Atoll butterflyfish
Encyclopedia
The Atoll Butterflyfish, Chaetodon mertensii, is a species
of butterflyfish
(family
Chaetodontidae). It is found in the Pacific Ocean
from the Ryukyu Islands
to the Philippines
and extending to Lord Howe Island
, Rapa Iti
and the Tuamotus
.
It grows to a maximum of 12.5 cm (5 in) long. Body color is white with 5-7 chevron-shaped dark grey bands on the sides. The posterior portion of the trunk, the adjacent dorsal
and anal fins, and the posterior portion of the caudal fin are orange or yellow. A vertical black bar runs across the eye and over the nape without a break; in the similar species there is a separate nape spot and eyestripe.
The Atoll Butterflyfish is found in deep lagoon
s and seaward reef
s at 10-120 m depth. It feeds on algae and small benthic invertebrate
s.
(C. paucifasciatus) and Seychelles Butterflyfish
es (C. madagaskariensis), and the more distant Pearlscale Butterflyfish
(C. xanthurus).
The "crowned" Chaetodon are a clearly recognizable clade
, but their further relationships are otherwise less clear. They were often placed in the subgenus
Exornator, or considered a distinct subgenus Rhombochaetodon with the Atoll Butterflyfish as type species
. According to various DNA sequence
studies, some older and more singular lineages. These include species such as the Asian Butterflyfish (C. argentatus), the Blue-striped Butterflyfish (C. fremblii) and Burgess' Butterflyfish (C. burgessi). C. burgessi is in fact so peculiar that it was placed in a monotypic
subgenus Roaops. But recognition of this would probably result in several other small or monotypic subgenera becoming justified, and the older Rhombochaetodon would be the more conveniently apply to the entire radiation.
But the expanded group is of unclear relationships to species like the Speckled Butterflyfish
(C. citrinellus) and the Four-spotted Butterflyfish (C. quadrimaculatus). These might be members of the subgenus Exornator – the lineages around the Spot-banded Butterflyfish (C. punctatofasciatus) – and C. citrinellus certainly looks somewhat similar to these. Yet phylogenetically, their position towards Rhombochaetodon is unresolved, and ultimately it might be better to merge both Rhombochaetodon and Roaops in Exornator. If the genus Chaetodon
is split up, Exornator might become a subgenus of Lepidochaetodon or a separate genus.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of butterflyfish
Butterflyfish
The butterflyfish are a group of conspicuous tropical marine fish of the family Chaetodontidae; the bannerfish and coralfish are also included in this group. Found mostly on the reefs of the Atlantic, Indian and Pacific Oceans, there are approximately 120 species in 10 genera...
(family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Chaetodontidae). It is found in the 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...
from the Ryukyu Islands
Ryukyu Islands
The , also known as the , is a chain of islands in the western Pacific, on the eastern limit of the East China Sea and to the southwest of the island of Kyushu in Japan. From about 1829 until the mid 20th century, they were alternately called Luchu, Loochoo, or Lewchew, akin to the Mandarin...
to the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
and extending to Lord Howe Island
Lord Howe Island
Lord Howe Island is an irregularly crescent-shaped volcanic remnant in the Tasman Sea between Australia and New Zealand, directly east of mainland Port Macquarie, and about from Norfolk Island. The island is about 11 km long and between 2.8 km and 0.6 km wide with an area of...
, Rapa Iti
Rapa Iti
Rapa or Rapa Iti as it is sometimes called in more recent years , is the largest and only inhabited island of the Bass Islands in French Polynesia. An older name for the island is Oparo Its area is 40 km2 with a population of almost 500 and a max elevation of 650 m...
and the Tuamotus
Tuamotus
The Tuamotus or the Tuamotu Archipelago are a chain of islands and atolls in French Polynesia. They form the largest chain of atolls in the world, spanning an area of the Pacific Ocean roughly the size of Western Europe...
.
