Abstract
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 techniques. Methods. We examined a total of 21 specimens, including 27 arm fragments, from the Gulf of Mexico and Honduras. Two specimens were dissected. Results. Detailed descriptions of pedicellariae, abactinal, intercostal, inferomarginal, adambulacral, ambulacral, odontophore, and oral ossicles, and their spines are provided, emphasizing the articulations and muscle attachments. C-shaped valves pedicellariae and small pedicellariae valves with shorter denticulation areas were recognized. Conclusions. The morphological description of M. xandaros is expanded, providing the most extensive description of abactinal, first adambulacral, first and subsequent inferomarginal ossicles, abactinal spines, and C-shaped, crossed pedicellariae, as well as the distal arm plates, for a brisingid species using SEM to date.
Highlights
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
The water circulation is mainly given by the Loop Current that originates at the Yucatan Channel, which connects the Gulf of Mexico with the Caribbean Sea and is a semi-enclosed basin located between 9° N and 22° N latitude and 60° W and 89° W longitude
Midgardia xandaros is considered the starfish with the longest arms, being described from a specimen with R = 680 mm by Downey (1972)
Summary
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. To describe the external and internal morphology of Midgardia xandaros including the skeletal arrangement, through multifocal and SEM techniques. We examined a total of 21 specimens, including 27 arm fragments, from the Gulf of Mexico and Honduras. Abactinal, intercostal, inferomarginal, adambulacral, ambulacral, odontophore, and oral ossicles, and their spines are provided, emphasizing the articulations and muscle attachments. C-shaped valves pedicellariae and small pedicellariae valves with shorter denticulation areas were recognized. The morphological description of M. xandaros is expanded, providing the most extensive description of abactinal, first adambulacral, first and subsequent inferomarginal ossicles, abactinal spines, and C-shaped, crossed pedicellariae, as well as the distal arm plates, for a brisingid species using SEM to date
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