Sea spider
Sea spiders Temporal range:
| |
---|---|
Left to right, top to bottom: Austrodecus bamberi (Austrodecidae), Colossendeis sp. (Colossendeidae), Pycnogonum stearnsi (Pycnogonidae), Ammothea hilgendorfi (Ammotheidae), Endeis flaccida (Endeinae), Nymphon signatum (Nymphonidae) | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Subphylum: | Chelicerata |
Class: | Pycnogonida Latreille, 1810 |
Order: | Pantopoda Gerstaecker, 1863 |
Type genus | |
Pycnogonum Brünnich, 1764
| |
Families | |
See text. | |
Synonyms | |
Arachnopoda Dana, 1853 |
Sea spiders are marine arthropods of the order Pantopoda[1] (lit. ‘all feet’[2]), belonging to the class Pycnogonida,[3] hence they are also called pycnogonids (/pɪkˈnɒɡənədz/;[4] named after Pycnogonum, the type genus;[5] with the suffix -id). They are cosmopolitan, found in oceans around the world. The over 1,300 known species have leg spans ranging from 1 mm (0.04 in) to over 70 cm (2.3 ft).[6] Most are toward the smaller end of this range in relatively shallow depths; however, they can grow to be quite large in Antarctic and deep waters.
Although "sea spiders" are not true
Description
Sea spiders have long legs in contrast to a small body size. The number of walking legs is usually eight (four pairs), but the family
Certain pycnogonids are so small that each of their very tiny
In total, pycnogonids have four to six pairs of legs for walking. A
The morphology of the sea spider creates an efficient surface area-to-volume ratio for respiration to occur through direct diffusion. Oxygen is absorbed by the legs and is transported via the hemolymph to the rest of the body.[12] The most recent research seems to indicate that waste leaves the body through the digestive tract or is lost during a moult.[citation needed] The small, long, thin pycnogonid heart beats vigorously at 90 to 180 beats per minute, creating substantial blood pressure. The beating of the sea spider heart drives circulation in the trunk and in the part of the legs closest to the trunk, but is not important for the circulation in the rest of the legs.[12][13] Hemolymph circulation in the legs is mostly driven by the peristaltic movement in the part of the gut that extends into every leg, a process called gut peristalsis.[12][13] These creatures possess an open circulatory system as well as a nervous system consisting of a brain which is connected to two ventral nerve cords, which in turn connect to specific nerves.
Reproduction and development
All pycnogonid species have separate sexes, except for one species that is
The larva has a blind gut and the body consists of a head and its three pairs of cephalic appendages only: the chelifores, palps and ovigers. The abdomen and the thorax with its thoracic appendages develop later. One theory is that this reflects how a common ancestor of all arthropods evolved; starting its life as a small animal with a pair of appendages used for feeding and two pairs used for locomotion, while new segments and segmental appendages were gradually added as it was growing.
At least four types of larvae have been described: the typical protonymphon larva, the encysted larva, the atypical protonymphon larva, and the attaching larva. The typical protonymphon larva is most common, is free living and gradually turns into an adult. The encysted larva is a parasite that hatches from the egg and finds a host in the shape of a polyp colony where it burrows into and turns into a cyst, and will not leave the host before it has turned into a young juvenile.[14]
Little is known about the development of the atypical protonymphon larva. The adults are free living, while the larvae and the juveniles are living on or inside temporary hosts such as polychaetes and clams. When the attaching larva hatches it still looks like an embryo, and immediately attaches itself to the ovigerous legs of the father, where it will stay until it has turned into a small and young juvenile with two or three pairs of walking legs ready for a free-living existence.
Distribution and ecology
These animals live in many different parts of the world, from
Sea spiders either walk along the bottom with their stilt-like legs or swim just above it using an umbrella pulsing motion.
Classification
The class Pycnogonida comprises over 1,300 species, which are normally split into eighty-six genera. The correct taxonomy within the group is uncertain, and it appears that no agreed list of orders exists. All families are considered part of the single order Pantopoda.
