| Volvox globator | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Plantae |
| Division: | Chlorophyta |
| Class: | Chlorophyceae |
| Order: | Chlamydomonadales |
| Family: | Volvocaceae |
| Genus: | Volvox |
| Species: | V. globator |
| Binomial name | |
| Volvox globator | |
Volvox globator is a species ofgreen algae in the familyVolvocaceae. Thetype species ofVolvox, the name was originally given byCarl Linnaeus in his 1758 workSystema Naturae.[1] In 1856 its sexuality was described byFerdinand Cohn and is the same asSphaeropleaannulina.[2] It is afreshwater alga with acosmopolitan distribution.[1]
Volvox globator is a colony of bi-flagellated cells; mature colonies are 400–575 μm long and 380–540 μm wide. The colony consists of thousands ofsomatic cells arranged in a single peripheral layer embedded in a gelatinous matrix, forming a hollow sphere.[3] Each cell is pyriform in side view, connected to each other bycytoplasmic strands, making them appear stellate in polar view. Each individual cell is surrounded by a gelatinous sheath.[3] Cells have two to sixcontractile vacuoles, a parietalchloroplast with several minutepyrenoids, a small redstigma.[4] Nutrition is holophytic.[citation needed]
Asexual colonies are usually filled with three to 17 (usually four to seven)gonidia irregularly distributed in the posterior of the colony. Gonidia are 10–13 μm in diameter; these divide bybinary fission to become embryos. After the cells in the embryo finish dividing, they undergocolony inversion; that is, the embryo turns itself inside out, so that the flagella are correctly oriented outwards. InVolvox globator, the posterior of the embryo first pushes inwards, then the anterior pole of the embryo produces an opening (called a phialopore), allowing the embryo to invert. This method of inversion is called Type B inversion, in contrast to the more well-studied Type A inversion inVolvox carteri.[5] Mature embryos are up to 250 μm in diameter.[3]
Sexual reproduction ishomothallic, with sexual colonies around the same size as asexual ones. Sexual colonies contain three to seven antheridial (sperm) packets and 11–72 (typically 20–30) eggs. The sperm packets are compressed globoids about 22–32 μm, and divide to form 256 antherozoids (sperm). Thezygotes are round and covered with straight, blunt spines; they are 36–44 μm (with spines, 45–54 μm).[3]
Volvox globator has been used as amodel organism for a over a century, to study cellular motion.Volvox colonies tend to swim towards the direction of light.[6]
As the type species ofVolvox, it is placed inVolvox sect.Volvox (also known asEuvolvox).[3] This section is characterized by having cells with thick cytoplasmic connections between each other, making the cells appear stellate, and having spiny zygotes. Within sectionVolvox, species are separated based onmonoicy/dioicy, number of eggs and sperm packets per spheroid, and zygote morphology.[7]