Halimeda | Green Algae | Red algae | Photosynthesis | Life history

Halimeda is a genus of green macroalgae. The algal body (thallus) is composed of calcified green segments. Calcium carbonate is deposited in its tissues, making it inedible to most herbivores. However one species, Halimeda tuna, was described as pleasant to eat with oil, vinegar, and salt. As in other members of the order Bryopsidales, individual organisms are made up of single multi-nucleate cells. Whole meadows may consist of a single individual alga connected by fine threads running through the substrate. Halimeda is responsible for distinctive circular deposits in various parts of the Great Barrier Reef on the north-east coast of Queensland, Australia. Halimeda beds form in the western or lee side of outer shield reefs where flow of nutrient-rich water from the open sea allows them to flourish, and are the most extensive, actively accumulating Halimeda beds in the world. The genus is one of the best studied examples of cryptic species pairs due to morphological convergence within the marine macroalgae. Some species grow so vigorously in tropical lagoons that the sediment is composed solely of the remains of their tissues, forming a calcareous “Halimeda sand“. In fact some tropical reef systems, such as atolls, consist largely of Halimeda sand accumulated over the aeons. Morphology The thalli of Halimeda is distinctly segmented and calcified. Calcium carbonate is deposited as aragonite and calcification begins as early as 36 hours. Their segments are composed of 60-80% aragonite[6][13] and are separated by nodes which are non-calcified. The thalli are composed of siphons which are ramified into medullary filaments surrounded by a cortex. The medullary filaments branch out trichotomously to form peripheral utricles which stick to each other to enclose the intersiphonal spaces of each segment. It is in these spaces that aragonite is precipitated. Halimeda has three types of holdfasts which serve as attachment points to the substrate. The “sprawler“ type has a few loose filaments growing at the ends or in between the segments. In the “rock-grower“ type, the matted holdfast is composed of branched filaments which secure the thallus to a rock surface. The last type is the “sand-grower“, where the filaments hold on to fine sand particles, forming a root-like structure. Halimeda is coenocytic and siphonous, meaning its cells are not divided by cross walls, and is instead, a continuous filament of cells. This differentiates the genus from Acetabularia, which is another genus of green seaweed that is calcified. Questions: The live history of halimeda is: A) Zygotic meiosis life history B) Sporic meiosis live history C) Gametic meiosis live history D) All the above E) None of the above One feature that red algae possess but green algae lack is: A) Siphous cell(s) B) Two or more flagella per swimming cell C) Phycobilins D) All the above E) None of the above #NikolaysGeneticsLessons #Halimeda #Rhodophyta #GreenAlgae #RedAlgae #Morphology #LifeHistory #LiveCycle #gamets #SporicMeiosis #GameticMeiosis #zygoticMeiosis #sporophyte #gametophyte #holocarpic #anisogamy #isogamy #Oogamy #photosyntheticPigments #syphonous #ChlorophylA #ChlorophylB #phycozyntines #Botany #plantEvolution #biology #marinBiology #exam #test #quiz #algae #blueGreenAlgae #cyanobacteria #seaweed #AsparagopsisTaxiformis #Sargassum #algaePlasticProduction