Amphoriscus semoni Breitfuss, 1896

Amphoriscus semoni Breitfuss, 1896

Citations: Amphoriscus semoni Breitfuss 1896: 435; 1898: 221; Dendy & Row 1913: 782; Burton 1963: 542; Van Soest & De Voogd 2015: 94; Klautau, Cavalcanti & Borojevic 2017: 105; Van Soest & De Voogd 2018: 130; Cóndor-Luján et al. 2019: 1825.

Type material: ZMB 2698 (Holotype; Ambon Island, Maluku, Indonesia). Not analysed in the present work.

Type locality: Ambon Island, Maluku, Indonesia.

Analysed material: BMNH 1886.6.7.32 (two slides containing sections of the skeleton). Port Jackson, Australia; previously identified as A. cylindrus in Burton, 1963: 634.

Morphology: The holotype of A. semoni was not available for redescription, and the material analysed here (deposited in the NHM) was comprised of two microscope slides. Aquiferous system is syconoid.

Anatomy: The material evaluated in the present study (BMNH 1886.6.7.32) was deposited at the Porifera collection of the NHM under the name A. cylindrus (Fig. 9). It is formed by giant cortical tetractines, with paired and unpaired actines laying on the cortex (Figs. 9A, B). The organisation of the skeleton is inarticulate due to the unpaired actine of the subatrial triactines and the apical actine of the cortical tetractines (Figs. 9A–C). The atrium is perforated by the apical actine of the small atrial tetractines (Fig. 9D).

Spicules (Tables 5 and 6): A figure containing only the spicule categories could not be prepared due to the lack of a slide of dissociated spicules.

Cortical tetractines: Irregular, conical, and sharp. The basal actines (paired and unpaired) are slightly curved from the base to the tips. The apical actine is straight and long.

Subatrial triactines: Irregular, cylindrical to slightly conical, sharp. The paired actines are straight. The unpaired actine is longer or the same size as the paired actines.

Atrial tetractines: Irregular, cylindrical, small, thin, and sharp. The paired actines are curved. The unpaired actine is similar to the paired ones. The apical actine is straight and short, always very thin.

Remarks: BMNH 1886.6.7.32 was deposited in the NHM as A. cylindrus (Burton 1963), but its subatrial skeleton is comprised of triactines and not tetractines, as in A. cylindrus. The only species of Amphoriscus whose organisation is consistent with this specimen—cortical tetractines, subatrial triactines, and atrial tetractines—is A. semoni. The specimen is from Port Jackson, Australia, in the same biogeographical region as the type locality of A. semoni (Ambon Island, Indonesia) and isolated from the type locality of A. cylindrus (the Adriatic Sea). Therefore, we suggest the identification of BMNH 1886.6.7.32 as A. semoni. Figure 9 shows its skeletal organisation, in which the subatrial and atrial layers are clearly evident. In our opinion, these illustrations are important for further recognition of specimens belonging to A. semoni.

Among the characters described by Breitfuss (1896), A. semoni is bright white when preserved, and the atrial surface is perforated by the apical actine of the colossal cortical tetractines. The specimens described as A. semoni by Van Soest & De Voogd (2015, 2018) present minor differences in the colour and length of these apical actines. The sample ZMAPOR 08073, collected in Sumbawa, Indonesia, was green alive and beige after fixation. The apical actine of its cortical tetractines does not exceed 600 μm (see Tables 8 and 9; Van Soest & De Voogd 2015), while in the holotype, they vary from 520 to 790 μm (Breitfuss 1896). In their most recent study, Van Soest & De Voogd (2018) described a new set of specimens of A. semoni (ZMAPOR 10527), sampled in Seychelles, Western Indian Ocean, which were white alive and beige after fixation. The apical actines of the cortical tetractines do not perforate the atrium, although they measure 239–882 μm (Van Soest & De Voogd 2018). The differences between the holotype and the other specimens described in both works by Van Soest & De Voogd provide a better understanding of the intraspecific variation of A. semoni. These are precious data, usually rare for Amphoriscus species since the original description, based on one or few specimens, is all that is available for many species of the genus.

Amphoriscus semoni resembles two species of the Adriatic Sea, namely A. gregorii and A. bucchichii. However, A. semoni differs in having a cortical skeleton comprised exclusively of tetractines.

Distribution: Ambon Island, Indonesia (Breitfuss 1896); Seychelles (Van Soest & De Voogd 2018); Port Jackson, Australia (present study). Corresponding MEOW: Banda Sea, Seychelles, and Manning-Hawkesbury (Spalding et al. 2007).