In most parasitic dinoflagellates, the infective stage resembles a typical motile dinoflagellate cell. Corals often form symbiosis with other organisms, particularly photosynthetic dinoflagellates. These are primarily composed of algal species, but can also consist of dinoflagellates and cyanobacteria. In these species (e.g., bacteria, ciliates, dinoflagellates and diatoms), "sex" and reproduction occurs separately. Many Protozoa are zooplankton, including dinoflagellates, zooflagellates, foraminiferans, and radiolarians. Pollen, spores and algae (dinoflagellates and acritarchs) are used for dating sedimentary rock sequences. Other dinoflagellates that may cause ciguatera include "Prorocentrum" spp. There are no thylakoid membranes invading the pyrenoid, which is unlike other symbiotic dinoflagellates. This family is also found in a group of eukaryotes known as dinoflagellates. Puffer fish and some marine dinoflagellates also produce saxitoxin. By trophic orientation dinoflagellates are all over the place. More complex life cycles occur, more particularly with parasitic dinoflagellates. This poisoning is usually due to a bloom of dinoflagellates (red tides), which contain toxins. About 1,555 species of free-living marine dinoflagellates are currently described. A number of dinoflagellates are known to have two nuclei.