Description of Idiomysis diadema sp. nov. (Mysida, Mysidae, Anisomysini), associated with Diadema urchins in the Red Sea; with nomenclatorial notes on its genus

in Crustaceana
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The mysid Idiomysis diadema sp. nov. is described from small swarms hovering between the spines of the sea urchin Diadema setosum (Leske, 1778) at the reef flat of Dahab, Red Sea. The most striking characters within its genus are the subdivided antennal scale, endopod of uropods longer than exopod, and a pair of minute spines on the terminal margin of the telson. With this first description, a total of six Idiomysis species are now known, two of which are associated with cnidarians and only the new one with echinoids. An updated definition is given for the genus Idiomysis W. M. Tattersall, 1922, in order to match the current species inventory. To avoid previously incorrect and ambivalent gender attribution, I propose using the feminine gender for this genus throughout. Consequently, the spelling of two of its taxa, I. mozambica Deprez, Wooldridge & Mees, 2001, and I. robusta Connell, 2008, is changed.


International Journal of Crustacean Research



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  • Colour and microdistribution of Idiomysis diadema sp. nov., associated with different individuals of the sea urchin Diadema setosum (Leske, 1778) from Bannerfish Bay at the coast of Dahab, Red Sea. In situ photos by Christian von Mach (A) and Mario Freinschlag (B). This figure is published in colour in the online edition of this journal, which can be accessed via

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  • Habitus and cephalic appendages in Idiomysis diadema sp. nov., holotype, male with 2.3 mm body length (A), allotype female 2.2 mm (B), paratype male 2.2 mm (C, E-G, J), and paratype female 3.3 mm (D, H). A, habitus of male, obliquely dorsal; B, cephalic region of female, dorsal, most setae omitted; C, male antennula, obliquely dorsal; D, female antennula, obliquely ventral; E, antenna, ventral; F, labrum, ventral; G, mandibles with right palpus, caudal; H, maxillula, caudal; J, maxilla, frontal.

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  • Thoracic appendages in Idiomysis diadema sp. nov., paratypes, male with 2.2 mm body length (A, C-H) and female 3.3 mm (B). A, thoracopod 1 with epipod, rostral; B, thoracopod 2, caudal; C, thoracic endopod 3, caudal; D, thoracic endopod 5, caudal; E; thoracopod 8 with penis, caudal; F-H, series of dactylus 3, 5, 8, including setae and nail.

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  • Abdominal appendages in Idiomysis diadema sp. nov., paratypes, male with 2.2 mm body length (A-E, G-J) and female 3.3 mm (F, K). A-E, series of male pleopods 1-5; F, female pleopod 4; G, uropods, dorsal, setae partly omitted; H, telson, dorsal; J, tip of telson in male; K, the same for female.

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