Pagurus excavatus

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Pagurus excavatus
Taxo Herbst et al. 1791

Taxo Herbst et al. 1791

Systematics
Trunk : Arthropod (arthropoda)
Class : Higher crabs (Malacostraca)
Order : Decapods (decapoda)
Family : Right-handed Hermit Crabs (Paguridae)
Genre : Pagurus
Type : Pagurus excavatus
Scientific name
Pagurus excavatus
( Autumn , 1791)

Pagurus excavatus is a hermit crab from the Paguridae family, which occurs in both the north-east Atlantic and the Mediterranean . It can be found on sediment soils at depths of up to 80 m, where itsearches forfood and suitable snail shells . Often the housing with other animals such. B.occupied sea ​​anemones that enter into a community with the hermit crab.

Appearance and characteristics

Like most hermit crabs, Pagurus excavatus has a very soft-skinned rear body that is hidden in gastropod shells for protection . It also has five pairs of walking legs ( pereiopods ), of which the first pair each having a hairless shears is fitted. The right scissors are visibly larger than the left scissors, which is typical of the Paguridae family. On the inside of the right scissors there is a high bulge in the middle, concave on both sides, which is less pronounced in smaller individuals. The remaining pairs of limbs make up two pairs of walking legs, with which P. excavatus moves, and two pairs of smaller legs, which are used to hold the snail in place. A species characteristic of the second pair of legs is the dactylus , which just exceeds the length of the propodus and carpus and is noticeably curved. P. excavatus has two pairs of antennae , the second pair being significantly longer than the first. Further features that distinguish P. excavatus from other hermit crabs are, on the one hand, the smooth appendage on the antenna base of the first antenna pair, which usually does not have any humps. In addition, there is also an extension on the second segment on the dorsal side of the second antenna base, which extends to the lower edge of the fourth segment of the antenna. The males of P. excavatus have four swimming legs ( pleopods ), which are formed in the second to fifth position. In terms of size, P. excavatus exhibits a sexual dimorphism, since the females with an average shield length of 7 mm of the carapace are smaller than the males with an average shield length of 10 mm of the carapace. P. excavatus can reach sizes up to 11.5 mm shield length.

distribution and habitat

Pagurus excavatus is found both in the north-east Atlantic and in large parts of the Mediterranean, its range includes eleven different countries. Occurrences of the species from the Bay of Biscay , the Spanish and Portuguese Atlantic coasts to Morocco and the island of Madeira have been recorded in the north-east Atlantic . In the Mediterranean, the distribution is concentrated in the western part of the basin. P. excavatus can be found there off Spain , France and Monaco , in the Tyrrhenian and Adriatic Seas around Italy , as well as off Croatia , Albania and Greece up to Cyprus and Turkey .

Pagurus excavatus lives benthically at depths between 15 and 80 meters. Sometimes individuals were also found at depths of up to 450 meters, with the animals usually staying no deeper than 80 meters. The species prefers different types of sedimentary soils on the continental shelf, with a sandy or muddy bottom and a slight slope.

Way of life

As a scavenger, P. excavatus wanders around the sediment floors in search of food. In the course of its life cycle, a new, suitable snail shell must be found regularly as a result of its growth. The availability of suitable snail shells can therefore have a significant impact on the life cycle and development of the hermit crab. Hermit crabs generally choose houses that are best suited for both their size and their individual shape. In the case of P. excavatus it is known that this species can be found in various snail shells due to its wide distribution and the locally different occurrences of gastropods. On the one hand, the Nauticarius hebraeus ( Hebrew moon snail ), as well as the shells of Bolinus brandaris ( Hercules club ), Galeopoda echinophora and Hexaplex trunculus ( blunt prickly snail ) nestle in larger shells . The choice of shells differs between adult and juvenile animals, so that juvenile P. excavatus, among others, also inhabit the shells of tower snails ( Turritella sp. ).

Reproduction

The reproduction of Pagurus excavatus takes place, as with all paguroids, through the transfer of sperm from the male to the female, encased in a spermatophore . This is done through the genital opening, which is located on the upper part of the last swimming leg. The genital opening of the males is a simple gonopore with numerous hairs, the sensory functions during copulation, such as z. B. take on better adhesion to the female and the transfer of the sperm. P. excavatus
reproductive activity lasts year round. Egg-bearing females can be found all year round, but the main spawning season is March and April. It is assumed that the females have a very long, seasonal maturation cycle. These can carry up to 1700 eggs, the number of which can vary widely depending on the size of the individual, the current environmental conditions and the availability of snail shells. Some P. excavatus females can lay eggs up to two consecutive times. As in many Crustacea genera, the gender distribution is not 1: 1 in P. excavatus , as the females are usually a little more common.

