A RECORD OF AN UNUSUAL ROSTRUM IN LONGIROSTRIS H. MILNE EDWARDS (, )

BY

SAMMY DE GRAVE1) and THOMAS MENTLAK Oxford University Museum of Natural History, Parks Road, Oxford OX1 3PW, United Kingdom

The range of morphological variation in rostrum morphology has been well doc- umented in Palaemonidae, and is especially pronounced in the genera Palaemon Weber, 1795 and Palaemonetes Heller, 1869. This variation comprises variation in the number of dorsal and ventral teeth, as well as the relative length and shape of the rostrum (Yaldwyn, 1957; De Grave, 1999a, b). Occasionally however, spec- imens are encountered with a rostral morphology well outside this background variation, a phenomenon not restricted to Palaemonidae (reviewed in Aguirre & Hendrickx, 2005). Although such cases hold a certain curiosity value, in the ge- nera Palaemon and Palaemonetes they also have scientific merit, as level identification within these genera is to a large extent based on rostral morphol- ogy. Here we report on a case of extreme rostral variation in Palaemon longirostris H. Milne Edwards, 1837, this being only the second time in over a century such an extreme case has been reported in the genus, the last record being by Fauvel (1900) for Palaemon serratus (Pennant, 1777). During routine sampling for Palaemon species at the Tilbury Power Station, Thames Estuary, United Kingdom, a single specimen of Palaemon was encoun- tered with an unusual double rostrum (fig. 1) on 28 November 2007. This speci- men could not be identified using routine keys (Ashelby et al., 2004; d’Udekem d’Acoz et al., 2005; Gonzalez-Ortegon & Cuesta, 2006), due to their over-reliance on rostral morphology. Based on closer morphological investigation, we here as- sign the specimen to P. longirostris, on account of the characteristic shape of the sixth pleuron (see Gonzalez-Ortegon & Cuesta, 2006), the lack of an anal spine (C. W. Ashelby, pers. comm.), as well as the relative proportions of the fused and free parts of the ventral antennular flagellum, and the proportions of the chelae.

1) e-mail: [email protected] © Koninklijke Brill NV, Leiden, 2008 Crustaceana 81 (11): 1403-1406 Also available online: www.brill.nl/cr DOI:10.1163/156854008X361049 1404 NOTES AND NEWS

Fig. 1. Deformed rostrum of Palaemon longirostris H. Milne Edwards, 1837, non-ovigerous female, Tilbury (OUMNH.ZC-2008.10.001), in lateral view.

The single example, a non-ovigerous female, has a post-orbital carapace length of 9.4 mm and is deposited in the Zoological Collections of the Oxford University Museum of Natural History (OUMNH.ZC-2008.10.001). The specimen bears a single post-orbital tooth, separated by a large interval to the next most posterior one, which is situated above the orbit (fig. 1). Distally from this, the rostrum forks with the ventral blade being more characteristic for the species; the bifurcation being at an angle of ca. 45◦. The ventral blade bears (past the bifurcation) four dorsal teeth, as well as four ventral teeth, with the usual setae in the intervals, and is relatively deep. In contrast, the dorsal blade is much narrower, bearing (counting from but not including the orbital tooth) eight dorsal teeth and three ventral teeth. Distally, the blade is truncated, due to damage. Although the intervals between the dorsal teeth bear setae, these are absent in- between the ventral teeth. In dorsal view, both blades are in the same plane. The only case so far reported in the literature of such an extreme variation in Palaemon is by Fauvel (1900) for P. serratus. Curiously, both cases are similar in morphology, although Fauvel (1900) does indicate a minor, third bifurcation.