Paradoris araneosa, Valdes, 2001

Dayrat, Benoît, 2006, A taxonomic revision of Paradoris sea slugs (Mollusca, Gastropoda, Nudibranchia, Doridina), Zoological Journal of the Linnean Society 147 (2), pp. 125-238 : 136-140

PARADORIS ARANEOSA ( FIGS 3 , 4 )

Paradoris araneosa Valdés, 2001: 281–285 , figs 13B, 32, 33.

Paradoris imperfecta Valdés, 2001: 285–288 , figs 13C, 34, 35. New synonym.

Type material: Holotype of araneosa , by original designation: south of New Caledonia, 23°03′S, 166°59′E, 452–464 m depth, station CP 736 of the BATHUS 2 expedition, 13 May 1993, one specimen 13/ 10 mm preserved, leg. P. Bouchet and B. Richer de Forges ( MNHN, no catalogue number). Three paratypes: south of New Caledonia, Banc Aztèque, 23°18′− 23°19′S, 168°05′E, 305–340 m depth, stations DW 182–184 of the SMIB 8 expedition, 31 January 1993, one specimen 35/ 25 mm preserved, leg. P. Bouchet and B. Richer de Forges ( MNHN, no catalogue number); New Caledonia, Norfolk Ridge, 23°01′S, 166°56′E, 400–402 m depth, station DW 838 of the BATHUS 3 expedition, 30 November 1993, one specimen 33/ 22 mm preserved, leg. P. Bouchet, B. Richer de Forges, and A. Warén ( MNHN, no catalogue number); southeast of New Caledonia, 21°43′S, 166°37′E, 314–364 m depth, station CP 851 of the HALIPRO 1 expedition, 19 March 1994, one specimen 13/ 10 mm preserved, leg. B. Richer de Forges ( CASIZ 121099 ). The holotype has not been dissected. Externally it is in good condition. The three paratypes were dissected by Valdés (2001). Radulae and jaws are missing in all paratypes. The SEM stubs with radulae and jaws have not been deposited with the rest of the specimens. The reproductive system is missing in the BATHUS 3 paratype. It is present in the SMIB 8 paratype, but largely destroyed (especially in the distal area). The reproductive system of the HALIPRO 1 paratype, extracted from the body cavity by Valdés, but not dissected, was dissected for the present study.

Holotype of imperfecta , by original designation: south of New Caledonia, 24°47′S, 168°09′E, 274 m depth, station CP 18 of the CHALCAL 2 expedition, 27 October 1986, one specimen 12/ 7 mm preserved, leg. B. Métivier and B. Richer de Forges ( MNHN, no catalogue number). The holotype was dissected by Valdés (2001). The buccal mass (radula and jaws) is missing. The SEM stubs with the radula and jaws have not been deposited with the rest of the specimen. The oral tube, stomach, intestine, digestive gland, and central nervous system are present. A few pieces of the reproductive system are present, but they are largely destroyed and no structure could be verified.

Type localities: South of New Caledonia: 23°03′S, 166°59′E, 452–464 m depth ( araneosa ), and 24°47′S, 168°09′E, 274 m depth ( imperfecta ).

Distribution: So far, araneosa is only known from the four type specimens of araneosa and the holotype of imperfecta . These five specimens were collected from deep water (from 274 to 464 m depth), south of New Caledonia (from 21°43′S to 24°47′S and 166°37′E to 168°09′E).