Socialization

The coexistence of hermit crabs with cnidarians is one of the most frequently observed cases of socialization in marine ecosystems. Sea anemones are the only cnidarians that are actively taken up by P. excavatus on their snail shell and do not grow on them by chance. Known species that enter into an optional association with P. excavatus are z. B. Calliactis parasitica ( parasite rose ) and Adamsia palliata ( mantle common ). In addition, other cnidarians, such as Hydractinia echinata ( spiny polyp ) and numerous protists such as z. B. Actineta tuberosa , Dendrosomites paguri and Zoothamnium sp. on the snail shells, which are also in a mutualistic connection to P. excavatus . This form of epibiosis has advantages for both partners. The hermit crab P. excavatus is better protected from predators by the nettles of the epibionts and at the same time better camouflaged. The epibionts in turn benefit from the mobility of the possibility of better geographical distribution and an increased supply of nutrients through the food remains of the hermit crab.

Individual evidence

  1. ↑ a b c d Ingle, Ray. "Hermit crabs of the northeastern Atlantic Ocean and Mediterranean Sea: an illustrated key. Vol. 4". Chapman & Hall.
  2. ↑ a b Mura, M., F. Orru, and Angelo Cau. "Reproduction strategy of the deep-sea hermit crabs Pagurus alatus and Pagurus excavatus of the Central-Western Mediterranean Sea." Hydrobiologia 557.1 (2006): 51-57.
  3. ↑ Lemaitre, R .; McLaughlin, P. (2018). World Paguroidea & Lomisoidea database. Pagurus excavatus (autumn, 1791). Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=107236 on 2018-12-29
  4. ↑ CHINTIROGLOU, CC, D. Doumenc, and D. Koutsoubas. "Allométrie d'une nouvelle association entre le Décapode Anomoure Pagurus alatus (Fabricius, 1775) et l'Actinie Acontiaire Sagartiogeton undatus (Müller, 1788)." Crustaceana 62.1 (1991): 1-12.
  5. ↑ Števcic, Z., 1990. Check-list of the Adriatic Decapod Crustacea. Acta Adriatica 31: 183-274.
  6. ↑ Cartes, Joan E., et al. "Feeding guilds of western Mediterranean demersal fish and crustaceans: an analysis based in a spring survey." Scientia Marina 66.S2 (2002): 209-220.
  7. ↑ Bertness, Mark D. "Conflicting advantages in resource utilization: the hermit crab housing dilemma." The American Naturalist 118.3 (1981): 432-437.
  8. ↑ Hazlett, Brian A. "The behavioral ecology of hermit crabs." Annual Review of Ecology and Systematics 12.1 (1981): 1-22.
  9. ↑ Koutsoubas, Drosos, Nikos Labadariou, and Athanasios Koukouras. "Gastropod shells inhabited by Anomura Decapoda in the North Aegean Sea." Bios 1 (1993): 247-249.
  10. ^ A b Macpherson, Enrique, and Núria Raventós. "Population structure and reproduction of three sympathetic species of hermit crabs in the north-western Mediterranean." Journal of the Marine Biological Association of the United Kingdom 84.2 (2004): 371-376.
  11. ↑ a b Vafeiadou, Anna-Maria, Chryssanthi Antoniadou, and Chariton Chintiroglou. "Symbiosis of sea anemones and hermit crabs: different resource utilization patterns in the Aegean Sea." Helgoland marine research 66.3 (2012): 385.
  12. ↑ Hess, Gregory S., and Raymond T. Bauer. "Spermatophore transfer in the hermit crab Clibanarius vittatus (Crustacea, Anomura, Diogenidae)." Journal of Morphology 253.2 (2002): 166-175.
  13. ↑ Fantucci MZ and Mantelatto FL (2011) Male reproductive apparatus and spermatophore morphology of the hermit crabs Pagurus brevidactylus and P. criniticornis (Anomura, Paguridae). Journal of Morphology 272, 1271-1280.
  14. ↑ Tudge, Christopher, and Rafael Lemaitre. "Studies of male sexual tubes in hermit crabs (Crustacea, Decapoda, Anomura, Paguroidea). I. Morphology of the sexual tube in Micropagurus acantholepis (Stimpson, 1858), with comments on function and evolution." Journal of Morphology 259.1 (2004): 106-118.
  15. ↑ a b Williams, Jason D., and John J. McDermott. "Hermit crab biocoenoses: a worldwide review of the diversity and natural history of hermit crab associates." Journal of experimental marine biology and ecology 305.1 (2004): 1-128.
  16. ↑ a b Gusmão, Luciana C., and Marymegan Daly. "Evolution of sea anemones (Cnidaria: Actiniaria: Hormathiidae) symbiotic with hermit crabs." Molecular Phylogenetics and Evolution 56.3 (2010): 868-877.
  17. ↑ Brooks, William R. "Hermit crabs alter sea anemone placement patterns for shell balance and reduced predation." Journal of Experimental Marine Biology and Ecology 132.2 (1989): 109-121.