Luapeleamoeba arachisporum (Olive & Stoianovitch 1969) Tice & Brown 2016
Description: During locomotion, the amoebae are shallowly dome-shaped in cross section, resembling a shield volcano (thus the genus name Shadwick et al. 2016). Locomoting amoebae range from nearly circular in outline to flabellate to elongate. Amoebae are as often wider than long as longer than wide with respect to the axis of locomotion. Mean cell length is 19.8 μm (standard deviation = 2.58 μm, n = 33) and mean cell breath is 15.4 μm (standard deviation = 2.78 μm, n = 33). The leading edge of a locomoting amoeba consists of a broad, hyaloplasmic, lobose pseudopodium from which extend numerous short, triangular, blunt subpseudopodia. The pseudopodium makes up between 15-20% of the length of the cell during locomotion. Subpseudopodia may extend from any part of the cell. There is usually no uroid. The granular cytoplasm contains a single nucleus (mean diameter is 4.9 μm) with a single, central nucleolus (mean diameter is 2.4 μm) that is usually more than half the diameter of the nucleus as whole. A large contractile vacuole is located just posterior to the nucleus during locomotion, usually less than one nuclear diameter from the nucleus, and it is usually greater in diameter than the nucleus at diastole. Sporocarps develop as an amoeba rounds up to form a refractile prespore cell that is nearly circular in outline. As the prespore cell develops into a stalk-depositing sporogen, it is more or less spherical. Once stalk deposition is complete, the sporogen develops into a spore either by laying down a spore wall and remaining nearly spherical or, more frequently, changes shape to become ovoid to sausage-shaped to peanut-shaped before laying down a spore wall.
Observations have not been made to determine if the spore changes shape continuously as is the case in L. hula. The spores are deciduous and flag readily in air currents. The stalks vary considerably in length, but are usually several times longer than the width of the spore. The stalk sits on a basal disk above which is a wide base that accounts for perhaps 5-10% of the total length of the stalk. The stalk then suddenly narrows and the remainder of the stalk is narrow and tapers slightly toward the apex. The very apex of the stalk widens to form a solid-appearing knob-like apophysis that is fully visible when the spore has been shed. The base of the apophysis is visible in the intact sporocarp, suggesting that the apex of the stalk is inserted into a shallow invagination at the base of the spore.
Neotype habitat: leaf litter from a deciduous forest in Mississippi, USA.