Larsonella pumilus ( Larson & Hoese, 1980 )

Hanahara, Nozomi, Higashiji, Takuo, Shinzato, Chuya, Koyanagi, Ryo & Maeda, Ken, 2019, First record of Larsonella pumilus (Teleostei: Gobiidae) from Japan, with phylogenetic placement of the genus Larsonella, Zootaxa 4695 (4), pp. 367-377 : 370-373

Larsonella pumilus ( Larson & Hoese, 1980)

[New Japanese name: Yuuna-haze]

( Figs. 1–4 ; Table 2 )

Lubricogobius pumilus Larson & Hoese, 1980: 41 (type locality: Indian Ocean, 3°25’N 47°14.8’E, 37–38 m depth). Larsonella pumilus ( Larson & Hoese, 1980) : Randall & Senou 2001: 11.

Material examined. OCF-P 3808, 21.6 mm SL, East China Sea off Seragaki, Onna Village, Okinawa, Japan, 11 August 2017.

Description. Counts and measurements are shown in Table 2 . Head depressed, trunk nearly cylindrical, and tail compressed. Eyes located dorsolaterally. Mouth strongly oblique with angle to body axis about 60 degrees. Lower jaw protruding beyond upper jaw. Posterior end of upper jaw reaching below middle point between anterior margin of iris and anterior margin of pupil. Canine-like teeth aligned on edges of anterior halves of premaxilla and dentary; four and three teeth on one side of premaxilla and dentary, respectively; posterior teeth larger ( Fig. 2A ). An inner row of conical teeth extending from anterior part to more posterior part of dentary than the outer canine-like teeth row ( Fig. 2B ). Additional small conical teeth observed on inner parts of premaxilla and dentary with a stereomicroscope, but no such small teeth with micro-CT.

First dorsal fin with six spines. Second dorsal fin with one spine and nine soft rays. First and second dorsal fins connected by a low membrane behind last spine of the first dorsal fin. Anal fin with one spine and eight soft rays. Caudal fin rounded, with 17 segmented rays. Pectoral fin with 18 soft-rays. Pelvic fin with one spine and five soft rays. Posterior tips of pectoral fins reaching or exceeding position of anus, according to a photograph taken in life ( Fig. 1A ), although they are broken in the preserved specimen. Pelvic fins without frenum. Vertebrae 10 + 16 = 26; dorsal-fin pterygiophore formula 3-22110; epural 1; anal-fin pterygiophores anterior to first haemal spine 2.

Head and body largely naked except for posterior part of caudal peduncle, involving three rows composed of 7–10 ctenoid scales along dorsal midline. A row of three ctenoid scales along lateral midline, and three rows composed of 6–8 ctenoid scales along ventral midline ( Fig. 3 ). No sensory canals or associated pores on head. Cephalic sensory papillae patterns illustrated in Fig. 3 . Infraorbital area with five transverse rows of sensory papillae.

Color in preservative ( Fig. 1C ): Background of head and tail white, trunk yellowish white. All fin membranes transparent. Melanophores scattered on dorsal half of trunk and on membranes of first and second dorsal, anal, and pelvic fins. Pectoral fin also with a few melanophores. Three rows of tiny melanophores arched between right and left eyes ( Fig. 4A ). Infraorbital area with two transverse rows of tiny melanophores ( Fig. 4B ) and another row of tiny melanophores behind eyes ( Fig. 4B ). These melanophore rows arranged radially around eyes.

Color in life ( Fig. 1A ): Body and all fins yellow or yellowish orange. Arrangement of melanophores same as after preservation, described above ( Fig. 1A ).

Habitat. We collected ten specimens of five invertebrate species from the muddy bottom at a depth of 209–220 m using the ROV, on 11 August 2017. These included five live comb jellies, Lyrocteis imperatoris , a sea cucumber, Holothuria dura , a starfish, Asterodiscides japonicus , a heart urchin, Pericosmus sp., and an empty shell of Xenophora chinensis ( Fig. 5 ). After these animals were put into a tank on the boat, the L. pumilus specimen was found in the tank. Because Lubricogobius species, close relatives of Larsonella pumilus , often inhabit empty shells, sea urchin tests, tunicate siphons, bottles, etc. ( Randall & Senou 2001; Allen & Erdmann 2016), we believe that the L. pumilus was inside the empty shell of X. chinensis (collected at a depth of 214 m) and was collected with it.

Mitochondrial DNA analysis. We succeeded in assembling the entire mitochondrial genomes of Larsonella pumilus and 19 related species ( Table 1 ). In the phylogenetic tree, using 15559 bp of aligned mitochondrial genomes ( Fig. 6 ), most nodes, including L. pumilus , were supported by high bootstrap values (100%) and bayesian posterior probabilities (1), indicating that L. pumilus was placed in a clade including Priolepis spp. and Trimma spp., while Gobiodon spp. was placed in another clade with Callogobius spp., Vanderhorstia sp., Asterropteryx semipunctata , Eviota spp., Amblygobius phalaena , Valenciennea longipinnis , and Parioglossus spp. Larsonella pumilus was paired with Priolepis cincta , and they were placed within the Priolepis lineage.

Figures

FIGURE 1. Larsonella pumilus, OCF-P 3808 (21.6 mm in standard length), in life (A), fresh (B), and after preservation (C).

FIGURE 2. Three-dimensional images of the head of Larsonella pumilus reconstructed from microcomputed tomography data. A, frontal view, showing the outermost teeth. B, mid-sagittal view of the right side (cut along section x-x’ in A), showing inner teeth without a part of ceratohyal and 5th branchiostegal ray to observe teeth easily. Red, premaxilla and outermost teeth on the premaxilla; blue, dentary and outermost teeth on the dentary. Triangles, vestiges of missing teeth. Scale bars, 1 mm.

FIGURE 3. Picture of the caudal peduncle, stained with cyanine-blue solution to show scale arrangements (left) and schematic illustrations of cephalic sensory papillae (right) of Larsonella pumilus (OCF-P 3808, 21.6 mm SL) in dorsal (top), lateral (middle), and ventral (bottom) views. AN and PN, anterior and posterior nares, respectively. Dotted lines, the probable undamaged states of the damaged parts.

FIGURE 4. Pigmentations around the eyes of Larsonella pumilus (OCF-P 3808, 21.6 mm SL) in dorsal (left) and lateral (right) views. Photos were taken after preservation.

FIGURE 5. Underwater photograph (A) and a dried shell (B and C) of Xenophora chinensis. A, Collecting the shell in which Larsonella pumilus may have taken refuge, using a Remotely Operated Vehicle at a depth of 214 m in the East China Sea off Seragaki, Onna Village, Okinawa, Japan. B (dorsal view) and C (ventral view) are likely the same shell as A. Scale bars, 10 mm.

FIGURE 6. Molecular phylogeny of Larsonella pumilus and 19 related goby species from the Ryukyu Archipelago. Tree topology and branch lengths were obtained from maximum likelihood analysis of aligned mitochondrial genomes (15559 bp) with 100 bootstraps based on the GTR+I+Gamma model. The scale bar indicates 0.1 substitutions per site. Numbers on major nodes represent ML bootstrap support. Bayesian posterior probabilities are summarized as asterisks for values equal to 1.