# Ostreopsis | Algae ID

Source: https://algaeid.com/identification/ostreopsis/

[ID guide](https://algaeid.com/identification/) › Dinoflagellates

# *Ostreopsis* sp.

**Extremely toxic.** *Ostreopsis* makes the same toxin as *Palythoa* corals, [palytoxin](https://en.wikipedia.org/wiki/Palytoxin). Before you try to kill it, ventilate the area around the tank, run fresh carbon, and keep pets and children away. Read the [safety notes](https://algaeid.com/treatment/#safety).

## How to recognize it

*Ostreopsis* can often be identified even at very low magnification because of its distinctive motion. Look for sesame-seed shaped cells **spinning around an anchor point like a tetherball**. Under higher magnification the cells are a teardrop or oval shape with a rounded end and a pointed end.

It is the most toxic of the dinos I tend to see in home aquaria. It also forms cysts, so if an eradication effort works you also need to address the nutrient problem that caused the bloom, or it can come back.

*Ostreopsis*: a flat, pointed oval. Looking down on it you see the top face and its plates, and the groove (cingulum) runs around the rim.

![Ostreopsis sp. cells at high magnification](https://algaeid.com/img/ostreopsis-6679.jpg)

A single Ostreopsis cell. Note the teardrop shape.

![Ostreopsis sp. cells at high magnification](https://algaeid.com/img/ostreopsis-6681.jpg)

Two Ostreopsis cells.

![Ostreopsis sp. cells at high magnification](https://algaeid.com/img/ostreopsis-6682.jpg)

A small group of Ostreopsis cells.

![Ostreopsis cells with eyepiece graticule marks](https://algaeid.com/img/ostreopsis-photo-1.jpg)

Ostreopsis from a home reef aquarium. The tick marks are the eyepiece graticule, which can be used to estimate cell size. Image courtesy of Sanjay Joshi.

![Ostreopsis cells with eyepiece graticule marks](https://algaeid.com/img/ostreopsis-photo-2.jpg)

Ostreopsis from a home reef aquarium. The tick marks are the eyepiece graticule, which can be used to estimate cell size. Image courtesy of Sanjay Joshi.

![Ostreopsis cells with eyepiece graticule marks](https://algaeid.com/img/ostreopsis-photo-3.jpg)

Ostreopsis from a home reef aquarium. The tick marks are the eyepiece graticule, which can be used to estimate cell size. Image courtesy of Sanjay Joshi.

## Low magnification

At 20X to 100X you see a scatter of small brown cells, and the spinning is easiest to spot in video.

![Ostreopsis sp. at low magnification](https://algaeid.com/img/ostreopsis-20x.jpg)

Ostreopsis sp. at 20X magnification.

![Ostreopsis sp. at low magnification](https://algaeid.com/img/ostreopsis-40x.jpg)

Ostreopsis sp. at 40X magnification.

![Ostreopsis sp. at low magnification](https://algaeid.com/img/ostreopsis-60x.jpg)

Ostreopsis sp. at 60X magnification.

![Ostreopsis sp. at low magnification](https://algaeid.com/img/ostreopsis-100x.jpg)

Ostreopsis sp. at 100X magnification.

## Videos

[Video: Ostreopsis sp. at 40X](https://www.youtube.com/watch?v=eZVmI9V-ZLc)

Ostreopsis sp. at 40X [Watch on YouTube](https://www.youtube.com/watch?v=eZVmI9V-ZLc)

[Video: Ostreopsis at 100X](https://www.youtube.com/watch?v=paBa3-9RHl8)

Ostreopsis at 100X [Watch on YouTube](https://www.youtube.com/watch?v=paBa3-9RHl8)

[Video: Ostreopsis at 400X](https://www.youtube.com/watch?v=G04hKQg9Rig)

Ostreopsis at 400X [Watch on YouTube](https://www.youtube.com/watch?v=G04hKQg9Rig)

[Video: Ostreopsis sp. at 400X](https://www.youtube.com/watch?v=hfgS582AS5w)

Ostreopsis sp. at 400X [Watch on YouTube](https://www.youtube.com/watch?v=hfgS582AS5w)

## What to do

- Remove as much material as you can by hand *before* you start killing it, and dispose of it where kids and pets cannot reach it.
- Expect dying cells to release toxin. Run carbon and ventilate well, especially while a large number are dying off. Several aquarists who contacted me reported respiratory symptoms.
- Look for the underlying cause. Very low nutrients and a lack of grazers can both favor dinos. See the [ecology notes](https://algaeid.com/treatment/#ecology).
- Ciliates can be a natural control. See [the ciliates section](https://algaeid.com/not-dinos/#ciliates).

More options are on the [treatment page](https://algaeid.com/treatment/).