Gastrotricha

1. Gastrotricha Chelsea Miller, Erica Caines, Emma Brown (Group 25)

2. What Are They? • Gastrotrich are divided into two orders which are  the Macrodasyida which are all marine, and the Chaetonotidae, some of which are marine and some freshwater Macrodasyida Chaetonotida

3. Gastrotricha • Includes 450 to 700 known species • Most are less than 1 mm long, although a few can reach up to 3 mm • Their body includes a head, trunk, and sometimes a tail • Gastrotricha means “hairy belly” • Body is bilaterally symmetrical, and vermiform • Body sports various combinations of spines, bristles, and scales or plates

4. Gastrotricha • Possesses a gut with a subterminal anus • Has “adhesive tubes” with glands that can be used to attach to objects • Contain a nervous system with ganglia • Does not contain a circulatory system • Adults lack a body cavity

5. Taxonomic Grouping

6. First Order: Macrodasyida • Composed of 300 species, which can be broken down into 6 families • Live in marine or brackish water • Can be distinguished from other gastrotrichs by the presence of two pores on either side of the pharynx • Body is dorsally flattened • Tubular adhesive glands at both ends of the body/on lateral surfaces • Contains cellular epidermis • Detritivores and hermaphrodites

7. Second Order: Chaetonotidae • Largest family of gastrotrichs with almost 400 species • Marine and freshwater • Classification is based on shape/external structures • Tenpin or bottle-like shape covered with a thick layer of soft cuticle • Do not have pores in the pharynx • Pathenogenetic

8. Diet Gastrotrichs are small marine flatworms that feed on other small organisms and/or materials such as: • Bacteria • Protists (like small molds, amoeba, and plankton) • Fungi • Blue or green algae • Unicellular algae • Debris or waste (they also decompose dead matter)

10. Reproduction Since there are two types of Gastrotricha. Those who are from Marine environments, and those who are from Fresh water & marine environments. They both have different mating techniques!

11. Reproduction • The Marine species are mainly hermaphrodites which means they do not have genders, so they have both male and female reproductive organs and transfer sperm into one another by a spermatophore. • There is no larval stage; they reach maturity in 2-3 days

12. Reproduction • The Fresh Water Gastrotricha are predominantly pathenogenic, which means they are all functionally female and perform asexual reproduction. • The produce two types of eggs • Eggs that take 1-4 days to hatch • Eggs that are more tough and can withstand extreme temperatures, allowing it to exist in unstable environments

13. Evolution • Evolutionary data is poor for gastrotrichs due to the difficulty in collecting and studying these microscopic soft bodied species • It is believed that the most primitive forms are possibly marine • The muscular system provides most data for evolution

14. Evolution • Gastrotricha has a distinct evolutionary line from nemotoda, but is suggested to be sister groups due to muscles • Monophyly, or clade, supported by the morphological and molecular analyses of the 18S rRNA sequences • Ancestors are believed to be the flatworm, fluke, tapeworm and ribbon worm

15. Facts • Gastrotrichs live in small, marine, brackish, and freshwater environments • The population density of Gastrotrichs in freshwater habitats may reach over 150 individuals per 10cm². •  live on and between particles of sediment or on other submerged surfaces, but a few species are terrestrial and live on land in the film of water surrounding grains of soil • The name "gastrotrich" comes from the Greek word for stomach