Dicyemid sp (Rhombozoan) from Octopus rubescens kidney Common name(s): Rhombozoan
Synonyms:
Phylum Dicyemida (Rhombozoa)
	A Dicyemid nematoform adult about 1 mm long. Isolated from a kidney of Octopus rubescens.
	(Photo by: Dave Cowles, June 2026 )

Description:  Dicyemids (Rhombozoans) are a phylum of obligate symbionts (perhaps parasites) inside cephalopod kidneys. The wormlike adults occur in two forms: Nematoform adults are wormlike, with a few dozen outer cells and one long inner cell. The inner (axial) cell buds asexually to form "vermiform" embryos, which do indeed look like worms and swim actively around in the kidney. When the vermiform embryos mature they can become nematoforms or rhomboforms, which look similar to nematoform adults but are hermaphrodites which reproduce sexually. The embryos from rhomboform adults are called "infusorigen" embryos. Instead of swimming around inside the kidney they leave the host and in some unknown manner locate and infect another cephalopod individual. In the new host they can grow up to be nematoform adults.

How to Distinguish from Similar Species:  I do not know of other similar-appearing symbionts which can be found abundantly in cephalopod kidneys.

Geographical Range:  Most common in cool marine waters.

Depth Range: 

Habitat:  Inside cephalopod kidneys, especially benthic octopuses.

Biology/Natural History:  The adults tend to hang onto the kidney tissues via an "apical cap" which is inserted into the kidney tissue, but they can also swim around as seen below.

References:

Dichotomous Keys:
  Kozloff, 1987, 1996

General References:

Scientific Articles:

Web sites:

General Notes and Observations: Locations, abundances, unusual behaviors:
Other photos and movies of nematoform adults:

This photo shows several dicyemids attached to the kidney tissue.

An individual swimming. Click on this image to watch a movie of several individuals swimming.

Click here to load a short movie of several nematoform individuals swimming.

Authors and Editors of Page:
Dave Cowles (2025):  Created original page
CSS coding for page developed by Jonathan Cowles

Salish Sea Invertebrates web site provided courtesy of Walla Walla University