Cadlina koreana, Do & Jung & Kil & Kim, 2020

Do, Thinh Dinh, Jung, Dae-Wui, Kil, Hyun-Jong & Kim, Chang-Bae, 2020, A report of a new species and new record of Cadlina (Nudibranchia, Cadlinidae) from South Korea, ZooKeys 996, pp. 1-18 : 1

Cadlina koreana sp. nov. Figures 1 , 4A

Type material.

Holotype. NIBRIV0000865970; South Korea, Gangwon-do, Goseong-gun, Jugwang-myeon, Munamjin-ri; 38°18'14.75"N, 128°34'1.05"E; collected on 02 June 2013 (COI GenBank number: MT420429). Paratype. NIBRIV0000865971; South Korea, Gangwon-do, Goseong-gun, Jugwang-myeon, Munamjin-ri; 38°18'14.75"N, 128°34'1.05"E; collected on 02 June 2013 (COI GenBank number: MT420430).

Other material.

Voucher: SMU00051; South Korea, Gangwon-do, Goseong-gun, Jugwang-myeon, Munamjin-ri; 38°18'14.75"N, 128°34'1.05"E; collected on 02 June 2013 (COI GenBank number: MT420431).

Diagnosis.

Ground color translucent white (Fig. 1A ). Rhinophores and gills opaque white to translucent yellow. Entire dorsum covered by small rounded tubercles with white coloration. Radula formula 57 × 23.1.23. Rachidian tooth rectangular with four main sharp cusps (Fig. 1B ). Innermost lateral teeth massive, wide base; cusp strong, slightly curved; two inner denticles and three to four outer denticles (Fig. 1C ). Outer lateral teeth hamate, well-defined denticles (Fig. 1D ).

Description.

Body elongated ovate; body lengths 10.3 mm (holotype), 14 mm (paratype), and 9 mm (additional specimen). Ground color translucent white (Fig. 1A ). Dorsum broad in front and posteriorly. Mantle broad and wider than foot; thin at the edge. Numerous white specks present at mantle edge, lacking a yellow marginal band. Dorsum covered with numerous small white tubercles. Rhinophores opaque white to translucent yellow; clavus lamellate; cylindrical stalk smooth. Rhinophoral sheath smooth. Gills opaque white to yellow, six multi-pinnate branchial leaves, retractable into gill cavity. Gill sheath bears small nodules. Oral veil forms triangular, lateral sides. Foot anteriorly rounded and thickened. Radula formula: 57 × 23.1.23. Rachidian tooth rectangular with four sharp denticles; two central denticles slightly longer than two lateral denticles (Fig. 1B ). Innermost lateral tooth massive with one large, slightly curved cusp; two short, inner denticles; and three to four outer denticles. Second lateral tooth with one cusp, no inner denticle and four or five outer denticles. Middle lateral tooth hamate with one large cusp and up to seven denticles (Fig. 1C ). Outer lateral teeth hamate, comb-shaped with 5-7 clearly visible denticles (Fig. 1D ). Reproductive system triaulic (Fig. 4A ). Ampulla moderate, convoluted, and connects with female gland and prostate. Prostate long and narrow. Seminal vesicle slightly more swollen than prostate. Vas deferens narrow, smooth, and distinct. Penis armed with spines. Vagina relatively narrow and connects with bursa copulatrix. Bursa copulatrix ovate and ca. 1.5 × larger than receptaculum seminis. Uterine duct short and narrow, bifurcates into female gland and receptaculum seminis.

Remarks.

A comparison of Cadlina species recorded in the northwestern Pacific region is presented in Table 2 . Cadlina koreana sp. nov. is most similar externally to C. paninae , differing in color variation of the rhinophores and gills as well as the structure of the radula. In C. paninae , the color of the rhinophores and gills are opaque white while in Cadlina koreana , color of the rhinophores can vary from opaque white to translucent yellow and that of the gills can vary from opaque white to yellow. Cadlina koreana also has fewer rows and fewer denticles on both the rachidian tooth and its lateral tooth compared to those of C. paninae . In addition, the rachidian tooth of C. paninae is often bifurcated at the tips while the rachidian tooth of Cadlina koreana is not bifurcated at the tips.

The external morphology of Cadlina koreana is relatively similar to C. umiushi , which also has small-sized tubercles on the dorsum. However, clear differences between these two species can be observed by comparing their coloration. The color pattern of Cadlina koreana is white without yellow tubercles or a yellow marginal band. In contrast, C. umiushi is semi-transparent white with yellow tubercles and a yellow marginal band. The rachidian tooth of Cadlina koreana is rectangular while it is trapezoid in C. umiushi . The inner denticles of the first lateral tooth of C. umiushi are half the length of the tooth body, but in Cadlina koreana it is less than half the length of the tooth body. Moreover, the outer lateral teeth of Cadlina koreana are hamate with clearly visible denticles. In contrast, the outer lateral teeth of C. umiushi are almost straight with inconspicuous denticles.

Cadlina japonica is distinguished from Cadlina koreana sp. nov. by brownish patches on the dorsum and an elongate rachidian tooth with lobe-like denticles. Cadlina kamchatica clearly differs from Cadlina koreana by its yellowish body color and the higher number of denticles on the rachidian tooth and lateral tooth. The common Cadlina species in the northeastern Pacific, C. luteomarginata MacFarland, 1966, differs from Cadlina koreana by yellow dots on the dorsum and a yellow rim to the mantle. The other species in this region, C. flavomaculata MacFarland, 1905, also has yellow dots on the dorsum that are not present in Cadlina koreana . The color of C. modesta MacFarland, 1966 is light yellowish to light brown while it is translucent white in Cadlina koreana . Compared to Cadlina koreana , three Cadlina species recently described by Korshunova et al. (2020), C. klasmalmbergi , C. jannanicholsae , and C. sylviaearleae have yellow mantle bands and yellow tubercles. In Cadlina koreana , the yellow mantle band is absent and the color of the tubercles is white. The maximum intraspecific distances in C. koreana are 0% for the COI marker and 0.23% for the 16S rRNA marker (Suppl. material 1: Table S3). The lowest COI interspecific distance of 5.78% is found between C. koreana and C. umiushi . The lowest 16S rRNA interspecific distance of 4.56% is found between C. koreana and C. paninae .

Etymology.

The species is named after the country of its type locality.

Distribution.

Cadlina koreana sp. nov. is currently known only from Munamjin-ri, South Korea.

Figures

Figure 1. Cadlina koreana A body; Radula B rachidian teeth C central and lateral region D outer lateral region. Scale bars: 2 mm (A); 10 μm (B); 50 μm (C); 20 μm (D).

Figure 4. Reproductive systems of Cadlina species A Cadlina koreana sp. nov. B Cadlina umiushi C Cadlina japonica. Abbreviations: a, ampulla; bc, bursa copulatrix; fgm, female gland mass; rs, receptaculum seminis; pr, prostate; sv, seminal vesicle; ud, uterine duct; v, vaginal duct; vd, vas deferens. Scale bars: 0.5 mm (A, B); 2 mm (C).