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Dissection tutorials

Snail dissection

Step 1: orient the specimen.

This is a photograph of a freshly preserved animal. Note the headHead:
The area of a mollusc's body that has the tentacles, eyes and mouth.
and tail region of the animal, as the specimen will appear different after removal of the shellShell:
A hard, inflexible, calcareous or chitinous structure that vary in size and may either completely encasing the animal, covering some part of it or be internal.
. For humane purposes, ensure that the animal is completely unresponsive to touch before initiating the dissection. See the 'getting started' section on how to relax the specimen.

  • Snail dissection step 1: orient the specimen (fig. 1)
     
    Figure 1
 
Step 2: remove the animal from the shell.

In some cases, it may be possible to remove the dead animal from its shellShell:
A hard, inflexible, calcareous or chitinous structure that vary in size and may either completely encasing the animal, covering some part of it or be internal.
using curved forceps. If this is not possible, slowly break the shellShell:
A hard, inflexible, calcareous or chitinous structure that vary in size and may either completely encasing the animal, covering some part of it or be internal.
from the apertureAperture:
The major opening of a shell that the body of the animal may be retracted.
backwards, following the whorlsWhorls:
Pleural of whorl. A whorl is a complete spiral turn/growth of the shell of a mollusc. The whorls are counted from the apex outwards.
, until the animal can be removed from the shellShell:
A hard, inflexible, calcareous or chitinous structure that vary in size and may either completely encasing the animal, covering some part of it or be internal.
intact. (It is important to retain the broken pieces of the shellShell:
A hard, inflexible, calcareous or chitinous structure that vary in size and may either completely encasing the animal, covering some part of it or be internal.
for identification purposes). A pair of needle-nose pliers may be used depending on the size of the animal’s shellShell:
A hard, inflexible, calcareous or chitinous structure that vary in size and may either completely encasing the animal, covering some part of it or be internal.
.

  • snail dissection step 2 remove the animal from the shell (fig. 2)
     
    Figure 2
  • snail dissection step 2 remove the animal from the shell (fig. 3)
     
    Figure 3
  • snail dissection step 2 remove the animal from the shell (fig. 4)
     
    Figure 4
  • snail dissection step 2 remove the animal from the shell (fig. 5)
     
    Figure 5
 
Step 3: submerge “shell-less” animal in 75% ethanol or water

Diagram showing a Helix species with the shellShell:
A hard, inflexible, calcareous or chitinous structure that vary in size and may either completely encasing the animal, covering some part of it or be internal.
removed (Figure 6) is provided to assist with the orientation of the specimen. Place the “shell-less” adult specimen in a dish with 75% ethanol or water covering it.

  • snail dissection step 3 submerge “shell-less” animal in 75% ethanol or water (fig. 6)
     
    Figure 6
  • snail dissection step 3 submerge “shell-less” animal in 75% ethanol or water (fig. 7)
     
    Figure 7
 
Step 4: uncoil snail and make an incision above the mantle skirt

Slowly uncoil the portion of the animal that was inside the shellShell:
A hard, inflexible, calcareous or chitinous structure that vary in size and may either completely encasing the animal, covering some part of it or be internal.
to expose its contents. Make an incision just above the mantleMantle:
A fleshy, membranous covering of the anterior portion of the body of a mollusc. It secretes the materials that form the shell.
skirt as indicated by the broken line in Figure 08. Be sure to make shallow incisions and angle the scissors upwards and away from the internal organs. Cut as far along the skirt as possible.

  • snail dissection step 4 uncoil snail and make an incision above the mantle skirt (fig. 8)
     
    Figure 8
  • snail dissection step 4 uncoil snail and make an incision above the mantle skirt (fig. 9)
     
    Figure 9
 
Step 5: cut along the length of the thin membrane

Cut along the dotted line as indicated in Figure 10. Avoid all internal organs/structures by only cutting the thin (transparent) membrane. Continue with the incision along the edge of the membrane all the way to the first whorlWhorl:
A complete spiral turn/growth of the shell of a mollusc. The whorls are counted from the apex outwards.
. This will expose portions of the reproductive and digestive system. Also, cut along the lines indicated in Figure 12 to expose the baseBase:
This is the lower or underside of the shell; opposite of apical.
of both systems.

