facilitating the decomposition process. Their activities influence the structure and function of marine habitats, making them essential for the stability and diversity of marine ecosystems.