Racodiscula borisi, Schuster & Cárdenas & Pisera & Pomponi & Kelly & Wörheide & Erpenbeck, 2018

RACODISCULA BORISI View in CoL SP. NOV.

( FIGS 12, 13; TABLE 3)

Diagnosis: Racodiscula with one perfectly circular apical cavity/osculum (0.8 cm)located at the centre; choanosomal spicules are articulated tetraclone desmas with short thick and strongly tuberculated branches, choanosomal spicules are thick strongyles with rounded tips.

Type material: Holotype: HBOM 003 View Materials :02001, Coll. JSL-I dive 3905 [18 October 1995, Galápagos , 5NM NE of Kicker Rock, San Cristobal Island, 0°43 ′ 08 ″ S, 89°27 ′ 14 ″ W, 215 m] GoogleMaps . Paratype: 003:02011 (242 m), Galápagos , 4 NM SE of Tortuga Island, 1°04 ′ 59 ″ S, 90°51 ′ 56 ″ W, Coll. JSL-I dive 3923 GoogleMaps .

Comparative material: Racodiscula radixa sp. nov. HBOM 003:02006. Racodiscula seymoura sp. nov. HBOM 003:02014; HBOM 003:02007.

Type locality: San Cristobal Island, Galápagos Islands (215 m) ( Fig. 1) .

Distribution: Known from the type locality and Tortuga Island, Galápagos.

Habitat: Attached to hard substratum, depth range 215–242 m.

Description: Morphology, massive subspherical with a centralized circular apical cavity/osculum opening on top of the surface ( Fig. 12A, B). Dimension of the holotype is 5.5 cm in diameter and about 4–5 cm high ( Fig. 12A, B). Texture, medium hard. Surface, smooth ( Fig. 12B). Colour, white in vivo ( Fig. 12A) and beige in ethanol ( Fig. 12B). Ectosomal skeleton contains phyllo- to discotriaenes ( Fig. 13B, F) with acanthorhabds in between and on top of this layer ( Fig. 13A, B, E). Tylostyles are located at the subectosomal region ( Fig. 12A, B, I). Choanosomal skeleton contains articulated tetraclone desmas, which form a dense skeleton ( Fig.12C–F). Spinose metaster/amphiasters ( Fig. 13C, D). Oxeas ( Fig. 13G) with pointed tips and thick strongyles ( Fig.13H). Megascleres, tetraclone desmas with short branches measuring 540–650 × 385–400 µ m (N15) ( Fig. 12E). Phyllo- to discotriaenes with cladomes 395– 504 –605 µ m (N25) and rhabdomes of 20– 66 –93 × 18– 21 –25 µ m (N10) ( Fig.13B, F). Tylostyles are 440– 410 –904 µ m (N15) ( Fig. 13I). Oxeas with pointed tips 140– 176 –204 × 4–5 µ m (N7). Thick strongyles with round ends 95– 194 –112 × 15–28 µ m (N4); Microscleres are massive acanthorhabds with irregularly distributed spined tubercles 12– 19 –27 × 3–4 µ m (N30). Spinose streptaster/amphiasters with long rays 12.0– 14.5 –17.2 × 11.5– 15.4 –20.0 µ m.

Etymology: Named in memory of the first author’s friend Dipl. Biol. Boris Knerr († 20 July 2012), for encouraging her scientific curiosity in sponge taxonomy.

DNA barcodes: We sequenced COI, 28S (C1-D2) and 18S of the holotype and paratype. All three markers show identical sequences. GenBank accession numbers: COI KY652821 View Materials – KY652822 View Materials ; 28S KY652791 View Materials – KY652792 View Materials ; 18S KY652834 View Materials – KY652835 View Materials . SBD record no. 1723, 1724.

Remarks: The most obvious key diagnostic character which differentiates this new species from the other two new Racodiscula species described here, is the presence of tetraclone desmas, which are strongly articulated with short root-like branches showing a strong tuberculation ( Fig. 12C–F). This strong tuberculation of the tetraclone desmas is not present in the two other new species described. Racodiscula asteroides also shows sparsely tuberculated rays and strongly tuberculated tips of tetraclone desmas; however, it lacks oxeas and strongyles ( Pisera & Lévi, 2002b). The rhabdome of phyllo- to discotrianes from R. borisi sp. nov. is much shorter and a bit thinner in size compared to the others newly described species ( Table 3). Oxeas and strongyles appear larger in size compared to R. seymoura sp. nov. R. borisi sp. nov. groups within the Racodiscula clade from the Galápagos and forms a sister-group relationship to the other two species ( Fig. 5).

SUBORDER SPIROPHORINA BERGQUIST & HOGG, 1969 View in CoL