Sertularella avrilia
Holotype: NMV G1964, microslide. Pearson Island, South Australia, 13m deep, on Sargassum sp.;
Paratypes: NMV G1965, G1966, G1967, microslides; SAM H35, microslide. Pearson Island, South Australia, 13m deep, on Sargassum sp.
Holotype: NMV G1964, microslide. Pearson Island, South Australia, 13m deep, on Sargassum sp.;
Paratypes: NMV G1965, G1966, G1967, microslides; SAM H35, microslide. Pearson Island, South Australia, 13m deep, on Sargassum sp.
S. avrilia resembles both S. robusta (Coughtrey, 1876) and S. gilchristi Millard, 1964: However, S. avrilia is smaller than S. robusta, the hydrothecae are more strongly annulated, and it is further distinguished by the long, curved thecal neck. Although S. avrilia shows some affinities with S. gilchristi, this South African species is a large, branching form, with fascicled stem, and a shorter, less conspicuously arched thecal neck.
Stems simple, short, to 4 mm long, unbranched, arising from a thin tubular hydrorhiza. First stem internodes short, with 3 proximal annulations; succeeding internodes of variable length, 0.320.53 mm, widening from a narrow oblique proximal node, 0.04-0.08 mm in diameter, to base of hydrotheca. Nodes sloping alternately left and right, with 1-2 oblique annulations, remainder of internode smooth.
Hydrothecae distal on internode, alternate, a maximum of 8 on stem, each sloping outwards parallel with line of internode, giving stem a zig zag appearance. Body of hydrotheca long, almost cylindrical, slightly swollen at junction with internode, 0.16-0.19 mm in diameter. Adcauline wall with 5-7 uniform, rounded annulations, most prominent across widest part of hydrotheca, but reduced to 4-6 on abcauline wall, fading out proximally. Adcauline wall arched outwards, abcauline wall inflexed into a long, narrow neck, 0.10-0.20 mm at narrowest diameter, expanding again to margin. Length of free adcauline wall, 0.36-0.45 mm, fixed adcauline wall, 0.12-0.14 mm; abcauline wall, 0.32-0.37 mm. Aperture facing outwards and slightly down. Margin, 0.11-0.14 mm in diameter, with 4 broad, low teeth, the adcauline tooth most prominent; 3 strongly developed internal submarginal teeth in thecal neck-2 identical dorso-lateral bract-like teeth, and 1 long peg shaped abcauline tooth. Hydranth insufficiently preserved for description, but shows evidence of an abcauline caecum.
Gonotheca- immature individual, arising from the base of a proximal hydrotheca; body strongly ribbed, with signs of the development of a slender terminal neck and 4 blunt spines.
Australia (Western Australia, South Australia).
Subtidal, epiphytic on algae such as Sargassum.