HETEROSCLEROMORPHA Cárdenas, Pérez & Boury-Esnault, 2012

Morozov, Grigori, Sabirov, Rushan Mirzovich & Anisimova, Natalia, 2018, New data on sponges from Svalbard Archipelago with a description of a new species of Halicnemia, Journal of Natural History (J. Nat. Hist.) 52 (7 - 8), pp. 491-507 : 493-495

Subclass HETEROSCLEROMORPHA Cárdenas, Pérez & Boury-Esnault, 2012 Order AXINELLIDA Lévi, 1953

Family STELLIGERIDAE Lendenfeld, 1898

Genus Halicnemia Bowerbank, 1864

Halicnemia wagini sp. nov.

( Figure 2 (a–f))

Type locality

The holotype is located in the Edward Eversman Zoology Museum (identification number – 2.2.5.397). The only specimen of sponge was found in the west of the southern tip of Spitsbergen (76.64°N, 13.568°E), on the continental slope at a depth of 423– 425 m. Temperature and salinity at the bottom layer were 3.33°C and 35.08‰.

Description

( Figure 2 (a)) Sponge cushion-shaped, up to 7 mm thickness, with small conules. No visible oscula. The consistency of body is soft and compressible, but tears easily. Surface is smooth, covered with evenly scattered small pores. Long ends of thick bundles of tornotes slightly project above the surface forming the ‘tuft’ on the sponge apex. Dermal membrane is supported by tangential layer of acanthose microscleres. Colour beige (in ethanol).

Skeleton

( Figure 2 (b)) Ectosomal skeleton is a tangential layer of centrangulate acanthostrongyles and acanthoxeas. Choanosomal skeleton consists of numerous thin bundles of megascleres which extend from the base to the surface of sponge, where their ends protrude through (at the apex of sponge) or are fastened into the surface tangentially, supporting the ectosome. Bundles are composed of large axial styles (with their heads based upon the substratum) and smaller thin tornotes which form sheaths around tylostyles.

Spicules

( Figure 2 (c), 2(d)) Ectosomal centrangulate acanthostrongyles and acanthoxeas, often centrotylote and strongly curved, evenly spined (rarely found smooth or only slightly spined immature spicules of both categories), dimensions of acanthostrongyles: 32–73.8– 146.9 (n = 100) × 3–6.6– 10.9 µm (n = 70), dimensions of acanthoxeas: 72.7–116.5–208 (n = 100) × 4.6–7.8– 10.7 µm (n = 70). Choanosomal oxea-like tornotes, also centrotylote (not common), which ends are generally not equal, one is a little shorter, while the other longer and more long-pointed, dimensions: 826–1479–1692 (n = 35) × 10.2–15.8– 20.3 µm (n = 20). Large sub-tylostyles or styles, with rounded apical ends and with regular slightly curved basal ends, in a large size variation, usually broken in the slides, largest unbroken style up to 3 mm and 31 µm in length and thickness, respectively.

Etymology

Species named in honour of Wagin Vladimir Lvovich – an outstanding Russian zoologist and parasitologist, researcher of the Arctic and Far Eastern Seas fauna . The year 2017 is the 110th anniversary of his birth.

Remarks

Topsent (1897) supposed a close relationship between Halicnemia and Higginsia , and noted that they share the same types of spicules, which play the same role and are arranged the same way. At the same time, he attached great importance to the differences in macrosclere morphology (tylostyles in Halicnemia vs styles in Higginsia ). However, despite a great similarity of both genera, he argued against their unification and contrasted differences in skeletal architecture. If Higginsia species have an elongated, branching body, with corresponding structure: a reticulate skeleton, which is more or less condensed axially, the incrusting Halicnemia has a skeleton presented by numerous paratangential spicular fascicles radiating from the base to the surface.

Later Van Soest (1987) supported this point of view, and noticed that only differences in skeletal architecture (reticulate skeleton in Higginsia vs radial in Halicnemia ) may serve as decisive in delimitation of both genera.

Currently, according to the various molecular data ( Morrow et al. 2012, 2013), both Halicnemia and Higginsia are placed in Stelligeridae von Lendenfeld, 1898 .

To date only 7 valid species belonging to genus Halicnemia are known (Van Soest 2017), three of them ( H. patera Bowerbank 1864 ; H. verticillata Bowerbank 1866 ; H. arcuata Higgin 1877 ) are registered in the northern part of the Atlantic Ocean.

Halicnemia verticillata distinctly differs in form of microscleres (which are only slightly curved and ‘verticillately-spined’).

The most distinctive character and difference between Halicnemia patera , H. arcuata and H. wagini sp. nov. is the presence of centrangulate acanthostrongyles in H. wagini sp. nov.

Particular qualities of hydrology of the study area, its close relationship with waters of the North Atlantic, as well as proximity of a new species to the North Atlantic representatives of Halicnemia genus, allow us to consider H. wagini sp. nov. both ecologically and morphologically as stood apart as a distinct biological species in the conditions of the Arctic.

Figures

Figure 2. H. wagini sp. nov., (a) habitus; (b) simplified diagram of a transverse section through the sponge body (abbreviations: at, axial styles which basal ends lying in contact with the substratum; sb, bundles of tornotes supporting the ectosome; dm, dermal membrane; pb, bundles which penetrate the dermal membrane forming conule); (c–f) SEM images of spicules; (c) tornote; (c1) details of apices of tornote; (d) style; (d1) details of apices of style; (e) acanthoxea; (f) acanthostrongyle.