﻿Seven new “cryptic” species of Discodorididae (Mollusca, Gastropoda, Nudibranchia) from New Caledonia

﻿Abstract The study of a well-preserved collection of discodorid nudibranchs collected in Koumac, New Caledonia, revealed the presence of seven species new to science belonging to the genera Atagema, Jorunna, Rostanga, and Sclerodoris, although some of the generic assignments are tentative as the phylogeny of Discodorididae remains unresolved. Moreover, a poorly known species of Atagema originally described from New Caledonia is re-described and the presence of Sclerodoristuberculata in New Caledonia is confirmed with molecular data. All the species described herein are highly cryptic on their food source and in the context of the present study the term “cryptic” is used to denote such species. This paper highlights the importance of comprehensive collecting efforts to identify and document well-camouflaged taxa.


Introduction
The systematics of sea slugs has benefited enormously from the introduction of molecular data analyses, which have dramatically improved species delimitation and phylogenetic reconstruction, facilitating the description and re-description of taxa belonging to notoriously difficult taxonomic groups (e.g., Jörger et al. 2012;Churchill et al. 2014;Ekimova et al. 2015;Martín-Hervás et al. 2021). In this context, the term "cryptic" is widely used to refer to taxa that are morphologically indistinguishable but can be identified or distinguished using molecular data (Jörger and Schrödl 2013). On the contrary, in ecological research, the term "cryptic" has long been used to denote organisms that are camouflaged on their environment or food source (Faulkner and Ghiselin 1983;Dalton and Godwin 2006;Cheney et al. 2014), and this is not uncommon in many sea slug lineages. But, while "cryptic" species of sea slugs and nudibranchs in the systematics sense have received a great deal of attention in recent years, resulting in the description and identification of numerous cryptic species (e.g., Epstein et al. 2019;Knutson and Gosliner 2022), "cryptic" sea slugs in the ecological sense have been somewhat neglected and have received significantly less attention compared to their often brightly colored, extravagantly shaped cousins.
"Cryptic" species of sea slugs in the ecological sense are difficult to collect, requiring a substantial effort by experienced collectors, or the collection and processing of substrate suspected to contain living specimens. With the exception of sacoglossans, for which substrate collection produces specimens relatively easily (Krug et al. 2016(Krug et al. , 2018, few examples of papers describing ecologically cryptic sea slug species have been published in recent years (e.g., Pola et al. 2012;Donohoo and Gosliner 2020).
In this paper we examine a few ecologically "cryptic" species of dorid nudibranchs collected during three research expeditions to Koumac, New Caledonia. These expeditions included a multidisciplinary team of expert collectors and taxonomists, using a combination of a variety of collecting techniques and methods (direct collecting, substrate collecting, autonomous reef monitoring structures (ARMS), underwater vacuum-cleaners, brush baskets, dredging, ROVs, etc.), resulting in an exceptionally well-curated collection. Among the specimens collected were several extraordinarily cryptic species in the ecological sense that would have been difficult to detect without the collecting infrastructure of the Koumac expeditions.
All the species described or re-described herein belong to the family Discodorididae. While this group has been the subject of several monographic reviews Valdés 2002;Dayrat 2010) there is no consensus on the taxonomic structure of the Discodorididae or the number of valid genera. Additionally, molecular phylogenies including substantial coverage of this group (e.g., Mahguib and Valdés 2015;Hallas et al. 2017) have failed to provide enough support to unravel the relationships among different clades. In the present study we use a newly generated molecular phylogeny, including a broad representation of Discodorididae genera, as well as morphological data to provide a framework of classification for the new species described. In some cases, this information is not sufficient to provide definitive generic placements and therefore they are left as tentative.

Source of specimens
The material examined in this study was collected during three expeditions to Koumac, New Caledonia, organized by the Muséum national d'Histoire naturelle, Paris, France (MNHN). All collected specimens were individually photographed, labeled, preserved in 95% ethanol, and deposited at the MNHN. A total of 56 specimens was examined in this study, 46 of which were successfully sequenced (Table 1).

DNA extraction, amplification, and sequencing
From each specimen a small tissue sample (~ 1 mm 3 ) was taken from the foot using sterilized forceps. DNA extraction was conducted using a Chelex protocol using a mixture of 200 µL of 10% Chelex 100 (Bio-Rad.com), blotted tissue (to remove any remaining ethanol), and 4 µL of proteinase K. The 1.7 mL microcentrifuge tubes with the mixture were placed in a water bath for 20 min at 55 °C (cell lysis and protein digestion) followed by placement in a heat block at 100 °C for 8 min (protein denaturation). Then, the microcentrifuge tubes were centrifuged to separate the Chelex beads from the supernatant containing the DNA, and 100 µL of the supernatant was aliquoted and used for DNA amplification.

Data analysis
Forward and reverse sequences were assembled, edited, and consensus sequences were extracted using the computer program Geneious v. 11.1.5 (Kearse et al. 2012). Additional sequences were downloaded from GenBank for comparison (Table 1). Sequences were aligned using the MUSCLE (Edgar 2004) plug-in in Geneious. Gaps in the 16S alignment were removed manually, and concatenation of all three genes was performed in Geneious. Bayesian and maximum likelihood phylogenetic analyses were conducted on the concatenated sequences (partitioned by gene) and on each gene fragment individually. Bayesian analysis was implemented using MrBayes v. 3.2.1 (Ronquist et al. 2012) with the GTR model, using two runs of six chains for 10 million repetitions with a sampling interval of 1,000 repetitions and burn-in of 25% removed. The maximum-likelihood analysis was conducted in RaXMLGUI v. 1.0 (Silvestro and Michalak 2012) using the bootstrap + consensus option and the GAMMAGI model with 10,000 bootstrap repetitions. Hexabranchus sanguineus (Rüppell & Leuckart, 1830) was used to root the resulting trees. Nodes in the resulting phylogenetic tree with Posterior probabilities (PP) ≥ 90% and bootstraps values (MLB) ≥ 70% were interpreted as supported. The Automatic Barcode Gap Discovery (ABGD) software (Puillandre et al. 2012) was used to provide statistical support to determine the number of species in the sample using COI sequences of 107 specimens. Pairwise p-distance values were calculated using MEGA v. 11.0.13 (Kumar et al. 2018) using the Kimura-2 model (Kimura 1980).

Morphological examination
At least two specimens (if available) from each species recovered in the ABGD analysis were dissected to study their reproductive system (including the penis), jaw (if present), and radula. Dissections were performed by a dorsal incision from the middle of the nudibranch to the anterior end. The reproductive system was carefully removed from each specimen and drawn with a camera lucida. The penis was dissected and examined under a compound microscope. The buccal mass (including the radula and jaw) was removed from the anterior end of each animal and placed in a 10% NaOH solution to dissolve soft tissue and expose the radula and jaws. After 20 min to several hours, the radula and labial cuticle (housing the jaw) were rinsed in distilled water and mounted on a small copper plate for Scanning Electron Microscopy (SEM) examination. The samples were sputter-coated with gold and observed under a JSM-6010PLUS/LA SEM at California Polytechnic State University, Pomona, California.
