Cephalopods: Difference between revisions
| Line 2: | Line 2: | ||
Cephalopods are molluscs, but have many physiological attributes that distinguish them from other molluscs, including predatory lifestyles and sophisticated nervous systems. Historically, cephalopods have been a prolific class, though research is sparse.<ref name="CBC"></ref> Today, the class encompasses octopuses, cuttlefish, squid, and nautiluses. Representatives of the class have been found in all the world's oceans. <ref name ="EOS">Boyle, P. "Cephalopods." Encyclopedia of Ocean Sciences 1 (2001): 436-42. Science Direct. Elsevier B.V., 11 Apr. 2013. Web. 22 Feb. 2014. <http://ac.els-cdn.com/B9780123744739001958/3-s2.0-B9780123744739001958-main.pdf?_tid=4e6f9af6-9e64-11e3-bd04-00000aacb360&acdnat=1393364120_b8c509396a239367521c18e75d90ee5a>.</ref> | Cephalopods are molluscs, but have many physiological attributes that distinguish them from other molluscs, including predatory lifestyles and sophisticated nervous systems. Historically, cephalopods have been a prolific class, though research is sparse.<ref name="CBC"></ref> Today, the class encompasses octopuses, cuttlefish, squid, and nautiluses. Representatives of the class have been found in all the world's oceans. <ref name ="EOS">Boyle, P. "Cephalopods." Encyclopedia of Ocean Sciences 1 (2001): 436-42. Science Direct. Elsevier B.V., 11 Apr. 2013. Web. 22 Feb. 2014. <http://ac.els-cdn.com/B9780123744739001958/3-s2.0-B9780123744739001958-main.pdf?_tid=4e6f9af6-9e64-11e3-bd04-00000aacb360&acdnat=1393364120_b8c509396a239367521c18e75d90ee5a>.</ref> | ||
== Evolution == | == Evolution == | ||
Revision as of 19:05, 14 April 2014
Cephalopods
Cephalopods are molluscs, but have many physiological attributes that distinguish them from other molluscs, including predatory lifestyles and sophisticated nervous systems. Historically, cephalopods have been a prolific class, though research is sparse.[1] Today, the class encompasses octopuses, cuttlefish, squid, and nautiluses. Representatives of the class have been found in all the world's oceans. [2]
Evolution
- Probably evolved from gastropods [3]
- More than 10,000 fossil species named [3]
- Belemnoids, from the Mesozoic, may be the ancestors of modern squids [3]
- 800 extant species [4]
Reproduction and Life Cycle
Reproduction
Cephalopods most frequently mate only once, which occurs near the end of their life cycle.[5] Courtship rituals between cephalopods can include a diverse array of color changes and body movements. Male cephalopods have a specialized arm (called a hectocotylus) which is used to transfer spermataphores, or packets of sperm, into the female's genital pore. Sometimes after mating, the hectocotylus is left behind in the female's mantle cavity. Females possess a single oviduct.[3] Females may mate with multiple males and have multiple paternity of offspring, ultimately increasing the genetic diversity of a population.[2]
Life Cycle
After being laid by the female, cephalopod eggs are usually covered in a tough coating which helps them attach to hard surfaces. Upon hatching, cephalopods emerge as paralarvae, surpassing a true larval stage.[3] Paralarvae are not morphologically distinct from adults; instead, they are like "miniature adults." Though they are similar in appearance, these paralarvae may occupy different ecological niches from adults. Sexual maturation occurs rapidly, reaching adult size in about one year. Most cephalopods die shortly after mating once, reflective of a monocyclic semelparous life cycle.[5] This uniseasonal breeding can cause extreme fluctuations in cephalopod populations and biomass, as most of a generation will die as a new one arises. These fluctuations are unpredictably variably and inconsistently patterned.[2]
Anatomy
