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Description of the main features in order to determine the species of Mediterranean Astropecten starfish.
Description of the main features in order to determine the species of Mediterranean Astropecten starfish.
ASTROPECTEN OF THE MEDITERRANEAN SEA Starfishes of genus Astropecten live on mobile seabed (sandy, muddy or gravel seabed) and they remain largely buried under sediment during the day. During the late afternoon and the night starfishes go out to hunt mainly bivalve molluscs, which are their favourite preys. In turn they are preyed by large molluscs such Charonia lampas, Charonia variegata and probably Tonna galea. In the Mediterranean area there are six species belonging to the genus Astropecten: - Astropecten aranciacus (Linnaeus, 1758) - Astropecten jonstoni (Delle Chiaje, 1827) - Astropecten irregularis (Pennant, 1777) - Astropecten spinulosus (Philippi, 1837) - Astropecten bispinosus (Otto, 1823) - Astropecten platyacanthus (Philippi, 1837) 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. All of the following are described the main elements found in thousands of specimens encountered and photographed in the Mediterranean Sea (Italy: Trieste, Sardinia; France: Corse; Croatia: Rab, Cres, Krk, Hvar; Greece: Lefkada, Karpathos, Milos, Naxos, Paros, Antiparos, Koufonissi, Kato Koufonissi, Donoussa, Mykonos, Thira, Creta, Limnos) and the features described by authors such as Enrico Tortonese, Rene Koehler, Emil Von Edler Marenzellerin necessary to make identifications. For species such as Astropecten aranciacus, Astropecten jonstoni, Astropecten irregularis and , Astropecten spinulosus usually it is an easy task, but for more complex species such as Astropecten bispinosus and especially Astropecten platyacanthus it needs a more thorough analysis. 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 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, turn in, or disturb the animal. The main elements of starfish genus Astropecten: 1 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 pedicellaria Starfishes have two sides: an upper side called “aboral side” (which is normally visible), and a bottom side called “oral side” (which resting on seabed). ______________________________________________________________________________________________ Astropecten aranciacus This starfish has superomarginal plates equipped with 1 to 3 small spines and inferomarginal plates with long, pointed, strong, regularly arranged spines. The inferomarginal spines have reddish-orange colour at the base and yellowish or white colour towards the tip. It is rugged with normal size disc and pointed arms. The colour of aboral side is given by a succession of paxillae (from the top they look like round points) with upper extremity red-orange in various combinations with paxillae with upper extremity grey or beige. The superomarginal plates are usually grey or beige homogeneous. This is the largest species of Astropecten in Mediterranean Sea with a maximum diameter of 55 cm (usually it measures about 30 cm). Astropecten aranciacus lives on sandy, muddy or gravel bottoms at depths between 2 and 100 m. This specie is active and easy to find in the late afternoon and during the night. It's a starfish with a lot of features and can be distinguished easily from the other species by colour and size. Sometimes it is confused with Astropecten irregularis. 2 Astropecten aranciacus Detail of superomarginal plates of Astropecten aranciacus and colour of aboral side given by succession of paxillae with the top red-orange in various combinations with paxillae grey- beige 3 ______________________________________________________________________________________________ Astropecten jonstoni This sea star has superomarginal plates with a very short spines or without spines (usually the plates between the arms are devoid of spines). The inferomarginal plate has a short and pot external spine, arranged with great regularity, normally kept parallel to one another and rather rigid. The inferomarginal spines have dark orange colour at the base and white-yellowish towards the tip on going to draw a sort of orange outline at the base of the sea star. The overall shape is very peculiar with bigger disc than other species and arms rather court, triangular and very pointed that accentuates the classic shape of the star. The colour of aboral side is pretty clear with various nuances that can be tending towards beige, turquoise-green or grey-brown. It is the smallest species of Astropecten in Mediterranean Sea with a maximum diameter of about 7-8 cm. It prefers sandy seabed at low depths as between 1 and 12 m. Unlike other Astropecten, this specie is active and easy to find during day, especially in early morning and late afternoon. This starfish has a lot of features and can be distinguished easily by its overall shape, size and colour. Rarely it is confused with very young specimens of Astropecten platyacanthus. Astropecten jonstoni 4 Detail of superomarginal plates of Astropecten jonstoni with a very short spines or without spines ______________________________________________________________________________________________ Astropecten irregularis This species live in the Atlantic Ocean and in the Mediterranean, but the two populations show differences in superomarginal plates. In particular, the specimens of Mediterranean have superomarginal plates devoid of spines (they are considered by some author as the subspecies Astropecten irregularis pentacanthus) while Atlantic populations are provided with one spine for each superomarginal plates (they are considered