The ABGD analysis recovered 52 distinct species in the sample, which matches the structure recovered in the phylogenetic analysis ( Table 2). The species recovered include all the taxa described below in the systematics section and species currently recognized as valid in the literature. The only exceptions are Diaulula sandiegensis and Diaulula odonohuei (Steinberg, 1963), which ABGD failed to recover as distinct, and  Carminodoris   There are consistent interspecific morphological differences among representative specimens in the clades recovered in the phylogenetic analyses, which also correspond to the species from the species delimitation analyses. These differences included aspects of internal morphology such as radular morphology and reproductive system differences that are discussed in the Systematics section below.

Remarks.
For an in-depth discussion of the characteristics of the genus Atagema and its synonyms see Valdés and Gosliner (2001). Description. Body oval, flattened, covered with large, rounded tubercles decreasing in size towards the mantle margin ( Fig. 2A, B). A central, longitudinal ridge runs between the rhinophores and gill. A series of depressions on each side of the central ridge, generally decreasing in size towards the mantle margin. Entire dorsal surface, except for the depressions, covered with caryophyllidia. Branchial sheath composed of three large lobes; gill composed of five tripinnate branchial leaves, arranged horizontally in the living animal. Rhinophoral sheaths elevated; rhinophores long, lamellated, with 24 lamellae. Juvenile specimens with less marked dorsal tubercles (Fig. 2B). Body color opaque greyish brown in adult specimens, except for the depressions, which are dark brown to black ( Fig. 2A); juveniles translucent gray (Fig. 2B). Rhinophores and branchial leaves are the same color as the dorsum.
Reproductive system (Fig. 3A) with a long, narrow, simple ampulla that connects with the female gland complex and an elongated, convoluted prostate, with several folds. Prostate ~ 3× as long as the ampulla. The prostate narrows slightly before expanding into the long, simple, wide deferent duct. Deferent duct several times as wide as the prostate, but shorter in length. The penis is unarmed. The vagina is long and wide, as wide as the deferent duct, and connects directly to the small, oval bursa copulatrix. The small elongate seminal receptacle also connects to the bursa copulatrix next to the vaginal connection and the short uterine duct that enters the female gland complex. The bursa copulatrix is ~ 2× as large as the seminal receptacle.
Biology. Geographic range including the Indian and Western Pacific oceans (see synonymy and remarks). In New Caledonia it is found under rocks during the day in shallow water, from 0-8 m depth. The specimens examined were obtained by direct collection during low tide and/or SCUBA diving; they were highly cryptic on rocks covered with sponges and other encrusting organisms.
Remarks. Doris spongiosa Kelaart, 1858 was originally described from Sri Lanka and re-described by Valdés and Gosliner (2001), who transferred it to the genus Atagema, and recognized two synonyms, Doris areolata Alder & Hancock, 1864 and Phlegmodoris mephitica Bergh, 1878. This species is common across the tropical Indo-Pacific region and is well characterized and illustrated in modern literature (Wells and Bryce 1993;Yonow 2008;Hervé 2010;Gosliner et al. 2018;Nakano 2018). The specimens here examined from New Caledonia match the original description as well as the common usage of the name in the references above (see Hervé 2010).
Trippa (Phlegmodoris) paagoumenei Risbec, 1928 was originally described based on a single specimen collected in Paagoumene, northern New Caledonia, but it was later reported from Nouméa, southern New Caledonia (Risbec 1930(Risbec , 1953. Risbec (1928) described T. paagoumenei as having a rather tough notum, dark violet in color, except towards the edges of the foot and the mantle, where it has a yellowish tint, and completely covered with purplish green, irregular tubercles. One of the specimens from Nouméa was unusual as it was covered by a bright green deposit of metallic appearance (Risbec 1953). Rudman (2002) considered T. paagoumenei a member of the genus Atagema and a synonym of A. spongiosa, and we concur with this opinion.
Atagema spongiosa is clearly distinct from other species of Atagema recognized as valid in the modern literature, such as Atagema ornata (Ehrenberg, 1831) [= Atagema intecta Kelaart, 1858] and Atagema carinata (Quoy & Gaimard, 1832), illustrated and/or redescribed in Willan and Coleman (1984), Valdés and Gosliner (2001), and Rudman (2005), as well as Atagema echinata (Pease, 1860), illustrated by Tibiriçá et al. (2017) and Gosliner et al. (2018). None of these species possesses the characteristic dorsal pattern of tubercles, depressions with a central ridge present in A. spongiosa. Atagema boucheti , described based in a preserved specimen from New Caledonia deep water (405-411 m depth), is characterized by having the dorsum covered by large, irregularly scattered tubercles, not aligned to form ridges. Although the live color of this species is unknown, the external morphology is clearly different from other species of Atagema including Atagema spongiosa (see Valdés and Gosliner 2001). (Risbec, 1928) Figs 2E, 3D, E, 4G-I Phlegmodoris papillosa Risbec, 1928: 90-91, pl. 8, fig. 2. Type locality: Nouméa, New Caledonia [not indicated in the original description], see Risbec (1953). ?Trippa albata Burn, 1962a: 101-102, text  Description. Body oval, flattened, covered with a complex network of small ridges with two levels of organization (Fig. 2E). The largest ridges cover the entire body, leaving some depressions in between. Smaller ridges occur in the depressions dividing them into smaller fragments. Entire dorsal surface, except for the depressions, covered with caryophyllidia. Branchial sheath composed of three large lobes; gill composed of five tripinnate branchial leaves, arranged horizontally in the living animal. Rhinophoral sheaths elevated; rhinophores long, lamellated, with 16 lamellae. Body color opaque grey with scattered yellow spots; depressions with gray ridges dividing dark grey to black fragments. Gill leaves are the same color as the dorsum. Rhinophores greyish to yellowish cream.

Atagema papillosa
Reproductive system (Fig. 3D, E) with a large, folded ampulla that connects with the female gland complex and an elongate prostate. The prostate is much longer and ~ 2× as narrow as the ampulla. The prostate narrows substantially into a long, folded tube before expanding into the short, curved, wide deferent duct. The deferent duct is ~ 2× as narrow as the prostate. The penis is unarmed. The vagina is long and narrow, slightly narrower than the deferent duct, and connects directly to the oval bursa copulatrix. The elongate seminal receptacle also connects to the bursa copulatrix next to the vaginal connection, and the short uterine duct, which enters the female gland complex. The bursa copulatrix is several times as large as the seminal receptacle (Fig. 3E).
Biology. Possibly a New Caledonia endemic, rare, 4-6 m depth. The single specimen was collected by dredging on coral debris and coarse sand bottoms.
Remarks. Phlegmodoris papillosa Risbec, 1928 was originally described based on a single specimen collected in Nouméa, New Caledonia, with a short description and an illustration of the live animal. Risbec (1928) described the species as having the notum covered with large papillae and bearing spots with the appearance of black ocelli standing out against a yellowish background. Risbec (1928) also mentioned that the elongated, perfoliate rhinophores of P. papillosa are retractile in funnel-shaped sheaths with a well-marked ocelliform spotted papilla; and the gill is retractile in a cavity with a starshaped orifice. The specimens here examined closely resemble the original description of P. papillosa with the exception that the notum is grey, not yellowish.
