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When Ontogeny Matters: A New Japanese Species of Brittle Star Illustrates the Importance of Considering both Adult and Juvenile Characters in Taxonomic Practice.

Martynov A, Ishida Y, Irimura S, Tajiri R, O'Hara T, Fujita T - PLoS ONE (2015)

Bottom Line: Here we show how the underestimation of ontogenetic changes may result in long term lack of recognition of a new species of one of the most common ophiacanthid brittle stars (Echinodermata: Ophiuroidea) from the North Pacific.Clark, 1911.For all three species in this complex, a clear bathymetric differentiation is revealed: O. rhachophora predominantly inhabits shallow waters, 0-250 m, the new species O. kokusai lives deeper, at 250-600 m, and the third species, O. trachybactra, is found at 500-2,000 m.

View Article: PubMed Central - PubMed

Affiliation: Zoological Museum, Moscow State University, Moscow, Russia.

ABSTRACT
Current taxonomy offers numerous approaches and methods for species delimitation and description. However, most of them are based on the adult characters and rarely suggest a dynamic representation of developmental transformations of taxonomically important features. Here we show how the underestimation of ontogenetic changes may result in long term lack of recognition of a new species of one of the most common ophiacanthid brittle stars (Echinodermata: Ophiuroidea) from the North Pacific. Based on vast material collected predominantly by various Japanese expeditions in the course of more than 50 years, and thorough study of appropriate type material, we revise the complex of three common species of the ophiuroid genus Ophiacantha which have been persistently confused with each other. The present study thus reveals the previously unrecognized new species Ophiacantha kokusai sp.nov. which is commonly distributed off the Pacific coast of Japan. The new species shows developmental differentiation from the closely related species Ophiacantha rhachophora H. L. Clark, 1911 and retains clearly expressed early juvenile features in the adult morphology. Another species, Ophiacantha clypeata Kyte, 1977, which had been separated from O. rhachophora, is in turn shown to be just a juvenile stage of another North Pacific species, Ophiacantha trachybactra H.L. Clark, 1911. For every species, detailed morphological data from both adult and juvenile specimens based on scanning electron microscopy are presented. A special grinding method showing complex internal features has been utilized for the first time. For all three species in this complex, a clear bathymetric differentiation is revealed: O. rhachophora predominantly inhabits shallow waters, 0-250 m, the new species O. kokusai lives deeper, at 250-600 m, and the third species, O. trachybactra, is found at 500-2,000 m. The present case clearly highlights the importance of considering developmental transformations, not only for a limited number of model organisms, but as part of the taxonomic process.

No MeSH data available.


Related in: MedlinePlus

Ophiacantha trachybactra H.L. Clark, 1911, subadult specimen 6.8 mm disk diameter NSMT E–7557, sta. KT-93-15 (M 3), off Sanriku, northern Honshū, external views.A, dorsal view; B, ventral view; C, proximal arm segments, dorsal view; D, proximal arm segments, ventral view; E, proximal arm segments, ventral view, SEM; F, proximal arm segments, ventral view, details, SEM. as, adoral shields; gs, genital slit; j, jaws; op, oral papillae; os, oral shield; red asterisks indicate the absence of the adoral shield papillae. Scales bars, 0.5 mm (F), 1 mm (A–E).
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pone.0139463.g018: Ophiacantha trachybactra H.L. Clark, 1911, subadult specimen 6.8 mm disk diameter NSMT E–7557, sta. KT-93-15 (M 3), off Sanriku, northern Honshū, external views.A, dorsal view; B, ventral view; C, proximal arm segments, dorsal view; D, proximal arm segments, ventral view; E, proximal arm segments, ventral view, SEM; F, proximal arm segments, ventral view, details, SEM. as, adoral shields; gs, genital slit; j, jaws; op, oral papillae; os, oral shield; red asterisks indicate the absence of the adoral shield papillae. Scales bars, 0.5 mm (F), 1 mm (A–E).

Mentions: Internal and microstructural adult characters (Figs 13, 15, 17, 18 and 19): Each disk spine has a short pedicel that bears a reduced rosette of short simple thorns (up to 4) (Fig 2E). The radial shield is an elongated plate, with a slightly elevated articulation surface. The articulation surface of the genital plate has a slightly elevated condyle. The abradial genital plate is well defined. Jaws are relatively high and slightly elongated. Adradial sides of the jaws bear folds distally. The dental plate has a series of elongated sockets. The adoral shield papilla is absent (Fig 2F). Arm segments of the two paratypes of O. trachybactra(Fig 14E and 14F), and the holotype of O. clypeata(Fig 12E and 12F) and several sub-adult (6.8 mm dd) (Fig 18E and 18F) and adult (10.9 mm dd) non-type specimens (NSMT E–7557) (Fig 16E and 16F) were studied using SEM. Arm spine articulations are of the ophiacanthid type [31, 57, 58] with a distinct sigmoidal fold (Figs 13A, 13E, 15A, 15E, 17A, 17E, 17O–17Q, 19A, 19E and 19N–19P). Vertebrae are rather long, completely strepspondylous, without any traces of zygospondylous articulation even on the most proximal segments (Figs 13L, 15L, 17M, 19L and 19R). The dorsal vertebral keel distally is narrowed to form an arrow-shaped structure, which is blunt or more sharpened (Figs 13J, 15J, 17K, 19J and 19Q). Vertebral dorsal median groove and lateral curved grooves [31, 59] are very distinct (Figs 13J and 15J). Podial basins are small. The dorsal arm spines are massive and semi-solid with several small cavities in the middle part of the spine (Figs 13G, 13H, 15G, 15H, 14G, 14H, 17G and 17H), instead of being entirely hollow (typical of the family Ophiacanthidae).


