Achramorpha glacialis Jenkin, 1908

Alvizu, Adriana, Xavier, Joana R. & Rapp, Hans Tore, 2019, Description of new chiactine-bearing sponges provides insights into the higher classification of Calcaronea (Porifera: Calcarea), Zootaxa 4615 (2), pp. 201-251 : 215-217

Achramorpha glacialis Jenkin, 1908

( Figs 5 A–H; Table 5 )

Original description. Jenkin 1908, p. 31, pl. XXIV, figs 98–102.

Type locality. Winter Quarters Bay , Antarctic .

Synonyms and citations. Achramorpha glacialis, Dendy & Row 1913, p. 765 ; A. glacialis Hôzawa 1918, p. 542 ; A. glacialis, Brønsted 1931, p. 31 ; A. glacialis, Burton 1963, p. 93 , 524, fig 330.

Material examined. Lectotype: BMNH-1907.8.6.101 (one complete specimen and one slide), National Antarctic Expedition ( HMS Discovery), collection date 05.09.1902 . Paralectotype: BMNH-1907.8.6.103-104 (three fragments of a specimen and three slides), National Antarctic Expedition ( HMS Discovery), collection date 23.01.1903 .

Morphology. Cylindrical sponge, slender at the base and towards the apical osculum. Surface slightly hispid due to cortical diactines that cross the surface. Colour is white-beige in ethanol ( Fig 5A ). Aquiferous system syconoid with long choanocyte chambers that taper at their distal ends, forming large inhalant cavities ( Fig 5B ). The lectotype is 5.6 mm long, 0.4–0.7 mm wide and 0.2–0.3 mm thick.

Skeleton. Cortical skeleton made up by triactines arranged tangentially, and by protruding diactines and trichoxeas ( Figs 5 B–C). Neither the diactines nor trichoxeas are arranged in tufts or bundles, but rather irregularly scattered. Minute and spined microdiactines are found also in the cortical skeleton ( Fig 5D ). The atrial skeleton is composed of chiactines which are placed radially with the unpaired actine pointed towards the choanosome, the paired actines adjacent to the atrial wall, and the apical actine projected towards the atrial cavity ( Fig 5B ). Tetractines are found only in the oscular region with the unpaired actines pointing downwards, the paired actines tangentially lined up with the atrial wall, and the apical actines pointing towards the atrium ( Fig 5E ). The oscular fringe is not well-developed and is composed mainly of short trichoxeas, and some scattered diactines ( Fig 5C ).

Spicules. Cortical diactines: bent, with sharp tip at the proximal end, while distal end is wider and has a blunt tip. Size: 338.4 ± 73.8 µm length, 14.8 ± 4.2 µm width ( Fig 5F ; Table 5 ).

Microdiactines: minute and slightly bent with scattered spines. Size: 63.1 ± 36.7 µm length, 2.8 ± 0.4 µm width ( Fig 5D ; Table 5 ).

Trichoxeas: straight and hastate, smaller than diactines. Size: 147.6 ± 5.9 µm length, 2.6 ± 0.4 µm width ( Fig 5C ; Table 5 ).

Cortical triactines: sagittal alate with acerate tips. The unpaired actines are longer but slightly slender than paired actines. Size: unpaired actines 235.3 ± 42.7 µm length, 10.5 ± 1.6 µm width; paired actines 146.9 ± 23.4 µm length, 10.9 ± 1.9 µm width ( Figs 5G ; Table 5 ).

Chiactines: unpaired actines straight, sharply pointed, and longer than paired actines, which bent irregularly. The apical actines taper to an acerate end and can be straight or slightly bent as the paired actines. Size: unpaired actines 334.2 ± 38.0 µm length, 13.4 ± 2.2 µm width; paired actines 160.4 ± 18.3 µm length, 12.5 ± 1.6 µm width; apical actine 85.0 ± 7.5 µm length, 9.9 ± 1.7 µm width ( Fig 5H ; Table 5 ).

Distribution and depth. A. glacialis has been reported in two different expeditions in Antarctic waters. The first one is the National Antarctic Expedition from where Jenkin obtained the samples used for the species description ( Jenkin 1908). The second expedition was the “Deutchen Süd-polar Expedition”, where A. glacialis was recorded in the station called “Winterstation” and in the nearby area, at 350–385 m depth ( Brøndsted 1931).

Molecular identification. Not available.

Remarks. Six specimens were reported in the original description by Jenkin (1908). However only two specimens were found in the collection of the BMNH, and none were marked as being the holotype. Because one of the specimens was selected as lectotype, and the remaining specimen is now erected as paralectotype according to recommendation 74F of the ICZN.

According to Jenkin (1908), the trichoxeas in A. glacialis are 400 µm length or more. The discrepancy in the size of the trichoxeas reported by Jenkin (1908) and ours (147.6 ± 5.9 µm length) is because these spicules were difficult to find intact in the slides. Despite this, we found that the trichoxeas present in A. glacialis are not as long as in Achramorpha antarctica sp. nov. (1106.7 ± 612.1 µm length), and they are not organized in bundles with the cortical diactines as in the new species A. antarctica .

Figures

FIGURE 5A–H. Achramorpha glacialis. A: preserved lectotype BMNH-1907.8.6.101. B: histological section including cortical layer, choanosome and atrial cavity. C: histological section of the cortical layer. D: SEM image of microdiactine. E: histological sections of the oscular region. F–H: SEM images of spicules; cortical diactine (F), cortical triactines (G) and chiactines (H). Abbreviations: Apa = apical actines of tetractines; At = atrial cavity; Chc = choanocyte chamber; Chi = chiactines; Cor = cortical layer/cortex; Ctr = cortical triactines; Di = diactines; Inc = inhalant cavity; Os = osculum; Tet = tetractines; Tric = trichoxeas.