Sea spiders have long been considered to belong to the
A competing hypothesis proposes that Pycnogonida belong to their own lineage, distinct from chelicerates, crustaceans, myriapods, or insects. This Cormogonida hypothesis contended that the sea spider's chelifores, which are unique among extant arthropods, are not positionally homologous to the chelicerae of Chelicerata, as was previously supposed. Instead of developing from the
Phylogenomic studies place the Pycnogonida as the sister group to the remaining
Group taxonomy
According to the World Register of Marine Species, the order Pantopoda is subdivided as follows:[27]
- suborder Eupantopodida,[28] including the following superfamilies:
- Ammotheoidea Dohrn, 1881
- Family Ammotheidae Dohrn, 1881
- Family Pallenopsidae Fry, 1978
- Ascorhynchoidea Pocock, 1904
- Family Ascorhynchidae Hoek, 1881
- Family incertae sedis
- Bango Bamber, 2004
- Bradypallene Kim & Hong, 1987 (uncertain)
- Chonothea Nakamura & Child, 1983
- Decachela Hilton, 1939
- Ephyrogymna Hedgpeth, 1943
- Hannonia Hoek, 1881
- Mimipallene Child, 1982
- Pigrogromitus Calman, 1927
- Pycnopallene Stock, 1950
- Pycnothea Loman, 1921
- Queubus Barnard, 1946
- Colossendeoidea Hoek, 1881 (Synonyms: Pycnogonoidea Pocock, 1904; Rhynchothoracoidea Fry, 1978)
- Family Colossendeidae Jarzynsky, 1870
- Family Pycnogonidae Wilson, 1878
- Family Rhynchothoracidae Thompson, 1909
- Nymphonoidea Pocock, 1904
- Family Callipallenidae Hilton, 1942
- Family Nymphonidae Wilson, 1878
- Phoxichilidioidea Sars, 1891
- Family Endeidae Norman, 1908
- Family Phoxichilidiidae Sars, 1891
- Ammotheoidea Dohrn, 1881
- suborder Stiripasterida Fry, 1978,[29]including the following family:
- Family Austrodecidae Stock, 1954
- suborder incertae sedis,[30] including the following genera and families:
- †Palaeopycnogonididae Sabroux, Edgecombe, Pisani & Garwood, 2023
- †Flagellopantopus Poschmann & Dunlop, 2005
- †Palaeothea Bergstrom, Sturmer & Winter, 1980
- Alcynous Costa, 1861 (nomen dubium)
- Foxichilus Costa, 1836 (nomen dubium)
- Oiceobathys Hesse, 1867 (nomen dubium)
- Oomerus Hesse, 1874 (nomen dubium)
- Paritoca Philippi, 1842 (nomen dubium)
- Pephredro Goodsir, 1842 (nomen dubium)
- Phanodemus Costa, 1836 (nomen dubium)
- Platychelus Costa, 1861 (nomen dubium)
Fossil record
The fossil record of pycnogonids is scant. The earliest fossils are known from the Cambrian 'Orsten' of Sweden (Cambropycnogon), though some researchers have argued that this putative larval sea spider is not a pycnogonid at all.[26] Unambiguous sea spider body fossils include the Silurian Coalbrookdale Formation of England (Haliestes) and the Devonian Hunsrück Slate of Germany (Flagellopantopus, Palaeopantopus, Palaeoisopus, Palaeothea and Pentapantopus). Some of these specimens are significant in that they possess a longer 'trunk' behind the abdomen and in two fossils the body ends in a tail, something never seen in living sea spiders.
In 2013, the first fossil pycnogonid found within an Ordovician deposit (Palaeomarachne) was reported from William Lake in Manitoba.[31]
In 2007, remarkably well preserved fossils were exposed in fossil beds at La Voulte-sur-Rhône, south of Lyon in south-eastern France. Researchers from the University of Lyon discovered about 70 fossils from three distinct species in the 160-million-year-old Jurassic La Voulte Lagerstätte. The find will help fill in an enormous gap in the history of these creatures.[32]
References
- ^ "Pycnogonida". World Register of Marine Species. Taxon details.
- ^ "Pantopoda". Merriam-Webster.com Dictionary.: "taxonomic synonym of Pycnogonida < Neo-Latin, from pant- + -poda"
- ^ "Pycnogonida". Merriam-Webster.com Dictionary.: "New Latin, from Pycnogonum [...] + -ida"
- ^ "pycnogonid". Merriam-Webster.com Dictionary.
- ^ "pycnogonid". The Free Dictionary.
From Neo-Latin Pycnogonida, class name, from Pycnogonum, type genus.
- ^ "Sea spiders provide insights into Antarctic evolution" (Press release). Department of the Environment and Energy, Australian Antarctic Division. 22 July 2010. Archived from the original on 31 July 2018. Retrieved 27 December 2017.
- S2CID 4427443.
- PMID 25107551.
- OCLC 30544625.
- ISBN 978-1-4020-6359-6.
- ^ Phylogenomic Resolution of Sea Spider Diversification through Integration of Multiple Data Classes
- ^ S2CID 35014992.
- ^ PMID 28238655.
- S2CID 84345599.
- ^ McClain, Craig (August 14, 2006). "Sea Spiders". Deep Sea News Info. Archived from the original on 9 July 2007.
- ISBN 978-0-7167-3027-9.[page needed]
- S2CID 4400419.
- S2CID 4307398.
- ^ "Chelifores, chelicerae, and invertebrate evolution | ScienceBlogs". scienceblogs.com. Retrieved 2022-01-10.
- S2CID 6048195.
- .
- PMID 25107551.
- PMID 30917194.
- PMID 31847768.
- PMID 35137183.
- ^ PMID 32915961.
- ^ "WoRMS - World Register of Marine Species - Pantopoda". marinespecies.org. Retrieved 2023-12-04.
- ^ "WoRMS - World Register of Marine Species - Eupantopodida". marinespecies.org. Retrieved 2023-12-04.
- ^ "WoRMS - World Register of Marine Species - Stiripasterida". marinespecies.org. Retrieved 2023-12-04.
- ^ "WoRMS - World Register of Marine Species - Pantopoda incertae sedis". marinespecies.org. Retrieved 2023-12-04.
- Konservat-Lagerstätte deposit in Manitoba, Canada, is also the first reported from Laurentia. It is the only record thus far of a fossil sea spider in rocks of demonstrably shallow marine origin.
- ^ "Fossil sea spiders thrill experts". BBC News. August 16, 2007.
External links
- Data related to Pycnogonida at Wikispecies
- Media related to Pycnogonida at Wikimedia Commons
- Encyclopædia Britannica (11th ed.). 1911. .
- PycnoBase: World list of Pycnogonida
- Introduction to the Pycnogonida
- Images of Pycnogonida, and Pycnogonids in literature
- Bibliography (compiled by Franz Krapp)