Phronima Sedentaria

Scientific Name:  Phronima sedentaria

Author:  Eduarda Ferro Braga Laurindo Correia

Size Range:  These are tiny creatures with sizes ranging from 1.2-4.2 cm (~0.5 to 1.7 inches). 

Life Expectancy:  They live around one year. 

Identifying Features:  Phronima sedentaria can be distiguished by its very large head which is composed of two very large transparent compound eyes.  It also has two lateral compound eyes and 4 distinct red retinae.  The internal anatomy of these creatures is reasonably similar to that of other amphipods, but there are some key characteristics that differentiate them. As an example, their foregut is reduced and surrounded by a midgut chamber. Their brain is circumesophageal with four pairs of major nerves, that lead to their 4 compound eyes and to their ventral nerve cord and antennules. This organism has numerous specialized legs including two large claws, as well as a tail with 3 pairs of swimmerets (pleopods) it uses for swimming.  They also have pigmented-cells called chromatophores that are responsible for camouflage; these cells contract to give the organism a transparent appearance so it will be unseen or mistaken as harmless plankton by the prey. 

Mating Behaviour:  Males use their antennae to find potential mating partners in response to the release of pheromones by the females. The male will then ride or hold onto the female until she is ready to molt, the male will then push the sperm into the marsupium and release the female when it is complete. After a couple of hours, the female will release her eggs into the marsupium for fertilization.

Habitat:  They are usually found in temperate and tropical waters around the world and can live anywhere between the surface and deep water. 

Food:  Their feeding behaviours depend on the consistency of the food being eaten. The specialized legs called pereiopods are used during feeding to pick and pull prey with soft bodies toward their mouths, where the mouthparts are responsible for removing smaller pieces and directing them to the esophagus. When the tissue of the prey is tough other pereiopods work to keep it across the mouth cone area while the mandible breaks it down into smaller pieces. If the tissue is fluid-like, the contents will be sucked into the foregut with the help of the muscles of the esophagus and gut. One example of food they might ingest is zooplankton.

Predators:  Fish are some of the most prominent predators.

The photo above shows the adult female that ventured outside of the salp containing her juvenile offspring within.  

Life Cycle:  Phronima sedentaria make their homes in hallowed salps. They attack their victims by slicing them open with their claws, eating the soft tissue of the prey and then using the barrel-like leftovers as a gelatinous home. Females will lay their eggs in this barrel, which also provides protection from predators and space for food storage. These eggs will hatch inside of the barrel, and it will, later on, serve as food for the young amphipods. These young amphipods can be seen swimming around the barrel.  At times both the adult and juveniles in our lab could be seen leaving the barrel and re-entering it. 

Two juveniles inside the salp with their mother’s head above.

The visual system of Phronima sedentaria has been described as extraordinary and has often been studied.  The two median compound eyes are unusual in their size with crystalline cones reaching up to 5mm in length.  The structure is thought to give Phronima resolution under very low light levels while also  being transparent, a benefit when avoiding detection by predators.

The illustration on the right is adapted from Ball, E. E. 1977.  Fine structure of the compound eyes of the midwater amphipod Phronima in relation to behavior and habitat.  Tissue & Cell 1977 9 (3) 521-536

Video Production: Eduarda Ferro Braga Laurindo Correia

Photos and Video:  Misha Young and David Young

Special thanks for Misha for finding the specimen off the shores of Victoria.


Amphipod: Salp Invader. (2018, May 18). Retrieved January 25, 2021, from

Ball, E. E. (1977). Fine structure of the compound eyes of the midwater amphipod Phronima in relation to behavior and habitat. Tissue and Cell, 9(3), 521-536. doi:10.1016/0040-8166(77)90010-6

Diebel, Carol. (1988, January 1). Observations on the Anatomy and Behavior of Phronima Sedentaria (Forskal) (Amphipoda: Hyperiidea). Journal of Crustacean Biology, 8(1). Retrieved January 25, 2021, from

Phronima sedentaria. (n.d.). Retrieved January 25, 2021, from

Phronima sedentaria. (n.d.). Retrieved January 25, 2021, from

Van Couwelaar, M. (n.d.). Zooplankton and Micronekton of the North Sea. Retrieved January 25, 2021, from

Young, L. (n.d.). A Plankton Species Straight Out Of A Horror Movie. Retrieved January 25, 2021, from

Common name: Sea Angel

Scientific name: Clione limacina

Author: Choe Stone

Photos: Special thanks to Alexander Semenov for allowing us to use his beautiful images of Clione limacina. 

