No abstract

SUMMARY: Tentacle cnidae of Metridium senile (Linnaeus, 1761) were examined by light microscopy. In addition to spirocysts, feeding-tentacles had 3 nematocyst categories grouped into medium and small size-classes, including 5 types. Spirocysts dominated, especially distally, followed by medium b-mastigophores. The density of cnidae decreased towards the tentacle base. Early cnidoblasts were numerous on the tentacle tip. Late cnidoblasts appeared in a moderate number on the mid-tentacle. Catch-tentacles, found in two Metridium specimens, had a maturity gradient of isorhizas and gland cells along their length. Their tip had two distinct types of mature isorhizas in great numbers and large gland cells, but lacked spirocysts. Mature isorhizas and gland cells decreased in number towards the tentacle base. On the mid-tentacle differentiating ages of isorhizas were numerous. Ordinary feeding-tentacle cnidae, abundant at the tentacle base, decreased in number distally along the tentacle.Keywords: sea anemone, nematocysts, cnidae, catch-tentacles. RESUMEN: Cnidoma de los tentáculos de la anémona de mar MetridiuM senile (Linnaeus, 1761) (Cnidaria: Anthozoa). -El cnidoma de los tentáculos de Metridium senile (Linnaeus, 1761) se examinó mediante microscopio óptico. Además de espirocistos, los tentáculos tenían 3 categorías de nematocistos agrupados en clases de talla medianas y pequeñas, incluyendo 5 tipos. Los espirocistos fueron dominantes, en particular distalmente, seguidos por b-mastigióforos medios. La densidad de cnidoma decreció hacia la base del tentáculo. En la punta del tentáculo fueron abundantes los cnidoblastos jóvenes. Los cnidoblastos avanzados aparecieron en número moderado a mitad del tentáculo. Los tentáculos hallados en dos especímenes de Metridium presentaron un gradiente de madurez de isorhizas y células glandulares a lo largo de su longitud. La punta tenía dos tipos distintos de isorhizas maduras en gran número y grandes células glandulares, pero les faltaban espirocistos. Las isorhizas maduras y las células glandulares disminuyeron en número hacia la base del tentáculo. A mitad del tentáculo, se observaron numerosas isorhizas de diferentes edades. Los cnidocistos de los tentáculos, abundantes en la base del tentáculo, disminuyeron en número distalmente a lo largo del tentáculo.Palabras clave: anémona de mar, nematocistos, cnidoma, tentáculos.

The cnidom of the sea anemone Sagartiogeton viduatus (Muller, 1776) is described from interference‐contrast light micrographs (LMs) and scanning electron micrographs (SEMs). Special attention is given to nematocyst maturation, including the differentiation of the shaft into proximal and main regions as helical folding of the shaft wall proceeds. Comparisons are made with Metridium senile (Linnaeus, 1761), whose cnidom, with a few exceptions, is closely similar to that of S. viduatus. The two anemones possess b‐ and p‐mastigophores, p‐amastigophores, isorhizas and spirocysts. Although the majority of cnidae in S. viduatus is smaller than corresponding ones in M. senile, they are grouped into the same size classes as those of M. senile, namely small, medium and large. The main differences from M. senile cnidae are the followings: (1) Large acontia p‐amastigophores are the largest nematocysts in S. viduatus. (2) They are noticeably larger than the large acontia b‐mastigophores, and (3) they are separated from the p‐amastigophores of M. senile by the sinusoid pattern of their U‐shaped capsular matrix. (4) The large acontia b‐mastigophores are microbasic and not mesobasic as in M. Senile, and (5) they do not produce darts. (6) Another difference from M. senile is the absence of catch‐tentacle isorhizas.