Acyrtus pauciradiatus Sampaio & Nunes & Mendes 2004, new species

Acyrtus pauciradiatus, new species

Fig. 1

Holotype. MZUSP 84516, 16.3 mm SL, Brazil, off State of Pernambuco, Fernando de Noronha Archipelago, Rata Island, in Ressurreta Bay, at a depth of 12m; L. F. Mendes, 12 Dec 1997.

Paratypes. UFRN 0001, 13.2 mm SL; MOVI 37363, 12.6 mm SL, collected with holotype.

Diagnosis. Acyrtus pauciradiatus can be readily distinguished from all its congeners by the following combination of characters: pelvic disc small (2.9­3.7 times in SL vs. 2.8­3.2 in Acyrtus rubiginosus, and 2.3­2.6 in Acyrtus artius), shallow body depth (5.4­6.6 times in SL vs. 4.9­5.4 in A. rubiginosus, and 4.2­4.3 in A. artius), broad interorbital width (2.2­2.5 times in head length vs. 3.0­ 3.8 in A. rubiginosus, and 2.8­3.6 in A. artius), broad peduncle depth (0.5­0.7 times in its length vs. 1.3­2.3 in A. rubiginosus, and 1.2­1.4 in A. artius), short snout (6.6­11.0 times in head length vs. 3.3­4.3 in Acyrtus rubiginosus, and 3.7­4.0 in A. artius), short post­dorsal length (1.1­1.5 times in dorsal length vs. 0.8­1.0 in A. rubiginosus, and 1.0­ 1.2 in A. artius), dorsal­fin rays 7­8 (vs. 9­10 in A. rubiginosus, and 8 ­ 9 in A. artius), anal­fin rays 6 ­ 8 (vs. 7­9 in A. rubiginosus, and 7 in A. artius), caudal­fin rays 11­12 (vs. 7­9 in A. rubiginosus, and 8 ­ 9 in A. artius) and pectoral­fin rays 20­22 (vs. 25­26 in A. rubiginosus, and 24 ­ 25 in A. artius). Furthermore, the new species can be diagnosed by ten rows of papillae across width of disc region A; ten rows across width of disc in region B, and four or five rows across width of disc in region C.

Description: Meristic and proportional measurements of the holotype and two paratypes given in Table 1. Body moderately depressed, depth 5.4­6.6 in SL. Caudal peduncle short 0.5­0.7 in its length. Head depressed, head width 2.5­2.6 in SL. Snout steep with a rounded outline, 6.6­11.0 in head length, lower lip mostly covered with small papillae. Diameter of eye 0.6­0.8 in interorbital space and 3.0­ 4.2 in head length. Disc suction large, 2.9­3.7 in SL. Posterior nostril in front of anterior edge of eye, anterior nostril with an intermediate, branched dermal flap extending from is posterior margin. Dorsal to caudal distance great, 1.1­1.5 in dorsal fin length. Anus closer to anal origin than to rear margin of disc. Skin granular, covered with small glands. Maximum known size 16.3 mm SL.

Color in alcohol. Ground color uniform pale and colorless in the type series. Fins hyaline. Very diminutive chromatophores, associated with small gland (visible only with stereomicroscope) on dorsal and lateral surfaces of body.

Color in life. L. F. Mendes made observations of pigmentation in live specimens at the time of collection. Body uniformly pale reddish pink, without marks or bands. The color of the type specimens contrasts with the color of the patch of brown algae (Sargassum sp. and Dictyota sp. Division Phaeophyta), and the living colonies of coral Montastrea cavernosa (predominant coral in Noronha), surrounding the hole from which it was collected.

Distribution. Known only in shallow water at Fernando de Noronha Archipelago, off northeastern Brazil. Probably endemic to the Noronha hotspot, which includes the Fernando de Noronha Archipelago and Atol das Rocas (Rocha, 2003).

Habitat notes. The new species is found in shallow waters at the Fernando de Noronha Archipelago, occurring on hardbottom habitats that consist of areas rich in calcareous and brown algae, corals and sponges. Acyrtus pauciradiatus was collected with the yellownose goby, Elacatinus sp.2 (sensu Moura et al., 2003); manyscaled blenny, Starksia multilepis Williams & Mounts, 2003 and brownbar Goby, Priolepis dawsoni Greenfield, 1989, all endemic cryptic species from Brazilian reefs. Acyrtus pauciradiatus apparently is uncommon at the Noronha Archipelago and only three specimens have been collected.

Etymology. The new species is named pauciradiatus (Latin: having few rays) with reference to the dorsal, anal and pectoral fins rays, which have fewer rays than the other members of genus. The common name “Noronha’s Clingfish” is suggested.