220 The Sarcodina 



inorganic materials such as calcium salts. Binuclearity and multinuclear- 

 ity are not uncommon. 



The group is usually divided into five orders: (1) Proteomyxida, which 

 often develop slender filopodia, sometimes delicate ones which super- 

 ficially resemble axopodia; (2) Mycetozoida, plasmodial organisms, which 

 move primarily by protoplasmic flow, and certain other types which de- 

 velop a pseudoplasmodium; (3) Amoebida, naked forms which usually 

 show lobopodia; (4) Testacida, which have a simple test and may form 

 filopodia or lobopodia in different genera; (5) Foraminiferida, which have 

 either a simple or a multi-chambered test and typically develop myxo- 

 podia. 



Order 1. Proteomyxida 



This order is not clearly defined and the interrelationships of the 

 families usually assigned to it need investigation. The mature stage in 

 certain genera is a large plasmodium; in others, an amoeboid uninucleate 

 organism. Both flagellate and amoeboid stages occur in certain genera; 

 in other cases, a flagellate stage is unknown. Three families are often 

 included in this order: (1) Labyrinthulidae, uninucleate organisms which 

 grow in "nets" and may form an aggregate (pseudoplasmodium) before 

 encystment; (2) Pseudosporidae, uninucleate forms with amoeboid and 

 flagellate stages; (3) Vampyrellidae, in which the mature stage is a plas- 

 modium. 



Family 1. Labyrinthulidae. These are little known Proteomyxida which 

 parasitize eel grass and various algae. The organisms usually form a 

 peculiar network (Fig. 5. 14, A, D), the organization of which has been 

 disputed in Lobyrinthula. According to one interpretation, the individual 

 organisms are joined by cytoplasmic processes; according to another view 

 (145), they are held together by a tubular membrane in L. zopfi (Fig. 5. 

 14, A, B). Neither interpretation is supported by the observations of 

 Young (162) on Labyrhitluila mocrocystis, in which the "connections" 

 are interpreted as filamentous "tracks" secreted by the individual organ- 

 isms. At the advancing end of a net the organisms first form a clump (Fig. 

 5. 14, D). Then, hyaline filaments, one from each individual, "dart" for- 

 ward to a length several times that of tlie organism. The filaments wave 

 about until they meet and fuse to form a track. The organisms, by a 

 method still undetermined, glide along such a track "like a drop of 

 glycerin rolling down a taut silk thread" (162). One organism may over- 

 take and pass another without either one leaving the track. Since the 

 organisms may leave the track independently, they apparently do not lie 

 within a tube. Growth of the net involves fission of the organisms. 



The life-cycles need more investigation. A slowly moving pseudoplas- 

 modium, composed of a mass of organisms embedded in a thin matrix, 

 has been observed in Labyrinthula macrocystis (162). Encystment of 1-8 



