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Midgardia xandaros Downey, 1972. ICML-UNAM 2.196.2. Ossicles and spines from gonadal region. A. Costae rows. B. Gonads. C. Costae (abactinal view). D. Costae spinelet. E. Intercostal (abactinal view). F. Inferomarginal spines. G. Arm bare (abactinal view). H. Inferomarginal (abactinal view). I. Inferomarginal (actinal view). J. Inferomarginal tubercle-shaped (abactinal view). K. Inferomarginal spine. L. Ambulacral (abactinal view). M.: Ambulacral (actinal view). N. Ambulacral wings (actinal view). O. Arm (actinal view). P. Arm bare (actinal view). Q. Adambulacral (actinal view). R. Adambulacral (abactinal view). S. Adambulacral spine. T. Subambulacral spine. In aqua (dashed): actam; blue: padam; green: imabt; green (dashed): lim; green (solid): ambulacral; orange: pada; pink: imim; pink (dashed): interadam; purple: abtam; red: dadam; white: dada; yellow: amim; yellow (dashed): lia; yellow (solid): inferomarginal.
Source publication
Introduction:
The deep-sea asteroid species of Brisingida have a nearly global distribution but have remained poorly understood due to their deep bathymetric distributions and fragile skeletons.
Objective:
To describe the external and internal morphology of Midgardia xandaros including the skeletal arrangement, through multifocal and SEM technique...
Contexts in source publication
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... 11 to 13 are long, thin, and fragile, except in the robust gonadal region. Two paired gonads with up to five saccules. This region has numerous irregular, narrow, well-marked costae; some rows may be incomplete ( Fig. 2A, Fig. 2B). Each costae row is made up of irregular, elongated, abactinal plates imbricated by two costcost articulations. Each abactinal plate has a low boss and an acute spinelet with a thick base that is shorter than the spinelets on the disk (Fig. 2C, Fig. 2D). The robust, tumid costae plates are joined to inferomarginal plates by imabt. ...
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... This region has numerous irregular, narrow, well-marked costae; some rows may be incomplete ( Fig. 2A, Fig. 2B). Each costae row is made up of irregular, elongated, abactinal plates imbricated by two costcost articulations. Each abactinal plate has a low boss and an acute spinelet with a thick base that is shorter than the spinelets on the disk (Fig. 2C, Fig. 2D). The robust, tumid costae plates are joined to inferomarginal plates by imabt. Between costae rows, there are small, asymmetrical, flat, fragile intercostal plates, and tiny, round granules embedded in the abactinal membrane (Fig. ...
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... has a low boss and an acute spinelet with a thick base that is shorter than the spinelets on the disk (Fig. 2C, Fig. 2D). The robust, tumid costae plates are joined to inferomarginal plates by imabt. Between costae rows, there are small, asymmetrical, flat, fragile intercostal plates, and tiny, round granules embedded in the abactinal membrane (Fig. ...
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... plates constitute the margin along the arms; proximally, they are wider than long and have a large, downwards boss with an oval spine pit; beyond the gonadal region, they are shorter like a tubercle. They are joined with the following inferomarginal plate through imim, and the ambulacral plates by amim (Fig. 2F, Fig. 2G, Fig. 2H, Fig. 2I, Fig. 2J). One inferomarginal spine very long, prominent, acute, hyaline, laterally adpressed and fragile, so frequently it is broken (Fig. 2K). Beyond the gonadal region, instead of costae rows, there are transversal bands of diminutive pedicellariae, and the abactinal membrane is thinner, making the adambulacral and ambulacral plates more ...
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... spine pit; beyond the gonadal region, they are shorter like a tubercle. They are joined with the following inferomarginal plate through imim, and the ambulacral plates by amim (Fig. 2F, Fig. 2G, Fig. 2H, Fig. 2I, Fig. 2J). One inferomarginal spine very long, prominent, acute, hyaline, laterally adpressed and fragile, so frequently it is broken (Fig. 2K). Beyond the gonadal region, instead of costae rows, there are transversal bands of diminutive pedicellariae, and the abactinal membrane is thinner, making the adambulacral and ambulacral plates more ...
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... plates are longer than wide, have a round top, with a shaft slightly waisted whose stereom is labyrinthic. The base has a semitriangular amim articulation and two very short, curved wings (Fig. 2L). Actinally, the plates possess two areas of short teeth and moderately broad abtam surface at the head, a shallow furrow and small, oval-shaped actam area. The wings are in contact with adambulacral plates through dadam and padam. Laterally, two ambulacrals of the same column are joined by lim and its lia articulation (Fig. 2M, Fig. ...
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... curved wings (Fig. 2L). Actinally, the plates possess two areas of short teeth and moderately broad abtam surface at the head, a shallow furrow and small, oval-shaped actam area. The wings are in contact with adambulacral plates through dadam and padam. Laterally, two ambulacrals of the same column are joined by lim and its lia articulation (Fig. 2M, Fig. 2N). Superambulacral plates absent. Ambulacral feet biseriate, long, robust, with a small sucker (Fig. ...