Cephalopods have a buccal cavity, or mouth, that usually is found at the center of their tentacles. Within this mouth is a radula, or a coarse, rasping tongue.[3][1] Cephalopods are also known for their ink glands, which can expel a dark cloud of melanin through the mantle cavity in the face of a threat. All families of cehpalopods, with the exception of Nautilus, possess cells that contain large amounts of pigments, as well as interacting contractile fibers. Together, these two structures are responsible for the ability of cephalopods to change color. This behavior frequently occurs in response to danger or a change of emotion (e.g. alarm).[3] The majority of cephalopods have reduced or absent calcareous shells, remnants of the prominent shells of their ancestral species. Today, squids and octopuses have completely lost the internal shell and its buoyant properties. Nautiluses have a complete external shell, while cuttlefish have a small, internal "bone."[2] While cephalopods have no true brain, some species exhibit an advanced cluster of ganglionic masses centered around the esophagus, constituting the most complex "brain" of any invertebrate. Cephalopods also have relatively well developed statocysts (gravity and movement senses).[2]
Diet
All cephalopods maintain carnivorous diets.[3] Most fed on a wide range of crustacea and fish, consuming up to 15% of their body weight daily. On occasion, cephalopods may exhibit cannibalism on smaller specimens. Prey are usually attacked with a forward strike from the cephalopod and are subsequently pulled toward the buccal cavity by the tentacles. Squid simply bite into their prey with their beaks; octopuses, however, exhibit slightly more complex feeding behaviors. Octopuses often inject a mix of enzymes and toxins into their prey, loosing the tissue for easier extraction (particularly, bivalves and crustaceans).[2]
Behavior
- Rapid color change [4]
- Centralized brain with highly developed sense organs [4]
- Jet propulsion [3]
- Inking [2]
Habitat
Importance
Economic value
Economically, cephalopods remain an important part of both coastal and inland areas, as many species are eaten by humans.[3] Human consumption of cephalopods dates at least as far back as classical times. Today, as many as 3 million tons are consumed annually by humans, having grown from about 1 million in the 1970s.[2]
Ecological value
Cephalopods are an important low level predator in oceanic food chains, as they consume a wide variety of fish, crustaceans, and other invertebrates. In addition to serving a wide niche as a predator, cephalopods themselves are consumed by fish, marine mammals, and oceanic birds, making them an indispensable food source for tertiary consumers. For example, sperm whales may consume up to 320 million tons of cephalopods annually from pelagic zones.[2]
Threats
Human Induced Threats [5]
- Bioaccumulation of toxins [5]
- Noise pollution [5]
- Altered seasonal migration patterns related to ocean warming [5]
- Possible decrease in availability of calcium carbonate, related to declining pH [5]
- Overfishing [5]
Species
Common Octopus Octopus vulgaris
Lifespan of 12-24 months [6]
- Geographic Range
- Found all over the world, including the Eastern Atlantic Ocean [6]
- Habitat
- Physical Appearance
- Reproduction and Development
- Eggs laid in shallow water [6]
- Females brood in isolation
- Behavior and Diet
- Conservation Status
- Potential for overfishing [6]
Caribbean Reef Octopus Octopus briareus [7]
- Geographic Range
- Warm, shallow water [7]
- Habitat
- Physical Appearance
- Reproduction and Development
- Males have a hectocotylus [7]
- Males initiate mating, which usually lasts between 30 and 80 minutes [7]
- Females can store sperm in oviducts for more than 3 months [7]
- Females brood multiple egg clusters of about 25, totaling anywhere between 100-500 eggs [7]
- Takes 50-80 days, but is accelerated in warmer waters [7]
- Hatch as miniature adults, capable of swimming, eating, inking, and changing color as adults can [7]
- Males reach sexual maturity around 140 days; females, 150 [7]
- Behavior and Diet
- Not social [7]
- Fighting occurs over living territory [7]
- Standard distance between living spaces is approximately 60ft [7]
- Frequently change dens, only remaining in one place while brooding [7]
- As a predatory defense, these octopuses swell their mantle with water before jet-propelling themselves away behind a cloud of ink [7]
- Eat mostly crab (preferred) and shrimp [7]
- May eat fish and lobsters as well [7]
- Hunt in early morning and evening hours [7]
- Conservation Status
- No current threat [7]
Caribbean Two-Spot Octopus [8]
- Geographic Range
- Found often in the Bahamas, Caribbean, and Florida[8]
- Habitat