by some authors as the subspecies Astropecten irregularis irregularis) or more spines (they are considered by some authors as the subspecies Astropecten irregularis serratus and by some others as a variety of Astropecten irregularis irregularis). This starfish has a well-developed and raised superomarginal plates and the specimens in the Mediterranean are totally devoid of spines. The inferomarginal spines are short, thin, fine-spines, highly mobile and white colour. Astropecten irregularis doesn’t keep these spines rigid and parallel to each other as the other species do. The arms make up among them, at their base where they join the disc, a very clean corner. The colour of aboral side is pink homogeneous, often violet in towards the end of the arms and sometimes there are many small darker spots in the central disc. Sometimes it has a bulge on centre of the disc that is highly developed in this specie. This bulge protrudes from the sediment where the animal is hidden and it has respiratory functions (called by Enrico Tortonese the "aboral- cone”). Usually it has diameter of about 10-12 cm with a maximum of 19 cm. It's a very common specie in all kind of mobile seabed from 1 to about 1,000 m deep. This specie is active and easy to find during the night, sometimes it is possible to find it in the late afternoon. Usually this starfish can be distinguished easily and safely from the others specie of Mediterranean for superomarginal plates devoid of spines and from colour. Sometime it is confused with Astropecten aranciacus for the similar colour, but it’s always possible to distinguish the two species by a closer inspection of superomarginal plates and inferomarginal spines or by the observation of the of single paxillae’s colour. 5 Astropecten irregularis Detail of superomarginal plates devoid of spines (feature of Astropecten irregularis pentacanthus) 6 Detail of "aboral-cone” sometimes visible in Astropecten irregularis ______________________________________________________________________________________________ Astropecten spinulosus It has very short superomarginal plates (the height of the vertical face is slightly larger than the width of plate), completely covered by scales and very small spines. Only from 1 to 3 small spines on the top of plate can be considered a real spines (the other spines are too small). The colour of these spines is the same of the superomarginal plates and it is brown or clear brown. The inferomarginal spines are long and pointed and they have the feature colour blue-purple. It looks like a slender starfish and sometimes it has rounded ends of the arms. The aboral side has always dark colour: brown, reddish-brown, rarely greenish but always with clear radial lines at the center of arms. It prefers sandy seabed near meadows Posidonia oceanica or Cymodocea nodosa or other mobile seabed in areas very rich in algae from 1 to 50 m deep. It is the only Astropecten that often moves away from mobile seabed and it is possible to meet them on hard bottoms, in cave or climbing on Posidonia oceanica. This specie is active and easy to find during the night, sometimes it is possible to find it in the late afternoon. It is a small starfish, usually 6-8 cm and maximum just under 10 cm in diameter. This sea star can be distinguished from very short superomarginal plates, the colour of aboral side, the colour of inferomarginal spines and size. This species can sometimes be confused with Astropecten platyacanthus. 7 Astropecten spinulosus Astropecten spinulosus 8 Detail of very short superomarginal plates (feature of Astropecten spinulosus) Detail of very short superomarginal plates (feature of Astropecten spinulosus) 9 ______________________________________________________________________________________________ Astropecten bispinosus This sea star has very narrow and high superomarginal plates with a bare area on vertical face of them (visible in the lateral side of arms between inferomarginal spines and superomarginal spines). Every superomarginal plate is equipped with 1 very long, sharp, clean conical spine usually white colour but sometime yellow or orange. The superomarginal spine is always placed on the top internal edge of plates so there aren’t any bare area on top of superomarginal plates. The maximum number of superomarginal plates, observed on each arm, is 77; normally the number is between 40 and 60, depending on the size of the starfish. The pair of superomarginal spines between the arms is often longer than the other. The inferomarginal spines are long, flat, not pointed, usually kept parallel and well separated. Feature shape of this Astropecten has a very small disc and very long and thin arms. The aboral side has uniform colour and can be dark green, dark brown or rarely light brown-pink. The oral side is light coloured, usually white but it can be also yellow or orange. It has size quite large and may reach about 21 cm in diameter. It prefers sandy seabed near meadows of Cymodocea nodosa and it lives at depths between 2 and 100 m. This specie is active and easy to find especially in the late afternoon, but sometimes it is possible to find it during the day or during the night. This is a kind of starfish that can be distinguished by feature’s shape, the high number of superomarginal plates, the bare area on vertical face of superomarginal plates, the conical superomarginal spines and by the colour. This species may be confused with Astropecten platyacanthus. Dark green specimen of Astropecten bispinosus 10 Dark brown specimen of Astropecten bispinosus Light brown-pink specimen of Astropecten bispinosus 11 Detail of the bare area on vertical