Remarks on the original description of araneosa ( Figs 3 , 4 ): The dorsal colour of one live paratype ( SMIB 8) was cream to light brown, with a few darker, large blotches, and several darker dots (Valdés, 2001: fig. 13B). Possible variations of the colour pattern were not mentioned in the original description. The colour of the ventral surface of the live animals is unknown. The preserved specimens are all homogeneously white: only four light, faded, darker spots could be observed in one paratype ( BATHUS 3). Valdés described ‘simple, rounded tubercles’. The latter are typically indecora -like: they are located in the median area of the notum ( CASIZ 121099) or on its entire surface (other specimens), although the granulation of live animals might be different ( Figs 3A, C, E ). An additional, dorsal, median crest is present in one specimen ( BATHUS 3), from the rhinophores to the gill opening. Also, in all specimens ( Fig. 3A ), the notum is covered by what Valdés described as ‘depressions surrounded by minute ridges’, which led Valdés to call this species araneosa , for ‘ araneosus (full of webs), in reference to the small ridges (…) that resemble cobwebs’. No wide holes were found on the dorsal surface of the notum. When they are present, wide holes can be observed with a dissecting microscope: either they are absent in araneosa , or they are present but inconspicuous. There are six multipinnate branchial plumes; the number of plumes could not be determined in one paratype ( BATHUS 3). Valdés reported 25 rhinophoral lamellae: I think that 15–20 lamellae are closer to the truth, although it is unclear because the lamellae are very difficult to count. The oral tentacles, simply described as ‘short and conical’ by Valdés, are distinctly grooved ( Fig. 3B, D ). Valdés did not mention the number of jaw plates present on the labial cuticle. Unfortunately, I could not check this character because Valdés has not deposited the SEM stubs that he prepared and the labial cuticle was missing in the three paratypes. The radular formula is 68 × (16-0-16) in the BATHUS 3 paratype (33 mm long, preserved). Valdés did not give the formulae of the two other radulae that he extracted ( CASIZ 121099, SMIB 8). Again, the SEM stubs have not been deposited and I could not re-examine the radulae of araneosa . The original description of the radula is incomplete and does not provide any of the important radular features found in Paradoris . However, one of those features, the presence of a lateral groove on the outer edge of the hook of the lateral teeth, can be seen in the SEM pictures published by Valdés (2001: fig. 32). The stomach is neither median and narrow, nor large and free: it is intermediary ( Fig. 3G, H ). My comments on Valdés’ description of the reproductive system are based entirely on the reproductive system of the SMIB 8 paratype, largely destroyed by Valdés, and the reproductive system of the HALIPRO 1 paratype ( CASIZ 121099). Valdés represented the reproductive system of one specimen ( SMIB 8): whether he used the other specimens in his description is uncertain. However, I guess that he only used the SMIB 8 paratype because my observations of the HALIPRO 1 paratype ( CASIZ 121099) contradict part of his description. Valdés represented a fusion of the ampulla with the deferent duct into a single duct entering the female gland mass. I could not re-observe this fusion ( Fig. 4F, G ): indeed, I only saw it a few times in several hundred discodorid dissections. The ‘unarmed penis’ mentioned by Valdés is probably the evaginable portion of the deferent duct, rather than a distinct copulatory organ. According to Valdés, the vagina is ‘very long’. Neither Valdés’ drawing (Valdés, 2001: fig. 33B) nor my observations indicate that this is the case ( Fig. 4F, G ). It is actually straight, and not particularly convoluted. The deferent duct ( Fig. 4G ), however, is tightly convoluted in the HALIPRO 1 paratype ( CASIZ 121099). Valdés did not represent a convoluted deferent duct for the SMIB 8 paratype, but this character can vary among individuals ( Fig. 4F ). In the SMIB 8 paratype, Valdés mentioned the presence of ‘a large, ramified accessory gland and two small sacs, containing one rigid spine each’ in the distal part of the reproductive system ( Fig. 4D ). I observed two distinct accessory glands and two stylet sacs ( Figs 4A, B ) in the HALIPRO 1 paratype ( CASIZ 121099). Also, I think that there may be two accessory glands in the reproductive system drawn by Valdés, although this is very uncertain because the area was largely destroyed – in particular, the stylet sacs were missing ( Fig. 4D, E ).

