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How To Describe A Eunicid

You should record:

  1. Where it was found
  2. If it was taken from a tube
  3. Measure the animals and record if you think its broken

Examine the animal under a low power microscope

If it is not stained record any colour pattern; if stained note any patterns of stain uptake. In some species, the cuticle is glossy or even iridescent and this will be evident whether stained or not.

Examine the prostomium and peristomium

The prostomium is a pre-oral lobe which may bear sensory organs (antennae) and feeding organs (palps). Note the number and relative length of the antennae and their arrangement on the prostomium. The antennae may originate from a a basal attachment, the ceratophore: record if this is annulated or not.

Prostomium etc...

Fig 1: the head of a Eunicida

The peristomium is an achaetous segment surrounding the mouth. It may well be annulated, giving the observer the impression that two segments are present. Some species have a pair of tentacular cirri originating from the peristomium; in animals apparently having 2 segments in this region the cirri come from the posterior segment.

Examine the parapodia and chaetae

In the case of small animals, most parapodial features will be seen under the compound microscope from a whole mount in glycerol. If the animal is larger, parapodia from the front mid and rear of the animal will need to be removed and viewed individually at high power. If the specimen is damaged, the search for a particular type of chaeta in this way can be both destructive to the specimen and time consuming. Note that chaetae are fragile; care must be taken in processing the samples.

Parapodia

Fig 2 Types of parapodia encountered in Eunicid polychaetes

For details of how to remove parapodia see How to describe a spionid.

The parapodium may then be examined by mounting it in a drop of glycerol or water and viewing it under a microscope using a minimum of a x20 objective

In examining the parapodium, note the position and structure of any aciculae as well as the form of the dorsal cirrus, which might arise from an enlarged cirrophore. The branchiae may also be observed at this stage, note their length, form and the number of filaments which are present.

In some species, the parapodia are greatly reduced. The removal of a small area of body wall, along with the limb, will assist in their observation. Make fine parallel cuts either side of the parapodium with an extremely sharp scalpel. Join the cuts dorsally and ventrally and, using 2 pairs of forceps (as above), gently ease out the cut section. In doing this, be aware that aciculae may protrude some distance into the body wall.

Examination of the jaws

Jaws

Fig 3: Jaws

Examination of the jaws is essential to the taxonomy of this group of animals. As for the chaetae, the jaws of small transparent animals may be viewed in a whole mount. Slightly larger animals may be mounted in polyvinyl lactophenol under a cover-slip ringed with a sealant such as Bioseal. The buccal musculature will often clear sufficiently for the jaws to be viewed when left at about 60ºC for 2 or 3 days,.

The simplest way to remove the jaws is shown in Figure 3. Make cut A then cuts B and C to release a flap of body wall. Pull this back to reveal the pharynx and the associated musculature. These muscles should be gently cut and the pharynx freed. Once this is done, the oesophegus is cut posterior to the musculature and pulled forwards until only attached at the lips. It is then cut away. It is transferred to a drop of liquid on a microscope slide and muscle tissue is cleared away using fine forceps or mounted needles to reveal the jaw elements. The maxillae are easily viewed but some care should be taken to extract the ventral (and often pale coloured and easily overlooked) mandibles before an enthusiastic dissection of the former is undertaken.

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