Bidderia bicolora sp. nov.

(Figs 2–4; Table 2)

" Bidderia with cortical and subcortical skeletons exclusively composed of triactines and atrial skeleton composed

of abundant tetractines and fewer triactines. Colour in life can be white or yellow. Sagittal spicules are located on the oscular membrane, surrounding the inhalant apertures and in the subcortical skeleton."

Material examined. Holotype, UFRJPOR 8227, Chico 2, Tintamare Island, Saint Martin, Caribbean Sea (18°06.501' N, 62°59.005' W), 20 m depth, coll. B. Cóndor-Luján, 27 May 2015. Paratypes, UFRJPOR 8146, Circus-Tintamare, Saint Martin, Caribbean Sea (18°06.510' N, 62°58.999' W), 14 depth, coll. T. Pérez, 26 May 2015; UFRJPOR 8290, Cathedrale Cave, Guadeloupe, Caribbean Sea (16°27.740' N, 61°31.837' W), 17 m depth, coll. B. Cóndor-Lujan, 29 May 2015. Additional material, UFRJPOR 7975, Chico 2, Tintamare Island, Saint Martin, Caribbean Sea (18°06.50' N, 62°59.005' W), 21.7 m depth, coll. F. Azevedo, 0 6 April 2015. UFRJPOR 8202, UFRJPOR 8215, Basses Espagnoles, Saint Martin, Caribbean Sea (18°07.821' N, 63°00.270' W), 6–10 m depth, coll. B. Cóndor-Luján, 27 May 2015. UFRJPOR 8226, UFRJPOR 8228, UFRJPOR 8229, UFRJPOR 8230, Chico 2, Tintamare Island, Saint Martin, Caribbean Sea (18°06.501' N, 62°59.005' W), 20 m depth, coll. B. Cóndor-Luján, 27 May 2015. UFRJPOR 8252, Scrub Island, Anguilla, Caribbean Sea (18°17.813' N, 62°56.700' W), 13–20 m depth, coll. B. Cóndor-Luján, 28 May 2015. UFRJPOR 8294, UFRJPOR 8295, UFRJPOR 8302, Cathedrale, Guadeloupe, Caribbean Sea (16°27.740' N, 61°31.837' W), 17.6 m depth, coll. B. Cóndor-Luján, 29 May 2015. UFRJPOR 8302, UFRJPOR 8310, UFRJPOR 8311, UFRJPOR 8312, UFRJPOR 8313, UFRJPOR 8314, UFRJPOR 8315, UFRJPOR 8316, UFRJPOR 8318, UFRJPOR 8319, UFRJPOR 8320, UFRJPOR 8321, UFRJPOR 8322, UFRJPOR 8323, UFRJPOR 8324, UFRJPOR 8325, UFRJPOR 8326, UFRJPOR 8327,

UFRJPOR 8328, Amédien Cave, Guadeloupe, Caribbean Sea (16°30.033' N, 61°28.774' W), 4–6 m depth, coll. B. Cóndor-Luján, 31 May 2015.

Etymology. From its colour alive, which can be white or yellow.

Type locality. Tintamare Island, Saint Martin, Caribbean Sea

Colour. Yellow (Fig 2A) or white (Fig 2B) when alive and beige or white (Figs 2 C–D) after preservation in ethanol.

Morphology. Cormus massive and lobate (Figs 2 A–B), firm and compressible. The holotype is 14 x 10 x 3 mm. The cormus is composed of tightly and regular anastomosed tubes (Figs 2 C–D) and it is covered by a thin cortical membrane (Fig 3A) rough to the touch. The atrial cavity is located underneath the osculum and it is surrounded by a detachable membrane (arrow in Fig 3A), which is brilliant and hispid. The number of oscula varies among specimens, but a thin membrane always surrounds them (Fig 3B). The aquiferous system is solenoid (Fig 3C). No granular cells were observed.

Skeleton. The oscular skeleton is composed of sagittal triactines and tetractines, the tetractines being more abundant than the triactines (Fig 4A). The cortical skeleton has large regular triactines (Figs 3E, 4B). Surrounding the inhalant apertures, there are small regular and sagittal triactines of the same category of those present in the tubes. A subcortical skeleton is present. It is composed of sagittal triactines whose paired actines support the cortical skeleton (Fig 3D). In the choanosome, the skeleton of the tubes is disorganized, composed of abundant small and regular triactines and tetractines, the tetractines being less abundant (Fig 3F). The atrial skeleton is also

composed of small and regular triactines and tetractines, but in this case, tetractines are the most abundant spicules (Fig 3C). Spicules (Figs 4 C–G, Table 2).

Oscular triactines and tetractines (Figs 3B, 4A): Sagittal. Actines are slightly conical with blunt to sharp tips. The unpaired actine is longer than the paired ones, which are bent. The apical actine of the tetractines is shorter than the basal ones, slightly cylindrical, sharp, smooth and curved at the tip. Size (triactines): 54.0–170.1/8.1–15.3 µm (paired actines) and 78.3–170.1/8.1–15.3 µm (unpaired actines). Size (tetractines): 75.0–130.0/8.2–15.0 µm (paired actines), 75.0–130.0/9.8–15.0 µm (unpaired actines) and 54.5–83.5/2.5–5.0 µm (apical actine).

Cortical triactines (Fig 4C): Regular (equiangular and equiradiate). Actines are conical with sharp tips. Size: 170.0–259.2/16.2–27.0 µm.

Subcortical triactines (Fig 4D): Sagittal. Actines are slightly conical to cylindrical with blunt to sharp tips. Usually, the unpaired actine is longer than the paired ones, which are bent. Size: 51.3–94.5/5.4–8.1 µm (paired actines), 72.9–126.9/5.4–8.1 µm (unpaired actines).

Choanosomal and atrial triactines and tetractines (Fig 4E, 4F): Regular (equiangular and equiradiate). Actines are slightly conical to cylindrical with blunt to sharp tips. The triactines around the inhalant canals are sagittal. The apical actine of the tetractines is shorter than the basal ones, slightly cylindrical, sharp, smooth, and slightly curved at the tip (Fig 4G). Size (triactines): 62.1–116.1/5.4–13.5 µm. Size (tetractines): 72.9–116.1/5.4–12.2 µm (basal actines) and 43.2–91.8/5.4–8.1 µm (apical actine).

Ecology. Specimens were found from 4.0 to 21.7 m of depth. The individuals collected at Amédien Cave (Guadeloupe) and at Circus (Tintamare Island, Saint Martin) were found on the roof and/or walls of a cave and they were white; whereas, specimens from Saint Martin were collected in semi-dark caves or in reef crevices (associated with ascidians or growing on corals), in a benthic community mainly dominated by sponges, and they were yellow.

Distribution. Anguilla, Saint Martin and Guadeloupe, Lesser Antilles, Caribbean Sea. MEOW ecoregion: Eastern Caribbean.