Dendronotus frondosus ( Ascanius, 1774 )

Ekimova, I. A., Schepetov, D. M., Chichvarkhina, O. V. & Chichvarkhin, A. Yu., 2016, Nudibranch molluscs of the genus Dendronotus Alder et Hancock, 1845 (Heterobranchia: Dendronotina) from Northwestern Sea of Japan with description of a new species, Invertebrate Zoology 13 (1), pp. 15-42 : 31-32

Dendronotus frondosus ( Ascanius, 1774)

Figs. 3–5 .

Amphitrite frondosa Ascanius, 1774: 155–158 , pl. 5, fig. 2.

See Robilliard (1970) and Ekimova et al. (2015) for a full list of synonyms

Material examined: W204, 1 specimen, Sea of Japan, Amursky Bay, near the Institute of Marine Biology, 2–5 m depth, coll. K. Dudka, 25 May 2014 ; W205, Sea of Japan, Amursky Bay, near the Institute of Marine Biology, 2–5 m depth, coll. K. Dudka, 25 May 2014 .

Description: External morphology ( Figs. 3 , 5A ). Body elongate, laterally compressed. Foot narrow, tail short. Oral veil with 10–14 short lip papillae and 4–5 secondary branched appendages. Rhinophoral sheaths with long stalk and five crown appendages. Lateral papilla moderate in size with small secondary branches. Rhinophores with 6–10 lamellae. 5 pairs of dorsolateral processes. Dorsolateral processes moderately branched by secondary and tertiary branches of similar size ( Fig. 5A ). Digestive gland diverticula penetrate dorsolateral processes and rhinophoral branched processes. These diverticula in first pair of cerata and rhinophores originate from anterior lobe of digestive gland; others arise from posterior lobe. Anal opening on right side of body about midway between first and second pair of dorsolateral processes. Reproductive openings lateral, below first pair of dorsolateral processes on right side.

Colour ( Fig. 3 ): Background colour usually white or light-pink. Brown spots, lines, stripes and dots placed on dorsal side of body und upper parts of foot. Body covered by opaque golden or white pigment on which placed in small tubercles or gathered in large spots. Digestive gland diverticula can be seen through transparent body wall, digestive gland brown. Rhinophores similar in colour to body.

Internalmorphology ( Figs.4 , 5B–D ):Length of dorsal processes of jaws about one-third length of jaw body. Inclined posteriorly at about 30°. Masticatory process about one-fifth as long as jaw body, slightly curved downwards. Masticatory border without denticles ( Fig. 4D ). Masticatory process strong, dark at base, transparent and subulate posteriorly. Jaw body yellow, brown towards masticatory border and ligament. Radula formula: 33 × 6–7.1.6–7 (W205). Rachidian tooth strong, triangular, approximately 1.2 times longer than width. Rachidian tooth bears 8–12 well-defined sharp denticles with large furrows on both sides of reduced cusp ( Fig. 4B, C ). Lateral teeth slightly curved towards midline and possess 5–10 large sharp denticles ( Fig.4E ). Outermost lateral teeth flattened with two or three reduced denticles. Innermost laterals thin and highly denticulated. Reproductive system triaulic ( Fig. 5C, D ). Ovotestis consists of numerous white rounded lobules. Long hermaphroditic duct leads to wide semicircular ampulla. Prostate discoid body consists of 16–30 small alveolar glands. Distal part of vas deferens long and winding, expanding to elongate penis. Oviduct connects through insemination duct into female gland complex. Vagina long, gradually narrowing into a rounded seminal receptaculum, and then connecting into oviduct and female gland mass. Bursa copulatrix small and rounded. Female genital aperture opens posterior to penis on right side of body, between first and second pairs of dorsolateral processes.

Ecology: Depth range does not exceed 20 m ( Ekimova et al., 2015; present study). Feeds on several tecaphoran hydrozoan species from genera Obelia , Dynamena , Gonothyraea , and Laomedea . Egg mass is narrow cord, forms an irregular, compressed off-white spiral. Reproduction period from June to October; the larva is a planctotrophic veliger with oval shell.

Distribution: North-West and North-East Atlantic, including the White and the Barents seas, north parts of the Sea of Japan

Figures

Fig. 3. Dendronotus frondosus, living animals. A — W204, specimen 16 mm in length, lateral view from the left. B — W205, specimen 19 mm in length, lateralviewfromtheright.PhotosbyA.Chichvarkhin. Рис. 3. Dendronotus frondosus, фотографии жи- вых особей. A — W204, особь 16 мм длиной, вид с левой латеральной стороны. B — W205, особь 19 мм длиной, вид с правой латеральной сторо- ны. Фотографии А. Чичвархина.

Fig. 4. Dendronotus frondosus, scanning electron micrographs of the radula and masticatory border of jaws. W205, specimen 21 mm in length. A — posterior part of the radula, main view; B — rachidian and lateral teeth; C — rachidian teeth; D — masticatory border of jaws, denticles are absent; E — lateral teeth. Scale bars: A — 100 µm; B, C, E — 20 µm; D — 30 µm. Рис. 4. Dendronotus frondosus, микрофотографии участков радулы и жевательной поверхности челюстей (СЭМ). W205, особь 21 мм длиной. A — ЗаднЯЯчасть радулы, обЩий вид; B — центральные и латеральные Зубы; C — центральные Зубы; D — жевательнаЯ поверхность челюстей, Зубчики отсутствуют; E — латеральные Зубы. МасШтаб: A — 100 мкм; B, C, E — 20 мкм; D — 30 мкм.

Fig. 5. Dendronotus frondosus, drawings of the external morphology and anatomy. A — dorsolateral appendages branching pattern; B — jaws; C — main view of reproductive system; D — reproductive system, detailed. Abbreviations: 1o — primary stalks; 2o — secondary branches; 3o — tertiary branches; amp — ampulla; bc — bursa copulatrix; bj — jaw body; dp — dorsal process of the jaw; fgm — female gland mass; hd — hermaphroditic duct; mp — masticatory process of the jaw; ov — oviduct; p — penis; pg — prostata; rs — receptaculum seminis; va — vagina; vd — vas deferens. Scale bars 1 mm. Рис. 5. Dendronotus frondosus, особенности внеШней и внутренней морфологии. A — особенности ветвлениЯ дорсолатеральных отростков; B — челюсти; C — обЩий вид половой системы; D — область овидукта, деталиЗировано. ОбоЗначениЯ: 1o — первичные ветви; 2o — вторичные веточки; 3o — третичные веточки; amp — ампулла; bc — копулЯтивнаЯ сумка; bj — тело челюстей; dp — дорсальный отросток челюстей; fgm — женские желеЗы; hd — гермафродитный проток; mp — жевательный отросток челюстей; ov — овидукт; p — пенис; pg — простата; rs — семЯриемник; va — вагина; vd — семЯпровод. МасШтаб 1 мм.