face of superomarginal plates (Astropecten bispinosus) Detail of the superomarginal spine is always placed on the top internal edge of plates so there aren’t any bare area on top of superomarginal plates (feature of Astropecten bispinosus) 12 ______________________________________________________________________________________________ Astropecten platyacanthus It has narrow and high superomarginal plates, laterally covered with scales and small spines (on vertical face). Every superomarginal plates is equipped with one strong spine, usually sharp but irregularly shaped, slightly flattened laterally, often yellow or orange but rarely off white. Sometimes, especially in young specimen, only superomarginal plates between the arms are equipped with one strong spine while others are not (in some rare specimens all the superomarginal plates are totally devoid of spines). In populations of certain areas of the Mediterranean (for example, the South of Corsica) this feature is very frequent. The superomarginal spines are (more or less) far from the inside edge of plates and they leave on top, on the base of them, a small bare area that it is white if there is a strong spine in the plate (usually in the plates near the disc) or blue-violet if the plate has very small spine or no spine (usually towards the tip of arms). The maximum number of superomarginal plates, observed on each arm, is 48; normally the number is between 29 and 43, depending on the size of the starfish. The inferomarginal spines are long, flat and quite pointed. It is an Astropecten with very variables features and it can have wide or narrow arms. The aboral side has very variables colours and it can be more or less dark brown, olive green, pink-brown, bluish-grey. The oral side usually is yellow-brown. It lives on all mobile seabed at depths between 1 and 60 m, but it is more frequently in seabed of mixed coarse sand and mud at 1-4 m depth. This specie is active and easy to find during the night but also during the day, especially in early morning and late afternoon. Normally it reaches a diameter of 9-12 cm and exceptionally it can measure up to 18 cm. It is the Mediterranean Astropecten hardest to identify both for the variability of features of the species, both for the resemblance to some other species. Astropecten platyacanthus 13 Astropecten platyacanthus Astropecten platyacanthus’s wide variety of colours 14 It is distinguished from Astropecten bispinosus mainly for the superomarginal spines far from the inside edge of plates and they leave on top, on the base of them, a small bare area. Another important Astropecten platyacanthus’s feature is that the superomarginal plates are laterally, on vertical face, covered with scales and small spines rather than nude. Moreover, it is different because it has smaller, irregularly shaped, laterally flattened (rather than clean conical spine) superomarginal spines and because it has average less superomarginal plates on each arm. In addition, on average Astropecten platyacanthus has a central disc larger, a darker oral side and a small red point in the point of arms have. A. platyacanthus’s superomarginal spines far from the inside edge of plates. They leave on top a small bare area that it is white if there is a strong spine in the plate (usually in the plates near the disc) or blue-violet if the plate has very small spine or no spine (usually towards the tip of arms). 15 Detail of narrow and high superomarginal plates, laterally covered with scales and small spines (feature of Astropecten platyacanthus) Astropecten platyacanthus has a small red point in the point of arms 16 Design of the main differences between Astropecten platyacanthus and Astropecten bispinosus A = Astropecten platyacanthus is distinguished from Astropecten bispinosus for the superomarginal spines far from the inside edge of plates. They leave on top, on the base of them, a small bare area. B = Astropecten platyacanthus is a bit different from Astropecten bispinosus for the superomarginal spines smaller, irregularly shaped, laterally flattened (rather than clean conical spine). C = Astropecten platyacanthus is distinguished from Astropecten bispinosus for the vertical face of superomarginal plates, that are laterally covered with scales and small spines rather than nude D = Astropecten platyacanthus is a bit different from Astropecten bispinosus for the inferomarginal spines, sometime less pointed. It is distinguished from Astropecten spinulosus by very different superomarginal plates: highest, defined and equipped with very big and strong superomarginal spines and they have very different plates. Secondly, the general appearance of the starfish and the colour are usually different: Astropecten spinulosus is always slenderer and dark brown with superomarginal spines brown and inferomarginal spines blue-purple. Astropecten platyacanthus reaches or exceeds 10 cm in diameter, while Astropecten spinulosus reaches at maximum just under 10 cm in diameter. 17 Young specimens of Astropecten platyacanthus sometimes can be confused with Astropecten jonstoni for the appearance and the colour, but it is always easy to distinguish them by very different superomarginal plates and superomarginal spines. 18 Text, designs and photos by: Roberto Pillon (email@example.com) ______________________________________________________________________________________________ Bibliography: - Tortonese Enrico (1965). Fauna d'Italia. Echinodermata. - Koehler Réné (1921). Faune de France. Echinodermes. - Emil Edler Von Marenzeller (1875)., Revision adriatischer Seesterne. 19
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