Phasmids are unicellular sensilia in the lateral tail region of certain species of nematode

Nematode

The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...

s. They are similar in their structure to amphid

Amphid

Amphids are inervated invaginations of cuticle in nematodes. They are usually found in the anterior region of the animal, at the base of the lips. Amphids are the principal chemosensory organs of nematodes. Each amphid is made up of 12 sensory neurons with ciliated dendrites....

 sensilla, but smaller. Phasmid neuron

Neuron

A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...

s were recently shown to function in modulation of chemorepulsion

Chemorepulsion

Chemorepulsion is the directional movement of a cell away from a substance. Of the two directional varieties of chemotaxis, chemoattraction has been studied to a much greater extent. Only recently have the key components of the chemorepulsive pathway been illucidated...

behavior.

The lateral caudal papillae connected with the lateral precaudal glands. Paired postanal lateral chemoreceptor sensory organs.