Bolitaenidae

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Bolitaenids
Eledonella pygmaea.jpg
Female Bolitaena pygmaea
from the Gulf of Guinea
Japetella diaphana2.jpg
Female Japetella diaphana
from northeastern São Tomé Island
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Order: Octopoda
Suborder: Incirrina
Family: Bolitaenidae
Chun, 1911
Genera

Bolitaena
Japetella

Bolitaenidae is a family of small, common pelagic octopuses 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.

Physical description[edit]

Bolitaenids are characterised by their small size—up to 8.5 centimetres or 3.3 inches mantle 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 spermatophores during mating.

Left: Arms and buccal mass of Japetella diaphana
Right: Dissected male Japetella diaphana

The eyes of both species are laterally compressed; they are distinctly smaller and set farther apart from the brain on longer optic stalks 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.

Habitat[edit]

Mature bolitaenids occupy depths in the meso- 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[edit]

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.

Immature bolitaenids at various stages of development: (left) immature specimens of J. diaphana from Sumatra (top left), southwestern Sri Lanka (top right), and southern Sierra Leone (bottom); (centre left) immature J. diaphana from the Gulf of Guinea; (centre right and right) juvenile female B. pygmaea.

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.

Species[edit]

Male B. pygmaea, probably taken during the Michael-Sars Expedition

External links[edit]