Crustacea Decapoda Crangonidae : Revision of the three closely related genera Aegaeon Agassiz, 1846, Pontocaris Bate, 1888 and Parapontocaris Alcock, 1901

Abstract

The species of Pontocaris Bate, 1888, and related genera, Aegaeon Agassiz, 1846 and Parapontocaris Alcock, 1901, are reviewed based on the abundant samples collected by ORSTOM (Institut français de Recherche scientifique pour le Développement en Coopération), the Muséum national d'Histoire naturelle, the Forschungsinstitut Senckenberg, and the National Taiwan Ocean University, as well as those deposited at other museums and institutions. Altogether 21 species and one subspecies are recognized which appear to form three natural groups. The genus Parapontocaris Alcock, 1901 is retained for the 6 species assigned to it by CHACE (1984), but different characters are used to differentiate them. An interlocking mechanism between the posterior thoracic sternites and the carapace is found in all species of the Pontocaris propensalata group, but not in the others. Furthermore, females of this group can modify their pereiopods, probably for the care of the eggs, when they molt for spawning. Such modification of the pereiopods is unique in the carideans according to present knowledge. Thus, the genus Pontocaris Bate, 1888, is now restricted to the species of this group and BRUCE'S (1988) Pontocheras becomes a junior synonym of the former. At present 10 species and one subspecies are recognized in this group, with the names P. affinis (Alcock, 1901) and P. hilarula (de Man, 1918) revived and four new species and one new subspecies described: P. major from the Philippines, P. laurentae and P. spinifera from Indonesia, P. profundior from the Red Sea and Gulf of Aden, and P. affinis allodactylus from the Red Sea. The name Aegaeon Agassiz, 1846 is revived for five species with characters intermediate between Parapontocaris and Pontocaris (as defined here), namely A. cataphractus (Olivi, 1792), A. lacazei (Gourret, 1887), A. orientalis Henderson, 1893, A. rathbuni de Man, 1918 and A. boschii (Christoffersen, 1988). Keys for distinguishing these three genera and the identification of the species are provided. The distribution and evolution, as well as sexual dimorphism and polymorphism in females, of these species are briefly discussed. Both the morphological characters and distribution patterns suggest that the genus Parapontocaris is relatively more ancient and has a typical Tethys distribution. On the other hand, species of Pontocaris possess many advanced characters and are still actively evolving in the Indo-West Pacific. The intermediate genus Aegaeon probably forms a link between the above two genera and has successfully invaded the Atlantic from the original Indo-West Pacific distribution.