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... surface at the head, a shallow furrow and small, oval-shaped actam area. The wings are in contact with adambulacral plates through dadam and padam. Laterally, two ambulacrals of the same column are joined by lim and its lia articulation (Fig. 2M, Fig. 2N). Superambulacral plates absent. Ambulacral feet biseriate, long, robust, with a small sucker (Fig. ...
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... plates small, high, slightly longer than wide (Fig. 2P). Abactinally, they have a curved top, a conspicuous, diagonal crest which separates padam and dadam muscles, as well as dada and pada articulations, allowing them the attachment with ambulacral plates. The adradial extension is quite short and angular. In actinal view, two adjacent adambulacral plates of the same row along the arm are ...
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... extension is quite short and angular. In actinal view, two adjacent adambulacral plates of the same row along the arm are joined laterally by interadam. Their ambulacral margin is slightly acute and has three or four small, shallow bosses for small, elongate, thin, tubercle base, acicular adambulacral spines in both proximal and distal edges (Fig. 2Q, Fig. 2R, Fig. 2S). One subambulacral spine long, acicular and more robust than adambulacral ones, with well-defined, straight trabeculae (Fig. 2T). The ambulacral groove is moderately broad. Actinal plates ...
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... short and angular. In actinal view, two adjacent adambulacral plates of the same row along the arm are joined laterally by interadam. Their ambulacral margin is slightly acute and has three or four small, shallow bosses for small, elongate, thin, tubercle base, acicular adambulacral spines in both proximal and distal edges (Fig. 2Q, Fig. 2R, Fig. 2S). One subambulacral spine long, acicular and more robust than adambulacral ones, with well-defined, straight trabeculae (Fig. 2T). The ambulacral groove is moderately broad. Actinal plates ...
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... interadam. Their ambulacral margin is slightly acute and has three or four small, shallow bosses for small, elongate, thin, tubercle base, acicular adambulacral spines in both proximal and distal edges (Fig. 2Q, Fig. 2R, Fig. 2S). One subambulacral spine long, acicular and more robust than adambulacral ones, with well-defined, straight trabeculae (Fig. 2T). The ambulacral groove is moderately broad. Actinal plates ...
Context 13
... 11 to 13 are long, thin, and fragile, except in the robust gonadal region. Two paired gonads with up to five saccules. This region has numerous irregular, narrow, well-marked costae; some rows may be incomplete ( Fig. 2A, Fig. 2B). Each costae row is made up of irregular, elongated, abactinal plates imbricated by two costcost articulations. Each abactinal plate has a low boss and an acute spinelet with a thick base that is shorter than the spinelets on the disk (Fig. 2C, Fig. 2D). The robust, tumid costae plates are joined to inferomarginal plates by imabt. ...
Context 14
... This region has numerous irregular, narrow, well-marked costae; some rows may be incomplete ( Fig. 2A, Fig. 2B). Each costae row is made up of irregular, elongated, abactinal plates imbricated by two costcost articulations. Each abactinal plate has a low boss and an acute spinelet with a thick base that is shorter than the spinelets on the disk (Fig. 2C, Fig. 2D). The robust, tumid costae plates are joined to inferomarginal plates by imabt. Between costae rows, there are small, asymmetrical, flat, fragile intercostal plates, and tiny, round granules embedded in the abactinal membrane (Fig. ...
Context 15
... has a low boss and an acute spinelet with a thick base that is shorter than the spinelets on the disk (Fig. 2C, Fig. 2D). The robust, tumid costae plates are joined to inferomarginal plates by imabt. Between costae rows, there are small, asymmetrical, flat, fragile intercostal plates, and tiny, round granules embedded in the abactinal membrane (Fig. ...
Context 16
... plates constitute the margin along the arms; proximally, they are wider than long and have a large, downwards boss with an oval spine pit; beyond the gonadal region, they are shorter like a tubercle. They are joined with the following inferomarginal plate through imim, and the ambulacral plates by amim (Fig. 2F, Fig. 2G, Fig. 2H, Fig. 2I, Fig. 2J). One inferomarginal spine very long, prominent, acute, hyaline, laterally adpressed and fragile, so frequently it is broken (Fig. 2K). Beyond the gonadal region, instead of costae rows, there are transversal bands of diminutive pedicellariae, and the abactinal membrane is thinner, making the adambulacral and ambulacral plates more ...
Context 17
... spine pit; beyond the gonadal region, they are shorter like a tubercle. They are joined with the following inferomarginal plate through imim, and the ambulacral plates by amim (Fig. 2F, Fig. 2G, Fig. 2H, Fig. 2I, Fig. 2J). One inferomarginal spine very long, prominent, acute, hyaline, laterally adpressed and fragile, so frequently it is broken (Fig. 2K). Beyond the gonadal region, instead of costae rows, there are transversal bands of diminutive pedicellariae, and the abactinal membrane is thinner, making the adambulacral and ambulacral plates more ...