When Ontogeny Matters: A New Japanese Species of Brittle Star Illustrates the Importance of Considering both Adult and Juvenile Characters in Taxonomic Practice.

Martynov A, Ishida Y, Irimura S, Tajiri R, O'Hara T, Fujita T - PLoS ONE (2015)

Ophiacantha trachybactra H.L. Clark, 1911, subadult specimen 6.8 mm disk diameter NSMT E–7557, sta. KT-93-15 (M 3), off Sanriku, northern Honshū, external views.A, dorsal view; B, ventral view; C, proximal arm segments, dorsal view; D, proximal arm segments, ventral view; E, proximal arm segments, ventral view, SEM; F, proximal arm segments, ventral view, details, SEM. as, adoral shields; gs, genital slit; j, jaws; op, oral papillae; os, oral shield; red asterisks indicate the absence of the adoral shield papillae. Scales bars, 0.5 mm (F), 1 mm (A–E).
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4625035&req=5

pone.0139463.g018: Ophiacantha trachybactra H.L. Clark, 1911, subadult specimen 6.8 mm disk diameter NSMT E–7557, sta. KT-93-15 (M 3), off Sanriku, northern Honshū, external views.A, dorsal view; B, ventral view; C, proximal arm segments, dorsal view; D, proximal arm segments, ventral view; E, proximal arm segments, ventral view, SEM; F, proximal arm segments, ventral view, details, SEM. as, adoral shields; gs, genital slit; j, jaws; op, oral papillae; os, oral shield; red asterisks indicate the absence of the adoral shield papillae. Scales bars, 0.5 mm (F), 1 mm (A–E).
Mentions: Internal and microstructural adult characters (Figs 13, 15, 17, 18 and 19): Each disk spine has a short pedicel that bears a reduced rosette of short simple thorns (up to 4) (Fig 2E). The radial shield is an elongated plate, with a slightly elevated articulation surface. The articulation surface of the genital plate has a slightly elevated condyle. The abradial genital plate is well defined. Jaws are relatively high and slightly elongated. Adradial sides of the jaws bear folds distally. The dental plate has a series of elongated sockets. The adoral shield papilla is absent (Fig 2F). Arm segments of the two paratypes of O. trachybactra(Fig 14E and 14F), and the holotype of O. clypeata(Fig 12E and 12F) and several sub-adult (6.8 mm dd) (Fig 18E and 18F) and adult (10.9 mm dd) non-type specimens (NSMT E–7557) (Fig 16E and 16F) were studied using SEM. Arm spine articulations are of the ophiacanthid type [31, 57, 58] with a distinct sigmoidal fold (Figs 13A, 13E, 15A, 15E, 17A, 17E, 17O–17Q, 19A, 19E and 19N–19P). Vertebrae are rather long, completely strepspondylous, without any traces of zygospondylous articulation even on the most proximal segments (Figs 13L, 15L, 17M, 19L and 19R). The dorsal vertebral keel distally is narrowed to form an arrow-shaped structure, which is blunt or more sharpened (Figs 13J, 15J, 17K, 19J and 19Q). Vertebral dorsal median groove and lateral curved grooves [31, 59] are very distinct (Figs 13J and 15J). Podial basins are small. The dorsal arm spines are massive and semi-solid with several small cavities in the middle part of the spine (Figs 13G, 13H, 15G, 15H, 14G, 14H, 17G and 17H), instead of being entirely hollow (typical of the family Ophiacanthidae).

Bottom Line: Here we show how the underestimation of ontogenetic changes may result in long term lack of recognition of a new species of one of the most common ophiacanthid brittle stars (Echinodermata: Ophiuroidea) from the North Pacific.Clark, 1911.For all three species in this complex, a clear bathymetric differentiation is revealed: O. rhachophora predominantly inhabits shallow waters, 0-250 m, the new species O. kokusai lives deeper, at 250-600 m, and the third species, O. trachybactra, is found at 500-2,000 m.

View Article: PubMed Central - PubMed

Affiliation: Zoological Museum, Moscow State University, Moscow, Russia.

ABSTRACT
Current taxonomy offers numerous approaches and methods for species delimitation and description. However, most of them are based on the adult characters and rarely suggest a dynamic representation of developmental transformations of taxonomically important features. Here we show how the underestimation of ontogenetic changes may result in long term lack of recognition of a new species of one of the most common ophiacanthid brittle stars (Echinodermata: Ophiuroidea) from the North Pacific. Based on vast material collected predominantly by various Japanese expeditions in the course of more than 50 years, and thorough study of appropriate type material, we revise the complex of three common species of the ophiuroid genus Ophiacantha which have been persistently confused with each other. The present study thus reveals the previously unrecognized new species Ophiacantha kokusai sp.nov. which is commonly distributed off the Pacific coast of Japan. The new species shows developmental differentiation from the closely related species Ophiacantha rhachophora H. L. Clark, 1911 and retains clearly expressed early juvenile features in the adult morphology. Another species, Ophiacantha clypeata Kyte, 1977, which had been separated from O. rhachophora, is in turn shown to be just a juvenile stage of another North Pacific species, Ophiacantha trachybactra H.L. Clark, 1911. For every species, detailed morphological data from both adult and juvenile specimens based on scanning electron microscopy are presented. A special grinding method showing complex internal features has been utilized for the first time. For all three species in this complex, a clear bathymetric differentiation is revealed: O. rhachophora predominantly inhabits shallow waters, 0-250 m, the new species O. kokusai lives deeper, at 250-600 m, and the third species, O. trachybactra, is found at 500-2,000 m. The present case clearly highlights the importance of considering developmental transformations, not only for a limited number of model organisms, but as part of the taxonomic process.

No MeSH data available.


Related in: MedlinePlus