Aisha Muhammad

Phylum Gastrotricha

                                   “Stomach Hair” or “Hairy Belly”

General Characteristics

o   Aquatic worms

o   Cilia on ventral surface of head and trunk

o   Bilateral symmetry

o   Forked tail for toes/feet

o   Acoelomate

o   Complete gut with anus

o   Cuticle with numerous scales and spines

o   Nervous system with ganglia

o   No circulatory system

o   Marine or freshwater habitats

o   Range 0.5mm to 4mm in size


Are Gastrotrichs important?

To most people, Gastrotrichs probably seem unimportant. However, to aquatic systems they are very important. Gastrotrichs consume various bacteria, microalgae and protozoans; and serve as food for larger organisms. Gastrotrichs also play a vital role in researching the origin of pseudocoelomates, the history of life and the connectedness of organisms.




The Phylum Gastrotricha is made up of 765 species. Organisms in the Phylum Gastrotricha can be identified easily by their defining characteristics. Like their name suggests, the Gastrotrichs appear to have a “hairy belly”. Their ventral surface is covered in cilia especially the head and trunk. The four tufts of beating cilia on the head pull in organic matter for the animal to consume. Their bodies are elongated and flattened and have a forked tail for the toes/feet. They have adhesive tubes that aid in attaching to vegetation or other substrates. Depending on the species, Gastrotrichs can have anywhere from 2-250 adhesive tubes. Gastrotrichs are functionally acoelomate; but have a complete gut. They have no gas exchange or circulatory systems; although some species have protonephridia. Gastrotrichs have a nervous system comprised of a small brain (ganglia) and a pair of longitudinal nerve cords.



Life cycle and Reproduction

Members of the Phylum Gastrotricha are either female only or hermaphrodites. Freshwater species tend to be all female. They produce a tough egg that will experience such conditions as drought or excessive heat or excessive cold in order to hatch. This is so the species will be able to survive in an unstable environment. A second egg type will hatch almost immediately which will be a small Gastrotrich.

Marine species tend to be hermaphrodites with only one set of gonads functional at a time (meaning that each individual is either functionally male or functionally female). A functional male Gastrotrich transfers sperm to a functionally female Gastrotrich via a spermatophore.

There is no larval stage. The young hatch out and feed and grow quickly and may reach sexual maturity in as little as 2 days. The average life span of a Gastrotrich is very short, about 3 to 21 days.




The exact taxonomy of the Phylum Gastrotricha is as follows:

o  Kingdom: Animalia

o  Subkingdom: Eumetazoa

o  Superphylum: Platyzoa

o  Phylum: Gastrotricha


Under the Phylum Gastrotricha, there is the Class Gastrotricha and there are two Orders, both with seven Families:

o  Order Macrodasyida (310 species)

·          Family Dactylopdolidae

·          Family Lepidodasyidae

·          Family Macrodasyidae

·          Family Planodasyidae

·          Family Thaumastodermatidae

·          Family Turbanellidae

·          Family Xenodasyidae

o  Order Chaetonotida (455 species)

·          Family Chaetonotidae

·          Family Dasydytidae

·          Family Dichaeturidae

·          Family Neodasyidae

·          Family Neogosseidae

·          Family Proichthydidae

·          Family Xenotrichulidae


The above organism is Dactylopodola agadasys


The taxonomy for Dactylopodola agadasys is as follows:

o   Kingdom Animalia

o   Phylum Gastrotricha

o   Class Gastrotricha

o   Order Macrodasyida

o   Family Dactylopdolidae

o   Genus Dactylopodola

o   Species agadasys


Dactylopodola agadasys has been reported in fine sediments around Macleay Island, Queensland, Australia. This species is characterized by the abundant cilia distributed around the lateral, dorsolateral and dorsal portions of the body. The head region is distinct in juveniles but indistinct in adults.





So…WHY Gastrotrichs??

When I found out that Gastrotricha meant “hairy belly” it instantly became one of my favorite Phyla. The name meaning something funny is what initially sparked my interest in these animals, and it is why I chose to do my webpage on them. As I learned more and more about them and their lifestyle I grew more and more intrigued. It amazed me that something so microscopic was not only a free living animal, but that it even had structures that humans have. When I observed a live Gastrotrich it was fascinating watching it eat and swim around so quickly. Seeing all of the cilia beating was one of my favorite things. Going into this project my knowledge of Gastrotrichs was somewhat limited, but I’ve learned tons of awesome information.







work cited


o   Ramel, Gordon. The Phylum Gastrotricha. The Gastrotrichs (Phylum Gastrotricha). Web. 10 Apr. 2012.



o   Todaro, Antonio. "Gastrotricha Overview." Gastrotricha Homepage. Antonio Todaro. Web. 11 Apr. 2012. <>.



o   "Gastrotricha." - New World Encyclopedia. Web. 10 Apr. 2012. <>.

o   Hochberg, Rick. "STRI - Office of Bioinformatics - Metas." Smithsonian Tropical Research Institute-obio Root. Rick Hochberg. Web. 10 Apr. 2012. <>.



o   Wxfix. "Gastrotrichiae." YouTube. YouTube, 04 Dec. 2007. Web. 13 Apr. 2012. <>.



o   "Smithsonian Tropical Research Institute-Dactylopodola Agadasys." Smithsonian Tropical Research Institute-obio Root. Web. 10 Apr. 2012. <>.


o   Any information not from the cited locations above was from the lecture notes given in class.