Extra-branchial processes manifest extra diversity: systematics of the genus Trapania (Nudibranchia: Goniodorididae) and nine new species descriptions Author Smirnoff, Dimitri S. Author Donohoo, Samantha A. Author Gosliner, Terrence M. text Zoological Journal of the Linnean Society 2022 196 270 313 journal article 133821 10.1093/zoolinnean/zlac009 cab69ef3-0fe3-4309-8df7-f8584c027c48 0024-4082 7037746 C288BAB2-A92C-4F13-B04D-D6D4510461F5 TRAPANIA AURATA RUDMAN, 1987 ( FIGS 2F , 4E , 8 ) Trapania aurata Rudman, 1987: 206 ; Rudman & Darvell, 1990 ; Ono, 2004: 97 , top photograph; Gosliner et al. , 2008: 138, top photograph; Hervé, 2010: 154 , top two photographs; Gosliner et al. , 2015: 141 , bottom-left photograph; Gosliner et al. , 2018: 59 , middle-right photograph. Trapania cf. aurata Wägele et al ., 2006 : fig. 12P. Materialexamined: CASIZ186205 ,onespecimen,dissected and sequenced, Anilao Harbor ( 13.75993°N 120.92617°E ), Balayan Bay , Batangas Province , Luzon Island , Philippines , 04 May 2011 , collected by Alexis Principe . Geographical distribution: Known from Hong Kong ( Rudman, 1987 ; Rudman & Darvell, 1990 ; Ono, 2004 ), New Caledonia ( Hervé, 2010 ) and the Philippines (present study). External morphology: The living animal is 6 mm ( Fig.2F ). The body coloration is opaque white with a powdery white appearance. The rhinophores are evenly wide throughout their length and have six lamellae and a pointed tip. They are translucent white at their base, opaque white along the lamellae and reddish orange at their tip and a bit along the front edge. The three gill plume branches are bipinnate and translucent, except for minor reddishorange fringing along the tips of the main branches. Both extra-rhinophoral and extra-branchial appendages are stocky with the same reddish orange coloration along the edges of their tips. The anterior margins of the foot extend laterally as elongate appendages and are more translucent than the rest of the body. Reddish orange coloration adorns their tips, as it does the tips of the elongate, digitiform oral tentacles. The dorsal ridge of the most posterior portion of the foot is tinted reddish orange. Buccal mass: The buccal mass is muscular with a moderately enlarged buccal pump on the dorsal surface. Inside the anterior portion of the mass is a pair of well-developed jaws. The jaws contain at least two rows of acutely pointed jaw elements of various sizes that are tightly packed together with a few gaps between them ( Fig. 8A ). The radular formula is 26 × 1.0.1 ( Fig. 8B ). The older teeth ( Fig. 8C ) are much smaller than the newer ones and the radula widens gradually towards the more newly developed teeth ( Fig. 8D ). The base of the teeth is wide and expanded. The teeth bear numerous acutely pointed denticles with the smallest ones being found on the inner edge of the tooth. There are approximately nine to 12 denticles on the inner side of the much larger primary cusp and one wide, triangular denticle on the outer side of the cusp. The older teeth have fewer denticles than the more recently developed ones and the denticles appear more uniformly graded from smaller to large denticles in the more newly developed teeth. Reproductive system: The mature reproductive system is triaulic ( Fig. 4E ). The narrow pre-ampullary duct enters the saccate ampulla near the distal end of the ampulla. The ampulla narrows again at the postampullary duct and divides into the short narrow oviduct, which enters the female gland mass, and the vas deferens. The vas deferens gradually widens into the thick prostatic portion that loops prior to narrowing briefly. Here it becomes a long smooth ejaculatory segment which transitions into a penial sac. The penial sac terminates adjacent to the vagina. The width of the vagina remains uniform along a long length until it enters the base of the large, spherical bursa copulatrix adjacent to the receptaculum duct. The receptaculum duct curves and enters the base of the smaller, slightly pyriform receptaculum seminis. The uterine duct emerges from the receptaculum duct near the base of the receptaculum and enters the female gland mass. The female gland mass is composed of the large mucous gland and the smaller albumen and membrane glands. Figure 8. Trapania aurata Rudman, 1987 . Scanning electron micrographs of buccal armature, CASIZ 186205. A, jaw rodlets. B, entire radular ribbon. C, older radular teeth. D, newly formed radular teeth. Remarks: The reproductive anatomy of T. aurata is described here for the first time. Following the publication of Gosliner & Fahey (2008) , Rudman (2008) discussed difficulties in distinguishing T. aurata from T. vitta . Our molecular phylogeny, the ABGD analysis and the bPTP analysis suggest that these two species are sister to one another with a strong genetic divergence of 16.3–17.8% in the COI gene and 6.8−7.3% in the 16S gene ( Tables 3 , 4 ). Due to the unavailability of additional specimens, T. aurata intraspecific variation was not studied here, but T. vitta has minimal intraspecific variation (0.0–0.8%) between four specimens collected in Palau and the Philippines . There are also consistent external and internal morphological features that permit the distinction between the two species. Externally, T. aurata has orange lines along the edges of the extra-branchial and extra-rhinophoral appendages that are absent in T. vitta . Rudman noted variation in the other orange markings on the head, gill and foot between the two species, but the pigment differences on the extrabranchial and extra-rhinophoral appendages remains consistent. Internally, Gosliner & Fahey (2008) noted radular differences between the width of the outermost denticle of the radular tooth. With the addition of the material studied here, other radular differences are evident. The teeth of T. aurata are more sharply curved than those of T. vitta ( Gosliner & Fahey, 2008 : fig. 20C, D). Additionally, the denticles on the inside of the primary denticle are more elongated in T. aurata and much shorter and evenly graded in size in T. vitta . The reproductive systems of the two are extremely similar with the possible exception that the prostatic portion of the vas deferens appears slightly more convoluted in T. aurata ( Gosliner & Fahey, 2008 : fig. 21; Fig. 4E ).