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Taxonomy Tournament: Annelids
Myzostomida. This order is made up of small parasites of echinoderms, tyically of feather stars
Amphinomida. This order is made up of marine polychaete worms, such as the bearded fireworm
Which clade of animals is better?
Myzostomida
Amphinomida
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Myzostoma cirriferum
Taxonomy: Animalia, Annelida, Myzostomida, Myzostomatidae, Myzostoma, M. cirriferum
Description: M. cirrifeum are short, squat annelids with translucent bodies and prominent marginal cirri. Their parapodia have evolved into small gripping appendages, with hooks for attaching themselves to their hosts. These polychaetes only reach a few mm in diameter.
Lifestyle: Alongside all other myzostomids, M. cirrifeum is an obligate parasite of echinoderms. This species in particular is found on the crinoid Antedon bifida, which are found on the coasts of north-western Europe. After birth, the larval worm is taken by the crinoid as if it were a food particle, where they attach themselves to the host’s podia. From there, they attach to the abulacral grooves, where they form a cyst-like structure for protection. Males and hermaphoriditic individuals more around on the host crinoids
Photos by Christoph Bleidorn and aphotomarine.
Myzostomids are tiny, flattened worms commonly found on crinoids.
Most of them cling to the crinoid's arms and consume the planktonic food that comes their way. There'll be quite a lot, since crinoids use those arms to catch plankton and shuffle it down to their hungry mouth. Now there's another hungry mouth standing in the way!
Many Myzostomids are free to walk around on their host's body, but there are some who stay in one place and may even cause the crinoid to grow a protective gall around them. There are also a few Myzostomids who are internal parasites.
It has taken a long time to work out what these things actually are. At first, some 200 years ago, they were thought to be flatworms. Then they were thought to be crustaceans, and then a separate group related to water bears.
These days it looks like they're highly modified polychaete worms. There are fossil crinoids more than 300 million years old that bear the tell-tale scars of Myzostomid activity. It looks like these worms have had a very long time to adapt to their unique habitat!
...Images: Pbsouthwood/Ria Tan
"Crinoid Worm" (Myzostoma fuscomaculatum)
...an unusual species of myzostomid polychaete worm that is endemic to the waters off of False Bay in South Africa. M. fuscomaculatum live on the elegant feather star (Tropiometera carinata) and are symbiotic, feeding on the crinoid's food scraps and waste products.
Classification
Animalia-Annelida-Polychaeta-Myzostomida-Myzostomidae-Myzostoma-M. fuscomaculatum
Images: Tracey-lee and Pbsouthwood
