Identify This…Conchs and Whelks

Identify This…Conchs and Whelks By:
Ronald L. Shimek, Ph.D.

Introductions:

For the average reef aquarist, some of most easily confused and misidentified animals are the snails called either “conchs” or “whelks.” Because these names have been derived from years of common usage, mostly at fish markets, there is often good reason for the ambiguity and confusion that occurs when one tries to determine if a given snail is a “conch” or a “whelk.” Additionally, the animals comprising these two categories often look alike; in fact, sometimes they are alike: the largest whelk in the Caribbean, the giant Pleuroploca gigantea, has the common name of “horse conch.” In the reef aquarium hobby, however, the term “conch” has most frequently been used to describe herbivorous snails in species designated as belonging to the genus Strombusor its near relatives.

Stromboidean snails are algae eaters that may be quite beneficial in reef tanks, but aquarists often have problems distinguishing them from many similarly shaped, but undesirably carnivorous, whelks. This short essay is not meant to resolve all the conflicts between the snail groups described by the terms “whelk” and “conch.” Rather, this page will give the reader a couple of “quick and dirty” ways of determining whether or not a mystery snail is a stromboidean conch. The tabular information below allows the specific differentiation of stromboidean conchs from all other groups of snails, particularly those whelks having a similar appearance, and it is quite robust. If followed closely, the number of false positives (the identification of whelks as conchs) will be nil. On the other hand, the information here will be useless in determining which type of whelk, if any, is present.

A conch is defined, for the purposes of this article, as a snail in the taxonomic superfamily Stromboidea. Specifically, these are animals in the genera, Tricornis, (the Queen conch, commonly known as Strombus gigas, is probably more correctly called Tricornis gigas), Strombus (1,2,3), Lambis, and several other taxonomically related genera. There are several hundred described species in these groups.

A whelk is defined as a snail taxonomically classified in one of the groups referred to as the Muricoidea, and specifically in the families: Buccinidae, Muricidae, Fasciolariidae and Melongenidae. There are several hundred genera and, quite literally, many thousands of species in this assemblage. There are a lot of jargon terms used in snail shell descriptions, and I have tried to minimize their usage (Figure 1).

Figure 1. Basic snail shell identification terminology used in this article. The siphonal canal is essentially a continuation of the edge of the siphonal notch out into a more-or-less tubular canal.

Table 1:
Characteristics of stromboidean conchs and generalized whelks. Characters that may always be used to separate the conchs and whelks are indicated by pink rows. Characters that may sometimes be used to separate conchs and whelks are indicated by green rows.
Group: Conch Whelk
Taxonomic Group: Superfamily Stromboidea Families Buccinidae, Muricidae, Fasciolariidae, Melongenidae.
Number of Species:
Overall: ≈ 200 ≈10,000+
In Hobby: 3-10 ?? 100+
Size: Up to 40 cm (16 inches) Up to 60 cm (24 inches)
Color: Variable Variable
Shell Characteristics:
Shell Shape: Biconical, Low Spires Biconical, High and Low Spires
Aperture: Ovoid To Rectangular. Flaring In Mature Animals. Ovoid To Teardrop Shaped, To Rectangular. Generally Not Flaring In Mature Animals.
Outer Apertural Lip: Often Thickened, Often With Flaring Projections Or Spines Often Thickened, Often With “Denticles”
Siphonal Notch: Present, Often Broad Present, Narrow, “Constrained” And Elongated To Form Siphonal Canal
Siphonal Canal: Absent
Present, Often Enclosed
Soft Part Anatomy:
Body Color: Variable, Tends To Greens Or Grays Variable, All Colors, Whites, Tans, Predominate But All Other Colors May Be Found.
Siphon (= Hollow “Breathing” Tube): Short (Less Than One Shell Length) Long (Often More Than One Shell Length)
Proboscis (= Tube With Mouth At The Tip): Long, Robust Long, Slender To Robust
Eyes: Stromboidean Eye With Eyeball

Whelk Eyespot Without Eyeball

Behavior:
Locomotion: When Small = Muscular Creeping When Large = Lurching All Sizes = Muscular Creeping
Diet: Algae (Only!!) Cannot Eat Meat Carnivorous (Live Prey or Scavenger). Cannot Eat Algae or Plant Material

Examination of the above table shows that a close examination of any “mystery” whelk-like snail can easily determine if the animal is stromboidean conch that would be a beneficial algal-eating animal in reef aquarium, or if it is a predatory whelk capable of destructive predation within the reef tank. Obviously, not all characteristics are of equivalent importance, but for the ease of differentiating the “good” from the “bad,” in this case it is probably best to “Look ‘em straight in the eyes.” The highly modified “eyeball” characteristic of the stromboideans is found in no other group of benthic snails. So… if the “eyes have it,” it is a Strombus or a near relative. The presence of front edge of the shell being modified into a broad siphonal notch and the absence of a narrow siphonal canal are useful correlative characters. The lurching locomotion (also know as “saltatory” locomotion) is found in the stromboideans and a couple of other related snail groups, but never in the whelks. Finally, all whelks are carnivores or scavengers, and no stromboidean can eat meat. So, watching the animal feed will also help you confirm its identity.

References:
Abbott, R. T. and S. P. Dance. 1982. Compendium of Sea Shells, A Color Guide to More than 4,200 of the World’s Marine Shells. E. P. Dutton, Inc. New York. 410 pp.