''Pycnogonum stearnsi'', commonly known as Stearns' sea spider, is a marine

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

in the family

Pycnogonidae Pycnogonidae is a family of sea spiders. Characteristics Sea spiders of the family Pycnogonidae are recognisable by their stubby legs, rough-surfaced exoskeleton and the significant reduction of cephalic appendages. Chelifores (feeding pincers) ...

. It is found on the western seaboard of North America.

Description

''Pycnogonum stearnsi'' grows to about 2.5 cm (1 in) in length. It has a head with a large

proboscis A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular arthropod mouthparts, mouthparts used for feeding and sucking. In vertebrates, a pr ...

and a segmented body. It does not have the

chelicerae The chelicerae () are the arthropod mouthparts, mouthparts of the subphylum Chelicerata, an arthropod group that includes arachnids, horseshoe crabs, and sea spiders. Commonly referred to as "jaws", chelicerae may be shaped as either articulated ...

pedipalps Pedipalps (commonly shortened to palps or palpi) are the secondary pair of forward appendages among Chelicerata, chelicerates – a group of arthropods including spiders, scorpions, horseshoe crabs, and sea spiders. The pedipalps are lateral to ...

typical of

sea spider Sea spiders are marine arthropods of the class (biology), class Pycnogonida, hence they are also called pycnogonids (; named after ''Pycnogonum'', the type genus; with the suffix '). The class includes the only now-living order (biology), order P ...

s but uses its barrel-shaped proboscis for feeding. It has no eyes or spiny processes. It has four pairs of stout walking legs tipped by claws and the male has a short additional pair of legs at the front for carrying the eggs. Its colour is plain white or cream, sometimes tinged pinkish or buff.''Pycnogonum stearnsi'' - Ives, 1883
WallaWalla. Retrieved 2011-11-22.

Distribution and habitat

''Pycnogonum stearnsi'' is found in the north-east Pacific Ocean. The range extends from

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

southwards to

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

and also includes Japan. It is most common in California, and is found from the mid shore down to low water mark. It hides under rocks or in dead barnacle shells and is often found in close proximity to its

prey Predation is a biological interaction in which 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 ki ...

, the

sea anemone Sea anemones ( ) are a group of predation, predatory marine invertebrates constituting the order (biology), order Actiniaria. Because of their colourful appearance, they are named after the ''Anemone'', a terrestrial flowering plant. Sea anemone ...

s '' Anthopleura sola'', ''

Anthopleura xanthogrammica ''Anthopleura'' is a genus of sea anemones, of the family Actiniidae. Etymology Anthopleura is Greek; anthōs, flowers and pleura, ribs. Species According to the World Register of Marine Species The World Register of Marine Species (WoR ...

'', '' Anthopleura elegantissima'', and ''

Metridium senile ''Metridium senile'', the Plumose, Fluffy, or Frilled anemone, is a species of sea anemone in the Family (biology), family Metridiidae. As a member of the genus ''Metridium'', it is a type of plumose anemone and is found in the seas off north-wes ...

''; the

hydroids Hydroids are a life stage for most animals of the class Hydrozoa, small predators related to jellyfish. Some hydroids such as the freshwater '' Hydra'' are solitary, with the polyp attached directly to the substrate. When these produce buds, ...

, ''

Obelia ''Obelia'' is a genus of hydrozoans, a class of mainly marine and some freshwater animal species that have both polyp and medusa stages in their life cycle. Hydrozoa belongs to the phylum Cnidaria, which are aquatic (mainly marine) organisms ...

'', and ''

Aglaophenia ''Aglaophenia'' is a genus of hydrozoans in the family Aglaopheniidae. Species The following 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 ...

''; and the

sea squirt Ascidiacea, commonly known as the ascidians or sea squirts, is a paraphyletic class in the subphylum Tunicata of sac-like marine invertebrate filter feeders. Ascidians are characterized by a tough outer test or "tunic" made of the polysaccharid ...

, '' Clavelina''. It feeds by thrusting its proboscis into the prey animal and sucking out fluids, leaving the animal flaccid but alive.

Biology

Individual ''Pycnogonum stearnsi'' are either male or female.

Eggs An egg is an organic vessel in which an embryo begins to develop. Egg, EGG or eggs may also refer to: Biology * Egg cell, the female reproductive cell (gamete) in oogamous organisms Food * Eggs as food Places * Egg, Austria * Egg, Switzerland ...

are released from

gonopore A gonopore, sometimes called a gonadopore, is a genital pore in many invertebrates. Hexapods, including insects, have a single common gonopore, except mayflies, which have a pair of gonopores. More specifically, in the unmodified female, it is ...

s on the female's legs and fertilised externally by the male who is standing on or under the female. The male then collects the eggs and presses them against his ovigerous legs where they adhere, forming a large white mass which he carries around.''Pycnogonum stearnsi''
Images of male with eggs. Retrieved 2011-11-22. The eggs later hatch into protonymph

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

e which can swim. These moult several times, passing through further nymphal stages before developing the proboscis and feeding method of the adult.

References

{{Taxonbar, from=Q2308031 Pycnogonids Animals described in 1883