Swartschewskia khanaevi, Bukshuk & Maikova, 2020

Bukshuk, Natalia A. & Maikova, Olga O., 2020, A new species of Baikal endemic sponges (Porifera, Demospongiae, Spongillida, Lubomirskiidae), ZooKeys 906, pp. 113-130 : 113

Swartschewskia khanaevi sp. nov. Figs 1 , 3 , 4 ; Tables 1, 2

Type material.

Holotype: ZIN 11986 (specimen in ethanol), ZIN 11986A (slide), Lake Baikal, the Olkhonskiye Vorota Strait, sampling site 1 (52°59.42'N 106°55.53'E), depth 10 m, SCUBA divers, September 9, 2016, collected by I. V. Khanaev, 1 specimen. Paratypes: ZIN 11987 (specimen in ethanol), ZIN 11987A (slide): ibid, 1 specimen; ZIN 11988 (specimen in ethanol), ZIN 11988A (slide): ibid, 1 specimen; ZIN 11989 (specimen in ethanol), ZIN 11989A (slide): ibid, 1 specimen; LIN-BS-1740-2 (specimen in ethanol, slide): ibid, 1 specimen. ZIN 11990 (specimen in ethanol), ZIN 11990A (slide): the Olkhonskiye Vorota Strait, sampling site 2 (53°01'03.40"N 106°55'47.00"E), depth 2.5 m, SCUBA divers, June 7, 2016, collected by I. V. Khanaev, 1 specimen.

Etymology.

Named after Dr Igor V. Khanaev, scientist and diver who organised a dive program and collected type material.

Description.

Thin encrusting sponge. Sponge thickness is maximal in the centre of the body (0.5-1 mm) and minimal at the edge (0.05-0.3 mm).

The natural colour is yellowish beige and almost white in ethanol with brown areas on the surface. Usually, sponges have from one to three oscula, and only paratype ZIN 11990 has six oscula. Oscula are almost round, deepened, edged with well-developed spicular vallum. Oscula size is 146-(585)-978 × 235-(663)-1148 μm. Dermal pores are non-uniformly distributed on sponge surface. They are mostly aggregated in pore fields. Those are not deepened relatively to sponge surface, diverse in shape and can join to each other. Round or ovoid inhalant apertures of 7-(42)-106 × 7-(54)-140 μm in size perforate dermal membrane. The apertures are located in meshes of ectosomal skeleton network. Pore fields size varies significantly: 0.07-(0.5)-1.5 × 0.09-(0.7)-2 mm. One field usually contains 4-40 pores; the maximum number of pores is 78. There are also isolated pores.

Up to 70-80 % of sponge surface is lacking in both oscula and pores and covered with dense accumulations of Cocconeis placentula Ehrenberg, 1838 and sporadic exemplars of other diatoms (identified by Dr N.A. Bondarenko). Additionally, some ciliated protozoa of genus Lagenophrys von Stein, 1851 (identified by Dr T.Ya. Sitnikova) were observed on all specimen of Swartschewskia khanaevi sp. nov.

Sponge surface is a hard but fragile crust, i.e., ectosomal skeleton; the inner part of the body is soft and can be easily detached from the crust. The ectosomal skeleton has a form of a cortical layer (cortex) of tangentially arranged tracts forming an alveolar network. Meshes are disordered; size and shape vary. In some parts of the cortex, meshes are indistinguishable; tracts cross irregularly. Megascleres in tracts are arranged in loose bundles, 2-8 megascleres in every bundle. The thickness of cortex varies significantly from 44 to 307 μm. The thickest cortex is observed near oscula, the thinnest one in the areas of pore fields. The choanosomal skeleton is weak; it consists of separated spicules and thin disordered fibres.

Megascleres are exclusively strongyles of 99-(127)-149 × 9-(15)-21 µm with different sorts of spines: simple spines, rosette spines, and a peculiar sort of spine, secondarily microspined tuberculated spines. The latter look like tubercles (4-9 µm in diameter and 1-5 µm in height) densely ornamented with simple spines (number 13-58) and these are the most abundant sort of spines. Rosette spines are comparatively rare (0.8-(1.4)-3.2 × 1-(1.6)-3.6 μm in size, contain 3-9 simple spines). The length of isolated simple spines and simple spines in both kinds of complex spines is similar: 0.1-(0.4)-0.9 µm. Microscleres absent.

Figures

Figure 1. Sampling sites in Lake Baikal: 1, 2 samples of S. khanaevi sp. nov, 3 samples of S. papyracea.

Figure 3. Swartschewskia khanaevi sp. nov., external view. Abbreviations: osc oscula, pf pore fields. Scale bar: 5 mm.

Figure 4. Swartschewskia khanaevi sp. nov. A sponge surface B ectosomal skeleton C cross section of skeleton D, E secondarily microspined tuberculated spines on strongyles F strongyles. Abbreviations: chs choanosomal skeleton, Cp Cocconeis placentula, dm dermal membrane, es ectosomal skeleton, ia inhalant apertures, Lsp Lagenophrys sp., st spicular tracts. Scale bars: 10 μm (D, E), 100 μm (F), 500 μm (A), 1 mm (B).