Pleurobrachia bachei
Encyclopedia
Pleurobrachia bachei is a member of the phylum
Ctenophora and is commonly referred to as a sea gooseberry. These comb jellies are often mistaken for medusoid cnidaria
, but are not dangerous to handle.
An individuals body length can reach up to 20mm (0.8in) across with each of the two tentacles stretching 150 mm (6 in). Their gelatinous globular bodies are composed of 99% water. They have eight rows of well-developed combed plates consisting of thousands of fused macrocilia controlled by an apical
organ. Unlike many previous contradictory statements have suggested, Pleurobrachia lacks a conventional photoprotein
and is therefore incapable of producing light. Their bodies are virtually transparent and the many cilia refract the light, producing rainbow-like colors that can give the false appearance of bioluminescence. The stomach has eight branches that are visible through the transparent body and there are numerous anal pores. The branched tentacles can be white, yellow, pink or orange. They have no nematocysts (stinging cells). Instead, the two long extensile branched tentacles are armed with colloblasts; specialized adhesive cells with which to ensnare their prey.
Pleurobrachia lack any sessile (attached) stages and are wholly planktonic in their life cycle. They are hermaphroditic with direct development.
Lifespan
They are relatively short-lived, around 4-6 months.
History
Traditionally, Ctenophora has been thought to represent an ancient metazoan phylum. Recent genetic data suggests that all extant Ctenophora taxa may have evolved from a relatively recent common ancestor and that this ancestral ctenophore was tentaculate and cydippid-like. Because of the virtual absence of ctenophores in the fossil record their evolutionary history holds many more questions than answers.
Foraging Behavior
Pleurobrachia bachei is a selective carnivore
and its feeding habits are analogous to other ambush "sit and wait" predators, such as the orb-weaving spider. When searching for prey the Pleurobrachia swims with its oral pole forward to set its tentacles. To allow the two main tentacles and numerous lateral tentilla to relax and expand behind it they are often in a curved or helical pathway. Once the tentacles are set, the ctenophore drifts passively. Occasionally, it will retract its tentacles to varying degrees into the sheaths before swimming to another location where it then resets them. This behavior appears to be regulated by its hunger level and can be construed as an attempt to find an area with more prey abundance.
When handling prey both tentacles contract and carry the prey to the mouth. This is achieved by several rapid rotations of the body which swipes the tentacle bearing the food across the oral
region. The Pleurobrachia has its oral end opposite of where its tentacles originate.
Occurs worldwide but is patchy in its distribution being one of the more common comb jellies found on the West coast of North America.
Habitat
Along with its wide distribution the sea gooseberry is found in surface waters near shore and in open ocean to considerable depths.
Trophic Strategy
They are insatiable feeders of copepods and other small plankton
as well as fish eggs and larvae. It has been shown that their prey is more susceptible at an early age (naupliar/larval stages) because of minimal swimming speeds and small size which makes handling more efficient. This generalization is not neccassarily true for all Pleurobrachia. In one experiment the ctenophore favored adult Pseudocalanus minutus more than other forms of zooplankton
.
Pleurobrachia bachei has not been evaluated by the International Union for Conservation of Nature (IUCN), but seems to be prevalent and is not considered threatened.
Although Pleurobrachia has not been associated with declines in other populations, a closely related species Mnemiopsis leidyi
has. This ctenophore had catastrophic effects on fish catches after its introduction into the Black
and Azor Seas. It is believed to have been the main cause of decline in these waters after dissection confirmed its stomach contents had large quantities of the local fish eggs and larvae. Because of their diets Pleurobrachia and other ctenophore species can directiy or indirectly effect trophic cascades and ultimately regulate yield of commercially important fish stocks.
Economic Importance for humans: Positive
As predators ctenophores have a tremendous capacity to regulate abundance of their prey and therefore help to balance an ecosystem. While they can decimate other populations they can also restrain an overabundance of copepods which when left to their own devices could virtually eliminate all phytoplankton from the water column. With the proper management, Pluerobrachia introduction would be very beneficial to regulate copepods and to stop them from overpowering the essential primary producers (phytoplankton) needed for a healthy environment.
Phylum
In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....
Ctenophora and is commonly referred to as a sea gooseberry. These comb jellies are often mistaken for medusoid cnidaria
Cnidaria
Cnidaria is a phylum containing over 9,000 species of animals found exclusively in aquatic and mostly marine environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance,...
, but are not dangerous to handle.
