One Of These Snails Is Not Like The Others – Helicinid Snails

The Mindo Proserpinid Snail, the only one I'd ever seen.

The Mindo Proserpinid Snail, the only one I’ve ever seen. Photos taken with my cell phone, cropped and set as a series of three. I wish I’d taken proper photographs of it! I don’t know how many photos of the live snails exist, but based on my searches – there are not many.

I contacted Bram Breure, a Neotropical snail specialist several days ago to see if I could get an ID for my unusual Helicinid. He could only confirm it as a helicinid, so he kindly asked Dr. Ira Richling (she has studied them in the Caribbean and in Costa Rica) for her opinion.

He shared my photo in his snail blog with the information she provided him. Awesome!

It was through his blog that I found photos of unusual snails with mantles covering their shells…something I was sure I was seeing in my photos, but had never seen elsewhere or ever before in person (except for this one time) so, it was nice to have that confirmed.

His blog post about my snail is here.

Dr. Ira Richling -“the most likely match I came up with would be Proserpinella cousini (Jousseaume, 1887), now perhaps better in the genus Archecharax”.

The really interesting, completely unfamiliar aspect of this snail was the fact that the mantle overlaps the shell. The mantle produces the calcium carbonate that composes the shell, and usually isn’t visible, or only partially visible – it is hidden by the shell itself. It reminds me of the nail matrix in a finger, slowly but surely pushing new, hardened material for protective cover. In the series of photos above, the shell of my unusual snail can be seen just below the very thin mantle that covers it. It glitters similarly to the rest of the snails body. I remember thinking the snail was strange when I’d seen it, I must have wondered what was going on with the body, but it actually didn’t dawn on me that what I was looking at was something I could have never really imagined. I knew of slugs with shells underneath their thicker mantles, but never thought that a proper snail would have such a large shell beneath that and especially that it would be so clearly visible.

I have only seen one other helicinid snail in Mindo, a very unusual looking animal that was my initial introduction to a gastropod family that is not even closely related to the typical terrestrial snails we have encountered in the past, and of which are quite abundant in Mindo, where the forest close to the earth is usually cool, damp and shady. Unlike the more common terrestrial snails, the helicinids have gills rather than lungs. They are most closely related to marine snails, and historically were one of the first snails to adapt to life above the water. Many helicinids have an operculum, a hardened protein structure that serves as a protective lid, or trap door. It is more commonly found in sea snails or freshwater snails rather than the terrestrial types.

Helicinidclosed

The disk-shaped operculum, pulled back into the aperture (the opening of the shell of the snail). This disk acts as a protective barrier. This snail was very shy, retreating for many minutes, usually coming out as soon as it was sufficiently dark.  In this photo, the periostracum is seen as the colored coating on the exterior of the shell – this coating is worn down by the operculum as the snail goes about its everyday activities, exposing the calcareous part below. The apex(the tallest point of the shell) is also lacking a good coat.

Helicinidopen

The snail slowly emerges – it does so very cautiously, zipping back inside the shell if a slight bump or bright light surprises it.

When the snail is active and crawling about, the operculum rests on the back of the snail (the dorsal side of the foot) just below the bulk of the shell. If threatened, the snail quickly pulls its body back into the shell, drawing the operculum neatly against the opening of the shell.

Snail belonging to the family Neocyclotidae, perhaps of the genus Poteria.

This snail belongs to the family Neocyclotidae. I previously had this snail in the family Helicinidae, but Bram Breure provided me with new information: “This is a group with several similar looking genera/species complexes in this region, for which even a preliminary identification would be unjustified on the basis of this picture alone. But you are correct that both families have opercula.” I asked how one would tell the two apart on a superficial level and he replied: Generally helicinid don’t show an umbilicus and cyclophorids usually have a large one. There are of course more differences, but – apart from size: h’s are smaller than c’s – this may be very obvious at first sight. Helicinids are usually found on trees, cyclophorids are ground-dwelling.” Thank you Bram! 🙂

There other most obvious difference to me was the placement of the eyes on the head and the rather pointed tentacles. Cartoonish, simple black eyes sit on the sides of the snails head. I have no idea how good their vision is, but it is definitely sufficient for telling when it is night or day (these snails are very active during the night!). The typical terrestrial snail I’ve seen throughout my life has four knobby tentacles, the larger of which are tipped with a simple eye, which is also a darkened spot. Apparently these types of snails have the most advanced gastropod vision, likely being able to see large shapes, albeit quite blurry, since they cannot focus their vision.

The typical snail one sees, also a Mindoan animal. These snails are quite large and active.

The typical snail one sees, also a Mindoan animal. These snails are quite large and active.

Mindo has a number of interesting snails – some are enormous, the largest species I have yet to see. Some are small, with incredibly delicate shells that are somewhat translucent due to their thinness. Others have elongate ones, ‘hairy’ ones, and colorful ones. It has always been fascinating for us to see what snails are up to, and when. They turn up in surprising places, in interesting population densities and can even be predatory. The ‘typical’ snail in the above photo seemed very keen on my finger, stretching its head out to incredible distances just to gulp at with its radula (sort of like teeth, set in rows that scrape and rasp) – perhaps it is a predatory type? I wasn’t too eager to find out!

Another large snail, a pulmonate variety.

Another large snail, a pulmonate variety.

Septimo-27

A near caricature of different pulmonate snail, abundant along the streams. These ones seem to have the extremely light, delicate shells that miraculously don’t suffer breaks too often. The eye stalk ends are so round! His name must be Gary! 😉

It is incredible to me all that a single patch of cloud forest can sustain – and that a universe of wondrous snails is a vital part of it! We never tire of exploring every inch. Aside from all the other forms of life to be found, from large mammals, colorful birds and massive spiders, snails like this are the reason you keep coming back.

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One response to “One Of These Snails Is Not Like The Others – Helicinid Snails

  1. Greetings estimated
    Interesting pictures greetings and especially the discovery and observation of terrestrial molluscs of Mindo, a place I have visited a lot in terms of making inventories of this group investigated a decade in Ecuador becomes more and had not seen the species . Congratulations on finding could tell me more precisely the area meeting.You can see my Ecuadorian page molluscs http://mangelsnail.blogspot.com/
    Prof. MCorreoso

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