_Floscularia campanulata.* Melicerta tubicolaria.* Rotifer citrinus.* Discopus synaptae. Synchaeta baltica, S. monopus, S. apus, S. tremula,* S. longipes, S. tavina. Asplanchna girodi.* Asplanchnopus syringoides. Hexarthra polyptera. Notommata naias, N. reinhardti. Proales decipiens. Furcularia forficula,* F. gracilis, F. reinhardti, F. marina, F. neapolitana. Diglena catellina,* D. suilla, D. putrida. Pleurotrocha leptura. Distemma raptor, D. marinum, D. platyceps.* Bothriocerca longicauda. Polyarthra platyptera.* Triarthra longiseta.* Rattulus calyptus. Diurella marina, D. brevidactylus, D. brevis. Diaschiza fretalis. Euchlanis luna. Monostyla quadridentata, M. lunaris. Colurus amblytelus, C. uncinatus,* C. dactylotus, C. coelopinus, C. pedatus, C. rotundatus, C. truncatus, C. caudatus.* Mytilia tavina. Pterodina clypeata. Brachionus bakeri,* B. mülleri. Anuraea valga,* A. biremis,* A. aculeata,* A. tecta,* A. cochlearis.* Notholca striata,* N. scapha,* N. thalassia, N. spinifera, N. inermis, N. jugosa, N. rhomboidea. Seison grubei, S. annulatus. Paraseison asplanchnus, P. nudus, P. proboscideus, P. ciliatus. Discobdella nebaliae._ Thus about seventy species are recorded as marine. _Synchaeta baltica_ is truly pelagic, and contributes to the phosphorescence of the ocean. {227}Other forms again are parasitic. _Proales werneckii_ is found in _Vaucheria_, a coarse, dark green, thread-like Alga found in fresh water; and the closely allied _P. parasita_ is not uncommon in the beautiful floating green spheres of _Volvox_.[277] _Albertia_, _Drilophagus_, and _Balatro_ are parasitic on or in fresh-water Oligochaetes; the curious Seisonaceae are parasitic on _Nebalia_, a small Crustacean easily obtained in masses of whelk's eggs; the aberrant Bdelloid _Discopus_ attaches itself to the surface of the Holothurian _Synapta_. Similarly among this last Order _Callidina parasitica_ attaches itself to the limbs of the fresh-water Crustacea _Gammarus_ and _Asellus_. These are rather commensals than true parasites. The species of _Brachionus_ often attach themselves temporarily to the common water-flea _Daphnia_.