Bornella johnsonorum, Pola, Marta, Rudman, William B. & Gosliner, Terrence M., 2009

Pola, Marta, Rudman, William B. & Gosliner, Terrence M., 2009, Systematics and preliminary phylogeny of Bornellidae (Mollusca: Nudibranchia: Dendronotina) based on morphological characters with description of four new species, Zootaxa 1975, pp. 1-57 : 40-42

publication ID	https://doi.org/ 10.5281/zenodo.185130
DOI	https://doi.org/10.5281/zenodo.5689413
persistent identifier	https://treatment.plazi.org/id/03F98793-FFB3-7219-2BCF-FF4FA18BFA8B
treatment provided by	Plazi
scientific name	Bornella johnsonorum
status	sp. nov.

Treatment

Bornella johnsonorum View in CoL sp. nov.

( Figures 16 View FIGURE 16 E–F, 15D, 19)

Material Examined: Holotype: CAS 175407, Marshall Islands, Oceanside Ennubuj-Ennylabegan reef, Kwajalein Atoll, in ledge at night, 15 m depth, 20 mm, alive, 21 April 2007, coll: S. Johnson. Paratypes: CAS 175405, Marshall Islands, Oceanside Ennubuj-Ennylabegan reef, Kwajalein Atoll, in ledge at night, two specimens 15 and 20 mm preserved (1 dissected), 12–15 m depth, 24 December 2004, coll: S. and J. Johnson. CAS 175406, Marshall Islands, Oceanside Ennubuj-Ennylabegan reef, Kwajalein Atoll, in ledge at night, one specimen 22 mm preserved (dissected), 15 m depth, 14 April 2007, coll: S. Johnson. CAS 175408, Marshall Islands, Oceanside Ennubuj-Ennylabegan reef, Kwajalein Atoll, in ledge at night, one specimen 20 mm preserved (dissected), 15 m depth, 12 November 1988, coll: S. Johnson. CAS 175409, Marshall Islands, Oceanside between Kwajalein and SAR Pass, Kwajalein Atoll, in ledge at night, one specimen 10 mm preserved (dissected), 12 m depth, 25 March 1989, coll: S. Johnson.

Etymology: This species is named after Scott and Jeannette Johnson, who kindly collected the specimens and provided highly valuable information about them.

Geographic distribution: Thus far this species is known only from Marshall Islands.

External morphology: The general body shape is elongate and limaciform with the posterior end of the foot being long and tapering. The background color is translucent clear with the orange to orange-brown viscera showing through ( Figs. 16 View FIGURE 16 E,F). Epidermal and sub-epidermal white flecks are scattered all over, mostly aggregated into patches of varying sizes. In some specimens, a faint, diffuse orange reticulation is visible around the whitish patches. On either side of the mouth is a lobe-like oral tentacle with 9–10 papillae arranged along the margin. The rhinophore sheaths have a narrow stalk and the posterior papilla is slender, about three times taller than the three anterior and anterolateral papillae. The rhinophore sheaths and anterior papillae are colored as in the rest of the body, while the tall posterior papilla, on each sheath, is mostly white. None of the papillae have an orange subapical ring. The rhinophores are translucent white with a minute orange tip and have approximately 16 to 18 lamellae. There are five to six pairs of dorsolateral processes, with one or two small, unpaired processes near the tail. The first dorsolateral process on each side has two or three bulbous papillae, usually one on the outside and two on the inside. The processes in the second and often the third pair have a single papilla on the outer side. The fourth through sixth processes are usually unbranched, lacking any papillae. They are arranged irregularly on either side of the dorsal midline. The final one or two single processes are very small and located in the dorsal midline. Like those on the rhinophore sheaths, the bulbous papillae are mostly white, without orange subapical rings. Small tripinnate gills are located on the inner surfaces of the first four to six pairs of processes, and become smaller posteriorly. The reproductive opening is on the right side, about two thirds of the way from the rhinophore stalk to the first dorsolateral process. The anus is more dorsal, also on the right, between the first and second dorsolateral process, a bit closer to the second.