Atagema albata (Burn, 1962a) is a similar species, originally described as Trippa albata, based on three specimens collected in Victoria, Australia. The specimens were described as pure white, sometimes with cream pigment, and characterized by having a soft, broad, flat body, with the mantle covered with low caryophyllidia, all similar in size, and with a mid-dorsal crest, extending from between the rhinophores to the branchial cavity. Burn (1962a) also described the branchial cavity as having an irregular outline and the rhinophores as perfoliate, with small, raised sheaths. Burn (1962a) compared T. albata with the New South Wales species T. intecta Kelaart, 1859 (= Goniodoris erinaceus Angas, 1864), which according to Burn (1962a) is usually much larger than A. albata and is of an ashy-brown color. With the available information is it not possible to confirm if A. albata and A. papillosa are the same species, and sequence data from A. albata would be needed to confirm this potential synonymy.
Finally, the specimen from the Philippines illustrated by Gosliner et al. (2018) as Atagema sp. 13 presents a similar external appearance and could be the same species. Examination of specimens is needed to confirm this possibility. Description. Body oval, flattened, covered with small, irregular tubercles and short ridges decreasing in size towards the mantle margin (Fig. 2C, D). A central, longitudinal area devoid of tubercles or ridges runs between the rhinophores and gill. A series of depressions on each side of the central ridge, generally decreasing in size towards the mantle margin. Entire dorsal surface, except for the depressions, covered with caryophyllidia. Branchial sheath composed of three large lobes; gill composed of five tripinnate branchial leaves, arranged horizontally in the living animal. Rhinophoral sheaths elevated; rhinophores long, lamellated, with 20 lamellae. Body color opaque greyish brown, with pale brown pigment mainly on top of the tubercles and ridges and scattered opaque white pigment; depressions dark brown to black (Fig. 2C). Rhinophores and branchial leaves are the same color as the dorsum.  (Risbec, 1928), MNHN IM-2013-86192 on black background.
Reproductive system (Fig. 3B, C) with a short, wide, simple ampulla that connects with the female gland complex and a convoluted prostate. The prostate has several folds and is approximately as wide as the ampulla. The prostate narrows slightly into a curved duct before expanding into the long, ovoid, wide deferent duct. At its widest point, the deferent duct is slightly wider than the prostate. The penis is unarmed. The vagina is long and narrow and connects directly to the spherical bursa copulatrix. The vagina is approximately as wide as the deferent duct. The small elongate seminal  (Risbec, 1928), MNHN IM-2013-86192, general view (D), detail of the bursa copulatrix and seminal receptable (E). Abbreviations: am, ampulla; bc, bursa copulatrix; dd, deferent duct; fg, female gland complex; pr, prostate; sr, seminal receptacle; vg, vagina.
receptacle also connects to the bursa copulatrix near the vaginal connection and the short uterine duct that enters the female gland complex. The bursa copulatrix is several times larger than the seminal receptacle (Fig. 3C). Radular formula 15 × 20.0.20 in a 20-mm long specimen (MNHN IM-2013-86191). Rachidian teeth absent. Inner and mid-lateral teeth hamate, having a small cusp and lacking denticles ( Fig. 4D-F). Innermost teeth very small in comparison to mid-laterals (Fig. 4D), elongate, with an inconspicuous secondary cusp mid-length. The teeth increase in size suddenly towards the medial portion of the half-row (Fig. 4E). Outermost teeth small, decreasing in size gradually, and hamate (Fig. 4F). No jaw was observed, labial cuticle smooth.
Biology. Possibly a New Caledonia endemic, rare, 5 m depth. The single specimen was obtained while SCUBA diving by direct collection on an unidentified sponge on which it was highly cryptic.
Etymology. This species is named after Kimberly García Mendez, who participated in two of the Koumac expeditions, collecting a number of specimens and helping enormously with the processing and photographing of samples.
Remarks. Atagema kimberlyae sp. nov. is assigned to the genus Atagema for two reasons, 1) the molecular phylogenetic analysis places the specimens sequenced in a clade containing A. spongiosa, a well stablished member of this genus (see above); 2) the morphological characteristics of this new species are consistent with the diagnosis of the genus provided by Valdés and Gosliner (2001), including a flexible body with series of tubercles all covered with caryophyllidia and depressions, the anterior border of the branchial sheath composed of three lobes and the gill leaves arranged horizontally; furthermore the prostate is tubular, with a single portion, the penis and vagina are unarmed, the labial cuticle smooth, and all radular teeth are hamate and smooth.
Atagema kimberlyae sp. nov. is morphologically similar to Atagema spongiosa (described above), particularly to the juvenile specimens, but is genetically distinct. Also, it lacks the distinctive dorsal ridge of A. spongiosa and presents a number of anatomical differences, including a comparatively much shorter and wider ampulla, a wider prostate, a rounded bursa copulatrix instead of oval, and comparatively larger innermost lateral teeth. A review of the literature reveals that no other described Indo-Pacific species of Atagema are morphologically similar to A. kimberlyae sp. nov., hence it is described as new.
The geographic range of Atagema kimberlyae sp. nov. is close to that of Atagema molesta (Miller, 1989 as Trippa molesta), introduced based on a single specimen collected from Te Hāwere-a-Maki (Goat Island), New Zealand. Miller (1989) described and illustrated the holotype, which differs from A. kimberlyae sp. nov. in several regards, including the more complex dorsal pattern of tubercles and ridges present in A. molesta, giving the animal a spikier appearance, and the reproductive system, which has a much larger deferent duct and a shorter prostate in A. kimberlyae sp. nov. While the radular morphology of the two species is similar, the radular formula is not, 23 × 32.0.32 in a 12-mm specimen of A. molesta versus 15 × 20.0.20 in a 20-mm long specimen of A. kimberlyae sp. nov.
Based on the species delimitation analysis presented here, A. kimberlyae sp. nov. is closely related but genetically distinct from specimens identified as Atagema cf. osseosa and Atagema notacristata whose sequences are deposited in GenBank. Description. Body oval, elevated, completely covered with a dense, complex network of delicate ridges (Fig. 5). Large caryophyllidia present at the points where ridges meet. A series of small depressions free of ridges and caryophyllidia present on each side of the mantle. A single, elevate dorsal hump present on the center of the dorsum, not visible in juvenile specimens (Fig. 5E). Branchial sheath composed of three lobes; gill composed of five tripinnate branchial leaves, arranged horizontally in the living animal. Rhinophoral sheaths elevated; rhinophores long, lamellated, with 8-10 lamellae. Body color opaque creamy grey, depressions a bit darker. Rhinophores and branchial leaves are the same color as the dorsum. Reproductive system (Fig. 6) with a short, convoluted ampulla that connects with the female gland complex and an elongated prostate. The prostate is as long as the ampulla and it narrows slightly into an elongate duct before expanding into the short,  simple, deferent duct. The penis is unarmed. The vagina is short and wide, approximately as wide as the deferent duct, and connects directly to the oval bursa copulatrix. The oval seminal receptacle also connects to the bursa copulatrix next to the vaginal opening and the short uterine duct that enters the female gland complex. The bursa copulatrix is slightly larger than the seminal receptable.
