Pycnogonum stearnsi or Stearns' sea spider is a marine arthropod

Arthropod

An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

 in the family Pycnogonidae

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 of the family Pycnogonidae have neither of these,...

. 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

Proboscis

A proboscis is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In simpler terms, a proboscis is the straw-like mouth found in several varieties of species.-Etymology:...

 and a segmented

Segmentation (biology)

Segmentation in biology refers to either a type of gastrointestinal motility or the division of some animal and plant body plans into a series of repetitive segments. This article will focus on the segmentation of animal body plans, specifically using the examples of the phyla Arthropoda,...

 body. It does not have the chelicerae

Chelicerae

The chelicerae are mouthparts of the Chelicerata, an arthropod subphylum that includes arachnids, Merostomata , and Pycnogonida . Chelicerae are pointed appendages which are used to grasp food, and are found in place of the chewing mandibles most other arthropods have...

 or pedipalps typical of sea spider

Sea spider

Sea spiders, also called Pantopoda or pycnogonids, are marine arthropods of class Pycnogonida. They are cosmopolitan, found especially in the Mediterranean and Caribbean Seas, as well as the Arctic and Antarctic Oceans. There are over 1300 known species, ranging in size from to over in some deep...

s but uses its barrel-shaped proboscis for feeding. It has no eyes or spiny processes

Process (anatomy)

In anatomy, a process is a projection or outgrowth of tissue from a larger body. The vertebra has several kinds of processes,such as: transverse process, prezygapophysis, postzygapophysis.-Examples:Examples of processes include:...

. 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.

Distribution and habitat

Pycnogonum stearnsi is found in the north east Pacific Ocean

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

. The range extends from British Columbia

British Columbia

British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...

 southwards to California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 and also includes Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

. 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

In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...

, the sea anemone

Sea anemone

Sea anemones are a group of water-dwelling, predatory animals of the order Actiniaria; they are named after the anemone, a terrestrial flower. Sea anemones are classified in the phylum Cnidaria, class Anthozoa, subclass Zoantharia. Anthozoa often have large polyps that allow for digestion of larger...

s Anthopleura sola

Starburst Anemone

The starburst anemone, is a species of sea anemone, of the family Actiniidae. It can be found in a low tide zone below the sea level....

, Anthopleura xanthogrammica

Anthopleura xanthogrammica

Anthopleura xanthogrammica, or the Giant Green Anemone, is a species of intertidal sea anemones, of the family Actiniidae.Other common names: Green Surf Anemone, Giant Green Sea anemone, Green Anemone, Giant Tidepool Anemone, Solitary Anemone, and Rough Anemone...

, Metridium senile

Metridium senile

Metridium senile, common name the plumose anemone or frilled anemone, is a species of sea anemone in the family Metridiidae. It is found in the seas off northwest Europe and the east and west coasts of North America.-Description:...

and Anthopleura elegantissima

Aggregating anemone

Anthopleura elegantissima, also known as the aggregating anemone 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 called zooxanthellae that contribute substantially to...

, the hydroids

Hydrozoa

Hydrozoa are a taxonomic class of very small, predatory animals which can be solitary or colonial and which mostly live in saltwater. A few genera within this class live in freshwater...

, Obelia

Obelia

Obelia is a genus in the class Hydrozoa, which consists of mainly marine and some freshwater animal species and have both the polyp and medusa stages in their life cycle...

and Aglaophenia and the sea squirt, Clavelina

Clavelina

Clavelina is genus of tunicates, containing the following species:*Clavelina amplexa Kott, 2002*Clavelina arafurensis Tokioka, 1952*Clavelina auracea Monniot, 1997*Clavelina australis...

. 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

Egg (biology)

An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

 are released from gonopore

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...

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. The eggs later hatch into protonymph larva

Larva

A larva 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.