Eggs of Arion vulgaris are laid in clutches. Each egg is 3 mm in diameter. There are 45 eggs in this clutch and dimension of this clutch is 21 mm × 18 mm. This is a fresh clutch laid in the same day as the photo was taken.
Arion vulgaris is an important pest in agriculture and it is quite a big slug. It can reach up to 12 cm. It is widely distributed through the Europe. I think, it could be more widely used as a model organism at least in education about basal anatomy of slugs. Despite that, I found no many photos of its anatomy. It is probably because of this species is not usually necessary to be dissected for identification. When some anatomy photos are available, then they are depicting only a part of the reproductive system dissected from the body of the slug and/or they are black-and-white only.
I have briefly dissected the slug: I have removed the body wall (with ovotestis (=glandula hemaphroditica) and with a part of hepatopancreas also accidentally removed) and I have kept the head undissected in detail. This specimen comes from Olomouc, the Czech Republic and I have collected and dissected it on the 11th August 2011.
There are visible the following structures of the reproductive system:
atrium. Atrium is short in comparison of Arion rufus.
oviductus. There should be a ligula within the oviductus that is an identification character of this species, but the ligula is not visible on the photo here, because I did not cut the wall of oviductus.
ductus hermaphroditicus (white thin meandering like tube)
glandula hemaphroditica and hepatopancreas. Part of hepatopancreas and probably the whole glandula hemaphroditica is accidentally removed from this dissected slug.
There is also visible tube like digestive system and glandulae mucosae:
oesophagus comes from the frontal part and is contected to the hepatopancreas
intestine comes from hepatancreas back to frontal part and it ends with anus, that is not visible here.
References and further reading:
(in Czech) Horsák M., Juřičková L., Beran L., Čejka T. & Dvořák L. 2010: Komentovaný seznam měkkýšů zjištěných ve volné přírodě České a Slovenské republiky. [Annotated list of mollusc species recorded outdoors in the Czech and Slovak Republics]. – Malacologica Bohemoslovaca, Suppl. 1: 1–37.
(in Russian) ГУРАЛЬ-СВЕРЛОВА Н. В. & ГУРАЛЬ Р. И. [Gural-Sverlova N. V. & Gural R. I.] 2011: Морфологические, анатомические и поведенческие особенности слизней из комплекса Arion lusitanicus (Arionidae) на западе Украины. [Morphological, anatomical and behavioural peculiarities of the slugs from the Arion lusitanicus complex in Western Ukraine]. – Ruthenica. 21(2): 97-111.
(in Polish) Riedel A. & Wiktor A. 1974: Arionacea. Ślimaki krążałkowate i ślinikowate: Gastropoda, Stylommatophora. Fauna Polski 2, Warszawa. 141 pp.
Pharynx (as one of frontal parts of the digestive system of gastropods) in number of carnivourous gastropods can be everted to draw the prey easily into the predator’s body.
Arion vulgaris is omnivorous and it is not known to evert its pharynx during feeding (as far as I know). This photo of Arion vulgaris shows the dead or nearly dead specimen with buccal mass everted out of the body . I am not sure what exactly has stimulated to this specimen to evert its pharynx, but I think that it was caused by some deadly conditions such as drowning in water with mucus.
The buccal mass consist of mouth and buccal cavity (=pharynx). Mouth has lips. There are visible lips on the the photo (the left part of the white extended part). Behind the lips there is oral tube (not visible on this photo) leading to the buccal cavity (=pharynx, the right part of the white extended part). Inside the buccal cavity there is the jaw, the radula sac containing the cartilaginous odontophore and the radula on the odontophore (all of them are hidden inside the pharynx). The radula sac can be seen on the posterior part of the buccal cavity (on the top righ of this photo), but I do not know exactly how much is the radula sac extended into the buccal cavity.
The head of this slug is dirty dark brown in color. I think, that there is also visible frontal part of the oesophagus, that starts normally on the dorsal part of the buccal mass. Oesophagus is visible in light brown-reddish color before the frontal part of the head.
The slug has also two ducts from salivary glands leading to the buccal mass. They are on sides of the oesophagus, but they are not visible on the photo and I have not find these ducts on this specimen. There should be also buccal retractor, but I was unable to identify that muscle also.
This photo shows main parts of the digestive system of gastropods, that are responsible for reception of the food.
Arion vulgaris is a serious agricultural pest in Europe. It is a hermaphroditic slug. They have gonad in male phase before and during mating. During the mating they “think”, that the other slug is female and they will exchange sperm reciprocally. Later, some time after mating, they will get to female phase, they will produce ova and they will use received and stored sperm to fertilize its ova.
That is not in ideal circle on the photo, because I have disturbed them to move them into glass to take photos.
Reproductive system is usually important in determination of species. There were usually black and white drawings of reproductive system of gastropods in scientific literature. Only sometimes there are photos of reproductive system in newer publications. I found no photos of reproductive system of Arion species on the internet.
End of visceral mass removed from tail end on the body of the slug. There are not parts, that could be useful in species identification in this photo. It shows hepatopancreas and ovotestis. The hepatopancreas is that brown mass. Maybe it shows the whole hepatopancreas, but I am not sure, because the whole part on the photo is roughly torned off the rest of the body. The grey part is ovotestis.
The most important part of the reproductive system in hermaphroditic pulmonate slugs is ovotestis (= gonad, = hermaphordite gland). Ovotestis consist of some lobes. Each lobe consist of number of acini. The ovotestis of Arion vulgaris (as far as I can see) has five lobes. Ovotestis produces sperm (spermatogenesis) in male phase and it produces ova (ovogenesis) in female phase. I do not know in which phase the ovotestis is on the photo. I think that it should be possible to identify histologically, but I do not know, if it is possible to identify macroscopically. Spermatozoa grows in the inner part of each acinus. Oocytes grows in cortex of each acinus.