''Chaetodon mertensii'', the atoll butterflyfish, yellowback butterflyfish or Merten's butterflyfish, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of marine ray finned fish, a

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. The approximately 129 species in 12 genera are found mostly on the reefs of the Atlant ...

belonging to the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Chaetodontidae. It is found in the western Pacific Ocean.

Description

''Chaetodon mertensi'' grows to a maximum of 12.5 cm (5 in) long. Body color is white with 5-7

chevron Chevron (often relating to V-shaped patterns) may refer to: Science and technology * Chevron (aerospace), sawtooth patterns on some jet engines * Chevron (anatomy), a bone * ''Eulithis testata'', a moth * Chevron (geology), a fold in rock lay ...

-shaped dark grey bands on the sides. The posterior portion of the trunk, the adjacent dorsal and

anal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

s, and the posterior portion of the

caudal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

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.

Habitat and biology

''Chaetodon mertensi'' is found in deep

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') a ...

s and seaward

reef A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic processes— deposition of sand, wave erosion planing down rock out ...

s at 10–120 m depth. It feeds on algae and small benthic

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

Distribution

''Chaetodon mertensii'' is found in the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

from the

Ryukyu Islands The , also known as the or the , are a chain of Japanese islands that stretch southwest from Kyushu to Taiwan: the Ōsumi, Tokara, Amami, Okinawa, and Sakishima Islands (further divided into the Miyako and Yaeyama Islands), with Yonaguni ...

to the

Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...

and extending to

Lord Howe Island Lord Howe Island (; formerly Lord Howe's Island) is an irregularly crescent-shaped volcanic remnant in the Tasman Sea between Australia and New Zealand, part of the Australian state of New South Wales. It lies directly east of mainland P ...

, Rapa Iti and the Tuamotus. It was first recorded from the

Kermadec Islands Marine Reserve Kermadec or de Kermadec may refer to: Geography * Kermadec Islands, a subtropical island arc in the South Pacific Ocean northeast of New Zealand * Kermadec Plate, a long narrow tectonic plate located west of the Kermadec Trench * Kermadec Trench, ...

north of

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

in 2015, after researchers examined hundreds of hours of unused documentary film footage.

Systematics

''Chaetodon mertensii'' was first formally described in 1831 by the

French French (french: français(e), link=no) may refer to: * Something of, from, or related to France ** French language, which originated in France, and its various dialects and accents ** French people, a nation and ethnic group identified with Franc ...

anatomist George’s Cuvier (1769-1832). The specific name honours the

German German(s) may refer to: * Germany (of or related to) **Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ger ...

naturalist and explorer Karl Heinrich Mertens (1796-1830) who showed Cuvier an illustration of this fish. ''Chaetodon mertensii'' is one of the "crowned" butterflyfishes. These form a group of largely

allopatric Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...

species sharing the overall color pattern of dark forward-pointing

s 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 Eritrean (''C. paucifasciatus'') and

Seychelles butterflyfish The Seychelles butterflyfish (''Chaetodon madagaskariensis'') is a species of marine ray-finned fish, a butterflyfish belonging to the family Chaetodontidae. It is found in the Indian Ocean from eastern Africa (as far south as Port Elizabeth in ...

es (''C. madagaskariensis''), and the more distant

pearlscale butterflyfish The pearlscale butterflyfish (''Chaetodon xanthurus''), also known as yellow-tailed butterflyfish, crosshatch butterflyfish or Philippines chevron butterflyfish is a species of marine ray-finned fish, a butterflyfish belonging to the family Chae ...

(''C. xanthurus''). The "crowned" ''Chaetodon'' are a clearly recognizable

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

, but their further relationships are otherwise less clear. They were often placed in the

subgenus In biology, a subgenus (plural: subgenera) is a taxonomic rank directly below genus. In the International Code of Zoological Nomenclature, a subgeneric name can be used independently or included in a species name, in parentheses, placed between t ...

''Exornator'', or considered a distinct subgenus ''Rhombochaetodon'' with the atoll butterflyfish as

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

. According to various

DNA sequence DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, guanine, cytosine, and thymine. Th ...

studies, some older and more singular lineages. These include species such as the

Asian butterflyfish ''Chaetodon argentatus'', the Asian butterflyfish, three band butterflyfish or black pearlscaled butterflyfish, is a species of marine ray-finned fish a butterflyfish belonging to the family Chaetodontidae. It is native to the western Pacific O ...

('' C. argentatus''), the

blue-striped butterflyfish The bluestripe butterflyfish or blue-striped butterflyfish (''Chaetodon fremblii'') is a species of butterflyfish (family Chaetodontidae) found in the waters surrounding the Hawaiian Islands. The fish is endemic to Hawaii where it is common on sha ...

('' C. fremblii'') and Burgess' butterflyfish ('' C. burgessi''). ''C. burgessi'' is in fact so peculiar that it was placed in a

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

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 In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...

. But the expanded group is of unclear relationships to species like the

speckled butterflyfish ''Chaetodon citrinellus'' is a species of butterflyfish (family Chaetodontidae). It is commonly known as the speckled butterflyfish or citron butterflyfish. It is found in the Indo-Pacific: the Red Sea, East Africa to the Hawaiian, Marquesan and ...

(''C. citrinellus'') and the four-spotted butterflyfish (''C. quadrimaculatus''). These might be members of the subgenus ''Exornator'' – the lineages around the

spot-banded butterflyfish The spot-banded butterflyfish or spotband butterflyfish (''Chaetodon punctatofasciatus'') is a species of marine ray-finned fish, a butterflyfish belonging to the family Chaetodontidae. It is from the western Pacific Ocean. It is found in the I ...

(''C. punctatofasciatus'') – and ''C. citrinellus'' certainly looks somewhat similar to these. Yet

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

ally, 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'' 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 migh ...

'' is split up, ''Exornator'' might become a subgenus of ''Lepidochaetodon'' or a separate genus.

References

External links

* {{Taxonbar, from=Q1054729 mertensiii Fish described in 1831 Taxa named by Georges Cuvier