''Pycnogonum litorale'' is a marine
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...
in the family
Pycnogonidae, the sea spiders. It is found in the northern Atlantic Ocean, the North Sea, the English Channel and the western Mediterranean Sea.
Description
''Pycnogonum litorale'' has a head, a small slender prosome (thorax) and a tiny opisthosome (abdomen), the trunk being up to in length. The head bears two pairs of eyes and a long, tapering proboscis, and in males, a pair of slender curved appendages called ovigers, which are used in reproduction. The prosome consists of four segments, each bearing a pair of relatively long, robust walking legs which each have nine segments and terminate with a claw; the prosome is too small to house all the internal organs, so these extend into the limbs. The colour of this sea spider is somewhat variable, being yellowish, pale brown or reddish-brown. Males tend to be darker than females, individuals that have recently fed tend to be darker than those that have not, while those that have recently moulted tend to be pale.
They grow up to 25mm
Distribution and habitat
In the northeastern Atlantic Ocean and the North Sea, ''Pycnogonum litorale'' occurs from Arctic Norway southwards to the western Mediterranean Sea. It is also present in the northwestern Atlantic, ranging from the
Gulf of St. Lawrence
The Gulf of St. Lawrence () is the outlet of the North American Great Lakes via the St. Lawrence River into the Atlantic Ocean. The gulf is a semi-enclosed sea, covering an area of about and containing about of water, at an average depth of .
...
southwards to
New York State
New York, officially the State of New York, is a state in the Northeastern United States. It is often called New York State to distinguish it from its largest city, New York City. With a total area of , New York is the 27th-largest U.S. stat ...
. It is found on the sea bed, usually on rocky
substrates, where its
prey
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...
are to be found. It has been recorded from the low tide mark down to depths of about .
[
]
Ecology
''Pycnogonum litorale'' feeds exclusively on Cnidaria
Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter.
Their distinguishing feature is cnidocytes, specialized cells that th ...
, with adults feeding on sea anemone
Sea anemones are a group of predation, predatory marine invertebrates of the order (biology), order Actiniaria. Because of their colourful appearance, they are named after the ''Anemone'', a terrestrial flowering plant. Sea anemones are classifi ...
s, while juveniles feed on hydroids, such as '' Clava multicornis''. The proboscis is inserted into the prey and some body fluid is sucked out; the sea spider can be considered a parasite
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
rather than a predator, as the food source is not killed; sea anemones that are targeted include ''Actinia equina
The beadlet anemone (''Actinia equina'') is a common sea anemone found on rocky shores around all coasts of the British Isles. Its range extends to the rest of Western Europe and the Mediterranean Sea, and along the Atlantic coast of Africa as f ...
'', '' Anemonia viridis'', ''Calliactis parasitica
''Calliactis parasitica'' is a species of sea anemone associated with hermit crabs. It lives in the eastern Atlantic Ocean and Mediterranean Sea at depths between the intertidal zone and . It is up to in size, with up to 700 tentacles, and is ...
'' and '' Metridium dianthus''.[ The green shore crab (''Carcinus maenas'') feeds on sea spiders, but avoids ''Pycnogonum litorale'' because it produces two hormones (]20-Hydroxyecdysone
20-Hydroxyecdysone (ecdysterone or 20E) is a naturally occurring ecdysteroid hormone which controls the ecdysis (moulting) and metamorphosis of arthropods. It is therefore one of the most common moulting hormones in insects, crabs, etc. It is als ...
) which disrupt the crab's ecdysis
Ecdysis is the moulting of the cuticle in many invertebrates of the clade Ecdysozoa. Since the cuticle of these animals typically forms a largely inelastic exoskeleton, it is shed during growth and a new, larger covering is formed. The remna ...
(moulting).[
The sexes are separate in this sea spider, and reproduction occurs between spring and autumn. The process is initiated by the male clinging to the female above her head, which stimulates her to expel her eggs from orifices at the base of her legs. The male scoops these up with his ovigers, fertilises them and secures them to his underside. Here he broods them for about three weeks until they are ready to hatch. The protonymphon-type ]larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
The ...
e have three pairs of legs, and will develop a fourth pair at metamorphosis
Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...
.[
]
References
{{Taxonbar, from=Q1637860
Pycnogonids
Animals described in 1762