(FIg. 5; TAbLE 7)
Arachnopusia tubula HAYWARD & THORPE, 1988: 793, FIGS 5E–F
Material examined. CRBA-58229, STN PAT 0209DR08, FRAgMENTS OF COLONY NOT EXCEEDINg 4 MM LONg, 2 MM WIDE, ENCRUSTINg CORAL. CRBA-58230, STN PAT 0209DR11, COLONY 15 MM LONg, 5 MM WIDE, ENCRUSTINg ROCK.
Description. COLONY ENCRUSTINg, FORMINg bROAD, THICK UNILAMINAR SHEETS; OVERALL SIZE NOT KNOWN. AUTOZOOIDS bROADLY HEXAgONAL, SEPARATED bY FAINT gROOVES. FRONTAL SHIELD SMOOTHLY CALCIFIED, WITH 18–25 SMALL, ROUND FORAMINA, EACH ALMOST OCCLUDED bY A WELL-DEVELOPED OVAL LIgULA. PROXIMAL APERTURAL RIM RAISED, bEARINg ONE SMALL MEDIAN AVICULARIUM, PERPENDICULAR TO FRONTAL PLANE AND DISTALLY DIRECTED, AND A PAIR OF LATERAL AVICULARIA, ALSO PERPENDICULAR bUT WITH THE ROSTRUM FACINg DISTOLATERALLY INWARDS; SINgLE OR PAIRED AVICULARIA OCCASIONALLY PRESENT ON THE LATERAL RIM OF THE APERTURE, AND SPORADICALLY ON THE FRONTAL WALL. THE APERTURE IS ENCLOSED bY A THICKENED RIM, DEVELOPINg A SINgLE MEDIAN AVICULARIUM ON THE DISTAL EDgE. LARgE VICARIOUS AVICULARIA ARE PRESENT.
Remarks. THE PRESENT MATERIAL ACCORDS WITH ArachnΟpusia tubula FROM ANTARCTICA AS DESCRIbED bY HAYWARD & THORPE (1988). THIS SPECIMEN REPRESENTS THE FIRST RECORD IN THE PATAgONIAN REgION. CHARACTERS IN COMMON INCLUDE A SIMILAR NUMbER OF LIgULATE FORAMINA IN THE FRONTAL SHIELD AND THREE ADVENTITIOUS AVICULARIA IN THE PROXIMAL APERTURAL RIM. WHEREAS OVICELLS ARE LACKINg IN OUR MATERIAL, LARgE VICARIOUS AVICULARIA ARE PRESENT, NOT RECORDED PREVIOUSLY bY HAYWARD & THORPE (1988). THESE AVICULARIA gREATLY RESEMbLE THOSE IN A. mΟnΟcerΟs (BUSK, 1854), WHICH, HOWEVER, DIFFERS IN HAVINg FEWER FRONTAL-SHIELD FORAMINA AND A SINgLE AVICULARIUM IN THE PROXIMAL APERTURAL RIM.
n, number of measurements made; SD, standard deviation