''Clistosaccus'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of barnacles which are

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

hermit crab Hermit crabs are anomuran Decapoda, decapod crustaceans of the superfamily (taxonomy), superfamily Paguroidea that have adapted to occupy empty scavenged mollusc shells to protect their fragile exoskeletons. There are over 800 species of hermit c ...

s. It is a

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

genus, and the single

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

is ''Clistosaccus paguri'', which is found in the northern Atlantic Ocean and the northern Pacific Ocean.

Taxonomy

In his 1861 paper,

Wilhelm Lilljeborg Wilhelm Lilljeborg (6 October 1816 – 24 July 1908) was a Swedish zoologist. He is particularly known for his work on the Cladocera of Sweden, and on the Balaenoptera. Lilljeborg was a member of the Royal Swedish Academy of Sciences The Roya ...

described two new monotypic genera, ''Apeltes'' (with the species ''A. paguri'') and ''Clistosaccus'' (with ''C. paguri''), both collected from ''

Pagurus ''Pagurus'' is a genus of hermit crabs in the family (biology), family Paguridae. Like other hermit crabs, their abdomen is not calcified and they use Gastropod shell, snail shells as protection. These marine Decapoda, decapod crustaceans are omn ...

'' hermit crabs. It was not until the 1920s that

Hilbrand Boschma Hilbrand Boschma (22 April 1893 – 22 July 1976) was a Dutch zoologist and director of the Rijksmuseum of Natural History in Leiden. Boschma studied botany and zoology at the University of Amsterdam. He went to the former Dutch East Indies, w ...

pointed out these two purported species, at the time placed in separate families, were but two distinct growth stages of the same organism and united them under ''Clistosaccus''.

Description

This parasitic barnacle starts life as an internal parasite in the abdomen of its

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County * Host Island, in the Wilhelm Archipelago, Antarctica People * ...

hermit crab. After about three months a protuberance, known as an "externa", pushes its way through the abdomen, usually on the left side. This bulge is at first globular, but elongates as it grows, becoming cylindrical. The mantle opening is at one end, and the parasite is attached to the host by a short, wide stalk about two thirds of the way towards the other end. The externa is white and can grow to a length of about . Host hermit crabs include ''

Pagurus bernhardus ''Pagurus bernhardus'' is the common marine hermit crab of Europe's Atlantic coasts. It is sometimes referred to as the common hermit crab or soldier crab. Its carapace reaches long, and is found in both rocky and sandy areas, from the Arctic w ...

'', '' Pagurus pubescens'', and '' Pagurus dalli''.

Distribution and habitat

''Clistosaccus paguri'' occurs in both the northern Atlantic Ocean and the northern Pacific Ocean. In the Atlantic its range extends from the

White Sea The White Sea (; Karelian language, Karelian and ; ) is a southern inlet of the Barents Sea located on the northwest coast of Russia. It is surrounded by Karelia to the west, the Kola Peninsula to the north, and the Kanin Peninsula to the nort ...

Nova Scotia Nova Scotia is a Provinces and territories of Canada, province of Canada, located on its east coast. It is one of the three Maritime Canada, Maritime provinces and Population of Canada by province and territory, most populous province in Atlan ...

, and in the Pacific, its range extends from

Alaska Alaska ( ) is a non-contiguous U.S. state on the northwest extremity of North America. Part of the Western United States region, it is one of the two non-contiguous U.S. states, alongside Hawaii. Alaska is also considered to be the north ...

and the

Bering Sea The Bering Sea ( , ; rus, Бе́рингово мо́ре, r=Béringovo móre, p=ˈbʲerʲɪnɡəvə ˈmorʲe) is a marginal sea of the Northern Pacific Ocean. It forms, along with the Bering Strait, the divide between the two largest landmasse ...

Kodiak Island Kodiak Island (, ) is a large island on the south coast of the U.S. state of Alaska, separated from the Alaska mainland by the Shelikof Strait. The largest island in the Kodiak Archipelago, Kodiak Island is the second largest island in the Un ...

, the

Sea of Japan The Sea of Japan is the marginal sea between the Japanese archipelago, Sakhalin, the Korean Peninsula, and the mainland of the Russian Far East. The Japanese archipelago separates the sea from the Pacific Ocean. Like the Mediterranean Sea, it ...

and the

Sea of Okhotsk The Sea of Okhotsk; Historically also known as , or as ; ) is a marginal sea of the western Pacific Ocean. It is located between Russia's Kamchatka Peninsula on the east, the Kuril Islands on the southeast, Japan's island of Hokkaido on the sou ...

. Its depth range is down to about .

Life cycle

After an infective female

cyprid Barnacles are arthropods of the subclass Cirripedia in the subphylum Crustacea. They are related to crabs and lobsters, with similar nauplius larvae. Barnacles are exclusively marine invertebrates; many species live in shallow and tidal water ...

larva has settled on a suitable host, it pierces the cuticle with its antennule and injects some cells into the abdomen of the hermit crab. These develop internally, sending out root-like processes into the surrounding tissues. The parasite has no gut, but after about three months, the externa pushes through the crab's abdomen. This is essentially a reproductive structure on a stalk, with a large ovary and a brood chamber. A male cyprid larva settles on the externa and fertilises the eggs by antennule penetration, the larvae developing inside the brood chamber. Here they develop directly into cyprid larvae, missing out the nauplius stage of more typical crustaceans. The cyprid larvae are at first unisex, becoming male or female according to what role they play in the reproductive cycle. The presence of this parasite effectively sterilises the host hermit crab, the gonads do not degenerate, but they fail to produce mature eggs and sperm.

References

{{Taxonbar, from=Q6550357 Barnacles Parasitic crustaceans Crustaceans described in 1861 Taxa named by Wilhelm Lilljeborg Monotypic Maxillopoda genera