- Cnidaria -

Epizoanthus sp.

Cnidaria (Phylum) > Anthozoa (Class) >

Hexacorallia (Subclass) > Zoantharia (Order) >

Epizoanthidae (Family)

The animal shown here is an cnidarian called a

zoanthid. Zoanthids superficially resemble the

anemones (Order Actiniaria) but are generally

colonial, with multiple polyps arising from shared

tissue on the substratum. This animal is most likely

Epizoanthus sp. Remarkably, when encountered

in ROV video footage it appeared that this bizarre, almost hand-shaped zoanthid colony

was scuttling along the seabed. Although difficult to distinguish in this image, it is actually

an association between two species. The polyps of the zoanthid arise from their

substratum, the shell of a hermit crab. The zoanthid settles on the hermit crab, growing

as the crab increases in size. This reduces the crab’s requirement to change its shell when

it out-grows it. While the zoanthid provides extra protection to the crab, it benefits from

the crab’s ability to move, probably accessing greater feeding opportunities.

Off Tanzania this zoanthid-hermit crab association was seen at most sites. It was often

encountered in video transects and opportunistic video observations. The number of

polyps ranged from one to fourteen. At Mzia-3 a specimen was attracted to the baited

camera, this was the largest example seen in the fieldwork with fourteen polyps visible

in the photographs. It spent several hours around the bait, moving away and returning

several times over the course of the deployment. This animal is shown, along with discussion

of the identity of the crab on page 41.

Unknown zoanthid colony

Cnidaria (Phylum) > Anthozoa (Class) > Hexacorallia

(Subclass) > Zoantharia (Order)

Zoanthid colonies encrust a variety of types of

hard substratum on the deep-sea floor. Here, a

colony of zoanthids is shown covering the stalk

of the hexactinellid sponge Hyalonema sp., a rare

hard surface on the seafloor at more than 1700 m

depth. This image is a close up of the stalk of the

sponge shown on page 20.

This association was only encountered on a single occasion off Tanzania but very similar

images have been taken collected at study sites elsewhere in the deep sea.


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