Both sea cucumbers and humans are part of the deutersomes group on the evolutionary tree. Besides recent DNA findings, their evolutionary connection is evident when looking at the stages of embryonic development. They are also both coelmates, meaning they have three cell layers that each create specific parts of the organism.
Habitat and niche
All sea cucumbers live in aquatic environments, specifically the ocean. Some live deep in the ocean, on the sea floor, or in shallow water. (1). Sea cucumbers thrive in "shallow coral reefs", and can survive during low tide in a dry "intertidal" ocean floor (2).
Predator avoidance
When some sea cucumbers are threatened, they release sticky threads that capture their enemies. Other sea cucumbers are capable of mutilating their own body to serve as a defense mechanism: they can violently contract their muscles and discharge some internal organs through their anus. The missing body parts are then quickly regenerated. (1) Sea cucumbers can also contract their muscles to squirt out water when threatened, making their bodies shorter, thicker, and more rigid (9).
Nutrient acquisition
Sea cucumbers capture food with their anterior tube feet, which are modified into feathery, large, sticky tentacles that can protruded from the mouth. They can also occasionally withdraw their tentacles and wipe off the material adhered to it for digestion. Sea cucumbers feed on tiny particles like algae, minute aquatic animals, or waste materials. The animals break down these particles into even smaller pieces, which become fodder for bacteria, and thus recycle them back into the ocean ecosystem (1).
Reproduction and life cycle
Sea cucumbers can breed sexually or asexually, but sexual reproduction is more typical. The animals release both eggs and sperm into the water and fertilization occurs when they meet. There must be many individuals in a sea cucumber population for this reproductive method to be successful (1). Sea cucumbers larva have symmetrical, ciliated larva.
Growth and development
Echinoderms not only have pentaradial symmetry, but also have an internal skeleton and a water vascular system. The internal skeletons are calcium-rich plates covered by slim layers of skin and muscle. The water vascular system creates water-filled channels spanning the body, leading to the creation of many advantages to sea cucumbers such as tube feet. In both organisms the mouth forms at the opposite end of the embryo from the blastophere, which develops into the anus.
Integument Sea Cucumbers have a rough cuticle outer layer of skin that protects them from the environment. Directly below that is a layer that is made largely out of collagen and a layer of epithelial cells. (4)
Movement
Some sea cucumbers move by tiny tube feet, hollow muscular projections, along the length of their body. Species without tube feet move by muscular movements of the body. (7)
Sensing the environment When a threat is detected, such as a predator, the sea cucumber expels a sticky string like substance in order to neutralize the threat while it escapes.(5)
Gas exchange Muscles in the body walls expand and contract, sucking water through the anus and into organs known as respiratory trees. These structure act like gills, extracting oxygen from the water with many branched appendages. The high surface area to volume ratio allows for more cells on the surface to extract the oxygen, and fewer on the inside that will only consume it (5).
Illustrates the respiratory trees that connect to the anus and bring water around the body
(10)
Waste removal
The sea cucumber has a cavity known as the cloaca. The cloaca is not only a chamber serving respiration, but it is also as a common exit for wastes from the digestive tract and sex cells from the reproductive system. (6) Sea cucumbers also often digest sand and release calcium carbonate and ammonia as waste (11).
Environmental physiology
All sea cucumbers live in oceans. Some live in shallow waters while other reside in the deepest trenches. No matter what depth of ocean sea cucumbers live in, they all settle on 'bottoms' of the water such as sand or coral reefs (2). Tidal fluctuations in the ocean can affect osmotic concentrations of body fluids in sea cucumbers. Some deep ocean living sea cucumbers have control of ion concentrations to a certain extent (3).
Internal circulation
Sea cucumbers have an internal water vascular system, which has channels containing water flowing throughout the body. This is where gas exchange occurs.
Review Question:
1) What does it mean to be a coelmate?
2) Explain the purpose of the cavity that sea cucumbers have known as the cloaca.
Sea cucumber (echinoderm)
Classification/Diagnostic characteristicsThe sea cucumber is an echinozoan, one of the two main groups of motile echinoderms.
Domain: Eukarya
Kingdom: Animalia
Phylum: Echinoderm
Class: Holothuroidia
Order: Aspidochirotida
Family: Holothuriidae
Genus: Holothuria
Species:
Relationship to humans
Both sea cucumbers and humans are part of the deutersomes group on the evolutionary tree. Besides recent DNA findings, their evolutionary connection is evident when looking at the stages of embryonic development. They are also both coelmates, meaning they have three cell layers that each create specific parts of the organism.
