The Mar Menor is a hypersaline coastal lagoon in the SW Mediterranean. A study of pycnogonids was based on 52 samples from the different benthic communities found in the lagoon, using 1001 individuals belonging to 5 species (Tanystylum conirostre, Achelia echinata, Ammothella longipes, A. appendiculata and Anoplodactylus pygmaeus), from infralittoral rock communities. Neither the meadows of Cymodocea nodosa, Caulerpa prolifera and Ruppia cirrhosa, nor the soft substrates revealed the presence of pycnogonids. All 5 species were found in the proximity of El Estacio channel (the main communication with the Mediterranean), while at sites within the lagoon only the first and last species were found. These were also the species with the highest population densities. Data about the abundance and development stages of the species, the diversity of samples and their affinity are reported. A study of the intermediary development between larva and juvenile is presented for Tanystylum conirostre.