Description of arm’s section of starfish genus Astropecten.
1- papulas: they are soft and retractable appendages with respiratory functions
2- paxilla
3- superomarginal spines
4- superomarginal plates
5- scales and small spines covering the vertical face of superomarginal plates
6- ambulacral plates
7- adambulacral plates
8- inferomarginal plates
9- inferomarginal spines
10- pedicellaria: special pedicels with prehensile termination necessary to grab bodies and detritus
11- external adambulacral spines
12- median adambulacral spines
13- internal adambulacral spines
14- ambulacral pedicellariaOssicles of an Astropecten irregularisOssicles of an Astropecten jonstoniFlat ossicles of an Astropecten platyacanthus
These sea stars are similar one to each other and it can be difficult to determine with certainty the species only from a photograph. To have a certain determination, in some cases, animals should be analyzed in the laboratory or using genetic testing, but often it isn’t possible. In order to determine the species, with a reasonable margin of error, it’s necessary to observe the appearance of the animal, in particular, based on some typical features described by principal authors that have analyzed over the years a large number of specimens in the laboratory.
The main elements, to determine the various species from photo, are: the appearance of the dorsal marginal plates and spines, the size, the shape of disc and arms. For a good identification by sea photo it is important to take a complete picture of all the subject, a picture of the detail of the marginal plates and to measure as precisely as possible the diameter of the sea star. All this can be done without touching, turning it, or disturbing the animal.
Starfishes have two sides: an upper side called “aboral side” (which is normally visible), and a bottom side called “oral side” (which rests on the seabed).[citation needed]
General look of an Astropecten
Cross-section of an arm. 1=papula and paxilla, 2=superomarginal plate, 3=inferomarginal plate, 4=ambulacral plates, 5=adambulacral plate
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