Habitat and niche
All sea cucumbers live in aquatic environments, specifically the ocean. Some live deep in the ocean, on the sea floor, or in shallow water. (1). Sea cucumbers thrive in "shallow coral reefs", and can survive during low tide in a dry "intertidal" ocean floor (2).
Predator avoidance
When some sea cucumbers are threatened, they release sticky threads that capture their enemies. Other sea cucumbers are capable of mutilating their own body to serve as a defense mechanism: they can violently contract their muscles and discharge some internal organs through their anus. The missing body parts are then quickly regenerated. (1) Sea cucumbers can also contract their muscles to squirt out water when threatened, making their bodies shorter, thicker, and more rigid (9).
Nutrient acquisition
Sea cucumbers capture food with their anterior tube feet, which are modified into feathery, large, sticky tentacles that can protruded from the mouth. They can also occasionally withdraw their tentacles and wipe off the material adhered to it for digestion. Sea cucumbers feed on tiny particles like algae, minute aquatic animals, or waste materials. The animals break down these particles into even smaller pieces, which become fodder for bacteria, and thus recycle them back into the ocean ecosystem (1).
Reproduction and life cycle
Sea cucumbers can breed sexually or asexually, but sexual reproduction is more typical. The animals release both eggs and sperm into the water and fertilization occurs when they meet. There must be many individuals in a sea cucumber population for this reproductive method to be successful (1).
Sea cucumbers larva have symmetrical, ciliated larva.
Growth and development
Echinoderms not only have pentaradial symmetry, but also have an internal skeleton and a water vascular system. The internal skeletons are calcium-rich plates covered by slim layers of skin and muscle. The water vascular system creates water-filled channels spanning the body, leading to the creation of many advantages to sea cucumbers such as tube feet. In both organisms the mouth forms at the opposite end of the embryo from the blastophere, which develops into the anus.
Integument
Sea Cucumbers have a rough cuticle outer layer of skin that protects them from the environment. Directly below that is
a layer that is made largely out of collagen and a layer of epithelial cells. (4)
Movement
Some sea cucumbers move by tiny tube feet, hollow muscular projections, along the length of their body. Species without tube feet move by muscular movements of the body. (7)
Sensing the environment
When a threat is detected, such as a predator, the sea cucumber expels a sticky string like substance in order to neutralize the threat while it escapes.(5)
Gas exchange
Muscles in the body walls expand and contract, sucking water through the anus and into organs known as respiratory trees. These structure act like gills, extracting oxygen from the water with many branched appendages. The high surface area to volume ratio allows for more cells on the surface to extract the oxygen, and fewer on the inside that will only consume it (5).
Waste removal
The sea cucumber has a cavity known as the cloaca. The cloaca is not only a chamber serving respiration, but it is also as a common exit for wastes from the digestive tract and sex cells from the reproductive system. (6) Sea cucumbers also often digest sand and release calcium carbonate and ammonia as waste (11).
Environmental physiology
All sea cucumbers live in oceans. Some live in shallow waters while other reside in the deepest trenches. No matter what depth of ocean sea cucumbers live in, they all settle on 'bottoms' of the water such as sand or coral reefs (2). Tidal fluctuations in the ocean can affect osmotic concentrations of body fluids in sea cucumbers. Some deep ocean living sea cucumbers have control of ion concentrations to a certain extent (3).
Internal circulation
Sea cucumbers have an internal water vascular system, which has channels containing water flowing throughout the body. This is where gas exchange occurs.
Review Question:
1) What does it mean to be a coelmate?
2) Explain the purpose of the cavity that sea cucumbers have known as the cloaca.
References:
1. http://animals.nationalgeographic.com/animals/invertebrates/sea-cucumber/
2. http://bioweb.uwlax.edu/bio203/s2008/hui_ka/03Habitat.html
3. http://www.asnailsodyssey.com/LEARNABOUT/CUCUMBER/cucuEnvi.php
4. http://jeb.biologists.org/content/62/3/733.full.pdf
5. http://bioweb.uwlax.edu/bio203/s2008/hui_ka/06Adaptation.html
6. http://eol.org/pages/2012/details
7. animal.discovery.com/marine-life/sea-cucumber-info.htm
8. http://animals.nationalgeographic.com/animals/invertebrates/sea-cucumber/
9. http://library.thinkquest.org/J001418/seacuc.html
10. http://www.cabrillo.edu/~jcarothers/lab/notes/deuterostomes/VISUALS/images/MainFrame_clip_image012.png
11. http://www.smh.com.au/environment/conservation/sea-cucumbers-may-save-great-barrier-reef-20120130-1qowc.html