Photo of the day (74): eggs of Arion obesoductus

This is a cluster of eggs of a land slug Arion obesoductus.

It was laid by a specimen, that I captured in central Moravia at October 26, 2017. I captured only one slug and it later laid this cluster of four eggs in captivity. At least two slugs successfully developed and hatched out from these eggs.

I am not sure if there are any informations available about the life cycle of Arion obesoductus. I do not know if laying of four eggs is a rule or exception. Arion obesoductus is a small slug with a maximum body length of 25 mm. So laying clusters with small number of eggs makes sense. Otherwise these eggs looks like any other eggs of slugs from the Arionidae family as well as similar to eggs of many other land gastropods.

The cluster of eggs at December 13, 2017:
eggs of Arion obesoductus

The same cluster of eggs at December 18, 2017:
eggs of Arion obesoductus



Dangling slug Arion fuscus

I found a slug Arion fuscus dangling on its mucus thread. I found it on a waste container in the street, in Olomouc city, the Czech Republic, on the September 16, 2014. Such species usually live in woods, but it can be found in gardens too.

dangling slug Arion fuscus 2
dangling slug Arion fuscus 1

It was moving down quite fast. The difference between the first and the second photo is 20 seconds.

As we know, some snails and slugs can move down on the mucus thread like a spider on a spider thread. Such locomotion is considered to be unusual.

There is a detail of Arion fuscus cropped from the first photo:

dangling slug Arion fuscus 1 detail

Further reading:

Breure B. 2011: “Dangling snails – an update“. Bram’s snailblog.

Breure B. 2011: “Dangling snails – update (2)“. Bram’s snailblog.

Breure B. 2013: “Dangling Jamaican snail“. Bram’s snailblog.

Wiktor A. & Stawarczyk T. 2012: “AN UNUSUAL MODE OF LOCOMOTION OF AN ECUADOREAN SLUG BELOCAULUS SP. (MOLLUSCA: GASTROPODA: VAGINULIDAE)“. Folia Malacologica 19(4): 277–278. (PDF free download after free registration)

Photo of the day (17): Arion rufus

Arion rufus (Linnaeus, 1758) is a large species of slug. It has an interesting defensive behiour: when irritated it can contract to hemispehrical shape.


Some authors consider Arion rufus as a subspecies of Arion ater (Linnaeus, 1758) or as the same species as Arion ater. Arion ater has the same defensive behaviour. Other Arion species can contact their body a little, but they can not contract their body so much. If you are unsure in determination, you can distinguish Arion rufus from Arion vulgaris (Moquin–Tandon, 1855) according to this defensive behaviour.


(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.

Taylor, J. W. (1907). Monograph of the land and freshwater Mollusca of the British Isles. Testacellidae. Limacidae. Arionidae. pt 8–14. Leeds: Taylor brothers. page 168, plate XVIII.

Overview of the anatomy of Arion vulgaris

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.




bursa copulatrix


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.




glandula albuminalis


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.

Photo of the day (9): Arion obesoductus

Arion obesoductus Reischütz, 1973 is a small Arion species that lives in undistrurbed forests. Its synonym includes Arion alpinus auct. nec Pollonera, 1887. It lives in Austria, Germany, Slovenia, Croatia, Italy, Switzerland and France. It is found in Alps and around Alps, but its distribution is more wide: also in Central Europe. The first records of this species from the Czech Republic were published in 2006 under the name Arion alpinus. It is not very common in the Czech Republic, but it was found in various areas there. It was neither found in Poland, nor Slovakia and Hungary.


It is often found on mushrooms and I have found it on mushrooms also. My record comes from the forest near the Pateřín village in the Central Moravia, Czech Republic. It is spruce forest (Picea abies) with beech (Fagus sylvatica). Arion obesoductus cooccur with slugs Arion fuscus, Malacolomax tenellus and Lehmannia marginata there. It is similar to Arion fuscus, but its foot is orange:


The orange foot of Arion obesodusctus (two specimen on the right) is easily recognizable even trough plastic translucent test-tube in comaprison of Arion fuscus (on the left). The length of the tube is 58 mm.



Dvořák L., Backeljau T., Reischütz P. L., Horsák M., Breugelmans K. & Jordaens K., 2006: Arion alpinus Pollonera, 1887 in the Czech Republic (Gastropoda: Arionidae). – Malacologica Bohemoslovaca, 5: 51–55.

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.

Buccal mass of Arion vulgaris

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.


Further reading:


Photo of the day (6): Arion vulgaris – mating and ovotestis

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.

Photo of the day (5): Arion fasciatus


Arion fasciatus lives in large part of Europe in open anthropic habitats such as gardens. It is quite easily distinguishable, because it has a yellow band bellow a dark band on each side.


I have collected this slug and placed it in the terrarium (a glass) with a piece of bark. After 24 hours this slug has taken this position as is on the photo instead of trying to hide in some crevice of the bark. It was “sleeping” like this and it did not move during the the photographing, that have taken 5 minutes. That is ideal cooperation.

I do not know the length of this contracted specimen, but the extended body of this specimen is 36 mm. While this species can reach the body length up to 50 mm.