Pontonia margarita Verrill, 1869 (Decapoda: Caridea: Palaemonidae) as a symbiont of Pinna rugosa Sowerby, 1835 (Mollusca: Bivalvia) on both coasts of the Baja California Peninsula, Mexico

Many caridean shrimps live in symbiosis with bivalves, the shrimps finding refuge and food in the mucus in their host's mantle cavity. We report for the first time the presence of Pontonia margarita Verrill, 1869 on both coasts of Baja California Peninsula, Mexico, as a symbiont of the pen shell Pinna rugosa Sowerby, 1835. The symbiont was found in Laguna Ojo de Liebre (LOL), which faces the Pacific Ocean, and in Bahia Concepcion (BC), on the eastern coast facing the Gulf of California. A total of 569 specimens of Pinna rugosa were studied, 472 from LOL (104-277 mm shell length (SL)) and 97 from BC (130-234 mm SL). A total of 376 Pontonia margarita individuals were extracted in LOL (19-41 mm total length (TL)) and 41 in BC (20-48 mm TL). The prevalence of Pontonia margarita was 46% in LOL and 28% in BC. The regression analyses for both sexes of Pontonia margarita showed a high correlation between TL and total weight and abdominal length and TL. The data showed a moderate correlation between TL and the length of the major and minor chelae, and TL and length of the minor chela. There was no significant relationship between biometric parameters of the host and the symbiont. The presence of gravid females of Pontonia margarita (52% in LOL and 39% in BC) in shells suggests reproduction during autumn.