Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

Fifty-seven species of mosses and fifty-four species of liverworts are reported from the Parque Nacional Volcán Poás, Costa Rica. Of these 5.3% are known solely from Costa Rica, 8% are of cosmopolitan distribution, 67.2% show floristic affinities with the continental floras of South America, 1.8% with those of North America while 17.7% have ranges that include continental or island stations in the Old World.

The ultrastructure of mitotic nuclei of the promastigote Leishmania mexicana ssp. was studied by serial thin sections and threedimensional reconstructions of each divisional stage. At the beginmng of nuclear division (equatorial stage), a set of six dense plaques located about the equatorial region of the nucleus and a microtubular spindle develops in the two opposing poles of the nucleus (two sets of polar microtubules). The microtubular mitotic spindle is entirely intranuclear with the nuclear membrane persisting through mitosts. The polar spindle consists of a discrete bundle of about 50 microtubules and the equatorial spindle is formed by about 100 microtubules. The spindle may contain several continuous microtubules, but no microtubular organizing centres were observed in association with the spindle. The plaques and hemiplaques are associated with microtubular bundles; some of the spindle microtubules converge on kinetochore-like plaques. It is suggested that the spindle has a special significance in the physiology of mitosis. The two sets of hemiplaques may guide the separation of the daughter genomes. At the beginning of the elongational stage the mitotic plaques split into halves and each set of half-plaques migrates to one pole. It is concluded that the dense plaques play a kinetochore-like role and thus Leishmania mexicana ssp. may have six chromosomal units. Mitotic events of this species are essentially similar to those of Trypanosoma cruzi.

During 1985 and 1986, censuses of the most abundant corallivore organisms were made at Caño Island reef, Costa Rica. These are the fishes Arothron meleagris, A. hispidus, Pseuaobalistes naufragzum, Sufflamen verres, Stegastes acapulcoensis and Microspathodon dorsalis; the gastropods Jenneria pustulata and Quoyula monodonta; the hermit crabs Trizopagurus magnificus and Aniculus elegans; and the equinoderms Acanthaster planci, Eucidaris thouarsii and Diadema mexicanum. The population densities of all species increased toward the year 1986, and their distribution across the different reef zones, i.e. reef flat, slope and base, was very similar between both years. The high densities of balistid fishes and damselfishes and their behavior may affect the abundance and distribution of other corallivore species. Since the high mortality of pocilloporid corals caused by the 1982/83 "El Niño" and the red tide (1985) events, corallivores such as hermit crabs, puffer fishes and the gastropod Quoyula, which feed mainly upon the coral Pocillopora, may have had a limiting effect on the recovery, growth and distribution of this species on the reef. On the other hand, the abundance of balistids on the reefs seems to favor the dispersion of the dominant coral species Porites lobata via fragmentation.

The distribution, karyotype and morphological characteristics of Bothrops ophryonegas from Costa Rica are described. This species presents a conspicuous sexual dimorphism and dichromatism. It is distributed in the dry forest areas of Guanacaste and Puntarenas. Its karyotype is indistinguisable from those described for other crotaline species.

An ecological study of a tree savanna was conducted at “El Escobio”, Liberia, Guanacaste, Costa Rica. The site shows a seasonal climate; with well defined dry and wet seasons. Soils are poor on nutrients, favouring a dominant coverage of herbaceous plants (Cyperaceae and Graminae) more or less xeromorphic, and the growth of some scattered tree species.A great number of rare and economically important species were found at the riparian forest. This forest plays a significative role in keeping a diverse fauna, due to the variety of fruits and flowers available throughout the year.

The predatory behavior of the gastropod Quoyula monodonta, a selective corallivore that feeds upon Pocillopora spp., is reported for the first time from the eastern Pacific. On average an individual eats tissue from 0.64 cm2 of coral per day. Larger individuals cause more damage.The high densities of Q. monodonta and two species of hermit crab, make it likely that all of these corallivores are acting together to increase the mortality of pocilloporid corals and thus limit the growth, abundance and distribution of Pocillopora on the Caño Island coral reefs (Costa Rica).

Es inegable que uno de los temas actuales de mayor controversia en el Pacífico tropical americano, es el relacionado con la biogeografía de los corales ahermatípicos, que fue desencadenada por los trabajos de Dana (1975) y Heck & McCoy (1978). Por lo tanto consideramos la crítica de Guzmán a nuestro trabajo (Prahl y Mejía 1985) más bien como una invitación a discutir el tema, a pesar de que el trabajo criticado mo es el más apropiado, dado que en él tan sólo se pretende informar por primera vez la existencia de un coral acropórido en el Pacífico tropical americano y no entrar en detalles biogeográficos.

The bioecology of the smooth clam Chione fluctifraga; was studied in the La Cruz estuary, Sonora, México. It is concluded that the species is relatively abundant, although there seems to be a strong capture pressure in the largest sizes. The preferred habitat is fine to very fine sand. Growth is relatively slow and about 3 years are required to reach commercial size. Reproduction occurs late in the spring and in the early summer.