  • snail dissection step 5 cut along the length of the thin membrane (fig. 10)
     
    Figure 10
  • snail dissection step 5 cut along the length of the thin membrane (fig. 11)
     
    Figure 11
  • snail dissection step 5 cut along the length of the thin membrane (fig. 12)
     
    Figure 12
 
Step 6: peel back the membrane to expose the internal organs

Peel back the transparent membrane to expose the internal organs. Continue with the incision made in Figure 12 all the way to the end of the coiled regions of the animal (portion that was retained inside the shellShell:
A hard, inflexible, calcareous or chitinous structure that vary in size and may either completely encasing the animal, covering some part of it or be internal.
). The animal may be inverted to accomplish this as indicated by the broken lines in Figure 15.

  • snail dissection step 6 peel back the membrane to expose the internal organs (fig. 13)
     
    Figure 13
  • snail dissection step 6 peel back the membrane to expose the internal organs (fig. 14)
     
    Figure 14
  • snail dissection step 6 peel back the membrane to expose the internal organs (fig. 15)
     
    Figure 15
 
Step 7: remove ovotestis from digestive gland

Slowly tease the ovotestis and the albumen gland away from the digestive gland. Both organs can be carefully separated with a pair of tweezers. Once dislodged, both systems can be separated as indicated in Figure 19.

  • snail dissection step 7 remove ovotestis from digestive gland (fig. 16)
     
    Figure 16
  • snail dissection step 7 remove ovotestis from digestive gland (fig. 17)
     
    Figure 17
  • snail dissection step 7 remove ovotestis from digestive gland (fig. 18)
     
    Figure 18
  • snail dissection step 7 remove ovotestis from digestive gland (fig. 19)
     
    Figure 19
 
Step 8: cut forward into the mantle skirt to expose the base of the reproductive system

Rotate the animal unto the side (may have to hold in hands) and cut into the mantleMantle:
A fleshy, membranous covering of the anterior portion of the body of a mollusc. It secretes the materials that form the shell.
skirt going forward, towards the headHead:
The area of a mollusc's body that has the tentacles, eyes and mouth.
. Be sure to make the incision between the ocular tentaclesTentacles:
Sensory projections on the head end of a mollusc. There are generally two pairs; upper (posterior) and smaller, lower (anterior). The upper pair bears the eyes. In many snails the eyes are located at the tips of this structure; however, in Basommatophoran snail species, the eyes are located at the base of the tentacles.
. This cut will expose the basal region of the reproductive system.

The pins can be removed from the specimen for photography or closer examination.

  • snail dissection step 8 cut forward into the mantle skirt to expose the base of the reproductive system (fig. 20)
     
    Figure 20
  • snail dissection step 8 cut forward into the mantle skirt to expose the base of the reproductive system (fig. 21)
     
    Figure 21
 
Step 9: detach the reproductive system

Gently separate the reproductive system from the digestive system. Note the genital opening in Figure 22. Make incisions along the broken lines as indicated in Figure 22. Be careful to avoid cutting through the atriumAtrium:
Opening or passage of the genitalia. OR Region for the reception of gametes.
. This incision will detach the entire reproductive system from the rest of the animal (Figure 23). Use an insect pin to gently unravel the vas deferens, bursa copulatrix, oviduct, flagellum, and penis by following the connection to each.

  • snail dissection step 9 detach the reproductive system (fig. 22)
     
    Figure 22
  • snail dissection step 9 detach the reproductive system (fig. 23)
     
    Figure 23
 
Step 10: treatment for photography

If a photograph of the reproductive system is required, the structures can be arranged and pinned as desired then fixed in place by immersion in 95% ethanol for approximately 15 minutes. DO NOT leave the reproductive structures in 95% ethanol for an extended period as dehydration and distortion will occur. The pins can be removed from the specimen for photography or closer examination.

  • snail dissection step 10 treatment for photography (fig. 24)
     
    Figure 24
  • snail dissection step 10 treatment for photography (fig. 25)
     
    Figure 25
 

    USDA Lucid