Description

Skeleton. Inarticulated skeleton composed of diactines, trichoxeas, chiactines and triactines. Sagittal tetractines can be found only in the oscular region (Fig 3 B). Cortical skeleton is formed by triactines tangentially positioned, and by long diactines and trichoxeas arranged in bundles (Figs 3 C – 3 E), which penetrate the choanosome and may reach the atrium. Smaller diactines are arranged radially penetrating the choanosome and protruding the surface (Fig 3 D). The choanosomal skeleton is composed of the bundles of diactines / trichoxeas (Fig 3 E), and of unpaired actines of atrial triactines and chiactines (Fig 3 F). Few triactines can also be found in the atrial skeleton (Fig 3 F). The atrial skeleton consists mainly of chiactines which are placed in the atrial wall with unpaired actines pointing towards the cortex, paired actines adjacent to the atrial wall, and apical actines straight and projecting towards the atrial cavity (Figs 3 B, 3 F). The oscular region is the only part of the skeleton with a proper atrial skeleton composed of triactines and tetractines with the unpaired actines pointing downwards. The apical actines from the tetractines are short and slightly bent pointing to the osculum (Fig 3 B). Spicules. Cortical diactines: highly variable in length and thickness. All diactines present smooth surface and are nearly straight with sharp tips (Figs 4 A – B). Size: 845.6 ± 322.9 µm length, 17.6 ± 5.5 µm width (Table 4). Atrial / oscular triactines: sagittal. T-shaped triactines with unpaired actines longer than the paired ones, and slender sharp tips. Size: unpaired actine 756.8 ± 138 µm length, 12.7 ± 3.1 µm width; paired actines 282.3 ± 90.1 µm length, 13.1 ± 3.4 µm width (Fig 4 D; Table 4). Chiactines: unpaired actines longer than the paired actines, with similar width. The apical actine is strait and slender with sharp tip. Size: unpaired actine 599.1 ± 176.3 µm length, 12.9 ± 2.3 µm width; paired actines 230.8 ± 44.5 µm length, 13.1 ± 1.9 µm width; apical actine 84.9 ± 29.2 µm length, 9.2 ± 1.7 µm width (Figs 4 E – F; Table 4). Oscular tetractines: measures not available because they were difficult to find intact in the spicule preparations and sections (Fig 3 B; Table 4).

Common Names

Taxonomic Hierarchy

Kingdom: Animalia

Phylum: Porifera

Class: Calcarea

Order: Leucosolenida

Family: Achramorphidae

Genus: Achramorpha

Species: Achramorpha antarctica Alvizu, Xavier & Rapp, 2019