Remarks on the original description of imperfecta: The dorsal colour of the live animal was cream, with a few darker, large blotches, and several darker dots (Valdés, 2001: fig. 13C). The colour of the ventral surface of the live animals is unknown. The preserved specimen is homogeneously white. The notum is very poorly preserved, and it is unclear whether it was granulated with indecora -like tubercles. The small ‘depressions surrounded by minute ridges’ described in araneosa , and supposedly characteristic of this species, are also present in the holotype of imperfecta . No wide holes were observed on the dorsal surface of the notum: either they are absent, they are present but inconspicuous, or the poor condition has obscured them. There are six multipinnate branchial plumes, not five, as described by Valdés. Also, I think that 15–20 rhinophoral lamellae are closer to the truth (instead of 25), although it is unclear because the lamellae are very difficult to count. The oral tentacles are distinctly grooved. Valdés did not mention the number of jaw plates present on the labial cuticle. Unfortunately, I could not check this character because Valdés has not deposited the SEM stubs that he prepared with the rest of the specimens. The radular formula is 46 × (13-0-13). Valdés’ original description of the radula is incomplete and does not provide any of the important radular features found in Paradoris . The presence of a lateral groove on the outer edge of the hook of the lateral teeth can be seen in the SEM pictures published by Valdés (2001: fig. 35). The stomach is neither median and narrow, nor large and free: it is intermediary. I cannot comment on the accuracy of Valdés’ description of the reproductive system because the latter was destroyed. The ‘unarmed penis’ described by Valdés is probably the evaginable portion of the deferent duct, rather than a distinct copulatory organ. Valdés described only two stylet sacs, but no accessory gland. He also described the shape of the receptaculum seminis as ‘irregular’.

Discussion: The first question that must be addressed is whether the specimens described under the names imperfecta and araneosa represent two species, as asserted by Valdés, or just one species. According to Valdés, the lack of an accessory gland in imperfecta ‘clearly’ distinguishes imperfecta from araneosa , which, according to Valdés, has one accessory gland. The problem is that this distinction was based on a maximum of three specimens ( SMIB 8 and BATHUS 3 paratypes of araneosa , and the holotype of imperfecta ). As I pointed out, Valdés overlooked the fact that the HALIPRO 1 paratype of araneosa has two accessory glands. The possibility that the number of accessory genital structures could vary infra-specifically, ignored by Valdés, easily explains the differences observed among specimens. There is no need to create different species names. This comment is true for the other differences mentioned by Valdés between araneosa and imperfecta . I have nothing against the idea that the shape of the receptaculum seminis could be used to distinguish species (according to Valdés, ‘irregular’ in imperfecta and oval in araneosa ); my concern is simply that such a feature can only be used if many individuals have been dissected. I do not pretend that there is only one species of Paradoris in deep water off New Caledonia. Rather, I argue that given the available data, it is more conservative to use one species name for these five specimens.

The second question that must be addressed is: how can araneosa be distinguished from the other species of Paradoris ? Valdés only compared araneosa and imperfecta with leuca and tsurugensis . He ignored all the other Paradoris species recognized at the time, and overlooked the fact that leuca is simply a synonym of dubia . Also, Valdés’ knowledge of leuca and tsurugensis was exclusively based on Miller’s (1995) and Baba’s (1986) descriptions. Valdés mentioned one valid difference between araneosa and leuca : the absence of accessory glands and stylet sacs in leuca . The two other differences mentioned by Valdés are erroneous. The tips of the rodlets of leuca (i.e. dubia ) are not ‘triangular cusps’. Miller’s (1995: fig. 3C) drawing is too schematic; in reality, the jaw rodlets of araneosa and dubia are not distinguishable. According to Valdés, the dorsal tubercles are ‘more evenly distributed’ in dubia than in araneosa . Valdés ignored the fact that the distribution and the size of the dorsal tubercles of dubia present a great deal of variation; the granulation observed in araneosa fits within the variation observed in dubia . However, Valdés overlooked two major differences between araneosa and dubia . In fact, araneosa does not share the two diagnostic features of dubia , i.e. the fused vaginal and fertilization ducts near the bursa copulatrix, and the tubular prostate. Note that the only difference mentioned by Valdés between imperfecta and leuca was the absence of accessory glands and stylet sacs in leuca .

