Baikalospongia abyssalis, Itskovich, Valeria B., Kaluzhnaya, Oxana V., Veynberg, Elena & Erpenbeck, Dirk, 2017

Itskovich, Valeria B., Kaluzhnaya, Oxana V., Veynberg, Elena & Erpenbeck, Dirk, 2017, Endemic Lake Baikal sponges from deep water. 2: Taxonomy and Bathymetric Distribution, Zootaxa 4236 (2), pp. 335-342 : 336-338

Baikalospongia abyssalis sp. nov.

Fig. 1 .

Spongillina n.sp. Itskovich et al. 2015a: 127, Fig. 2 .

Type material. Holotype: MIRY_2008_BS99; Paratype MIRY _2008_BS100. The holotype and paratype were collected on September 21, 2008 by GOA Mir 1 and Mir 2 at 750 m depth near the northwest coast of Lake Baikal 1 km south to the Olkhon Gate (52°57'35.4"N 106°53'36.3"E). Sponge samples were scraped off a rock, collected by a manipulator, and deposited in the collection of the Limnological Institute SB RAS , Irkutsk, Russia .

Type locality. Lake Baikal.

Etymology. The name represents the abyssal depths of the Lake Baikal from which the samples were collected.

Diagnosis. Encrusting sponge. Consistency soft, not fragile. Megascleres very long and thin oxeas (length 370–470 µm, width 10–15 µm) covered with simple and polymorphic spines. Microscleres absent. Gemmules absent.

Description. Holotype: Encrusting sponge, 3 cm in diameter, 1.5 cm thick. Two fragments were collected of size 15 mm in diameter and 7 mm thick, and 5 mm in diameter, 2 mm thick. Consistency soft but not fragile. Color light blue in life and in the preserved state in ethanol and white in the preserved state in formalin. Surface uneven, rough. Oscula not seen in preserved specimen.

Megascleres very long and thin, slightly curved oxeas (length 370–470 µm, width 10–15 µm). Megascleres covered by simple and polymorphic spines located throughout the length of spicules, at the ends of spicules spines curved down (see Fig. 1 ).

Ectosomal and choanosomal skeleton indistinguishable. Skeleton anisotropic, with paucispicular primary fibres and rare cross bundles ( Fig. 1 ). Variable amount of spongin. There are no spicular tufts on top of the main bundles.

Paratype: matching description above for holotype, Paratype is encrusting sponge 1 cm thick, 0.5 cm in diameter. A fragment was collected with size 15 mm in diameter and 7 mm thick. Color light blue in life and white in the preserved state in formalin.

Taxonomic remarks. Baikalospongia abyssalis sp. nov. belongs to the Baikalian endemic family Lubomirskiidae . This species differs from other Lubomirskiidae by very thin and long spicules, which are similar to the spicules of Trochospongilla sp. (family Spongillidae ) from Lake Baikal ( Efremova 2001) or the fossil genus Palaeoephydatia ( Veynberg 2009). However, the molecular data clearly identified this species as Lubomirskiidae ( Itskovich et al. 2015a) .

Spicule dimensions of Baikalospongia abyssalis sp. nov. differ significantly from spicule dimensions of other Lubomirskiidae species with oxeas. Also spicules are covered with characteristic polymorphous spines with a few edges while other Lubomirskiidae species have simple spines. This species is placed under the genus Baikalospongia Annandale, 1914 based on the structure of the ectosomal skeleton in which there are no spicular tufts on top of the primary fibres ( Rezvoi1936). According to Rezvoi (1936) the structure of the skeleton is diagnostic to determine the genera within Lubomirskiidae . Based on the differences in morphological features and sequences of CO1 and ITS ( Itskovich et al. 2015a) our samples MIRY_2008_BS99, MIRY_2008_BS100 are considered to represent a novel species of the genus Baikalospongia , for which the name Baikalospongia abyssalis sp. nov. is proposed. Probably this is an exclusive deep-water species, as it has never been recorded from the shallow waters, despite numerous collections made in the littoral zone of Lake Baikal ( Masuda 2009, Itskovich et al. unpubl.).

Figures

FIGURE 1. Baikalospongia abyssalis sp. nov. A: Holotype: BS 99. Scale bar 1 cm. B: Paratype: BS 100. Scale bar 1 cm. C: fragment of holotype BS 99 fixed in ethanol. Scale bar 1 mm. D: fragment of holotype BS 99 fixed in formalin. Scale bar 1 mm. E, F: the skeleton of holotype BS 99. Scale bars 1 mm and 100 µm. G – J: SEM photos of megascleres. Scale bars 100 µm and 10 µm.

FIGURE 2. Vertical distribution of Lubomirskiidae in the Lake Baikal at depths of more than 120 m.