''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 Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or hor ...

, 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 Atla ...

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 ...

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

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal co ...

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

alga Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mi ...

e 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 Rapa, also called Rapa Iti, or "Little Rapa", to distinguish it from Easter Island, whose Polynesian name is Rapa Nui, is the largest and only inhabited island of the Bass Islands in French Polynesia. An older name for the island is Oparo. The ...

and the

Tuamotus The Tuamotu Archipelago or the Tuamotu Islands (french: Îles Tuamotu, officially ) are a French Polynesian chain of just under 80 islands and atolls in the southern Pacific Ocean. They constitute the largest chain of atolls in the world, extendin ...

. 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

anatomist Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having its ...

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 Exploration refers to the historical practice of discovering remote lands. It is studied by geographers and historians. Two major eras of exploration occurred in human history: one of convergence, and one of divergence. The first, covering most ...

Karl Heinrich Mertens Karl Heinrich Mertens (Russian: Андрей Карлович Мертенс, 17 May 1796 – 18 September 1830 Kronstadt), was a German botanist and naturalist, and son of the botanist Franz Carl Mertens. Mertens was aboard the Russian vessel ' ...

(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 butterflyfishes (''C. madagaskariensis''), and the more distant pearlscale butterflyfish (''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 ('' 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 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 (''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

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