Pycnogonida, a group of Arthropoda (q.v.) the position of which is very doubtful, as it combines the characters of the Arachnids and Crustacea, Thus, though they are all marine, they possess no special organs for respiration, while they have only eight legs, an Arachnid character. The embryos, when not internal parasites, closely resemble the larva known as Nauplii (q.v.), and this suggests that they are Crustacean. It is possible that the order is a primitive one which resembles the ancestral form of both Crustacea and Arachnida. They are popularly known as Sea-Spiders; some genera, such as Nympkon and Pycnogonum, are not uncommon on the English coast.