Chimerism, the evolutionary perplexing outcome of fusion between conspecific individuals, is widely documented in nature. Several reports assign a variety of benefits to the state of chimerism, especially in cases of fusions between kins, rating a chimera as a congruous entity. For the first time, we describe here a follow-up study on chimeras of soft corals that occur only between ontogenetically immature conspecifics, prior to development of a histocompatibility recognition system. Four soft coral species from the Red Sea were investigated: Nephthea sp., Heteroxenia fuscescens, Parerythropodium fulvum fulvum and Clavularia hamra. Co-settlement of planulae resulted in high frequencies of spontaneous allogenic fusions between primary polyps. Tissue fusion between allogenic partners was confirmed histologically. During the observation periods (up to 450 d) chimeras were detached, or chimerism resulted in the death of 1 or more partners, or in morphological resorption of the partners. The results also document slower growth and growthretarding disorders such as disruption of the structural patterns of polyp budding and polyp configuration. These cumulative effects were only manifested by individuals comprised of incongruous components. Such chimeras are likely to be less suited to field conditions than genetically homogeneous individuals, raising the ecological-evolutionary question of why soft-coral chimeras arose in the first place. We propose that juvenile cnidarian chimerism represents a case in which ontogenetic allorecognition is not infallible, and that it is further promoted by the gregarious settlement of larvae characteristic of many coral species.

Skeletal tumor formations in the massive coral Pavona clavus were investigated for 3 yr on the northern Pacific coast of Costa Rica in a reef composed almost exclusively of this species. A field survey of tumor incidence showed that more than half of the population presented this phenomenon and that frequencies increased with depth. Up to 37 tumors per colony were recorded, and the largest tumor size was 37.5 m 2 , covering the whole colony surface area. Tumors and healthy skeletons and tissues were studied by scanning and transmission electron microscopy, histology, in situ alizarin marking for growth rates, and x-ray radiographs of skeletal slabs. Macroscopic and microscopic analyses of skeletons revealed the presence of 3 types of tumors (Types I to III). No cytological changes or intracellular infection by parasitic agents were recorded. The only cellular change observed was the reduced numbers of zooxanthellae in tumorigenic tissues. Tumors begin their growth as a single polyp and develop for scores of years without any sign of cellular necroses. Tumors grew faster than healthy parts; however, their skeletal density was lower, with a higher Mg content making it less resistant to bioerosion. Two yr of in situ isogeneic and allogeneic contacts between healthy and tumor fragments revealed no infection or transfer of the tumor to the healthy tissue, even following isogeneic fusion combinations of healthy versus tumor fragments. We suggest that the terminology often used to characterize tumors in hard corals ('tumor', 'neoplasm', 'hyperplasia') does not reflect the pathogenesis and etiology of this phenomenon. The terms 'skeletal tumor' or 'calicoblastic epithelioma' seem more fitting for this de novo genesis.

The gastrovascular system in the Red Sea soft coral Parerythropodium fulvum fulvum comprises two interconnected networks of canals filled with fluid and circulating cells. The first network is composed of narrow canals (50-80 {mu}m in width) located below the upper ectodermal layer; the second network includes larger canals (300-500 {mu}m in width) that are located deeper in the coral tissue. Particle movement in the second network is faster than in the superficial network, but in both, coral cells with and without healthy zooxanthellae circulate freely. To investigate the movement of metabolites and cellular components within the colony, coral fragments were exposed to 14C-labeled seawater for 24 h in the laboratory and in situ under saturating photosynthetic photon flux and then grafted back to their original colonies. Grafts fused after 24 h. In the laboratory experiment, up to 45% of the fixed 14C was translocated to the unlabeled colony within 48 h after fusion. In the in situ experiment, significant translocation of labeled materials occurred at the furthest parts of the colonies, 390 mm away from the fusion line, in 24 h. Even though the amount of labeling varied between colonies, labeled material spread throughout all the unlabeled parts. It thus appears that the gastrovascular system in Parerythropodium fulvum fulvum functions as an effective circulatory apparatus for fast translocation of organic compounds and cellular components within the colony.

The population genetic profiles of 60 specimens of thecommon intertidal sea anemone Actinia equina taken from foursampling sites (Peroj, Barbariga and the north and south shoresof the Limski Canal), along a 25 km strip of the coastof the Istra Peninsula, Croatia, were evaluated by AFLP markers(144 loci). All populations were characterized by aggregates ofspecimens confined within a few square meters. One of the populations(on the north shore of the canal) contained both large and small‐sizedindividuals. Results revealed high within‐aggregate genetic heterogeneity(36.1–55.6%). With respect to interpopulationprofiles, geographically remote populations from Peroj, Barbarigaand the south shore of the canal were more closely related geneticallythan those on the north and south shores of the canal. The small‐sizedsubpopulation from the north shore exhibits a distinct AFLP pattern,suggesting that it warrants recognition as a cryptic species. © 2002The Linnean Society of London, Zoological Journal of the LinneanSociety, 2002, 136, 315−320

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