Bertella idiomorpha is a species of deep-sea anglerfish

Anglerfish

Anglerfishes are members of the teleost order Lophiiformes . They are bony fishes named for their characteristic mode of predation, wherein a fleshy growth from the fish's head acts as a lure; this is considered analogous to angling.Some anglerfishes are pelagic , while others are benthic...

 found in the northern Pacific Ocean

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

. It is the only species in the genus Bertella, in the family Oneirodidae

Oneirodidae

The dreamers are a family, Oneirodidae, of deep-sea anglerfishes in the order Lophiiformes. They are the largest and most diverse group of deep-sea anglerfish, and also the least well-known with several genera represented by only one, two, or three female specimens. They are found in deep,...

, and can be distinguished from other members of the family by the structure of its hyomandibular bone.

Distribution and habitat

Specimens of B. idiomorpha have only been collected in the northern Pacific Ocean

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

, including off Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

, in the Bering Sea

Bering Sea

The Bering Sea is a marginal sea of the Pacific Ocean. It comprises a deep water basin, which then rises through a narrow slope into the shallower water above the continental shelves....

, and in the Gulf of California

Gulf of California

The Gulf of California is a body of water that separates the Baja California Peninsula from the Mexican mainland...

. The depths ranged from 580 m to 3475 m.

Description

Like other oneirodids, B. idiomorpha is a small, globular-bodied fish with a large head and jaws, and a bioluminescent lure (esca) on a stalk (illicium) attached to the head. The skin is scaleless and covers the base of the caudal fin. There are numerous small, rounded, darkly pigmented papillae on the head, body, and tail, associated with the lateral line

Lateral line

The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...

 system. The fish is dark brown to black in color, except for the clear tips of the papillae and the end of the esca. The jaws are filled with slender, straight teeth. The females measure up to 8.4 cm in length. Only one male is known, a 11-mm specimen attached to a 77-mm female. B. idiomorpha is unique amongst the oneirodids in having a hyomandibular bone (the bone that attaches the lower jaw to the cranium) with a single head. In its family, B. idiomorpha most resembles the genus Dolopichthys, differing in having a wider and deeper skull, shorter and fewer jaw teeth, and in details of the mandibular spines and the esca.

Biology and ecology

In contrast to the closely related Dolopichthys, which feeds on fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

 and squid

Squid

Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...

, B. idiomorpha feeds on amphipods, krill

Krill

Krill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...

, and small decapod

Decapoda

The decapods or Decapoda are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns and shrimp. Most decapods are scavengers. It is estimated that the order contains nearly 15,000 species in around 2,700 genera, with...

s. This difference in prey items is reflected in the body shape of B. idiomorpha, which is shorter and deeper, suggesting that it is a more sluggish swimmer than Dolopichthys. B. idiomorpha also has smaller and fewer teeth, and its single-headed hyomandibular bone reduces the strength of its bite, again consistent with preying on smaller, slower prey items.

B. idiomorpha and Leptacanthichthys gracilispinis are the only oneirodids known to have parasitic males. Both the tips of the upper and lower jaws of the male B. idiomorpha become fused to the female. Small openings to the mouth and opercular cavities of the male are maintained on both sides. Mature female B. idiomorpha contain around 7500 eggs per ovary

Ovary

The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...

, and have some of the largest eggs amongst the deep-sea anglerfish.