Bolitaenidae
Encyclopedia
Bolitaenidae is a family of small, common pelagic
octopus
es found in all tropical and temperate oceans of the world. The family's taxonomy
is not entirely certain; recent research suggests there should be just two genera, Bolitaena and Japetella, both of which are thought to be monotypic. Under this view, the family would represent two very similar species: Bolitaena pygmaea and Japetella diaphana.
length and 12 centimetres total length in Japetella species—and their comparatively short arms, much shorter than their dome-shaped mantles. The arms have a single series of suckers; in males, these suckers are greatly enlarged on the third right arm. In Bolitaena (but not Japetella) this arm is also modified into a hectocotylus
, an appendage used to facilitate transfer of spermatophore
s during mating.
The eyes of both species are laterally compressed; they are distinctly smaller and set farther apart from the brain
on longer optic stalk
s in Bolitaena than in Japetella—this feature may be the only way to differentiate the two genera when examining subadults. Mature males are rarely encountered. Their translucent, gelatinous bodies are fragile and easily damaged during collection.
Perhaps the most striking feature of the family is seen in mature females; upon maturity a ring-shaped photophore
—a light-producing organ—develops to encircle the mouth. This is believed to be an adaptation to life in gloomy, deep ocean waters; the bioluminescent
ring may help males and females to find each other.
- to bathypelagic zones of the water column, down to about 1,425 metres. Younger animals (under 20 millimetres mantle length) are known to remain in shallower waters, either from 170-270 metres or 500-800 metres depending on size. Japetella is known to venture into far northern waters.
After mating the female then rises to about 800 metres to brood. Her eggs are interconnected by a number of stalks; the whole mass is held safely by means of suckers near her mouth. Due to the cold (4–5°) environment, brooding likely takes several months; the female is thought to forgo food during this entire period. After hatching, the young octopuses rise to the productive, upper 300 metres of the water column where they remain until reaching a certain size (7–20 millimetres). As they mature the young begin their gradual descent to the mesopelagic
and eventually bathypelagic zones.
Pelagic zone
Any water in a sea or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means "open sea". The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes...
octopus
Octopus
The octopus is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms...
es found in all tropical and temperate oceans of the world. The family's taxonomy
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
is not entirely certain; recent research suggests there should be just two genera, Bolitaena and Japetella, both of which are thought to be monotypic. Under this view, the family would represent two very similar species: Bolitaena pygmaea and Japetella diaphana.
Physical description
Bolitaenids are characterised by their small size—up to 8.5 centimetres or 3.3 inches mantleMantle (mollusc)
The mantle is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.In many, but by no means all, species of molluscs, the epidermis of the mantle secretes...
length and 12 centimetres total length in Japetella species—and their comparatively short arms, much shorter than their dome-shaped mantles. The arms have a single series of suckers; in males, these suckers are greatly enlarged on the third right arm. In Bolitaena (but not Japetella) this arm is also modified into a hectocotylus
Hectocotylus
A hectocotylus is one of the arms of the male of most kinds of cephalopods that is modified in various ways to effect the fertilization of the female's eggs. It is a specialized, extended muscular hydrostat used to store spermatophores, the male gametophore...
, an appendage used to facilitate transfer of spermatophore
Spermatophore
A spermatophore or sperm ampulla is a capsule or mass created by males of various animal species, containing spermatozoa and transferred in entirety to the female's ovipore during copulation...
s during mating.
The eyes of both species are laterally compressed; they are distinctly smaller and set farther apart from the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
on longer optic stalk
Optic stalk
The optic vesicles project toward the sides of the head, and the peripheral part of each expands to form a hollow bulb, while the proximal part remains narrow and constitutes the optic stalk....
s in Bolitaena than in Japetella—this feature may be the only way to differentiate the two genera when examining subadults. Mature males are rarely encountered. Their translucent, gelatinous bodies are fragile and easily damaged during collection.
Perhaps the most striking feature of the family is seen in mature females; upon maturity a ring-shaped photophore
Photophore
A photophore is a light-emitting organ which appears as luminous spots on various marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors...
—a light-producing organ—develops to encircle the mouth. This is believed to be an adaptation to life in gloomy, deep ocean waters; the bioluminescent
Bioluminescence
Bioluminescence is the production and emission of light by a living organism. Its name is a hybrid word, originating from the Greek bios for "living" and the Latin lumen "light". Bioluminescence is a naturally occurring form of chemiluminescence where energy is released by a chemical reaction in...
ring may help males and females to find each other.
Habitat
Mature bolitaenids occupy depths in the mesoMesopelagic
The mesopelagic is that part of the pelagic zone that extends from a depth of 200 to 1000 metres below the ocean surface. It lies between the photic epipelagic above and the aphotic bathypelagic below, where there is no light at all...
- to bathypelagic zones of the water column, down to about 1,425 metres. Younger animals (under 20 millimetres mantle length) are known to remain in shallower waters, either from 170-270 metres or 500-800 metres depending on size. Japetella is known to venture into far northern waters.
Reproduction
Mating is thought to occur at or below 1,000 metres depth. In the darkness, whether mating is successful or not may depend on the female; she can choose whether to signal the male with her circumoral photophore. The light emitted by the photophore is believed to be of a specific wavelength, possibly both preventing miscommunication and the attraction of predators.After mating the female then rises to about 800 metres to brood. Her eggs are interconnected by a number of stalks; the whole mass is held safely by means of suckers near her mouth. Due to the cold (4–5°) environment, brooding likely takes several months; the female is thought to forgo food during this entire period. After hatching, the young octopuses rise to the productive, upper 300 metres of the water column where they remain until reaching a certain size (7–20 millimetres). As they mature the young begin their gradual descent to the mesopelagic
Mesopelagic
The mesopelagic is that part of the pelagic zone that extends from a depth of 200 to 1000 metres below the ocean surface. It lies between the photic epipelagic above and the aphotic bathypelagic below, where there is no light at all...
and eventually bathypelagic zones.
Species
- Genus Bolitaena
- Bolitaena pygmaea
- Genus Japetella
- Japetella diaphana