It grows to a maximum of 12.5 cm (5 in) long. Body color is white with 5-7 chevron-shaped dark grey bands on the sides. The posterior portion of the trunk, the adjacent dorsal
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
and anal fins, and the posterior portion of the caudal fin are orange or yellow. A vertical black bar runs across the eye and over the nape without a break; in the similar species there is a separate nape spot and eyestripe.
The Atoll Butterflyfish is found in deep lagoon
Lagoon
A lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier. The EU's habitat directive defines lagoons as "expanses of shallow coastal salt water, of varying salinity or water volume, wholly or partially separated from the sea by sand banks or shingle,...
s and seaward reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
s at 10-120 m depth. It feeds on algae and small benthic invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s.
Systematics
C. mertensii is one of the "crowned" butterflyfishes. These form a group of largely allopatric species sharing the overall color pattern of dark forward-pointing chevrons on silvery hues, a (usually) black-and-white crown spot and yellow to red hindparts to a stunning degree; they differ in the exact combination of hues and some small pattern details. Other members of this lineage are the closely related EritreanEritrean butterflyfish
The Eritrean Butterflyfish or Crown Butterflyfish, Chaetodon paucifasciatus, is a species of butterflyfish . It is essentially just known from the Red Sea and the Gulf of Aden, but has been reported from East Africa....
(C. paucifasciatus) and Seychelles Butterflyfish
Seychelles butterflyfish
The Seychelles Butterflyfish, Chaetodon madagaskariensis, is a species of butterflyfish . It is found in the Indian Ocean from eastern Africa east to Cocos-Keeling Islands and Christmas Island, north to Sri Lanka...
es (C. madagaskariensis), and the more distant Pearlscale Butterflyfish
Pearlscale butterflyfish
The Pearlscale Butterflyfish is a species of butterflyfish also known as Yellow-tailed Butterflyfish or Philippines Chevron Butterflyfish...
(C. xanthurus).
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
, but their further relationships are otherwise less clear. They were often placed in the subgenus
Subgenus
In biology, a subgenus is a taxonomic rank directly below genus.In zoology, a subgeneric name can be used independently or included in a species name, in parentheses, placed between the generic name and the specific epithet: e.g. the Tiger Cowry of the Indo-Pacific, Cypraea tigris Linnaeus, which...
Exornator, or considered a distinct subgenus Rhombochaetodon with the Atoll Butterflyfish as type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
. According to various DNA sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
studies, some older and more singular lineages. These include species such as the Asian Butterflyfish (C. argentatus), the Blue-striped Butterflyfish (C. fremblii) and Burgess' Butterflyfish (C. burgessi). C. burgessi is in fact so peculiar that it was placed in a monotypic
Monotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
subgenus Roaops. But recognition of this would probably result in several other small or monotypic subgenera becoming justified, and the older Rhombochaetodon would be the more conveniently apply to the entire radiation.
But the expanded group is of unclear relationships to species like the Speckled Butterflyfish
Speckled butterflyfish
Chaetodon citrinellus is a species of butterflyfish . It is commonly known as the Speckled Butterflyfish or Citron Butterflyfish...
(C. citrinellus) and the Four-spotted Butterflyfish (C. quadrimaculatus). These might be members of the subgenus Exornator – the lineages around the Spot-banded Butterflyfish (C. punctatofasciatus) – and C. citrinellus certainly looks somewhat similar to these. Yet phylogenetically, their position towards Rhombochaetodon is unresolved, and ultimately it might be better to merge both Rhombochaetodon and Roaops in Exornator. If the genus Chaetodon
Chaetodon
Chaetodon is a tropical fish genus in the family Chaetodontidae. Like their relatives, they are known as "butterflyfish". This genus is by far the largest among the Chaetodontidae, with about 90 living species included here, though most might warrant recognition as distinct genera.Several subgenera...
is split up, Exornator might become a subgenus of Lepidochaetodon or a separate genus.