Class Myzostomida

Edison LucianoZOO 11 YZ-1L

Phylum Annelida

The name "myzostomid" comes from the Greek myzo, meaning "to suck," and stoma, meaning "mouth.“

Class Myzostomida

Evolution and Systematics

Early assignments of myzostomids• Trematoda (Platyhelminthes)• Crustacea (Arthropoda)

Because they exhibit characters such as:

• parapodia with chaetae• trochophore-type larvae• segmentation (although incomplete)

Now classified as a family of Polychaeta or as a class of Annelida.

Class MyzostomidaPhysical Characteristics• minute, soft-bodied marine worms associated with echinoderms

• body consists of an anterior cylindrical introvert (also called a proboscis) and a flat, disk-like trunk

• there are usually five pairs of parapodia, located lateroventrally in two rows

• most species have four pairs of slit-like or disk-like lateroventral sense organs, commonly named lateral organs

Myzostoma cirrifera morphology

Class Myzostomida

Distribution Myzostomids are found in all oceans from shallow waters to depths of over 9,840 ft (3,000 m). Most occur in tropical waters, but a few are found in the Arctic and Antarctic Oceans.

Habitat

These marine animals live in association with echinoderms.

Class Myzostomida

Behavior

Most species (90% of myzostomids) are ectocommensals of crinoids, but a few are parasites of crinoids, asteroids, or ophiuroids, infesting their gonads, coelom, integumental, or digestive systems.

Feeding ecology and diet

Very few myzostomids feed on host tissues or coelomic fluid, most feed on particles that they divert from the host using their introvert.

Class Myzostomida

Reproduction

Most are hermaphroditic even though the male genital system develops a bit earlier than the female genital system during organogenesis.

Takes place by the emission of spermatophores followed by the intradermic penetration of sperm cells.

Contact between the two individuals is very brief and they separate quickly after mating.

Class Myzostomida

Where is the myzostomid?

Myzostoma fuscomaculata on its host the crinoid Tropiometra carinata

Class Myzostomida

Thank You So Much!