Alimentary Canal: The buccal bulb is very small. The labial cuticle is thin, consisting of small overlapping scales, arranged in fairly regular rows. The rodlets are elongate and numerous ( Fig. 19A View FIGURE 19. A – H ). The jaws are roughly oval, without a distinct masticatory process ( Fig. 19B View FIGURE 19. A – H ). The radular formulae of the specimens dissected are: 35 x 14.1.14 (CASIZ 175405, 20 mm preserved), 35– 36 x 10.1.10 (CASIZ 175406, 22 mm preserved; CASIZ 175408, 20 mm preserved), 35 x 9.1.9 (CASIZ 175409, 10 mm preserved). The rachidian teeth are stout, higher than wider, with a large and narrow cusp ( Figs. 19C,D View FIGURE 19. A – H ). On both sides of the cusp there are about 10 to 13 small denticles increasing in size away from the cusp ( Figs. 19E View FIGURE 19. A – H ). The inner laterals have a long basal portion and then are blade-like and pointed, increasing in size away from the center. But usually after the sixth (or eleventh) there is a denticle with a short cusp followed by two plate-like laterals ( Fig. 19C View FIGURE 19. A – H ). A long unpaired oral gland is found ventrally. It extends back from the ventral side of the mouth to the region of the reproductive system. A pair of small, yellowish salivary glands is attached to the posterior side of the oesophagus. The oesophagus is relatively long and runs back to the rounded stomach. The two anterior digestive glands open on the upper surface of the stomach, and each has a single branch entering the first dorsolateral process on its side. The posterior portion of the digestive gland opens on the lower left surface of the stomach. All but the first pair of dorsolateral processes receive branches from the posterior portion of the digestive gland. The posterior chamber of the stomach is thin-walled and its anterior section is armed with longitudinal rows of stubby brown chitinous spines. Because of the distortion in the preserved specimens it was impossible to accurately count the number of rows of spines ( Fig. 19F View FIGURE 19. A – H ). The posterior part of the chamber is wide and raised into well-defined longitudinal folds. From here the intestine descends to the ventral side and then bends dorsally to the anus.

Reproductive system: ( Fig. 15D View FIGURE 15. A – E ). The ovotestis usually consists of four closely packed, rounded or somewhat pyriform follicles lying over the posterior digestive gland. The hermaphrodite duct runs beneath the stomach on the left side, between the stomach and the posterior branch of the digestive gland before expanding into the ampulla which lies on the dorsal side of the female gland mass. On leaving the ampulla, the hermaphrodite duct shortly branches to give rise to the vas deferens and the oviduct, which descends into the female gland mass. The long and greatly folded vas deferens appear to be enclosed in a thin layer of prostate gland tissue, except for a short narrower length near the penial bulb. The opening into the penial bulb is armed with two irregular rings of chitinous hooked spines ( Figs. 19G,H View FIGURE 19. A – H ). A medium-sized pyriform allosperm receptacle opens at the end of the vagina.

Remarks: Although Bornella johnsonorum from Marshall Islands is very similar to B. stellifer , external and internal features can distinguish both species. In color, Bornella johnsonorum lacks the orange subapical rings found on the papillae of the oral tentacles, rhinophore sheaths and dorsolateral processes, which characterize B. stellifer . Structurally, the rhinophore sheaths are very similar to those of B. stellifer , except that the stalk is narrower and the posterior papilla is slender. Internally, the rachidian teeth of B. johnsonorum are approximately equal in height to those of B. stellifer but those of B. johnsonorum are narrower, with a relatively larger cusp and greater number of smaller denticles on either side. Another difference concerns the posterior chamber of the stomach, which in B. stellifer is very long, with very well defined longitudinal rows of pointed spines, while in B. johnsonorum it is shorter and the spines are blunt. Also, in all the specimens dissected of the new species, the penis had two rings of penial spines, while most of the specimens of B. stellifer had more than two rings and the arrangement of the spines appear to be different (see Figures 3 View FIGURE 3. A – F I and 19G,H).

Notes from the collector say that between July 1981 and September 1983, fourteen specimens of the new species were observed, all nocturnally in ledges and caves on Enewetak and Kwajalein Atoll Lagoon pinnacles, at depths ranging from eight to 15 m. When observed under artificial light in caves at night, the animal frequently rises up the anterior third or so of its body, and waves its head back and forth, reminding an observer of a snake.