Achramorpha truncata ( Topsent, 1907 )

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 : 209-210

Achramorpha truncata ( Topsent, 1907)

( Figs 2 A–F; Table 3 )

Original description. Grantia truncata Topsent 1907, p. 540 ( Topsent 1908, p. 6, pl. V, fig 4).

Type locality. Booth-Wandel Island, Antarctic ( Topsent 1907) .

Synonyms and citations. Grantia truncata, Topsent 1907, p. 540 ; Topsent 1908, p. 6, pl. V, figure 4; Achramorpha truncata Dendy & Row 1913, p. 765 ; A. truncata Hôzawa 1918, p. 542 ; A. truncata, Downey et al. 2012 .

Material examined. Holotype: MNHN C1968-810 (one complete specimen), Booth-Wandel Island, Antarctic, 40 m depth . Additional material: BMNH-1926.10.26.250: dry material, British Antarctic Expedition 1910–1913 (Terra Nova), st. nr. 339.

Morphology. Tubular sponge with one apical osculum. Surface slightly hispid due to diactines protruding the surface. Colour is yellowish in ethanol ( Fig 2A ). Consistency fragile. Aquiferous system syconoid with radial chambers straight and from 0.10 to 0.13 mm wide ( Topsent 1907). The holotype is 20.7 mm long and 2.5–2.8 mm wide.

Skeleton. Inarticulated, composed of diactines, chiactines and two types of triactines. Cortical skeleton is made up of sagittal triactines placed tangentially and perpendicular diactines ( Fig 2B ) which present a fairly distinctive shape at their distal ends ( Figs 2 C–D). The choanosomal skeleton is composed of the unpaired actines of atrial tri- actines and chiactines, which are placed with the paired actines adjacent to the atrial wall, and apical actines straight and projecting towards the atrial cavity.

Spicules. Cortical diactines: slightly curved, with proximal ends sharper and thinner than the distal ends which present two oblique discs that form a kind of fissure at the tip ( Figs 2 C–D). Size: 226.5 ± 32.2 µm length, 17.3 ± 2.6 µm width ( Table 3 ).

Cortical triactines: unpaired actines straight and longer than the paired actines which are slightly irregular. Size: unpaired actines 171.5 ± 26.9 µm length, 11.2 ± 1.3 µm width; paired actines 123.1 ± 19.4 µm length, 11.1 ± 1.8 µm width ( Fig 2E ; Table 3 ).

Atrial triactines: T-shaped triactines with unpaired actines straight and longer than the paired actines. Size: unpaired actines 446.7 ± 59.2 µm length, 12.4 ± 2.4 µm width; paired actines 158.4 ± 29.0 µm length, 11.8 ± 1.5 µm width ( Fig 2F ; Table 3 ).

Chiactines: unpaired actines longer than the paired actines. Apical actines straight, slender, and sharply pointed ( Fig 2E ). Size: unpaired actines 464.7 ± 31.7 µm length, 13.8 ± 0.9 µm width; paired actines 153.3 ± 18.0 µm length, 13.5 ± 1.6 µm width; apical actines 63.8 ± 10.1 µm length, 8.0 ± 1.0 µm width ( Table 3 ).

Distribution and depth. A. truncata is considered an endemic species from Antarctic waters. The species presents a wide depth range from shallow waters to a maximum depth record of 1500 m ( Downey et al. 2012).

Molecular identification. Not available.

Remarks. Topsent (1907; 1908) mentioned that “a remarkable characteristic” of this species was the lanceshape of the diactines, which present a conspicuous form at the distal end. After checking the holotype, we confirm that this characteristic is unique for the species and it was not found in the additional material examined and previously identified as A. truncata . Because of this and other differences mentioned below, we considered that the record by Barthel et al. (1997) is not conspecific with A. truncata and this material is here described as A. antarctica sp. nov. (see below).

Figures

FIGURE 2A–F. Achramorpha truncata. A: preserved holotype MNHN C1968-810. B: SEM image of the cortical layer. C–D: SEM images of the cortical diactines and details of the distal end. E: SEM images of chiactines and cortical triactines. F: atrial triactine. Abbreviations: Chi = chiactines; Ctr = cortical triactines; Di = diactines.