Size range: 3 cm to 8 cm

Identifying features: Clione limacina are a type of pelagic sea slug, They have a unique pair of swimming wings, called peropoida, connected to the sides of their anterior at the midline. Three pairs of buccal cones (eversible tentacles without suckers), a radula and chitinous hooks are used to capture and hold prey, pulling it towards their mouths. The translucent body of these creatures show the pink or yellow couloured internal organs of the sea angel. 

Habitat: Clione limacina inhabit the cold ocean waters of the Pacific, Arctic and sub-Arctic along with some C. limacina being found in the Sea of Okhotsk, Japan. They live anywhere from the surface of the water up to 600 meters deep. 

Food: The Sea Angel feeds exclusively on the Sea Butterfly (shelled Pteropods). C. limacina use their buccal cones to drag the thecosome towards their mouth where they use their radula and chitinous hooks to pull the prey out of its shell. 

Predators: Sea Angels main two predators are Baleen whales, such as right whales, blue whales, and humpback and Oncorhynchus keta, more commonly known as Chum salmon. Baleen whales take in filtered water that has lots of different types of microscopic species, usually including Clione limacina. 

Life cycle: The sea angel is a hermaphrodite, meaning that they can become whatever sex they needed to be to mate with another C. Limacina. Mating between the angels involves cross-fertilization and results in about 20-30 fertilized eggs. The eggs are laid in a gelatinous mass where they hatch into a larval form. The larval stage of Clione limacina is a shelled pteropod. The larva’s shell is thimble shaped and it’s mouth has a ciliated ring. Once they grow out of the larval stage, the Sea Angel loses its shell and ciliated band, grows wings and elongates its body. Clione limacina live up to two years. 


Brady, H. (2017, September 20). Rare Video Shows Sea Angels’ Graceful Mating Dance. Retrieved from

Maoka, T., Kuwahara, T., & Narita, M. (2014, March 13). Carotenoids of sea angels Clione limacina and Paedoclione doliiformis from the perspective of the food chain. Retrieved from

Pteropoda by Alexander Semenov. (n.d.). Retrieved from

Wrobel, D., & Mills, C. E. (2003). Pacific coast pelagic invertebrates: a guide to the common gelatinous animals. Monterey CA: Monterey Bay Aquarium.

Brachysira – Diatom

Plankton Tow: Cadboro Bay, Victoria, British Columbia, September 18, 2019

Photo: Zoe Jennings

Hermit Crab Megalops (Pagurus sp.)

Plankton Tow: Cadboro Bay, Victoria, British Columbia, September 18, 2019

Photo: Sophie and Nele

Thalassiosira – Diatom

Plankton Tow: Cadboro Bay, Victoria, British Columbia, September 18, 2019

Photo: Riyanna 

Chaetoceros – Diatom

Plankton Tow: Cadboro Bay, Victoria, British Columbia, September 18, 2019

Photo: Chloe Stone

Hermit Crab Zoea

Photo – Darian Yap

Plankton tow:

September 18, 2019

Cadboro Bay, Victoria, British Columbia

Leuckartiara spp.

Author: D. Young

Common Name: A member in the family Pandeidae within the order Anthomedusae of the subclass Hydromedusae.

Scientific NameLeuckartiara spp.

Total Length of Specimen in photo is 3cm (30mm).

Coscinodiscus wailesii

Author: Micaela Day

Photos:  Zoe Jennings and D. Young

Common Name: Diatom

Size: Diameter is between 300um and 500um

Brief Description: This phytoplankton is apart of the Biddulphiales order and is typically considered as one of the largest marine planktonic diatom genera.

The photo below is the girdle view, viewed from the side of the diatom.

Habitat: It is commonly found in the both the Pacifc Ocean and Atlantic Ocean.  It is thought to be an introduced species to the Atlantic Ocean.  It’s ability to survive long periods in the dark suggests that it may have been introduced to the Atlantic through the emptying of ballast water from ships.

Identifying Features: Cells are solitary, and either disc-shaped, cylindrical or wedge shaped. They have numerous chloroplasts.


Kudela Lab (date unknown) Genus: Coscinodiscus | Diatom. Phytoplankton Identification Retrieved November 16, 2018 from

Hargraves, PE. (June 14, 2011) Indian river lagoon species inventory. Smithsonian Marine Station at Fort Pierce. Retrieved November 16, 2018 from


Photos by D. Young