Okenia picoensis, Paz-Sedano & Ortigosa & Pola, 2017

Paz-Sedano, Sofía, Ortigosa, Deneb & Pola, Marta, 2017, A new Okenia Menke, 1830 from the Azores Islands, Portugal, Spixiana 40 (1), pp. 13-22 : 15-17

Okenia picoensis spec. nov.

Figs 1-3

Etymology. The specific epithet, a Latin adjective, refers to the island where the new species was found.

Distribution. This species is known only from Pico Island, Azores Archipelago ( Portugal) (present study).

Type material. Holotype: Azores, Pico Island, Porto Calhau , near shore, 8 m depth, 5 mm (alive), 3 mm (preserved), collected by J. Hart, 25 Jun. 2013 (Photo_6, “yellow”; COI; SEM: radula, penis) ( MB28-004386 ) . – Paratypes: Azores, Pico Island , Porto Calhau , 12 m, 3 mm (alive), 1.5 mm (preserved), collected by J. Hart, 26 Nov. 2013 (Photo _1, “white”; COI; SEM: radula) ( MB28- 004387 ) . Azores, Pico Island , Porto Calhau. 8 m, 4 mm (alive), 2 mm (preserved), collected by J. Hart, 30 Nov. 2013 (Photo _3, “white”; COI y 16S; SEM: radula, penis, mantle). ( MNCN15 .05/60181) . Azores, Pico Island , Porto Calhau. 8 m, 3 mm (alive), 2 mm (preserved), collected by J. Hart, 19 Nov. 2013 (Photo _4, “yellow”; 16S) ( ZSM Mol 20170110) . Azores, Pico Island, Santo Mateus , 16 m, 4 mm (alive), 2.5 mm (preserved), collected by J. Hart, 25 Nov. 2013 (Photo _5, “yellow”; SEM: radula, spicules, mantle) ( MB28-004388 ) .

Additional material. Azores, Pico Island , Porto Calhau. 8 m, 4 mm (alive), 2 mm (preserved), collected by J. Hart, 30 Nov. 2013 (Photo _2, “white”) ( ZSM Mol 20170111) . Azores, Pico Island, Santo Mateus , 16 m, 3 mm (alive), 2 mm (preserved), collected by J. Hart, 25 Nov. 2013 (Photo _5, “yellow”; COI; SEM: penis, mantle) ( MNCN15.05 /70406) . Azores, Pico Island , near shore, 8 m, 3 mm (alive), 2 mm (preserved), collected by J. Hart, 25 Jun. 2013 (Photo _7, “yellow”; SEM: radula) ( MNCN15.05 /70407) . Azores, Pico Island, Sao Caetano , 30 m, 2.5 mm (alive), 1.5 mm (preserved), collected by J. Hart, 2 Nov. 2013 (Photo _8, “yellow”; SEM: radula, penis) ( MB28-004389 ) .

Description

External morphology ( Fig. 1 ). Living animals up to 5 mm in length. Body high and elongate. Mantle covered by long spicules of different sizes and with bulges along them. There is a well-developed notal border with five lateral papillae, symmetrically distributed on each side of body. Two anteriormost papillae situated in front of rhinophores, two behind gill and remaining three on each side between rhinophores and gill. Papillae elongate, narrow and cylindrical, increasing in length and width from anterior to posterior papillae. A single medial papilla present mid-dorsally anterior to gill. It arises from a mid-dorsal ridge, which extends from rhinophores to beginning of papilla. Rhinophores elongated and slender bearing between 7 and 9 lamellae at the dorsal and lateral portion, but not at anterior part. Tips of rhinophores lack any lamellae. Gill comprised by 4 unipinnate branches arranged in an arch around anus; their shape and length similar to those of papillae. Two anterior branches share same stalk. Foot long and slender. A thick muscle ring surrounding mouth. Two oral tentacles relatively short at anterior part, on both sides of mouth. Reproductive opening on right side of body.

Colour pattern ( Fig. 1 ). Species showing intraspecific colour variation. Some specimens bright yellow with ends of rhinophores, gill branches and tail coloured in orange ( Fig. 1A ). Some specimens white but with same ends coloured in yellow ( Fig. 1B ). There are also specimens with yellowish transparent ground colouration that may or may not have tips of these structures orange or yellow coloured ( Fig. 1C- D ). In all cases specimens entirely covered by bright spicules.