Radular Rachidian teeth absent. Inner and mid-lateral teeth hamate, having a small cusp and lacking denticles (Fig. 7A, B). Innermost teeth very small in comparison to mid-laterals (Fig. 7A). The teeth increase in size gradually towards the medial portion of the half-row (Fig. 7A). Outermost teeth small, decreasing in size gradually, and hamate (Fig. 7C). No jaw was observed, labial cuticle smooth.
Biology. This species could be widespread in the Western Pacific (see remarks). Found in shallow water (1-10 m depth). The specimens were exclusively collected on an unidentified species of grey sponge inhabiting the surface of scallops; the nudibranchs were highly cryptic on the sponge and often found buried in the sponge tissue. Few specimens were obtained by direct collection while SCUBA diving but more of them were found in the lab while searching for crustaceans associated with the sponges.
Etymology. This species is named after Anna Šobáňová, crustacean expert who originally discovered this species in the field while looking for crustaceans living in sponges.
Remarks. Atagema sobanovae sp. nov. is assigned to the genus because of its position in the molecular phylogenetic trees, in a clade containing other species of Atagema such as A. spongiosa and A. cf. osseosa. Also, the morphological characteristics of this new species are consistent with the diagnosis of the genus by Valdés and Gosliner (2001). Atagema sobanovae sp. nov. has a flexible body with series of dorsal ridges and a central conspicuous tubercle, all covered with caryophyllidia, the anterior border of the branchial sheath is composed of three lobes and the gill is arranged horizontally; the prostate is tubular, with a single portion, the penis and vagina are unarmed; the labial cuticle smooth and all radular teeth are hamate and smooth.
A review of the literature shows that no other described species of Atagema possesses the external characteristics of A. sobanovae sp. nov. The only other tropical Indo-Pacific species with a uniform color is Atagema carinata (Quoy & Gaimard, 1832), which was described from the coast of Thames, New Zealand, as yellowish white with a dorsal longitudinal ridge between the rhinophores and the gill. The illustration provided by Quoy andGaimard (1832-1833: pl. 16, figs 10-14) represents an animal with a distinct dorsal ridge very different from the complex dorsal pattern of A. sobanovae sp. nov. with depressions, ridges, and a central tubercle. The specimens of A. carinata described and illustrated by Rudman (2005) are consistent with the original description.
A specimen from the Philippines illustrated by Gosliner et al. (2018) as Atagema sp. 9 could belong to A. sobanovae sp. nov. but this needs anatomical and molecular confirmation.  (Er. Marcus, 1955)], by original designation.

Remarks.
For an in-depth discussion of the characteristics of the genus Jorunna and its synonyms see Camacho-García and Gosliner (2008). Description. Body oval, narrow, elongate, completely covered with numerous caryophyllidia (Fig. 8A-C). Branchial and rhinophoral sheaths low, simple, circular; gill composed of nine short, tripinnate branchial leaves, imbricated, arranged upright, with the apices close to each other in the living animal. Rhinophores short, lamellated, with eight or nine lamellae. Body color grey, with a complex network of white lines of different thicknesses; in some specimens some of the lines are very thick and contain darker areas (Fig. 8A), whereas in others thicker lines form the main network and thinner lines form a secondary network (Fig. 8) and in others all lines are approximately the same thickness (Fig. 8B). Rhinophores and branchial leaves are the same color as the dorsum but the rhinophoral lamellae and in some cases the gill lamellae are white. Reproductive system (Fig. 9A) with a long, narrow, curved ampulla that connects with the female gland complex and an elongate prostate. The prostate is as wide as the ampulla but narrows substantially before expanding into the short, curved, narrow deferent duct. The deferent duct is much narrower than the prostate. The penis is unarmed. The vagina is very elongate and wide distally, several times wider than the deferent duct, narrowing considerably proximally and connecting directly to the irregular bursa copulatrix. The oval seminal receptacle also connects to the bursa copulatrix next to the vaginal connection, and the short uterine duct that enters the female gland complex. The bursa copulatrix is ~ 3× as large as the seminal receptable. A large accessory gland connects to a narrow and convoluted duct that opens into the genital atrium, where a curved, sharp stylet is located.
Biology. Range includes New Caledonia and possibly Papua New Guinea and Japan (see Remarks section below); uncommon, found at ~ 6 m depth on an unidentified grey sponge on which it is highly cryptic. All the specimens were found directly on the sponges while SCUBA diving.
Etymology. This species is named after Alain Daoulas, outstanding collector and naturalist, who participated in two of the Koumac expeditions, collecting a number of important specimens.
Remarks. Jorunna daoulasi sp. nov. is placed in the genus Jorunna because it fits morphologically within the diagnoses of the genus provided by Valdés and Gosliner (2001) and Camacho-García and Gosliner (2008). Specifically, J. daoulasi sp. nov. has a soft mantle covered with long caryophyllidia, the radular teeth are hamate, and the reproductive system has an accessory gland and a copulatory stylet. Finally, in the molecular phylogenetic analyses, J. daoulasi sp. nov. is a member of a well-supported clade containing other members of Jorunna.
Camacho-García and Gosliner (2008)    Description. Body oval, flattened, completely covered with numerous caryophyllidia ( Fig. 8D-F). Branchial and rhinophoral sheaths low, simple, circular; gill composed of nine short, tripinnate branchial leaves, slightly imbricated, arranged fully upright in the living animal. Rhinophores short, lamellated with elongate apices, seven or eight lamellae. Body color variable from pale brown to grey, with numerous irregular dark patches, surrounded by white pigment (Fig. 8E). Rhinophores and branchial leaves are the same color as the dorsum.
Reproductive system (Fig. 9B) with an elongate, curved ampulla that connects with the female gland complex and an elongate prostate with a single fold. The prostate is as wide as the ampulla but narrows substantially into a long tube before expanding slightly into the short, curved, narrow deferent duct. The penis is unarmed. The vagina is narrow, as wide as the deferent duct, and very elongate, connecting directly to the oval bursa copulatrix. The oval seminal receptacle also connects to the bursa copulatrix next to the vaginal connection, and the long uterine duct that enters the female gland complex. The bursa copulatrix is many times larger than the seminal receptacle. A large accessory gland connects to a wide duct that opens into the genital atrium, where a sharp, curved stylet is located.
Biology. The pale brown egg mass is a highly coiled ribbon with ca. seven tightly packed whorls with a wavy upper edge (Fig. 8E). Eggs are ~ 105 µm in diameter. The geographic range includes New Caledonia and could be an endemic species; uncommon, found at 3-8 m depth on an unidentified brownish grey sponge on which is highly cryptic. All the specimens were collected directly from the sponges while SCUBA diving.
Etymology. This species is named after Jean-François Hervé, pioneer in the study of the sea slugs of New Caledonia and excellent collector; he participated in two of the Koumac expeditions, finding numerous specimens.
Remarks. As in the case of Jorunna daoulasi sp. nov., Jorunna hervei sp. nov. is placed in the genus Jorunna because it fits morphologically within the diagnoses of the genus provided by Valdés and Gosliner (2001) and Camacho-García and Gosliner (2008). Jorunna hervei sp. nov. has a soft mantle covered with long caryophyllidia, the radular teeth are hamate, and the reproductive system has an accessory gland and a copulatory stylet, all of which are characteristics of Jorunna. Furthermore, in the molecular phylogenetic analyses, Jorunna hervei sp. nov. is sister to J. daoulasi sp. nov. as well as a member of a well-supported clade containing other members of Jorunna.