According to Valdés, the number of accessory glands and stylet sacs distinguishes tsurugensis from araneosa and imperfecta : two accessory glands and two stylet sacs in tsurugensis , one accessory gland and two stylet sacs in araneosa , and two accessory glands in imperfecta . The problem is that I found two accessory glands and two stylet sacs in one paratype of araneosa ( CASIZ 121099). One solution is to conclude that this paratype is part of tsurugensis . The other solution, which I prefer, is to conclude that this character varies among individuals. The other difference mentioned by Valdés between araneosa and tsurugensis is the radular formula −90 × (20/25-0-20/25) in tsurugensis in a 50 mm long specimen, alive, and 68 × (16-0-16) in tsurugensis in a 33 mm long specimen, preserved. However, Valdés’ comparison was only based on two individuals (he did not give the formulae of the two other radulae that he extracted, and Baba only provided one radular formula). I consider that this feature cannot be used to distinguish species without a careful analysis of the individual variation. Interestingly, the radula of the holotype of imperfecta (13 mm long, preserved), has fewer rows, which strongly suggests that infra-specific variation cannot be excluded. I cannot compare araneosa with tsurugensis , because I could not re-examine the holotype of tsurugensis . Baba did not give any diagnostic feature for tsurugensis . A potential difference is the presence of a distinct copulatory organ in tsurugensis .

Finally, let us compare araneosa with the other species of Paradoris : araneosa does not share the diagnostic features of erythraeensis , liturata , sp. A, sp. B, and sp. C. The peculiar ridges found on the surface of the notum of araneosa (and imperfecta ) are also present in specimens of indecora and dubia , and are not diagnostic of araneosa . However, it is still unclear whether these ridges are natural, i.e. present on the surface of live animals. The dorsal colour of araneosa is compatible with the colour of all Paradoris species , except for liturata , sp. B, and sp. C, which have distinct dorsal colour patterns. Comparing araneosa with lora is jeopardized by the fact that our knowledge of the anatomy of lora is very limited. Currently, no feature distinguishes them unambiguously. Two similarities are also worth mentioning. According to the SEM pictures published by Valdés (2001: figs 32, 35), the hooks of the outermost lateral teeth of araneosa do not have a dorsal spur: dubia is the only species in which I never observed such a spur; the absence of this dorsal spur will have to be checked in additional specimens of araneosa . Also, some specimens (not all) of araneosa have a dorsal, median crest, from the rhinophores to the gill opening. I found the exact same crest in a large, Neo-Caledonian ( MNHN) specimen of sp. A. The presence of this median crest may be correlated with the large size of the animals.

In summary, araneosa can clearly be distinguished from several species of Paradoris , but not all of them. In particular, its comparison with two other species from the west Pacific, lora and tsurugensis , will have to be addressed when new material is available. Here I consider araneosa as a distinct entity despite the fact that no diagnostic character could be found. The name araneosa refers to five animals that have been collected in deep water, off New Caledonia.

Figures

Figure 3. Paradoris araneosa. A, dorsal hollows and ridges, paratype, CASIZ 121099, scale = 3 mm. B, left oral tentacle, paratype, CASIZ 121099, scale = 0.8 mm. C, dorsal tubercles of various sizes, paratype, CASIZ 121099, scale = 3.3 mm. D, anterior, ventral view, holotype, scale = 2.5 mm. E, dorsal tubercles of various sizes, holotype, scale = 1.5 mm. F, rhinophoral sheath, paratype, MNHN-SMIB 8, scale = 2.5 mm. G, part of the digestive system, paratype, MNHN-BATHUS 3, scale = 6.8 mm. H, stomach and part of the intestine, paratype, CASIZ 121099, scale = 3 mm.

Figure 4. Paradoris araneosa, reproductive system. A, two accessory glands and one stylet sac in the distal part (the second stylet sac not visible on this side), paratype, CASIZ 121099, scale = 0.9 mm. B, same as (A), on the other side, scale = 0.9 mm. C, spermatic pouches and ducts, paratype, CASIZ 121099, scale = 1.2 mm. D, one accessory gland and two stylet sacs in the distal part, paratype, MNHN-SMIB 8, after Valdés (2001: fig. 33C), scale = 2.1 mm. E, remaining pieces of possibly two accessory glands in the distal part (stylet sacs missing), paratype, MNHN-SMIB 8, scale = 0.8 mm. F, remaining genital pieces, paratype, MNHN-SMIB 8, scale = 2.3 mm. G, general view, paratype, CASIZ 121099, scale = 1.6 mm.