Foregut anatomy ( Figs. 2A , 3 ). Buccal bulb ( Fig. 2A ) thick and muscular. Buccal pump large expanding dorsally and posteriorly. Radular sac short descending ventrally. Thin oesophagus inserts into buccal bulb behind buccal pump. Nervous system surrounding this union. Rounded salivary gland present on either side of buccal bulb at point where oesophagus enters mass. Labial cuticle surrounding lips and expanding inside buccal pump; with signs of individual jaw elements ( Fig. 3A- B ). Radular formula of all dissected specimens 19× 1.1.0.1.1 ( Fig. 3C ). Inner lateral teeth have a pointed cusp with a masticatory margin bearing between 20 and 30 denticles ( Fig. 3D- E ). Denticles at either end of row shorter. Outer teeth small, with broad quadrangular base and large hook cusp ( Fig. 3F ).

Reproductive system ( Fig. 2B ). Located at anterior third of body. Thin and elongate hermaphroditic duct begins at ovotestis, inside digestive-hermaphrodite gland. It expands into a small oval ampulla. A short postampullar duct runs inside female gland mass and splits into a thin short oviduct and large and tubular prostatic portion of vas deferens. Distal end of prostatic part narrows into relatively short and thin ejaculatory duct that terminates in penis lacking penial spines. Vagina shorter than vas deferens but similar in width. It connects to a large spherical bursa copulatrix. A short duct emerges from vagina before entering bursa copulatrix and leads to a large and elongate seminal receptacle. Bursa copulatrix and seminal receptacle more or less similar in size. Uterine duct runs from base of seminal receptacle and enters female gland mass.

Molecular results

Amplifications were not successful for some genes ( Table 1). Therefore, we only aligned the COI sequences of 658 bp. The phylogenetic tree based on COI sequences including all Okenia available at the moment is shown in Figure 4 . It shows that the monophyly of the genus (IB= 1, ML =97, MP = 100) is highly supported. It also confirms that all colour patterns found in Okenia picoensis spec. nov. are intraspecific variation (IB =1, ML = 97, MP = 100). Nevertheless, the relationship between the included species within this genus is not resolved.Three clades of sister species were well supported, clustering Okenia rosacea (MacFarland, 1905) and Okenia hiroi (IB= 1, ML = 96, MP= 75), Okenia amoenula (Bergh, 1907) and Okenia aspersa (IB =0.99, ML = 83, MP =75) and Okenia felis Gosliner, 2010 and Okenia picoensis spec. nov. (IB= 1, ML =94, MP =51). The COI genetic distance between O. felis and Okenia picoensis spec. nov. is 16.8 %. Table 2 depicts the minimum COI gene pairwise uncorrected p -distances amongst sister species of Okenia in Figure 4 .

Figures

Fig. 1. Okenia picoensis spec. nov. Photographs of the living animals from Pico Island. A. Holotype, MB28-004386 (5 mm). B. Paratype, MNCN15.05/60181 (4 mm). C. MB28-004389 (2.5 mm). D. MNCN15.05/70406 (3 mm). Photographs by Justin Hart.

Fig. 2. Okenia picoensis spec. nov. A. Buccal bulb. B. Reproductive system. Abbreviations: am, ampulla; bc, bursa copulatrix; bp, buccal pump; fgm, female gland mass; hd, hermaphroditic duct; oe, oesophagus; pr, prostate; ra, radular sac; rs, seminal receptacle; sgl, salivary gland; ud, uterine duct; va, vagina; vd, vas deferens. Scale bars: 0,5 mm.

Fig. 3. Okenia picoensis spec. nov. Scanning electron micrographs (Holotype, MB28-004386). A. Labial cuticle. B. Detail of the cuticle. C-D. Radula. E. Outer laterals. F. Inner laterals. Scale bars: A, 100 µm; B, 30 µm; C, 300 µm; D, 50 µm; E, 10 µm; F, 30 µm.

Fig. 4. Phylogenetic hypothesis based on COI. Numbers above branches represent posterior probabilities from BI and bootstrap values for ML. Numbers below branches show values for MP.