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The sand dollar Dendraster excentricus has been extensively used in diverse studies in Baja California (Mexico). This study shows annual variations in the gonad index and describes larval development under laboratory conditions of D. excentricus. Over a period of one year, adult sand dollars (6.73 ± 0.56 cm diameter and 23.22 ± 6.90 g) were collected monthly. Both the monthly analysis of the gonad index (male and female) and the measure of mature eggs were considered to estimate the reproductive period of the sand dollar in Punta Banda Estuary (Baja California). Our results suggest that D. excentricus has two maximum reproductive peaks, one during the early spring and another during the summer, although viable gametes were obtained in the laboratory year round. Larval development took 21–23 days from fertilization to metamorphosis under laboratory conditions (19 ± 2 oC, salinity 33.5). The blastula stage was observed 5 h postfertilization, while four-armed echinopluteus larvae, with an average size of 387.00 ± 23.25 m (from aboral to dorsal arms), were observed two days after fertilization. A different larval stage was attained approximately every two days. Eight-armed echinopluteus larvae were 744.60 ± 69.45 m in size. The completely developed juvenile rudiment was detected 18 days after fertilization and metamorphosed larvae were observed 72 h after induction. These results, while not new for the species, show the reproductive behavior and larval period for the D. excentricus populations associated with an estuary at the southern limit of its distribution, and will be useful to document variation in the response of species of ample geographic distribution in global change scenarios.   La galleta de mar Dendraster excentricus ha sido extensivamente utilizada en diversos estudios en Baja California (Mexico). El presente trabajo muestra la variacion anual del indice gonadal y describe el desarrollo larvario de D. excentricus en condiciones de laboratorio. Durante un periodo de un ano, se recolectaron mensualmente galletas adultas (6.73 ± 0.56 cm de diametro, 23.22 ± 6.90 g). El analisis mensual del indice gonadal (hembras y machos) y la determinacion del tamano de los huevos fueron considerados para estimar el periodo reproductivo de esta especie en el estero de Punta Banda (Baja California). Los resultados sugieren que D. excentricus presenta dos picos reproductivos maximos, uno durante el inicio de la primavera y otro en el verano, aunque se observaron gametos viables todo el ano. El desarrollo larvario tuvo una duracion de 21–23 dias desde la fertilizacion hasta la metamorfosis en condiciones de laboratorio (19 ± 2 oC, 33.5 de salinidad). La formacion de la blastula se observo a las 5 h postfertilizacion. Las larvas equinopluteus de cuatro brazos, con un tamano de 387.00 ± 23.25 m desde el brazo aboral al dorsal, se observaron a los dos dias de la fertilizacion. Se desarrollo un estadio larval diferente aproximadamente cada dos dias. Las larvas equinopluteus de ocho brazos alcanzaron un tamano promedio de 744.60 ± 69.45 m. El rudimento juvenil completamente desarrollado se detecto al dia 18 postfertilizacion y las larvas metamorfoseadas se observaron 72 h despues de la induccion. Los resultados aqui presentados, si bien no son nuevos para la especie, muestran el comportamiento reproductivo y la duracion del periodo larvario para las poblaciones de D. excentricus asociada a un estero en la parte sur de su distribucion y resultan de utilidad para documentar la variabilidad de la respuesta de especies de amplia distribucion geografica en escenarios de cambio global.

Gonad index and larval development of the sand dollar Dendraster excentricus (Echinodermata; Echinoidea) in Baja California, Mexico