NO. 1 DAWSON : MARINE RED ALGAE OF PACIFIC MEXICO 21 



Acrochaetium ascidiophilum sp. nov. 

 Plate 10, figs. 5-6 



Thallis endozoicis in Styela_, e filamentis irregulariter ramificatis 

 efformatis, in hospitem penetrantibus ad altitudinem 400 jx, in superficie 

 filamenta libera 1-2 cellulata parientibus ; cellulis endozoicis tortis, 10- 

 20 [x longis, 3.0-5.5 /a diametro ; chromatophorio parietali ; monosporangiis 

 terminalibus lateralibusve in filamentis liberis. 



Thalli endozoic in the test of the ascidian Styela, consisting of irre- 

 gularly ramified endophytic filaments penetrating the host to a depth of 

 400 /x and producing at the surface short, 1-2 (rarely 3-) celled free, 

 simple or once-branched filaments; cells of endozoic filaments crooked, 

 curved, contorted, elongate, 10-20 (30) /a long 3.0-5.5 /x, in diameter, 

 generally smaller at the ends than in between ; cells of external filaments 

 tending to be slightly smaller in diameter than the internal and with 

 short cells 1-3 diameters long; chromatophore parietal; reproduction by 

 monosporangia borne terminally or laterally on the free filaments; 

 sporangia ovoid, larger in diameter than the sterile free filament cells. 



Type: Holotype is Dawson 9642, April 14, 1951, in vial 2293 and 

 on slides 1686-1687 in HAHF. 



Type locality: In the test of a partially decomposed ascidian of 

 the genus Styela cast up in drift 1 mile inside Bahia San Quintin from 

 the end of the peninsula. 



The endozoic habit, deeply penetrating endozoic filaments and short 

 free filaments are distinctive in this species. It appears to be most closely 

 related to A. infestans Howe & Hoyt (1916, p. 116, pi. 14) found in- 

 habiting hydroids, Dictyota and Sargassum at Beaufort, North Carolina. 



Acrochaetium penetrale (Drew) Papenfuss 



Papenfuss, 1945, p. 316; Taylor, 1945, p. 134. Rhodochorton pene- 

 trale Drew, 1928, p. 187, pi. 44, figs. 57-58, pi. 45, figs. 59-60. 



Thalli endozoic in hydroids ; endozoic filaments growing in the 

 chitin both around and between the animals of the colony, irregularly 

 branched, commonly forming pseudo-parenchymatous groups of angular 

 cells of variable size, 6.5-10.5 /x in diameter, bending outward in places 

 and producing free parts beyond the chitin; free parts of filaments of 

 1-10 (usually 7-10) cells, with multilateral branches sometimes termin- 

 ating in a hair, of cylindrical cells 5-8 /a in diameter and 2-3 times as 

 long ; chromatophore parietal with a prominent pyrenoid ; reproduction 

 by monosporangia; sporangia terminal and lateral on the branchlets, 

 ellipsoid to ovoid, 5.0-7.0 /* wide, 8-11 /x long. 