Jorunna hervei sp. nov. differs from Jorunna daoulasi sp. nov. in several regards. Externally, J. hervei sp. nov. is less elongate than J. daoulasi sp. nov. and lacks the network of white pigment; instead it has numerous irregular dark patches, in some specimens surrounded by white pigment. The reproductive system of J. hervei sp. nov. is similar to that of J. daoulasi sp. nov., but the accessory gland is comparatively smaller, the bursa copulatrix is much larger in comparison to the seminal receptable, and the deferent duct is shorter in comparison to the vagina. The main anatomical difference between these two species is the radular morphology, while Jorunna hervei sp. nov. has inner and mid-lateral teeth hamate, having a long cusp and lacking denticles, in J. daoulasi sp. nov. the innermost lateral teeth are wide, having a short cusp with four or five irregular denticles. Finally, the ABGD analysis recovered J. hervei sp. nov. and J. daoulasi sp. nov. as distinct species.
Jorunna liviae Tibiriçá, Strömvoll & Cervera, 2023 recently described from Mozambique (Tibiriçá et al. 2023) is sister to J. hervei sp. nov. and is morphologically similar but differs in several important respects. First of all, the species delimitation analysis recovered J. hervei sp. nov. and Jorunna liviae as different species. Additionally, the body of J. liviae appears to be narrower and more elongate than that of J. hervei sp. nov. More importantly, the outermost radular teeth of J. liviae contain multiple elongate denticles, which are absent in all specimens examined of J. hervei sp. nov. Also, the prostate of J. liviae is flattened, whereas the prostate of J. hervei sp. nov. is tubular an elongate, and the accessory gland appears to be comparatively much larger in J. liviae than in J. hervei sp. nov. although is it variable in size (Tibiriçá et al. 2023). Finally, the eggs of J. liviae are white, whereas they are pale brown in J. hervei sp. nov. It is clear that these two species are similar but distinct.
A review of the literature does not reveal any other species morphologically similar to J. hervei sp. nov. Rostanga sp. 7 in Gosliner et al. (2018) has some superficial resemblance but there are some obvious differences, including the background color, grey in J. hervei, pink in Rostanga sp. 7, and the egg mass, having one or two loosely packed whorls with ochre, large eggs in Rostanga sp. 7, versus seven tightly packed whorls with pale brown eggs in J. hervei.

Remarks.
For an in-depth discussion of the characteristics of the genus Rostanga and its synonyms see Rudman and Avern (1989) and Valdés and Gosliner (2001). Description. Body oval, elongate, completely covered with numerous caryophyllidia (Fig. 11). Branchial and rhinophoral sheaths low, simple, circular; gill composed of seven wide, tripinnate branchial leaves, extended laterally, lying on the dorsum in the living animal. A low, irregular, inconspicuous ridge runs between the rhinophores and the gill, not clearly visible in all specimens. Rhinophores very elongate, almost conical, lamellated, with 15 or 16 lamellae. Body color pinkish to orange, with irregular darker patches all over the dorsum. Rhinophores reddish; branchial leaves the same color as the dorsum.
Reproductive system (Fig. 12) with a long, narrow, curved ampulla that connects with the female gland complex and an irregular, elongate prostate. The prostate is wider than the ampulla, but it narrows substantially into a long, folded tube, before expanding into the short, wide deferent duct. The penis is unarmed. The vagina is elongate, several times narrower than the deferent duct, connecting directly to the large, oval bursa copulatrix. The smaller, elongate seminal receptacle also connects to the bursa copulatrix next to the vaginal connection, and the short uterine duct that enters the female gland complex. The bursa copulatrix is several times larger than the seminal receptacle.  and mid-lateral teeth hamate, having a small cusp and lacking denticles (Fig. 13A, B). Innermost teeth very small in comparison to mid-laterals (Fig. 13A). The teeth increase in size gradually towards the medial portion of the half-row (Fig. 13B). Outermost  teeth small, decreasing in size gradually, and hamate (Fig. 13C), outermost one with 13-20 irregular denticles. No jaw was observed, labial cuticle smooth.
Biology. All the specimens were found on an unidentified species of sponge while SCUBA diving. The presence of these highly cryptic nudibranchs was initially determined in the field by observing the egg masses on the sponges. In most cases, to separate the nudibranchs, the sponges were brought to the lab and examined under a microscope.
Etymology. This species is named after Marina Poddubetskaia, indefatigable collector and diver, who first discovered the animals here described during the two of the Koumac expeditions.
Remarks. Rostanga poddubetskaiae sp. nov. is provisionally assigned to the genus Rostanga based on the results of the molecular phylogenetic analyses, which place this species solidly nested within a clade containing other species identified as members of Rostanga. However, there are some notable differences between Rostanga poddubetskaiae sp. nov. and the diagnoses of the genus Rostanga provided by Rudman and Avern (1989) and Valdés and Gosliner (2001), such as the absence of jaws and elongate outermost radular teeth, and the presence of short caryophyllidia; moreover, the arrangement of the branchial leaves flattened against the dorsum and the presence of a dorsal ridge are unusual for a species of Rostanga. Additional resolution in the phylogeny of dorid nudibranchs and a larger sample are needed before this species can be placed in a genus with confidence.
Rostanga poddubetskaiae sp. nov. appears to be sister to Rostanga elandsia Garovoy, Valdés & Gosliner, 2001 from South Africa, but additional species need to be included in the analysis to confirm those relationships. Morphologically, R. poddubetskaiae sp. nov. exhibits a number of differences from other members of this genus, including the presence of a dorsal ridge, elongate rhinophores, a gill flattened against the body, and smooth, hamate inner and mid radular teeth, and short, pectinate outermost lateral teeth. The Indo-Pacific species of Rostanga have been reviewed in papers by Rudman and Avern (1989), Baba (1991), and Garovoy et al. (2001), and none of them have external and internal characteristics present in R. poddubetskaiae sp. nov. The only exception is Rostanga crawfordi (Burn, 1969), described as Rostanga australis Rudman & Avern, 1989, which appears to have a dorsal ridge in some specimens (see Rudman and Avern 1989;Coleman 2008) and a similar external coloration to R. poddubetskaiae sp. nov., but the radular teeth are very different: specifically, the outer teeth are elongate with numerous denticles on the tip.

Remarks.
For an in-depth discussion of the characteristics of the genus Sclerodoris and its synonyms see Valdés and Gosliner (2001).  Eliot, 1904: 382-383. Type locality: reef off the east coast of Zanzibar, Tanzania. Halgerda rubra Bergh, 1905: 126-127, pl. 4 fig. 2 Description. Body oval, flattened, with an irregular, coriaceous texture (Fig. 14A). Branchial and rhinophoral sheaths somewhat elevated, simple, circular. Gill composed of eight short, tripinnate branchial leaves, arranged upright. Rhinophores short, lamellated, with 18 lamellae. Visceral hump clearly elevated over the rest of the mantle, with several lateral protuberances and a conspicuous depression mid-length. Dorsum completely covered with small caryophyllidia. Body color red, with several large, irregularly opaque white patches, mainly on the mantle margin and some white pigment irregularly scattered all over. Rhinophores and branchial leaves are the same color as the dorsum.

