Tuesday, October 02, 2012

Horn Shells & Creeper Snails (Phylum Mollusca: Superfamily Cerithioidea) of Singapore

Horn shells are snails with a long and pointed spire (much like a horn) from the superfamily Cerithioidea. Many horn shells are found on sandflats or mudflats, creeping slowly over the substrate feeding on the algae or detritus (tiny decaying particles), and hence they are often called creeper snails as well. Many of the bigger species are collected for food by human.

As they are mostly gregarious and very numerous, horn shells play an important role in the ecosystem by feeding on the algae and detritus, so that our shores will not be overpopulated with algae, and not flooded with decaying matter. Also because they are so numerous, it is important that shore visitors stick to the trails and walk with care, so as to reduce damage done to these shells.

While some of the more commonly seen species are easy to recognise, it is often hard for amateurs like me to differentiate members of the different families. I have learned a bit from our malacologist, Siong Kiat, hence I have decided to share what I have learned from him, and also the materials I have read from books and online here.

Three families of horn shells are commonly seen in Singapore - Cerithiidae, Batillariidae and Potamididae. They can be differentiated by looking at the aperture (i.e. the mouth of the shell). You may want to take a look at my diagram on the parts of a snail's shell if you are not familiar with the names of the parts, so as to better understand the terms used below.

Members of the family Cerithiidae has a long and open siphonal canal at the front end extending from the aperture. The operculum is not circular as those of other horn shells, and is marked by a rapidly expanding spiral pattern. The middle of the spiral is not in the centre of the operculum.

Members of the family Batillariidae have a short and encircled siphonal canal. The operculum is circular and marked very tightly with concentric circles on the surface

Members of the family Potamididae have a very reduced open siphonal canal. The operculum is usually circular and marked with concentric circles spaced further apart compared to the batillariids.

In some potamidids, the siphonal canal may not even be obvious at all, being very short and enclosed by an extension of the inner lip.

And now, we will look at some of the horn shell species that I have photographed in Singapore.

Chinese Horn (Rhinoclavis sinensis)
Chinese Horn (Rhinoclavis sinensis) - From the family Cerithiidae, the Chinese Horn has a turret-like spire with spiral rows of blunt nodules. The shell is usually cream-coloured, with some dark patches, reaching about 6cm. Brown patches can usually be seen around the nodules.

Pellucid Horn (Clypeomorus pellucida)
Pellucid Horn (Clypeomorus pellucida) - Also from the family Cerithiidae, the Pellucid Horn grows to about 3cm long. It has numerous prominent axial ribs (small ridges along the sides) and is densely marked with spiral cords around the whorls. The most prominent feature, however, is a thick ridge-like bump (or varix) across the body whorl.

Pellucid Horn (Clypeomorus pellucida)
When placed horizontally, the varix of the Pellucid Horn appears like a thick ridge running over and across the body whorl.

Necklace Horn (Clypeomorus batillariaeformis)
Necklace Horn (Clypeomorus batillariaeformis) - Also from the family Cerithiidae, this snail has a less prominent varix. It can grow to about 3cm long as well.

Necklace Horn (Clypeomorus batillariaeformis)
The Necklace Horn got its common name from the spiral rows of tiny nodules.

Coral Horn (Cerithium coralium)
Coral Horn (Cerithium coralium) - Also from the family Cerithiidae, the Coral Horn (or Coral Cerith), despite the name, does not live in coral reefs. It also has spiral rows of tiny nodules - usually 3 rows per whorl, but lacks the ridge-like bulging varix seen in the Clypeomorus species above. It is about 2 cm long.

Zoned Cerith (Cerithium-zonatum)
Zoned Cerith (Cerithium-zonatum) - From the family Cerithiidae, this species is rather variable in colour, but generally, the spiral rows of nodules tend to be more spiky than those of the Coral Horn, and usually bigger about 3cm long.

Zoned Cerith (Cerithium-zonatum)
Also, the spiral rows of the Zoned Cerith may be of a different colour from the background, or different rows may come in different colour tones.