- Physical Appearance
- Mottled appearance
- Blue rings make ocelli beneath the eyes
- Reproduction and Development
- Behavior and Diet
- Conservation Status
Caribbean Reef Squid Sepioteuthis sepioidea [9]
Important as a food source for humans
- Geographic Range
- Found all throughout the Caribbean [9]
- Habitat
- Newly hatched organisms live very close to shore [9]
- Found anywhere between .2-10m deep and frequently near vegetation [9]
- Older specimens are denizens of turtle grass in the shallows near shore [9]
- Non-breeding adults prefer open water, enjoying ample space in depths of up to 100m at night [9]
- Breeding adults spend their time in coral reefs, reaching depths of no greater than 8m [9]
- Newly hatched organisms live very close to shore [9]
- Physical Appearance
- Reproduction and Development
- Behavior and Diet
- Highly social [9]
- Complex signal communication [9]
- Can change the color of their brow ridges and central arms to express alarm [9]
- Can eject ink in open water as a means of evading predation [9]
- At rest, individuals may adopt a red or brown color [9]
- Younger squid often display bars that make them more closely resemble vegetation, presumably a defense mechanism [9]
- Primarily consume sardines and other fish [9]
- Sometimes shrimp [9]
- Hunting is dependent on vision[9]
- Highly social [9]
- Conservation Status
- No special status [9]
Notes
- ↑ 1.0 1.1 Judkins, Heather L. "Cephalopods of the Broad Caribbean: Distrution, Abundance, and Ecological Importance." Diss. University of South Florida, 2009. Scholar Commons. Graduate School at Scholar Commons. Web. 21 Feb. 2014. <http://scholarcommons.usf.edu/cgi/viewcontent.cgi?article=3033&context=etd&sei-redir=1&referer=http%3A%2F%2Fwww.google.com%2Furl%3Fq%3Dhttp%253A%252F%252Fscholarcommons.usf.edu%252Fcgi%252Fviewcontent.cgi%253Farticle%253D3033%2526context%253Detd%26sa%3DD%26sntz%3D1%26usg%3DAFQjCNF6Q0NU3If5jMRKW7UQ1KtCo117qQ#search=%22http%3A%2F%2Fscholarcommons.usf.edu%2Fcgi%2Fviewcontent.cgi%3Farticle%3D3033%26context%3Detd%22>.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 Boyle, P. "Cephalopods." Encyclopedia of Ocean Sciences 1 (2001): 436-42. Science Direct. Elsevier B.V., 11 Apr. 2013. Web. 22 Feb. 2014. <http://ac.els-cdn.com/B9780123744739001958/3-s2.0-B9780123744739001958-main.pdf?_tid=4e6f9af6-9e64-11e3-bd04-00000aacb360&acdnat=1393364120_b8c509396a239367521c18e75d90ee5a>.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 Wheeler, Kristen, and Daphne G. Fautin. "ADW: Cephalopoda: INFORMATION." Animal Diversity Web. Regenst of the University of Michigan, 2001. Web. 22 Feb. 2014. <http://animaldiversity.ummz.umich.edu/accounts/Cephalopoda/>.
- ↑ 4.0 4.1 4.2 Jann, Vendetti. "The Cephalopoda." University of California Museum of Paleontology. UC Berkeley, n.d. Web. 24 Feb. 2014. <http://www.ucmp.berkeley.edu/taxa/inverts/mollusca/cephalopoda.php>
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 LaRosa, Ginni A.. "Learning from the Soft Intelligence: Cephalopods as Indicators of Ocean Changes." UMD Library. University of Maryland, 01 Dec 2011. Web. 25 Feb 2014. <http://drum.lib.umd.edu/bitstream/1903/12427/11/LaRosa_ResearchPaper.pdf>.
- ↑ 6.00 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.10 6.11 6.12 6.13 6.14 Case, R. 1999. "Octopus vulgaris" (On-line), Animal Diversity Web. Accessed February 25, 2014 at http://animaldiversity.ummz.umich.edu/accounts/Octopus_vulgaris/
- ↑ 7.00 7.01 7.02 7.03 7.04 7.05 7.06 7.07 7.08 7.09 7.10 7.11 7.12 7.13 7.14 7.15 7.16 7.17 7.18 7.19 7.20 7.21 7.22 7.23 7.24 Robinson, A. 2000. "Octopus briareus" (On-line), Animal Diversity Web. Accessed February 25, 2014 at http://animaldiversity.ummz.umich.edu/accounts/Octopus_briareus/
- ↑ 8.0 8.1 Tokarz, Jessica. " Caribbean Two-Spot Octopus." Field guide to marine inhabitants - Invertebrates. Marine Science Center of Florida. Web. 25 Feb 2014. <http://www.marinesciencecenter.com/Octopodidae.htm>.
- ↑ 9.00 9.01 9.02 9.03 9.04 9.05 9.06 9.07 9.08 9.09 9.10 9.11 9.12 9.13 9.14 9.15 9.16 9.17 9.18 9.19 9.20 9.21 9.22 9.23 9.24 9.25 9.26 9.27 9.28 9.29 Ritter, S. 2000. "Sepioteuthis sepioidea" (On-line), Animal Diversity Web. Accessed February 25, 2014 at http://animaldiversity.ummz.umich.edu/accounts/Sepioteuthis_sepioidea/