Sclerodoris tuberculata
Reproductive system (Fig. 15A, B) with a long, wide, convoluted ampulla with several folds, which connects with the female gland complex and the oval, flattened prostate. The prostate narrows substantially into a long, straight duct, before expanding into the short, wide deferent duct. The penis is armed with triangular spines, varying in size (Fig. 15C) with thickened bases and sharp cusps. The vagina is elongate, narrow, as wide as the deferent duct, connecting directly to the large, oval bursa copulatrix. The elongate seminal receptacle also connects to the bursa copulatrix next to the vaginal connection, and the short uterine duct that enters the female gland complex (Fig. 15B). The bursa copulatrix is ~ 4× as large as the seminal receptable. An accessory gland connects to the genial atrium where the deferent duct and the vagina meet. The accessory gland is granular in texture and approximately as large as the seminal receptable.
Radular formula 38 × 49.0.49 in a 44-mm long specimen (MNHN IM-2013-86197). Rachidian teeth absent. Inner and mid-lateral teeth hamate, having an elongate cusp and lacking denticles (Fig. 16A, B). Innermost teeth very small in comparison to mid-laterals (Fig. 16A). The teeth increase in size gradually towards the medial portion of the half-row. Outermost teeth small, decreasing in size gradually, composed of a short, blunt cusp with numerous small denticles (Fig. 13C). No jaw was observed, labial cuticle smooth.
Biology. Rare, found under rocks at 7 m depth. Widespread in the Indo-Pacific region. The single specimen was found under a rock while SCUBA diving where it was highly cryptic. Remarks. Eliot (1904) described Sclerodoris tuberculata based on one specimen collected in Zanzibar as follows: "Dark brown with sandy spots, exactly like a sponge splashed with sand. Underside clear bright brownish red. Branchial pocket crenulate. The middle part of back covered with conical warts, which form an irregular keel; smaller warts on mantle-edge. Rhinophores red; branchiae eight, voluminous; axes red, tips white. Animal alters shape, sometimes rather high, sometimes quite flat like Platydoris. Consistency quite hard and rather rough. Two depressions with deep black markings as in some species of Trippa." In the same paper Eliot (1904) introduced two additional species also resembling sponges, Sclerodoris minor Eliot, 1904, and Sclerodoris rubra Eliot, 1904, both synonyms of S. tuberculata. Sclerodoris tuberculata is considered a widespread species in the Indo-Pacific region and is well documented in the literature Yonow 2008;Gosliner et al. 2018;Nakano 2018). The material here examined is consistent with the original description of S. tuberculata and subsequent records; however, a record of this species from New Caledonia (Hervé 2010) is probably the closely related species Sclerodoris rubicunda (Baba, 1949). Eliot (1906) suggested that Doris castanea Kelaart, 1858 was possibly the same species as Sclerodoris tuberculata Eliot, 1904, but indicated the identity of the latter could not be established with certainty based on the type material. Eliot (1906: pl. 42, figs 6, 7) reproduced the original drawing by Kelaart, which clearly resembles a dark specimen of S. tuberculata. Later, Eliot (1908) regarded Sclerodoris rubra Eliot, 1904 as a senior synonym of Halgerda rubra Bergh, 1905. Allan (1947 reported S. tuberculata from New South Wales, Australia, under the genus name Peronodoris Bergh, 1904 and commented on Eliot's (1906) proposed synonymy between this species and D. castanea. Allan (1947) indicated that "although the colour sketch of the upper surface of Kelaart's specimen resembles that of our specimen to a very slight degree," the undersurface is exactly like the color sketch of the New South Wales material of S. tuberculata. Allan (1947) concluded that whether S. tuberculata was eventually to become a synonym of D. castanea remained to be seen, as fresh material from the two type localities needs to be examined before this can be determined. Rudman (1978) endorsed Eliot's (1908) decision to synonymize Halgerda rubra Bergh, 1905 with Sclerodoris rubra Eliot, 1904. At the same time Rudman (1978) regarded Sclerodoris rubra Eliot, 1904 andSclerodoris minor Eliot, 1904 as synonyms of Sclerodoris tuberculata Eliot, 1904, and based on the Principle of First Reviser (ICZN 1999: Article 24), Rudman (1978) established S. tuberculata as the valid name for this species. Rudman (1978) also commented that the original description of D. castanea by Kelaart (1858) was most inadequate and therefore best to ignore it. In this paper we follow Rudman's (1978) conclusion and regard Sclerodoris tuberculata Eliot, 1904 as the valid name for this species with the synonymies established above. We also leave the question of the identity of D. castanea as unresolved. Hervé (2010) reported Sclerodoris tuberculata from New Caledonia but based on the photographs published (Hervé 2010: 214), it seems that these records correspond to Sclerodoris rubicunda (Baba, 1949). The present study is the first confirmed record of Sclerodoris tuberculata from New Caledonia.   -2013-86193. Abbreviations: ag, accessory gland;am, ampulla;bc, bursa copulatrix;dd, deferent duct;fg, female gland complex;pr, prostate;sr, seminal receptacle;vg, vagina. Description. Body oval, flattened, with an irregular, coriaceous texture (Fig. 14E). Branchial and rhinophoral sheaths somewhat elevated, simple, irregular. Gill composed of five short, tripinnate branchial leaves, arranged upright. Rhinophores short, lamellated, with 15 lamellae. Visceral hump elevated over the rest of the mantle. Dorsum completely covered with small caryophyllidia, a longitudinal ridge, and several large, rounded tubercles. Body color yellowish brown, with scattered opaque white pigment, and areas or dark brown and dark gray. Branchial leaves and rhinophores dark brown.
Reproductive system (Fig. 15D, E) with a long, wide, convoluted ampulla with several folds, which connects with the female gland complex and the elongate, convoluted prostate. The prostate is as wide as the ampulla, but narrows substantially into a very long duct, before expanding into the long, narrow deferent duct. The penis is armed with rounded spines having a short, sharp cusp (Fig. 15F). The vagina is elongate, narrow, as wide as the deferent duct, connecting directly to the large, spherical bursa copulatrix. The elongate seminal receptacle also connects to the bursa copulatrix and the uterine duct that enters the female gland complex. The bursa copulatrix is ~ 3× wider than the seminar receptable, but similar in volume (Fig. 15D). No accessory gland was observed.
Radular formula 32 × 68.0.68 in a 25-mm long specimen (MNHN IM-2013-86198). Rachidian teeth absent. Inner and mid-lateral teeth hamate, having an elongate cusp (sometimes bifurcate) and lacking denticles (Fig. 16G-I). Innermost teeth very small in comparison to mid-laterals (Fig. 16G). The teeth increase in size gradually towards the medial portion of the half-row. Outermost teeth small, decreasing in size gradually, elongate, with a short cusp and numerous denticles (Fig. 13I). No jaw was observed, labial cuticle smooth.
Biology. Rare, found intertidally under rocks, possibly a New Caledonia endemic. The single specimen was obtained by brushing blocks of dead coral on the margin of a fringing reef flat.
