37 o LOWER FORMS OF MARINE LIFE 



of the group. Instead of burrowing like Balanoglossus, this species lives 

 under stones, where it often makes its way through the mud at the place of 

 contact between it and the stone beneath which it is concealed. While some 

 examples have been found at extreme low tide, others occurred much nearer 

 high-water mark than is the case with any other members of the group. There 

 are several other allied genera, which collectively constitute the ordinal group 

 Enteropneusta, which forms a section of the higher group or class known as 

 Hemichordata. A second group, Pterobranchia, of equivalent rank to the Entero- 

 pneusta, is represented by two genera, Cephalodiscus, ranging from the Antarctic 

 and the Straits of Magellan to Borneo and Japan, and Rhabdopleura ; but for an 

 account of these the reader must be referred to more technical works. It may, 

 however, be mentioned that the genus Cephalodiscus has a somewhat curious his- 

 tory. It was first described in 1876 from specimens collected by H.M.S. Challenger. 

 In 1905 a new species from the Antarctic was named C. nigrescens; and in 1912 

 it was discovered that specimens collected during the voyage of the Erebus and 

 Terror under Sir James Clark Ross in 1841 or 1842, and preserved in the British 

 Museum, are apparently referable to this species. 



A third order of hemichordates, the Phoronidea, has been made 

 for the reception of the remarkable organism known as Phoronis, 

 which is, however, classed by some naturalists with the worms. Phoronis is a 

 sedentary animal living in tubes aggregated into colonies, the inhabitant of each 

 tube being, however, completely isolated from its neighbours. The largest species 

 is Ph. austrcdis, which grows to a length of six inches, and lives in communities 

 of a score or more individuals, in the substance of the outer wall of the tube 

 inhabited by and formed by a species of sea-anemone of the genus Cerianthus. 

 The mouth of the delicate transparent tube of each worm opens on to the outer 

 surface of the anemone, which thus lives alone within its own tube, where it 

 stretches forth its tentacles in all directions from its mouth above the purple 

 Phoronis living on the wall. In addition to Ph. cmstralis, a second species, Ph. 

 psanwrnophila, is found in Port Jackson, as well as in the Mediterranean. The 

 typical Ph. hippocrepis, so named from the horseshoe form of the tuft of tentacles, 

 was, however, first discovered at Ufracornbe. 



A small group of jointed marine animals, some of which, in 

 their long, slender limbs, recall harvest-spiders, form a group known 

 as the Pycnogonida or Pantopoda, and are believed to represent a very abnormal 

 section of the Arthropoda. They may be found alike under pebbles on the shore 

 between tide-marks and at comparatively great depths in the ocean itself, 

 frequently in vast numbers. The tj'pical Pycnogonidum littorale, which may 

 often be found clinging to large anemones, on which the members of the genus 

 are parasitic, is a curious-looking squat creature, with a jointed, rod-like body, 

 and four pairs of thick, jointed, and terminally clawed legs, supported on lateral 

 pedicles ; while the head terminates in a long, tubular, sucking mouth. A very 

 different type is, however, presented by Nymphon stroemii, in which the slight 

 body is carried high above the ground on long slender legs somewhat like those 

 of a harvest-spider. In the males some of the legs are shorter than the rest, and 

 are used for carrying the capsules of eggs produced by the females. 



Pycnogonids. 



