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

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...

in the family

Pycnogonidae Pycnogonidae is a family of sea spiders. Characteristics Most sea spiders in the class Pycnogonida have appendages on the anterior end of the body called chelifores which are used for gathering food and palps which bear sensory organs. Members ...

. 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 mouthparts used for feeding and sucking. In vertebrates, a proboscis is an elong ...

and a segmented body. It does not have the

chelicerae The chelicerae () are the 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 fangs, or similarl ...

pedipalps Pedipalps (commonly shortened to palps or palpi) are the second pair of appendages of chelicerates – a group of arthropods including spiders, scorpions, horseshoe crabs, and sea spiders. The pedipalps are lateral to the chelicerae ("jaws") and ...

typical of

sea spider Sea spiders are marine arthropods of the order Pantopoda ( ‘all feet’), belonging to the class Pycnogonida, hence they are also called pycnogonids (; named after ''Pycnogonum'', the type genus; with the suffix '). They are cosmopolitan, fou ...

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 (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...

southwards to

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

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 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 sea anemones '' Anthopleura sola'', ''

Anthopleura xanthogrammica ''Anthopleura xanthogrammica'', or the giant green anemone, is a species of intertidal sea anemone of the family Actiniidae. Other common names for this anemone include green surf anemone, giant green sea anemone, green anemone, giant tidepo ...

'', ''

Anthopleura elegantissima The aggregating anemone (''Anthopleura elegantissima''), or clonal anemone, is the most abundant species of sea anemone found on rocky, tide swept shores along the Pacific coast of North America. This cnidarian hosts endosymbiotic algae calle ...

'', and ''

Metridium senile ''Metridium senile'', or frilled anemone, is a species of sea anemone in the family Metridiidae. As a member of the genus ''Metridium'', it is a type of plumose anemone and is found in the seas off north-western Europe and both the east and west ...

''; 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 t ...

'', and '' Aglaophenia''; and the

sea squirt Ascidiacea, commonly known as the ascidians, tunicates (in part), and sea squirts (in part), is a polyphyletic class in the subphylum Tunicata of sac-like marine invertebrate filter feeders. Ascidians are characterized by a tough outer "tunic" m ...

, ''

Clavelina ''Clavelina'' ("little bottle") is genus of sea squirts (the Ascidiacea Ascidiacea, commonly known as the ascidians, tunicates (in part), and sea squirts (in part), is a polyphyletic class in the subphylum Tunicata of sac-like marine in ...

''. 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 Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...

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 t ...

s on the female's legs and fertilised externally by the male who is standing on or under the female. He 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 (; 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. ...

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