Etymology. This species is named after Sébastien Faninoz whose efforts were critical for the organization of the Koumac expeditions.
Remarks. In the phylogenetic analyses conducted herein, Sclerodoris faninozi sp. nov. is sister to Sclerodoris tuberculata, the type species of Sclerodoris, forming a wellsupported clade; for this reason, S. faninozi sp. nov. is placed in the genus Sclerodoris. Moreover, most of the anatomical characteristics of S. faninozi sp. nov. match the diagnosis of the genus Sclerodoris provided by Valdés and Gosliner (2001). Specifically, S. faninozi sp. nov. has a flattened, coriaceous dorsum covered with caryophyllidia, the rhinophoral sheaths are somewhat elevated; the penis is armed with hooks and the vagina is unarmed; the labial cuticle and radular teeth are smooth, hamate with the outermost lateral teeth multi-denticulate. The only exception is the accessory gland, which is a diagnostic trait for Sclerodoris, but was not observed in S. faninozi sp. nov. Although the absence of an accessory gland in S. faninozi sp. nov. could have been result of damage to the specimen, it appears that the presence of this organ is variable in Sclerodoris.
Sclerodoris faninozi sp. nov. is externally similar to Sclerodoris coriacea Eliot, 1904 introduced based on a specimen collected near Chwaka (as Chuaka), on the east coast of Zanzibar, Tanzania. Eliot (1904) described S. coriacea as yellowish brown in color with the dorsal surface covered with a "distinctly raised but somewhat irregular reticulate pattern." Rudman (1978) redescribed S. coriacea also based on specimens from Zanzibar, and a color photograph of a live animal was illustrated by Gosliner et al. (2018). The specimen of S. faninozi sp. nov. here examined is similar to all these descriptions with the exception of the presence of a dorsal ridge, absent in S. coriacea. The radular morphology of S. faninozi sp. nov. is also similar to that of S. coriacea as described by Rudman (1978) but the innermost teeth of S. faninozi sp. nov. have a bifurcated cusp, whereas they are simple in S. coriacea (Rudman 1978: fig. 13 Description. Body oval, flattened, with an irregular, coriaceous texture ( Fig. 14B-D). Branchial and rhinophoral sheaths somewhat elevated, simple, irregular. Gill composed of five short, tripinnate branchial leaves, arranged upright. Rhinophores short, lamellated, with 12-14 lamellae. Visceral hump elevated over the rest of the mantle. Dorsum completely covered with small caryophyllidia and a complex network of ridges and scattered large, rounded tubercles. Body color variable, yellow to pale brown with scattered opaque white pigment and some specimens with rounded black spots. Branchial leaves are the same color as the dorsum; rhinophores brown proximally, with white apices.
Reproductive system (Fig. 15G) with a long, wide, convoluted ampulla with several folds, which connects with the female gland complex and the oval, flattened prostate. The prostate narrows substantially into a long, convoluted duct, before expanding into the short, wide deferent duct. The penis is unarmed. The vagina is elongate, much narrower than the deferent duct, connecting directly to the large, oval bursa copulatrix. The elongate seminal receptacle also connects to the bursa copulatrix next to the vaginal connection, and the short uterine duct that enters the female gland complex. The seminal receptable possesses a spherical tip and it is similar in volume to the bursa copulatrix. An accessory gland connects to the genial atrium where the deferent duct and the vagina meet. The accessory gland is granular in texture and approximately as large as the bursa copulatrix.
Radular formula 37 × 54.0.54 in a 20-mm long specimen (MNHN IM-2013-86195). Rachidian teeth absent. Inner and mid-lateral teeth hamate, having a short cusp and lacking denticles (Fig. 16D, E). Innermost teeth very small in comparison to mid-laterals (Fig. 16D). The teeth increase in size gradually towards the medial portion of the half-row. Outermost teeth small, decreasing in size gradually, elongate, with a short cusp and lacking differentiated denticles (Fig. 16F). No jaw was observed, labial cuticle smooth.
Biology. Found under rocks at 0-3 m depth. All the specimens were obtained by direct collection while SCUBA diving. The specimens were very cryptic on rocks with sponges and other encrusting organisms.
Etymology. This species is named after Valentine Dutertre whose hard work, dedication, and skill were critical for the collection of numerous important sea slug species during the Koumac expeditions.
Remarks. The phylogenetic analysis places "Sclerodoris" dutertrei sp. nov. in a well-supported clade containing two other species identified as members of Sclerodoris. These two species were sequenced and submitted to GenBank but never formally studied, thus their morphological characteristics remain undescribed. This clade is not closely related to the clade containing the rest of the species of Sclerodoris, including the type species, Sclerodoris tuberculata. Therefore, "S." dutertrei sp. nov. cannot be definitely included in the genus Sclerodoris and the generic placement of this species is regarded as tentative until a well resolved phylogeny of the Discodorididae permits a more accurate taxonomic placement. "Sclerodoris" dutertrei sp. nov. is tentatively placed in Sclerodoris (as indicated by the quotation marks) because anatomically this species is for the most part consistent with the diagnosis for Sclerodoris provided by Valdés and Gosliner (2001), including a flattened, coriaceous dorsum covered with caryophyllidia, rhinophoral sheaths somewhat elevated; a lobate accessory gland, without stylet; labial cuticle and radular teeth smooth, hamate with the outermost lateral teeth multidenticulate. The only exception is the penis, which appears to be unarmed in "S." dutertrei sp. nov., but the presence of penial spines is a characteristic of Sclerodoris sensu stricto (see Valdés and Gosliner 2001).
"Sclerodoris" dutertrei sp. nov. is distinct from other species previously assigned to Sclerodoris: no other species described to date possesses a yellow to pale brown dorsum with scattered opaque white pigment (sometimes with rounded black spots), completely covered with small caryophyllidia and a complex network of ridges and scattered large, rounded tubercles. As mentioned above, Sclerodoris tuberculata is red with several large, irregularly shaped, opaque white patches and a conspicuous depression mid-length on the dorsum, not present in "Sclerodoris" dutertrei sp. nov.; Sclerodoris faninozi sp. nov. is yellowish brown, with scattered opaque white pigment, and areas of dark brown and dark gray but also has a longitudinal ridge, and several large, rounded tubercles, also absent in "Sclerodoris" dutertrei sp. nov. Other Indo-Pacific species described also present external characteristics that distinguish them from "Sclerodoris" dutertrei sp. nov. For example, Sclerodoris apiculata (Alder & Hancock, 1864) is characterized by having a network of ridges radiating from elevated conical centers, each with an elongated filament (see Alder and Hancock 1864;Hervé 2010;Gosliner et al. 2018;Nakano 2018). Sclerodoris coriacea has the dorsum completely covered with large, elongate tubercles joined by conspicuous ridges (see Rudman 1978;Gosliner et al. 2018), very different from those in "Sclerodoris" dutertrei sp. nov. Sclerodoris japonica (Eliot, 1913), originally described as a member of the genus Halgerda (see Eliot 1913) is characterized by having a yellowish grey dorsum covered with small ridges, and numerous, large roundish areas of a darker grey, varying in intensity, which correspond to dorsal depressions or pits. Sclerodoris rubicunda is a red species with two large patches of white and purple pigment and a series of conspicuous dorsal ridges (Baba 1949;Gosliner et al. 2018;Nakano 2018). Sclerodoris trenberthi (Burn, 1962b) and Sclerodoris tarka Burn, 1969 both described from Victoria, Australia are also distinct from "Sclerodoris" dutertrei sp. nov. Sclerodoris trenberthi has a characteristic longitudinal dorsal structure composed of "irregularly sized and spaced low hard pustules surmounting a low ridge" running from the rhinophores to the gill (Burn 1962b), which is absent from "Sclerodoris" dutertrei sp. nov. Sclerodoris tarka is a dusky yellow to yellowish orange species with a pattern of conspicuous dorsal ridges (Burn, 1969) and an indistinct medial ridge, also absent in "Sclerodoris" dutertrei sp. nov. Finally, Sclerodoris virgulata Valdés, 2001 is the only species of Sclerodoris with a white dorsum lacking dorsal ridges or depressions (Valdés 2001), also very different from "Sclerodoris" dutertrei sp. nov.

