When you see horseshoe snails, foodies may be more familiar with horseshoe cake. However, there is no direct connection between the two. In terms of shape, the horseshoe snail is more similar to the calla lily, because they both look more like "horseshoes".
Left: Calla lily (picture from the Internet), Right: Horseshoe snail (Source: Zhang Shu trunk, Institute of Oceanography, Chinese Academy of Sciences)
Horseshoe snails are mollusks. Mollusks are also collectively referred to as shellfish. When it comes to shellfish, you may first think of species with shells, such as conchs, river mussels, and scallops. But in fact, many shellfish are shellless (such as octopus, fur shells, etc.) or only have inner shells (such as squid, sea hare, etc.).
Molluscs are the second phyla of invertebrates in the animal kingdom, with traces from land to sea, from poles to the tropics, and nearly 100,000 species are known, second only to arthropod phylum.
The known molluscs can be divided into seven classes according to their body structure: fur shells (such as fur shells, etc.), crescent shells (such as Australian moon shells, etc.), polyplates (collectively known as stone turtles), diggers (collectively referred to as horned shells), gastropods (including various snails), bivalves (such as river mussels, scallops, etc.), and cephalopods (such as octopus, squid, etc.). Among them, the body of fur shellfish is worm-like, no shell, and only 1 species has been reported along the coast of China, while crescent shells have not been reported in China.
Some species of the family Horseshoe snails distributed off the coast of China (Source: Zhang Shuqian, Institute of Oceanography, Chinese Academy of Sciences)
The family Horseshoe snails belong to the mollusk phylum , gastropods , and primitive gastropods , and are one of the most primitive taxa of the gastropods. Most of the species in this family are conical or gyro-shaped, and some horseshoe snails look like ears and vary greatly in morphology. The surface of the shell of the horseshoe snail often has particles, knots or spines. Small horseshoes are less than 5 mm long, while larger horseshoes can be up to 130 mm long. The nacre inside the horseshoe snail shell is thick, and the large shell can be made into a blingbling button.
The species of the horseshoe snail family are all marine, and are an important ecological group among marine macrobenthic organisms, and the type and nature of the substrate are crucial to their lives. The habitat of horseshoe snail mainly includes rock reefs, sand or sedimentous seabeds in the intertidal zone or shallow sea, and the more common representative species are large horseshoe snail, single-tooth snail, rusty snail, snail and so on.
Horseshoe snail species are free-living taxa, and their main mode of action is to crawl with particularly wide feet, and a few species can do short swims with their swinging and extended feet.
For example, the large horseshoe snail will slowly move forward by the squirming of the foot, and during the crawling process, its 5 pairs of slender antennae swing at the edge of the shell, which is very beautiful and moving; the snail can rely on its elongated leaf-like feet to move rapidly on the surface of the beach; and those small conchs, they will use their extremely stretched leafy feet (more than 2-3 times the usual) to do a short swim in the water body, under the swing of the leaf-like feet, they march forward in an S-shape, at this time the shell top is facing upwards, and when they sink, the shell top will turn below.
Horseshoe snails mainly eat algae in rocky reefs or sediments, including green algae, red algae, brown algae and so on. Recent studies have shown that there are a large number of sediment debris in the digestive tract of the tower horseshoe snail, of which foraminifera, fungi, and prozoans are the most important taxa. Animals such as snails, on the other hand, filter the flow of water into the coat cavity through cilia to obtain organic particles in the water body.
Horseshoe snails are hermaphroditic, camp ivory fertilization, and reproductive behavior mostly occurs in the spring or at the turn of spring and summer. The eggs and sperm are excreted through the female and male reproductive tubes respectively and fertilized in seawater. Fertilized eggs adhere to reef or seaweed leaves individually or in clumps. At water temperatures of 16-17 ° C, after about 7-10 days, the fertilized eggs hatch into crawlable juvenile shells.
At present, more than 1,000 species of horseshoe snails (except fossil species) have been discovered and reported worldwide, including 10 subfamily and nearly 100 genera, mainly distributed in the Indo-West Pacific Ocean, especially in the Indo-Pacific junction. So far, many scholars in this region have investigated and studied the species of horseshoe snails in different seas such as China, the Philippines, Malaysia, papua new guinea and so on. However, most of these studies have focused on the shallow waters of the continental shelf and are less involved in deep-sea areas. In the past few decades, limited by the backwardness of deep-sea exploration equipment, China can only "look at the ocean and sigh".
In recent years, the Institute of Oceanography of the Chinese Academy of Sciences has carried out many scientific surveys on the hydrothermal area, cold spring area and seamount area of the deep sea of the western Pacific Ocean, relying on the "Science" research vessel and the "Discovery" cable-controlled submersible (4000-meter level) and tv grabs, and collected a large number of mollusks.
Wyeth rib horseshoe snail in situ, Caroline Seamount, water depth: 1332 m (Source: Zhang Shu trunk, Institute of Oceanography, Chinese Academy of Sciences)
Among them, on two seamounts near the Mariana Trench, the researchers collected two horseshoe snails with special morphological characteristics. The researchers used light microscopy and scanning electron microscopy to observe the subtle morphology of these two horseshoes, and found that they were significantly different from all known horseshoe species in terms of shell morphology, tooth and tongue characteristics, and anatomical features of the soft part. In addition, the researchers used molecular biology to analyze their affinity with other horseshoes, and the results showed that they were far-flung relatives with known horseshoe species.
Based on the above research, the researchers established 1 new subfamily- Carinotrochinae subfamily Riboshoe and 1 new genus- Carinotrochus, and named these two horseshoes as Mari ribs Carinotrochus marianaensisZhang S.Q., Zhang J.L. & Zhang S.P., 2020 and Carinotrochus williamsae Zhang S.Q., Zhang J.L. & Zhang S.P., 2020.
Among them, the Marie rib horseshoe snail lives on bamboo corals and feeds on the hydra attached to it. This is also the first time that a species of horseshoe snail has been found to feed on hydra. In addition, through fossil age calibration and molecular clock analysis, it is speculated that the taxa may have spread from shallow to deep seas during the Late Cretaceous period (about 80 million years ago).
Shells and tongues of mali rib horseshoe snail (A) and Wyeckers rib horseshoe snail (B) (Image source: Zhang Shu trunk of the Institute of Oceanography, Chinese Academy of Sciences)
Horseshoe snails play an important role in marine ecosystems and are also important materials for studying the phylogeny of molluscs. Therefore, the study of the species composition and fauna characteristics of the horseshoe snail can not only enrich the diversity of this taxon, but also provide new ideas and references for the origin, diffusion and evolution of deep-sea mollusks.
It is believed that with the continuous development of science and technology and the continuous deepening of research, more and more unknown species will be discovered and reported in the future.
Source: Institute of Oceanology, Chinese Academy of Sciences