Acrochaetium infestans M.Howe & Hoyt

1

Acrochaetium infestans sp. nov.

Endo- and epizoic, minute; interior filaments tortuous, intri-
cate, serpentine, or labyrinthine, mostly 2.0-5.5 n in diameter,
thin-walled, the branching very irregular, lateral, subdichotomous,
or very rarely opposite, commonly divaricate from near the middle
of a cell, the branches often subcircinately reflexed or inflexed, the
interior cells mostly 12-60 ­x long, 3-18 times as long as broad,
commonly curved or contorted and of irregular or fluctuating
diameter, the terminal cells of branches often enlarged, suhhamate,
irregularly clavate, or subdivaticately forking, sometimes attaining
a diameter of 7-8 /x, or, rarely, interior filaments forming a sort
of pseudoparenchyma, with irregular cells sometimes 10-13 M
broad; chromatophore small, substellate or irregularly discoid,
near the center of the cell or subparietal, showing a single pyrenoid;
sporangiiferous filaments external, up to 90 /x high (or 230 ju,
including hairs), the simpler consisting of a single pedicel cell
bearing 1-3 sporangia (or, very rarely, the exserted sporangium
sessile on an endozoic filament), the larger showing 1-9 short,
1-3-celled, rarely secund branches, the cells 4.5-6.5 ju in diameter,
1-2 times as long as broad; hairs commonly present on the larger
external filaments, flexuous and attaining a length of 125-170^;
sporangia terminal or lateral, solitary, binate, or ternate, ovoid
or ellipsoid, 10-14 M X 6.0-8.5 m- [Plate 14.]

In and on the -stalks, stolons, and less commonly hydranths of
small campanularian hydroids (perhaps representing more than
one genus) attached to Dictyota dichotoma and other algae, dredged

HOWE AND HOYT: MARINE ALGAE FROM BEAUFORT, N. C. II7

in 133^-14 fathoms of water on reef about 23 miles off shore from
Beaufort, North Carolina, August 11, 1914, by Lewis Radcliffe.
The endozoic parts are embedded principally in the inner layers
of the perisarc of the stalks, stolons, and occasionally the hyd-
ranths.

Acrochaetium infestans doubtless finds its nearest ally in Chan-
transia endozoica Darbish. (Ber. Deutsch. Bot. Ges. 17: 13-17.
pi. 1. 1899), originally described as occurring in a bryozoan,
Alcyonidium gelatinosum, on the southern coast of Ireland, and
since reported also from Denmark by Rosenvinge (Kgl. Danske
Yidensk. Selsk. Skrift. VII. 7: 128. 1909). From this species,
as described and figured by Darbishire, Acrochaetium infestans
appears to differ in having the diameter of both immersed and
exserted filaments averaging about one half as great, in the much
more tortuous, more irregularly branched interior filaments, the
more curved and irregular cells of which are actually, on the
average, two or three times as long, and relatively to their width,
four to six times as long, as in the European species. The spor-
angia of Chantransia endozoica, as figured by Darbishire, are only
slightly broader than the subtending sterile cells; in A. infestans,-
the mature sporangia are nearly twice as broad as the subtending
cells. Darbishire noticed one possible hair in his C. endozoica,
but was not sure that it really belonged to the organism in question.
In Acrochaetium infestans, the larger exserted filaments commonly
show hairs of remarkable length.

Acrochaetium infestans is associated with various mostly smaller
algae that penetrate the hydrozoan little if at all. The more
common and conspicuous of these are Acrochaetium affine and a
closely adherent filamentous blue-green (Phormidium sp.?), the
latter with trichomata 0.75-1.5 ­x in diameter and cells mostly
1-2 (^-3) times as long as broad. The interior parts of the
Acrochaetium infestans are, in our formalin-preserved material at
least, so nearly colorless, and the plant in general is so small that
it might easily escape observation if one did not happen to empha-
size its existence through the use of differential stains. By
applying iodine (potassium-iodide solution) the little plant is
thrown into bold relief, its protoplasts becoming violet-red or
brownish crimson, while its host becomes a light yellowish
brown.

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Plate 14

Acrochaetium infestans

1.	Endozoic filaments of the usual form, with two short exserted filaments. In the
endozoic parts the outlines of protoplasts only (for the most part) are indicated, the
cell walls being almost invisible.

2.	An exserted sporangium sessile on an interior filament.

3.	An exserted filament of three cells, one of which is a sporangium and another of
which is probably an immature sporangium.

4.	An exterior filament, with short branches, short hairs, and a single lateral spor-