- Annelida -


Segmented worms such as earthworms, ragworms and

leeches are part of the phylum Annelida. Each segment

of the annelid body contains the same set of organs, repeating

along the body.

The majority of annelid worms visible in photography off

Tanzania were polychaetes or “bristle worms”, which includes

the “ragworms” from shallow-water muddy habitats. The Polychaeta is the most

diverse class of annelids. In most polychaetes each segment supports a set of appendages

(parapodia) with chaetae, or bristles. The chaetae are visible in the larger animals seen in

photography, clearly demonstrating the repeating segments along the annelid body (see

the “squidworm” images below).

Although some are large, the majority of polychaetes are tiny. Most live within the sediment

so they are not seen in photography but the tell-tale signs of their presence, such

as tubes and burrows on the sediment surface, are often visible in seabed photographs.

Within the restrictions of the annelid body plan there is wide diversity of body shape.

Thus diversity reveals the variety of polychaete life-history strategies including predators

and suspension feeders, free-swimming pelagic animals, tube dwelling animals and

those living within the sediment. The different feeding apparatus and parapodia of some

can be spectacular when examined under a microscope.

Teuthidodrilus sp. Annelida (Phylum) > Polychaeta

(Class) > Terebellida (Order) > Acrocirridae (Family)

While many polychaetes are small and live in the sediment

or in tubes attached to hard substratum, some are

pelagic, living in the water column. One such species is

Teuthidodrilus sp., which was seen on occasions in the

water column within 10 m of the sediment.

Teuthidodrilus sp. is known as the “squidworm”

because of the squid-like appearance

of its branchiae and palps. At around 10 cm

in length it is a relatively large polychaete but

it was usually difficult to collect good images

as they drift past in the current. In the upper

image the animal was hanging motionless in

the water. The animal in the lower image was

much more actively swimming.

Calcareous tubes of serpulid tubeworms

on a rock at the seabed


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