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How to Describe a Spionid

Describing a specimen can be difficult for a beginner, but we have tried to list the characters you need to look for to ease your way through this process and to introduce some consistency.

You may find staining the worms in methyl green useful in highlighting certain features.

We start with some basic observations and measurements: colour of pigment in the live animal, number of setigers, is the animal whole, width of 5th setiger, note anything unusual about the shape, staining pattern, etc?

Now starting at the front (anterior) of the specimen, note the shape of the prostomium, presence of any tentacles, the way the prostomium fits with the next segment - the peristomium.

Prostomium Shape

Figure 1. Prostomium shapes: a. pointed; b. incised; c. rounded; d. bottle-shaped; e. bell-shaped; f with frontal horns; g. wirh small accessory horns; h. multilobed.

The next major feature to look for is the presence of gills (branchiae), the setiger they start on, their shape, arrangement, are they joined to the post-setal lobes (folds of skin which project from the parapodia just posterior to the setae)? Branchiae drop off very easily in preserved specimens, so be careful to search for any scars on the setiger which might give clues as to their presence.

Branchiae

Figure 2. Branchiae attachment: a. free; b. attached to dorsal laminae along the whole length; c. only attached to the dorsal laminae at the base.

The shape of post-setal lamellae of the notopodia is more difficult to describe but it is an increasingly important character in spionid taxonomy. The shape of these lobes changes down the body and these changes in shape are important. To observe them, it may be necessary to pull off parapodia and make permanent preparations which can be kept with the specimens. Such preparations will also help in the examination of the various setal types.

How to do a parapodial preperation

How to do a parapodial prep.

The removal of parapodia

The removal of parapodia is best accomplished with the aid of 2 pairs of fine forceps. Right-handed people would :

  1. Steady the animal with the left hand pair while seizing the base of a suitable parapodium with the right;
  2. Gently roll the animal so that the tips of the right hand forceps lie parallel to the body wall and hold as much as possible of the base of the parapodium;
  3. Move the left hand forceps close to the parapodium and then gently pull it away with the right hand pair.

Other features of the body include: whether there are folds of skin running across the dorsal part of the setiger from one setal lobe to the other, whether there are pouches running from one parapodia to the one behind it (best observed in lateral view), the shape of the pygidium (although don't worry too much if it is missing).

The final characters to look for are the setae. In certain groups of spionids the fifth setiger may be modified and have different setae from the adjacent setigers. In general you will need to note the distirbution of different types, shape and textures of setae. You will need a high power compound microscope to examine them. Note the different types of setae, their shape and any patterns on the shaft. Note the occurrence of the hooks, which setiger

Figure 3. Spionid body with lateral pouches and dorsal ridges running from one dorsal lamina across the body to another

Figure 3. Spionid body with lateral pouches and dorsal ridges running from one dorsal lamina across the body to another

they first appear on, whether they occur in the notopodia (usually seen in the posterior part of the specimen), their shape, presence of a hood (transparent covering).

There is a glossary for terms you might not understand.

Please contact us if you have any problems or questions.

Gordon Paterson, The Natural History Museum, London SW7 5BD, UK

Mike Kendall, Plymouth Marine Laboratory, Prospect Place, Plymouth, UK

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