Discussion
The phylogeny presented here is largely consistent with previous morphological studies and the classification of the Discodorididae proposed by Valdés and Gosliner (2001) and Valdés (2002) with some exceptions. For example, the genus Atagema is sister to the rest of Discodorididae + Cadlinidae, but due to the poor representation of Cadlinidae in this study, these results should be taken cautiously. There is also a discrepancy with the molecular analysis by Hallas et al. (2017), who found Atagema + Aphelodoris as sister to remaining members of Discodorididae, but Aldisa + Cadlina forming a distinct clade, as also recovered by Johnson (2010) and Johnson and Gosliner (2012). On the contrary, in the present analyses Aldisa is nested within the Discodorididae. The more limited taxon sampling in the present study could explain this discrepancy, but the goal of the present analysis is only to place the new species here described in a phylogenetic context, not to provide a reliable reconstruction of the phylogeny of Discodorididae, which may only be achieved with next generation sequence data. There are some other differences between the present analyses and previous classification attempts of species included herein. For example, Discodoris coerulescens was regarded by Dayrat (2010) as a member of a metaphyletic group branching from near the basal node of Discodorididae he named "Montereina," but the present analyses appear to suggest a close relationship with the genus Tayuva Er. Marcus and Ev. Marcus, 1967. Tayuva was considered a synonym of Discodoris by Valdés (2002) and T. lilacina, originally described as Doris lilacina Gould, 1852, is regarded as a member Discodoris by some authors (e.g., Gosliner et al. 2018); however, other authors following Dayrat (2010) placed this species in Tayuva, a distinct genus with a single pantropical species (e.g., Ballesteros et al. 2016;Yonow 2017). The results of the present analysis appear to confirm that Tayuva is distinct from Discodoris as suggested by Dayrat (2010), but it is unclear how many species are present in this pantropical complex. Finally, the genus Montereina MacFarland, 1905 was synonymized with Peltodoris by Valdés (2002), but the results of the present analyses suggest that these two groups are distinct as suggested by Dayrat (2010).
Based on the phylogenetic analyses here presented, it appears that the genus Sclerodoris is paraphyletic. The new species "Sclerodoris" dutertrei sp. nov. was recovered in a well-supported clade containing two other species identified as members of Sclerodoris, but not in the clade including Sclerodoris tuberculata Eliot, 1904, which is the type species of Sclerodoris. Thus, the description of a new genus name for the clade including "Sclerodoris" dutertrei sp. nov. is an option. However, due to the limited sample size in our molecular phylogenies and the lack of support for several clades, we prefer to postpone any decisions regarding this group until a more reliable phylogeny of the Discodorididae is available, as there could be available genus-level names for this group. Therefore, the generic placement of "Sclerodoris" dutertrei sp. nov. is regarded as tentative, indicated by the quotation marks. Bouchet et al. (2007) argued that "it can safely be affirmed that, as a result of the recent sampling programs, both in shallow and in deep-water, no other South Pacific island group has been so intensively surveyed as New Caledonia." However, recent field work during the Koumac expeditions seems to have revealed additional diversity missed during early work, suggesting that documenting the New Caledonia molluscan diversity is still a work in progress. As Bouchet et al. (2007) indicated, the question of how many mollusk species are present in New Caledonia remains unanswered and this is particularly true for sea slugs. This paper is a small contribution towards the goal of describing the sea slug diversity of New Caledonia as field work continues to produce previously unseen taxa.
It is unclear how many of the species here described are endemic to New Caledonia. Payri et al. (2019) suggested that probably < 15% of the New Caledonia marine mollusks are endemic, although they also indicated that "several scientists have already demonstrated connections between the marine life of New Caledonia, the Great Barrier reef, and the center of maximum diversity of the Coral Triangle." Based on photographs published in field guides or other publications, it is likely that Atagema papillosa (Risbec, 1928), Atagema sobanovae sp. nov., and Jorunna daoulasi sp. nov. are widespread in the Western Pacific, but we have been unable to find photographs of Atagema kimberlyae sp. nov., Jorunna hervei sp. nov., Rostanga poddubetskaiae sp. nov., Sclerodoris faninozi sp. nov., and "Sclerodoris" dutertrei sp. nov. in other publications outside New Caledonia. But due to the very cryptic nature of these species, it could very well be that they have been overlooked. While the small size of the eggs of J. hervei sp. nov. suggests planktotrophic development and therefore a potentially large geographic range, the recent description of a very similar species from the Indian Ocean, J. liviae, may indicate there is a species complex of species with similar external morphologies present in different ocean basins. Much more work on these neglected dorid nudibranchs is needed to have a better understanding of their taxonomy, diversity, and evolution.
The specimens here examined where collected using different techniques, including dredging, direct collecting (intertidally and SCUBA diving), and substrate collecting. Due to the highly cryptic coloration and morphology of some of the species, their presence was detected initially by the observation of egg masses on the sponges. In the particular case of A. sobanovae sp. nov., most of the specimens were collected by dissecting the sponges in the laboratory as the nudibranchs were buried in the tissue, and almost invisible. The diversity of collecting techniques and specialized methods used during the Koumac expeditions were critical in the discovery of the species here examined. This paper provides a rare example of the description and re-description of ecologically cryptic sea slug species using contemporary taxonomic techniques and focusing on a narrow geographic region that, despite substantial collecting efforts (Bouchet et al. 2007), appears to remain under-sampled. Naturels (CEN) de Nouvelle-Calédonie, funded mainly by the Gouvernement de la Nouvelle-Calédonie, Province Nord, Agence Française de la Biodiversité (AFB), the Lounsbery Foundation, and Office des Postes et Télécommunications (OPT). The expedition operated under a permit issued by Direction du Développement Economique et de l'Environnement (DDEE) of Province Nord. We are especially grateful to Philippe Bouchet for the invitation to participate in the expedition and to Sébastien Faninoz, Virginie Héros, Philippe Maestrati, Pierre Lozuet, Alain Daoulas, Jean-François Hervé, Yves Thévenet, and many others for their help and support. We also thank Jenelle Innabi, Tatiana Vargas, and Jade de Souza for their assistance with the molecular work.