Kaloplocamus japonicus Bergh, 1880

Wei, Jingcheng & Kong, Lingfeng, 2023, Taxonomic review of Kaloplocamus from the Yellow Sea, China with the description of a new species (Nudibranchia, Doridina, Polyceridae), ZooKeys 1168, pp. 107-129 : 107

Kaloplocamus japonicus Bergh, 1880

Figs 6 , 7 , 8 , 9

Euplocamus japonicus : Bergh, 1880, 32, pl. XIII, fig. 17, pl. XIV, figs 3-10.

Type locality.

Japan.

Material examined.

Alcohol-fixed, two specimens, original label: "CN, SD, Tianheng, 36°33.7′N, 120°58.6′E, 04 May. 2022, J.C. Wei " "LSGB hb266000 0201 to 0202"; alcohol-fixed, three specimens, original label: "CN, SD, Tianheng, 36°33.7′N, 120°58.6′E, 04 May. 2022, J.C. Wei " "LSGB hb266000 0203 to 0205" .

Description.

External morphology (Fig. 6 ) Living animals are up to 21 mm in length. The body is elongate, limaciform, and translucent white with pink dots. The entire dorsum is covered in small, opaque, white tubercles. The oral tentacles are flat and thin. The head bears eight velar appendages, approximately half of the length of the rhinophores. These appendages are also translucent white and have elongate, sharp, secondary ramifications. There are four pairs of lateral appendages on the dorsum that are approximately twice as long as the ones on the veil, and they have thicker ramifications. All the appendages share the same coloration as the body. The branchial leaves are situated between the second and third pair of appendages. There are five tripinnate branchial leaves which have the same coloration as the body; the stalks of the branchial leaves have small, dense, white protuberances. The rhinophores have a semitranslucent stalk and an orange-red lamellate clavus with approximately 26-28 rhinophoral lamellae; the clavus has a white tip and a white line on the anterior side. The rhinophoral sheath is short and has small, opaque, white tubercles around its margin.

Radula (Fig. 7 ) The radula formula of a 20 mm specimen is 24 × 17.3.0.3.17, and this species is characterized by two different types of teeth (Fig. 7A-D ). There are three inner lateral teeth per side; the innermost two teeth are similar in shape and have a sharp, hook-like portion at the apex, and the tip is not bifurcated, while the third one has a blunt bifurcation on the tip (Fig. 7D ). All the inner lateral teeth have a secondary cusp, but this structure on the third tooth is not as pronounced as that of the innermost two. The outer marginal teeth are flat and roughly rectangular, and the size of these teeth decreases along the row (Fig. 7C ). The rachis is granulated and does not transversally divide into rachidian plate rows (Fig. 7E ). The jaws have thin, elongate, laminar rodlets which are densely packed (Fig. 7F ).

Reproductive system (Fig. 8 ) The reproductive system is triaulic (Fig. 8 ). The vas deferens is differentiated into an oblong-oval prostate in its distal portion, which is connected to the oval bursa copulatrix. The vagina is thin and approximately half of the length of the vas deferens, entering directly into the bursa copulatrix. From the bursa copulatrix protrudes a short, thick duct with an ampoule-like extension; the female gland mass is connected to that duct via the uterine duct, and on the other side of it, a crooked duct exits that connects to the oval receptaculum seminis. The ampulla is long, coiled, and enters into the female gland mass in a relatively distal position. The penis has spines and is slightly inflated in the distal position (Suppl. material 4).

Egg mass (Suppl. material 5). The egg mass of this species is flat, belt-like, coiled, and translucent with white eggs within.

Remarks.

This species is characterized by several features that are very different from those of the other known species of Kaloplocamus . The most apparent one is its translucent white-pink body coloration, which has never been reported before. Additionally, the way its bursa copulatrix connects to the receptaculum seminis and female gland mass is also different. Most Kaloplocamus species have a Y-shaped structure composed of three ducts of approximately the same width which link these organs, while K. japonicus has an ampoule-like extension on the duct connected to the bursa copulatrix. The extension is approximately twice as wide as the uterine duct and protrudes from the join (Fig. 8 ). This structure was also described by Bergh (1880) and is the main reason we consider our specimens to be K. japonicus . Although Bergh (1880) described K. japonicus as having six appendages on head, it is likely that the last pair of velar appendages were misidentified as dorsal appendages considering that he noted K. japonicus has five pairs of appendages on the dorsum. Eliot (1913) also reported two specimens from Japan, but the coloration of his specimens was not mentioned because they were fixed in alcohol when he examined them. The structure of reproductive system was also absent, and it is impossible to know if the specimens were K. japonicus . The color forms B and C described by Baba (1989) resemble K. japonicus in coloration; however, the reproductive system structures of these forms remain unknown and more evidence is needed to determine whether they are K. japonicus or other undescribed Kaloplocamus species.

Interestingly, there seems to be an aberration on the radula of the specimen examined (Fig. 7C ). The two outer marginal teeth on each row of the left side merges into one, making that side have only 16 outer lateral teeth, while on the right side there are 17 outer marginal teeth without a merged tooth. The merged tooth is approximately twice the width of the largest outer lateral teeth and is erupted from two independent roots. These merged teeth are found in every row of the left side of the radula and this has neither been reported in other species of Kaloplocamus nor found in examined K. japonicus specimens (Fig. 9A, B ).

Figures

Figure 6. Kaloplocamus japonicus, living specimen, 18 mm in length. A dorsal view B lateral view.

Figure 7. Specimen LSGB hb 266000 0203 of Kaloplocamus japonicus, SEM photographs of the radula and jaws A whole radula B, C outer lateral teeth D inner lateral teeth E rachis F jaws. Scale bars: 1000 μm (A); 200 μm (B); 100 μm (C, D); 20 μm (E); 200 μm (F).

Figure 8. Specimen LSGB hb 266000 0203 of Kaloplocamus japonicus, diagram of the reproductive anatomy. Abbreviations: am - ampulla; bc - bursa copulatrix; f - female gland mass; p - prostate; s - receptaculum seminis; u - uterine duct; v - vagina; vd - vas deferens. Scale bar: 1000 μm.

Figure 9. Specimen LSGB hb 266000 0204 of Kaloplocamus japonicus, SEM photographs of the radula A whole radula B outer lateral teeth. Scale bars: 1000 μm (A); 200 μm (B).