Turrid

Turrids are a diverse group of predatory sea snails. They are marine gastropod mollusks that live in oceans across the entire world. These animals inhabit every sea, from the cold poles to the warm tropics. They live in many different environments, from shallow coastal zones to the deep ocean. Some species have been found at depths exceeding 8,000 meters. For example, *Xanthodaphne levis* was collected in the Bougainville Trench at depths between 7,974 and 8,006 meters. While they live everywhere, most species prefer the neritic zone, which is the relatively shallow part of the ocean.

These snails are active carnivores that use specialized tools to hunt. Most species possess a poison gland to help them catch prey or defend themselves. They use this gland alongside a toxoglossan radula to hunt animals. Their prey often includes invertebrates, such as polychaete worms, but they can also prey on vertebrates. The radula is a structure used for feeding. In many turrids, the radula has only two or three teeth in a row. These teeth lack lateral teeth. The marginal teeth are of the duplex or wishbone type. These teeth do not come from two separate pieces. Instead, they grow from a flat plate. They form by thickening at the edges and elevating the rear edge from the membrane. Some turrids have actually lost both the poison gland and the radula.

Looking at a shell can reveal many details about a turrid. Most of these shells are quite small, often under 2 cm in height. However, adult shells can vary in size from 0.3 cm to 11.4 cm. The shells generally have a fusiform shape, which means they are spindle-shaped. The whorls of the shell can be broadly conical or elongate. The surface sculpture on the shells is very diverse. Some shells have axial sculpture or spiral sculpture. Others may be beaded, nodulose, striate, or reticulate. A very important feature is the aperture, which is the shell opening. The aperture often has a V-shaped indentation called a sinus or notch. This is located on the upper end of the outer lip. It is commonly called the "turrid notch." This notch accommodates the anal siphonal notch. Scientists have traditionally used the position of this notch and the shell's sculpture to classify them.

For a long time, scientists grouped these snails into one massive family called Turridae. This was once the largest family of mollusks and the largest group of marine caenogastropods. The original family contained more than 4,000 species. There were approximately 27,000 described scientific names, including both accepted names and synonyms. In some parts of the world, turrids made up more than half of all predatory gastropod species. However, researchers discovered that this large family was polyphyletic. This means the members of the group did not all share a single common ancestor. Because of this discovery, the way we classify them had to change completely.

In 2011, a major change occurred in turrid taxonomy. Researchers Bouchet, Kantor, Sysoev, and Puillandre published a new classification for the Conoidea group. They moved away from the old system to create a more accurate one. This new system was based on anatomical characters and molecular phylogeny. Molecular phylogeny is the study of evolutionary relationships using DNA. This work resolved the polyphyletic Turridae into 13 distinct monophyletic families. These families include Conorbidae, Borsoniidae, Clathurellidae, Mitromorphidae, Mangeliidae, Raphitomidae, Cochlespiridae, Drilliidae, Pseudomelatomidae, Clavatulidae, Horaiclavidae, Turridae s.s., and Strictispiridae. This new classification includes 358 currently recognized genera and subgenera.

Studying turrids has historically been a difficult task for malacologists. One reason is the massive number of taxa described at levels above the species level. The high level of species diversity also makes identification complicated. Additionally, while some species are common, many others are quite rare. Some species are known to science from only a single specimen. This rarity makes it hard to gather enough data for study. One of the most important collections of these snails is in the Academy of Natural Sciences of Philadelphia. This collection is so complete because of the specialized work of Virginia Orr Maes. She was an American malacologist who lived from 1920 to 1986.

Understanding turrids helps us understand the complex systems of marine life. They represent a huge portion of the predatory snails in our oceans. Their evolution of specialized hunting tools, like the poison gland and unique radula, shows how marine life adapts to survive. By studying their DNA through molecular phylogeny, scientists can better map the history of life in the sea. The transition from one large, incorrect family to 13 correct families shows how science constantly improves. As we find more species in deep trenches or rare habitats, our map of the ocean's biodiversity grows more detailed.