Description
MorphologyAn individuals body length can reach up to 20mm (0.8in) across with each of the two tentacles stretching 150 mm (6 in). Their gelatinous globular bodies are composed of 99% water. They have eight rows of well-developed combed plates consisting of thousands of fused macrocilia controlled by an apical
Apical
Apical, from the Latin apex meaning to be at the apex or tip, may refer to:*Apical , an anatomical term of location for features associated with the base of an organism or structure...
organ. Unlike many previous contradictory statements have suggested, Pleurobrachia lacks a conventional photoprotein
Photoprotein
Photoproteins refer to bioluminescent proteins from luminous organisms. These proteins do not exhibit a luciferin-luciferase reaction, that is, a normal enzyme-substrate reaction. Instead, these proteins display luminescence proportional to the amount of the protein...
and is therefore incapable of producing light. Their bodies are virtually transparent and the many cilia refract the light, producing rainbow-like colors that can give the false appearance of bioluminescence. The stomach has eight branches that are visible through the transparent body and there are numerous anal pores. The branched tentacles can be white, yellow, pink or orange. They have no nematocysts (stinging cells). Instead, the two long extensile branched tentacles are armed with colloblasts; specialized adhesive cells with which to ensnare their prey.
Reproduction and Life History
ReproductionPleurobrachia lack any sessile (attached) stages and are wholly planktonic in their life cycle. They are hermaphroditic with direct development.
Lifespan
They are relatively short-lived, around 4-6 months.
History
Traditionally, Ctenophora has been thought to represent an ancient metazoan phylum. Recent genetic data suggests that all extant Ctenophora taxa may have evolved from a relatively recent common ancestor and that this ancestral ctenophore was tentaculate and cydippid-like. Because of the virtual absence of ctenophores in the fossil record their evolutionary history holds many more questions than answers.
Foraging Behavior
Pleurobrachia bachei is a selective carnivore
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
and its feeding habits are analogous to other ambush "sit and wait" predators, such as the orb-weaving spider. When searching for prey the Pleurobrachia swims with its oral pole forward to set its tentacles. To allow the two main tentacles and numerous lateral tentilla to relax and expand behind it they are often in a curved or helical pathway. Once the tentacles are set, the ctenophore drifts passively. Occasionally, it will retract its tentacles to varying degrees into the sheaths before swimming to another location where it then resets them. This behavior appears to be regulated by its hunger level and can be construed as an attempt to find an area with more prey abundance.
When handling prey both tentacles contract and carry the prey to the mouth. This is achieved by several rapid rotations of the body which swipes the tentacle bearing the food across the oral
Oral
The word oral may refer to:As an adjective:* the mouth, the first portion of the alimentary canal that receives food and saliva* speech communication as opposed to writing* oral administration of medicines...
region. The Pleurobrachia has its oral end opposite of where its tentacles originate.
Ecology and Distribution
Geographic RangeOccurs worldwide but is patchy in its distribution being one of the more common comb jellies found on the West coast of North America.
Habitat
Along with its wide distribution the sea gooseberry is found in surface waters near shore and in open ocean to considerable depths.
Trophic Strategy
They are insatiable feeders of copepods and other small plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
as well as fish eggs and larvae. It has been shown that their prey is more susceptible at an early age (naupliar/larval stages) because of minimal swimming speeds and small size which makes handling more efficient. This generalization is not neccassarily true for all Pleurobrachia. In one experiment the ctenophore favored adult Pseudocalanus minutus more than other forms of zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
.
Conservation
Conservation StatusPleurobrachia bachei has not been evaluated by the International Union for Conservation of Nature (IUCN), but seems to be prevalent and is not considered threatened.
Relevance
Economic Importance for humans: NegativeAlthough Pleurobrachia has not been associated with declines in other populations, a closely related species Mnemiopsis leidyi
Mnemiopsis leidyi
The warty comb jelly or sea walnut is a species of tentaculate ctenophore , originally native to the western Atlantic coastal waters. Three species have been named in the genus Mnemiopsis, but they are now believed to be different ecological forms of a single species M...
has. This ctenophore had catastrophic effects on fish catches after its introduction into the Black
Black Sea
The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...
and Azor Seas. It is believed to have been the main cause of decline in these waters after dissection confirmed its stomach contents had large quantities of the local fish eggs and larvae. Because of their diets Pleurobrachia and other ctenophore species can directiy or indirectly effect trophic cascades and ultimately regulate yield of commercially important fish stocks.
Economic Importance for humans: Positive
As predators ctenophores have a tremendous capacity to regulate abundance of their prey and therefore help to balance an ecosystem. While they can decimate other populations they can also restrain an overabundance of copepods which when left to their own devices could virtually eliminate all phytoplankton from the water column. With the proper management, Pluerobrachia introduction would be very beneficial to regulate copepods and to stop them from overpowering the essential primary producers (phytoplankton) needed for a healthy environment.