Largest organisms photosynthetic unicellular and multicellular protists that are related to land plants. The thallus of the unicellular mermaid's wineglass, "Acetabularia", can grow to several inches (perhaps 0.1 to 0.2 m) in length. The fronds of the similarly unicellular, and invasive "Caulerpa taxifolia" can grow up to a foot (0.3 m) long. A member of the order Cetacea, the blue whale ("Balaenoptera musculus"), is thought to be the largest animal ever to have lived. The maximum recorded weight was 190 metric tonnes for a specimen measuring , whereas longer ones, up to , have been recorded but not weighed. The African bush
Largest prehistoric animals is "Ptychodus", which was about long. The largest-known placoderm was the long "Dunkleosteus". It is estimated to have weighed around . Its relative, "Titanichthys", may have rivaled it in size. The largest-known is "Aegirocassis" at least long. The largest-known in this group was "Jaekelopterus rhenaniae" at in length. A close contender was "Pterygotus" at in length. There are two contenders for largest-known ever arachnid: "Pulmonoscorpius kirktonensis" and "Brontoscorpio anglicus". Pulmonoscorpius was Brontoscorpio was . The biggest difference is that "Brontoscorpio" was aquatic, and "Pulmonoscorpius" was terrestrial. "Brontoscorpio" is not to be confused with various Eurypterids: it was a true scorpion