Zoned Horn Shell (Batillaria zonalis)
Zoned Horn Shell (Batillaria zonalis) - From the family Batillariidae, the Zoned Horn Shells are gregarious, and thousands and thousands of them can be seen on the shore, feeding on algae and detritus.

Zoned Horn Shell (Batillaria zonalis)
This species has a short and encircled siphonal canal and has a somewhat circular operculum marked with concentric circles on the surface. The shell has distinctive triangular patterns repeating round and up the spire. It grows to about 3cm long.

Winged Creeper (Cerithidea microptera)
Winged Creeper (Cerithidea microptera) - From the family Potamididae, the Winged Creeper is easily recognised with the wing-like outer lip. It is also important to note that the various stripes on the "wing" are yellowish or creamy in colour, but there should not be a single main pale band, as that will be a different species, Cerithidea alata, which I do not have the photos here. It is usually about 2-3cm log.

Note that the posterior canal is at the posterior tip of the outer lip is not joined to the body whorl, unlike the species below. It has three spiral rows of blunt nodules per whorl.

Cingulate Creeper (Cerithidea cingulata)
Cingulate Creeper (Cerithidea cingulata) - Also from the family Potamididae, this horn shell's outer lip's posterior end is joined to the body whorl, instead of flaring out like the previous species. It has three spiral rows of blunt nodules per whorl. The shell is about 2-3cm long.

Chut-chut (Cerithidea spp.)
Chut-chuts (Cerithidea obtusa and Cerithidea quadrata) - Also from the family Potamididae, the Chut-chuts are named as such as the locals eat the cooked ones by breaking the apex (tip of the spire) and sucking the meat out from the aperture, making a "chut-chut" sound in the process. They can be recognised by the often eroded apex (tip of the spire). The shells are about 4-5cm long.

Chut-chut (Cerithidea obtusa)
Cerithidea obtusa has a foot marked with a red or orange fringe.

Chut-chut (Cerithidea obtusa)
The anterior siphon canal is very much reduced, and like other potamidids the operculum is circular and marked with concentric circles. Both species have obvious spiral grooves (or suture).

Chut-chut (Cerithidea quadrata)
Cerithidea quadrata has a grey foot instead.

Belitong (Terebralia sulcata)
Belitong (Terebralia sulcata) - Also from the family Potamididae, mature Belitong has a thickened and flaring outer lip shells, and obvious suture. The shell reaches about 6cm long.

Belitong (Terebralia sulcata)
The round operculum does not cover the entire aperture, and the siphon canal is very short and enclosed by an extension of the inner lip, and hence does not extend out from the aperture.

Telescope Creepers (Telescopium telescopium)
Telescope Creeper (Telescopium telescopium) - Also from the family Potamididae, the Telescope Creeper got its name from its elongate cone-shaped shells - much like a telescope. The Chinese call it "coffin nails" for its conical shape. They are commonly found on mudflats and mangroves, and are sometimes collected for food, being a large shell reaching length of up to 10cm.

Telescope Creeper (Telescopium telescopium)
Looking at the underside, the columella is somewhat twisted, and the spiral ridges are fairly flat. The aperture and outer lip extend towards the anterior side.

Mud Creeper (Terebralia palustris)
Mud Creeper (Terebralia palustris) - Also from the family Potamididae, the Mud Creeper is also found in mangroves and can grow to more than 10cm long. The shell is not as wide as the Telescope Creeper, and both inner and outer lips are slightly flared. It has a deep posterior canal, and a short anterior canal slight enclosed by the flaring of the lips. Unlike most of the other horn snails which feed on algae and detritus, this species has been observed to feed on fallen leaves, with a preference for green leaves rather than dry leaves.

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Anonymous said...

very useful information, it is very helpful for our school projects on Potamididae. thank you somuch.

Anonymous said...

For the Belitong, do you mean: The round OPERCULUM does not cover the entire aperture? Just wanted to point it out in case it was a mistake. Thanks so much for the hard work that goes into your posts!

Ron Yeo said...

Thanks! Have made the correction.