Pycnogonum stearnsi

Distinguished from other sea spiders by the complete absence of eyes, chelicerae, and pedipalps. The barrel-shaped proboscis and plain white to cream coloration are additional diagnostic features. Males can be identified by the presence of ovigerous legs, which females lack. Among Pycnogonum species, the specific combination of eyelessness, proboscis shape, and northeastern Pacific distribution helps confirm identification.

Intertidal zone from mid shore to low water mark. Shelters under rocks or inside dead barnacle shells. Frequently found in close association with its prey organisms.

Northeast Pacific Ocean from British Columbia, Canada south to California, USA; also recorded from Japan. Most abundant in California.

Fluid-feeding predator of soft-bodied marine invertebrates. Prey includes sea anemones (Anthopleura sola, Anthopleura xanthogrammica, Anthopleura elegantissima, Metridium senile), hydroids (Obelia, Aglaophenia), and sea squirts (Clavelina). Feeds by thrusting proboscis into prey and sucking fluids, leaving prey flaccid but alive.

• Anthopleura sola - preysea anemone
• Anthopleura xanthogrammica - preysea anemone
• Anthopleura elegantissima - preysea anemone
• Metridium senile - preysea anemone
• Obelia - preyhydroid
• Aglaophenia - preyhydroid
• Clavelina - preysea squirt

Gonochoristic (separate sexes). Eggs released from female gonopores on legs and fertilized externally by male. Male collects eggs and presses them onto ovigerous legs, forming a large white adhering mass that he carries. Eggs hatch into swimming protonymph larvae, which undergo multiple molts through nymphal stages before developing adult proboscis and feeding morphology.

Hides under rocks and in dead barnacle shells during non-feeding periods. Males actively collect and transport egg masses. Larvae are free-swimming prior to settlement.

Specialist predator of sessile marine invertebrates in intertidal communities. Parasitoid-like feeding strategy removes prey fluids without immediate host death. Serves as prey for larger intertidal predators (specific predators not documented).

No documented economic importance. Occasionally encountered by tidepool observers and marine biologists studying intertidal communities. Not harmful to humans.

• Other PycnogonidaeMost sea spiders possess chelicerae and pedipalps, which P. stearnsi lacks
• Other Pycnogonum speciesMany congeners have eyes or spiny body processes; P. stearnsi is eyeless and lacks spines

• marine
• intertidal
• predator
• eyeless
• direct development with larval stage
• external fertilization
• male parental care

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life