Luiz Francisco Lembo Duarte

Evidence of an alarm signal in Ophiuroidea (Echinodermata)

Numerous marine species are able to assess predation risk through chemical signals, and this capacity is usually found among animals that experience intense predation and possess chemoreception ability, such as brittle stars. We investigated the occurrence of chemical alarm signals and responses in four species of brittle stars: Amphipholis squamata , Ophionereis reticulata , Ophiactis savignyi and Ophiothrix angulata . Additionally, the effect of microhabitat on alarm-signal recognition was tested for O. savignyi . Brittle-star homogenate was released above individuals in an aquarium, and the duration of their immediate escape response was noted and compared to the control. The broadest recognition was observed for A. squamata , which showed an escape reaction to the damage-released stimuli of all brittle stars tested. Similarly broad recognition was observed for individuals of O. savignyi that were collected from the same algal species occupied by A. squamata , a microhabitat where these individuals co-occurred with each other and with juveniles of O. angulata . The similar size and habit of these species probably expose them to the same predators, and therefore, the alarm signal of one species represents a real risk of predation to the others. In contrast, individuals of O. angulata and O. savignyi collected from sponges did not respond to stimuli from either conspecific or heterospecific individuals. The reduction in predation pressure granted by their chemically protected hosts seems to be responsible for this lack of response. The fourth species, O. reticulata , only responded conspecifically. This brittle star is found buried among rubble, and is not observed associated with other organisms; it is known for its cannibalistic and predatory habit.

Reproductive cycle of Ophionereis reticulata (Ophiuroidea, Echinodermata) on the southeast coast of Brazil

Summary The reproductive cycle of Ophionereis reticulata, a common sediment-rocky shore-interface ophiuroid, was examined monthly from January 2002 to January 2003 at Praia Grande beach (São Sesbatião, state of São Paulo, Brazil). Mature individuals were found from January 2002 to April 2002 and from November 2002 to January 2003. Spawning was regcorded from January 2002 to March 2002 and from November 2002 to January 2003. Mature sperm is still present in April which could be involved in the fertilization of the last oocytes spawned in March and April. November and December marked the final point in the maturation process, with a high concentration of yolk and lipid nutrients in the oocytes. Ophionereis reticulata showed, for the period analyzed, a single spawning period, during spring and summer.

Locomotion of Stramonita haemastoma (Linnaeus) (Gastropoda, Muricidae) on a mixed shore of rocks and sand

Mixed shores of rocks and sand are appropriate systems for the study of limitations that the isolation of rocks may impose for gastropods that typically inhabit rocky shores. We marked 52 Stramonita haemastoma (Linnaeus, 1767) snails on a mixed shore and found that 34 of them moved between rocks one to four times during 15 surveys in a period of 72 days. In the experiments, the snails moved on rock by continuous, direct, ditaxic, alternate undulations of the foot sole but on submerged sand they used slower arrhythmic discontinuous contractions of the foot sole. They switched between modes of locomotion in response to the type and topography of the substrate and possibly to water dynamics. In nature, snails moved between rocks forming aggregations where they oviposited. This may have masked other causes of movement, such as availability of prey. Most snails burrowed into the sand when the rocks became exposed during low tides. Further experiments are needed to explicitly address the possible causes of movements among rocks and burial.