Context 18
... plates are longer than wide, have a round top, with a shaft slightly waisted whose stereom is labyrinthic. The base has a semitriangular amim articulation and two very short, curved wings (Fig. 2L). Actinally, the plates possess two areas of short teeth and moderately broad abtam surface at the head, a shallow furrow and small, oval-shaped actam area. The wings are in contact with adambulacral plates through dadam and padam. Laterally, two ambulacrals of the same column are joined by lim and its lia articulation (Fig. 2M, Fig. ...
Context 19
... curved wings (Fig. 2L). Actinally, the plates possess two areas of short teeth and moderately broad abtam surface at the head, a shallow furrow and small, oval-shaped actam area. The wings are in contact with adambulacral plates through dadam and padam. Laterally, two ambulacrals of the same column are joined by lim and its lia articulation (Fig. 2M, Fig. 2N). Superambulacral plates absent. Ambulacral feet biseriate, long, robust, with a small sucker (Fig. ...
Context 20
... surface at the head, a shallow furrow and small, oval-shaped actam area. The wings are in contact with adambulacral plates through dadam and padam. Laterally, two ambulacrals of the same column are joined by lim and its lia articulation (Fig. 2M, Fig. 2N). Superambulacral plates absent. Ambulacral feet biseriate, long, robust, with a small sucker (Fig. ...
Context 21
... plates small, high, slightly longer than wide (Fig. 2P). Abactinally, they have a curved top, a conspicuous, diagonal crest which separates padam and dadam muscles, as well as dada and pada articulations, allowing them the attachment with ambulacral plates. The adradial extension is quite short and angular. In actinal view, two adjacent adambulacral plates of the same row along the arm are ...
Context 22
... extension is quite short and angular. In actinal view, two adjacent adambulacral plates of the same row along the arm are joined laterally by interadam. Their ambulacral margin is slightly acute and has three or four small, shallow bosses for small, elongate, thin, tubercle base, acicular adambulacral spines in both proximal and distal edges (Fig. 2Q, Fig. 2R, Fig. 2S). One subambulacral spine long, acicular and more robust than adambulacral ones, with well-defined, straight trabeculae (Fig. 2T). The ambulacral groove is moderately broad. Actinal plates ...
Context 23
... short and angular. In actinal view, two adjacent adambulacral plates of the same row along the arm are joined laterally by interadam. Their ambulacral margin is slightly acute and has three or four small, shallow bosses for small, elongate, thin, tubercle base, acicular adambulacral spines in both proximal and distal edges (Fig. 2Q, Fig. 2R, Fig. 2S). One subambulacral spine long, acicular and more robust than adambulacral ones, with well-defined, straight trabeculae (Fig. 2T). The ambulacral groove is moderately broad. Actinal plates ...
Context 24
... interadam. Their ambulacral margin is slightly acute and has three or four small, shallow bosses for small, elongate, thin, tubercle base, acicular adambulacral spines in both proximal and distal edges (Fig. 2Q, Fig. 2R, Fig. 2S). One subambulacral spine long, acicular and more robust than adambulacral ones, with well-defined, straight trabeculae (Fig. 2T). The ambulacral groove is moderately broad. Actinal plates ...
Citations
Freyastera (Downey 1986) is a derived group of deep-sea starfish in the order Brisingida with 6 arms and slender ambulacral plates, whose taxonomy and phylogeny have rarely been investigated. In this research, two new species of Freyastera are reported from the northwest Pacific Ocean, both characterized by fairly long and numerous lateral spines and the presence of furrow spines. Freyastera delicata n. sp. is further distinguished from other species by having 6-8 spinelets arranged in a transverse line on each abactinal arm plate. Freyastera basketa n. sp. is similar to the Atlantic species Freyastera sexradiata (Perrier 1885), but differs from the latter by the presence of pedicellariae on the abactinal surface and number of mouth spines and lateral spines. A revised key to Freyastera and potential Freyastera spp. from the genus Freyella (Perrier 1885) is provided. Phylogenetic analysis was conducted using available molecular data for the order Brisingida. The intraspecific and interspecific divergence within Freyastera are recognized from a COI genetic distance matrix, in which some abnormal intraspecific distances are found between the known species, which might indicate the existence of cryptic species and an underestimated diversity in the genus. A phylogenetic tree of Brisingida is constructed based on a concatenated sequence dataset of COI, 16S and H3 gene fragments. The tree supports the affinity of Freyastera and Freyella, which together form a crown clade within the order. The global distribution and in situ observations of Freyastera are discussed to provide information on their ecological characteristics and diversity.
