Strombidae

Lore & Background

Strombid gastropods live mainly in tropical and subtropical waters, widespread in the Indo-West Pacific, where most species and genera occur. Nearly 40 of the living species that used to belong to the genus Strombus can be found in the Indo-Pacific region. They also occur in the eastern Pacific and Western Atlantic, and a single species can be found on the African Atlantic coast. Six species of strombids are found in the wider Caribbean region, including the queen conch Aliger gigas, the goliath conch Titanostrombus goliath, the hawk-wing conch Lobatus raninus, the rooster tail conch Aliger gallus, the milk conch Macrostrombus costatus, the West Indian fighting conch Strombus pugilis, and the Florida fighting conch Strombus alatus. Until recently, all of these species were placed in the genus Strombus, but now many species are being moved into new genera.

Strombids have long eye stalks. The shell has a long and narrow aperture and a siphonal canal, with an indentation near the anterior end called a strombid or stromboid notch that accommodates one of the eye stalks. The shells of most species grow a flared lip upon reaching sexual maturity. They lay eggs in long, gelatinous strands. The genera Strombus and Lambis have many similarities, both anatomical and reproductive, though their shells show some conspicuous differences. Strombids were widely accepted as carnivores by several authors in the 19th century, an erroneous concept that persisted into the first half of the 20th century. Nowadays, strombids are known to be specialized herbivores and occasional detritivores, usually associated with shallow-water reefs and seagrass meadows. Unlike most snails, they use their pointed, sickle-shaped, horny operculum to propel themselves forward in a leaping motion. Burrowing behavior is also frequent, with smaller species such as Strombus canarium and Strombus epidromis burying themselves even after adulthood.

Reader's Guide

The family Strombidae has undergone significant taxonomic revision. For a long time, all conchs were classified in only two genera, Strombus and Lambis, a classification still found in many textbooks and websites. Based on morphological and molecular phylogenies and an extensively documented fossil record, both genera have been subdivided into several new genera by different authors. The family currently comprises 31 extant genera and 10 extinct genera. Evolutionary relationships have been studied using various approaches. One analysis identified the Strombidae as a monophyletic group based on 13 shared derived traits, recognizing at least eight distinct genera. It considered Terebellum the most primitive member, standing apart by its own set of 13 unique features. Another analysis based on nuclear histone H3 and mitochondrial cytochrome-c oxidase I genes included 32 strombid species and indicated that Strombus sensu lato was paraphyletic, supporting an earlier suggestion that it was polyphyletic. Relationships within Lambis were consistent with earlier systematics, though subgeneric classifications did not align with the new phylogeny. The study also proposed that Tricornis might be the sister group to Lambis. The character of a glazed lip showed mixed support for uniting many strombid subgenera, with some taxa lacking outer lip glazing but still clustering with those that possess it, suggesting the character might be homoplastic.

Did You Know?

• Strombids use a sickle-shaped operculum to propel themselves forward in a leaping motion.
• Strombids were once erroneously thought to be carnivores but are now known as specialized herbivores and occasional detritivores.
• The family includes 31 extant genera and 10 extinct genera.