Marine rhizopods, globular or irregular in form, and slow to change shape.  Dimorphic.  Both forms multinucleate during vegetative life.  Pseudopodia are long, thin, and thread-form, with rounded ends.  Their function is neither food-getting nor locomotion, but probably tasting.  The plasm of both forms is inclosed in a soft gelatinous membrane.  In one form the jelly is impregnated with needles of magnesium carbonate (Schaudinn), but these are absent in the other form.  The membrane is perforated by clearly defined and permanent holes for the exit of the pseudopodia.  Reproduction occurs by division, by budding or by fragmentation, but the parts are invariably multinucleate.  At the end of vegetative life the needle-bearing form fragments into numerous mononucleate parts; these develop into adults similar to the parent, but without the spines.  At the end of its vegetative life this new individual fragments into biflagellated swarm-spores which may conjugate, reproducing the form with needles.  Size up to 2 mm.

Trichosphaerium sieboldi Schneider.  Fig. 3.

With the characters of the genus.  A form which I have taken to be a young stage of this interesting rhizopod is described as follows: 

A minute, almost quiescent, form which changes its contour very slowly.  The membrane is cap-like and extends over the dome-shaped body, fitting the latter closely.  The endoplasm is granular and contains foreign food-bodies.  Nucleus single, spherical, and centrally located.  Pseudopodia short and finger-form, emerging from the edge of the mantle-opening and swaying slowly from side to side or quiescent.  The most characteristic feature is the presence of a broad, creeping sole, membranous in nature and hyaline in appearance.  This membrane is the only evidence of ectoplasm, and it frequently shows folds and wrinkles, while its contour slowly changes with movements of body.  The pseudopodia emerge from the body between this membrane and the shell margin.  Contractile vacuole absent.  Length 42 mu, width 35 mu.  In decomposing seaweeds, etc.

Only one specimen of this interesting form was seen, and I hesitate somewhat in placing it on such a meager basis.  It is so peculiar, however, that attention should be called to it in the hope of getting further light upon its structure and mode of life.  Its membranous disk recalls the genus Plakopus; its mononucleate condition, its membranous disk, and the short, sometimes branched, pseudopodia make it difficult to identify with any phase in the life-history of Trichosphaerium.  I shall leave it here provisionally, with the hope that it may be found more abundantly another time.

[Illustration:  Fig. 3.—­Trichosphaerium sieboldi]

Genus GROMIA Dujardin ’35.

(Dujardin 1835; M. Schultze ’62; F. E. Schultze ’74; Leidy ’77;
Buetschli ’83; Gruber ’84.)