Paradoris tsurugensis, Baba, 1986

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 : 202-204

PARADORIS TSURUGENSIS ( FIG. 56 )

Paradoris tsurugensis Baba, 1986: 1–8 , figs 1–3. – Baba, 1989: 73–78, figs 1–3.

Type material: Holotype, by original designation: Japan, western coast of Honshu, Tsuruga Bay (c. 35°40′N), Okazaki, 31 July 1961, one specimen 50 mm alive, leg. Takaoka Biological Club (OMNH-Mo 34831). The holotype was requested from the Osaka Museum of Natural History , but could not be borrowed. The holotype of tsurugensis was entirely dissected by Baba, but its condition is unknown. I ignore whether the reproductive system, the radula, and the jaws are available on slides.

Distribution: So far, tsurugensis is only known from three specimens collected from three different Japanese localities. In addition to the holotype, one specimen was collected from Ogi, Toyama Bay, c. 37°20′N, western coast of Honshu, and the third one was collected from Tomioka, Amakusa, c. 32°30′N, western coast of Kyushu. I ignore whether these specimens were deposited in a museum collection. Note that Baba published twice the exact same paper: his 1989 contribution does not provide any new data.

Remarks on the original description ( Fig. 56 ): Baba’s (1986) description was mainly based on the holotype, especially the internal anatomy (only one radular formula is provided). Baba surely observed the colour of the live animal that he collected from Tomioka. The description of the colour of the other specimens, including the black and white drawings of the holotype, was probably based on other people’s field notes ( Fig. 56A ). The ground colour is ‘greyish yellow’ in the holotype and the specimen from Tomioka, and ‘greyish brown’ in the specimen from Toyama Bay. In the three specimens, the dorsal notum is ‘scattered with a small number of blackish brown flecks’. Also, there is a ‘narrow line of chocolate brown dots around the base of the larger tubercles’. Other colour features described by Baba are: ‘The upper half of the rhinophore is chocolate brown. The branchial plumes are greyish yellow to greyish brown. The underside of the mantle and the sole are white closely covered with chocolate spots’.

Live animals were 50 mm (holotype), 40 mm (Toyama Bay), and 30 mm (Tomioka) long. Baba mentioned ‘granular tubercles of various sizes’ on the surface of the dorsal notum, six tri- or quadripinnate branchial plumes, grooved oral tentacles, a notched upper lip of the bilabiate anterior foot, ‘entire’ rhinophoral and branchial openings. Baba only drew one blood gland (anterior to the nervous system), but he probably pulled out the posterior gland from the body cavity. According to one of Baba’s drawings ( Baba, 1986: fig. 2A), the stomach is median; a small caecum is also represented. Baba mentioned two lateral plates, and an additional ventral one. His description and drawing of the jaw elements are not very helpful (‘rod-like and simple at tips’). However, some of the rodlets he drew ( Baba, 1986: fig. 2C) seem to have a curved tip. The radular formula is ‘about 90 × (20-25- 0-20–25)’. All teeth are simply hamate and not denticulate. It is not possible from Baba’s drawing to determine whether tsurugensis presents several radular features such as laterally grooved teeth, a spur on the base of the outermost tooth, and a dorsal spur on the hook of the outermost teeth.

Baba mentioned a ‘large and massive’ prostate. According to his drawing ( Baba, 1986: fig. 3A), the prostate is not tubular ( Fig. 56C ). Baba did not mention whether it is homogeneous or divided into two parts. Baba’s description of the copulatory organ is confusing. On the one hand he mentions that: ‘The distal part of the vas deferens does not appear to be specialized into a penial papilla. It is unarmed’. On the other hand he drew a distinct, 1 mm long penis within a penial sheath. There are two accessory glands and two stylet sacs in the distal part of the reproductive system, near the genital openings ( Fig. 56B ). Stylets are approximately 1 mm long. Baba’s (1986: fig. 3A) drawing of the reproductive system does not allow us to determine the exact length of the duct of the receptaculum seminis (called ‘spermatocyst’ by Baba). Finally, the presence of a large female gland mass indicates that the specimen dissected by Baba was fully mature (less mature individuals have a smaller female gland mass).

Infra-specific character variation: The original description of tsurugensis was largely based on a single specimen, except for the ground colour of the dorsal notum whose variation is briefly mentioned (greyish yellow or greyish brown). In particular, the variation in the ‘blackish brown flecks’ will have to be addressed: are those ‘flecks’ also present in younger, smaller specimens? Are they always present, regardless of the habitat? One will also have to address individual infra-specific variation in several characters, such as the number of accessory glands and stylet sacs, and the radular formula – note that the high number of rows may be due to the fact that that the specimen dissected by Baba was particularly long (50 mm alive, i.e. approximately 40 mm preserved).

Diagnostic character: It is impossible to propose a diagnostic character for tsurugensis because our knowledge of this species is mainly based on a single, incompletely described specimen.

Discussion: Baba (1986) only compared tsurugensis with granulata , although he also mentioned the existence of mulciber . According to Baba, similarities between the two species are: a granulated back, grooved oral tentacles, the colour (except for the presence of ‘blackish brown flecks’ in tsurugensis ), the labial armature, and the radular teeth. The elongated, narrow radula is a synapomorphy of Paradoris , as well as the presence of a third ventral jaw plate. Concerning the dorsal tubercles, Baba drew more tubercles than usually found in Paradoris . However, I cannot comment on this feature without re-examining the type material; the distribution and abundance of dorsal tubercles may vary infra-specifically, and are also modified through preservation. The nature and variation in the granulation in tsurugensis will have to be addressed. The only difference recognized by Baba was the number of accessory glands and stylet sacs: two vestibular glands and two stylet sacs in tsurugensis , and four to five vestibular glands and three stylet sacs in granulata . The present study demonstrates that the presence of two stylet sacs and two accessory glands is compatible with the variation observed in indecora ; it also demonstrates that two stylet sacs and two accessory glands can be found in several other species, such as araneosa , erythraeensis , liturata , and sp. B. Finally, the variation in the ‘blackish brown flecks’ described by Baba will have to be addressed before one can evaluate whether those flecks are diagnostic of tsurugensis .

It is currently difficult to clarify the status of tsurugensis because our knowledge is too limited. For example, the fact that Baba’s drawing of the reproductive system does not allow us to determine the exact length of the duct of the receptaculum seminis prevents us from rejecting a synonymy of tsurugensis with erythraeensis (the rest of Baba’s description is compatible with what we know of erythraeensis ). Also, the fact that Marcus’ original description of lora was so brief and based on a single specimen (see this species for further discussion) prevents us from rejecting a synonymy of tsurugensis with lora .

According to Ortea (1995), tsurugensis differs from the Atlantic and Mediterranean species by having two vestibular glands and two stylet sacs: in reality, Ortea overlooked the variation in this character among Atlantic and Mediterranean individuals (see indecora ). Miller (1995) rightly emphasized that leuca does not have accessory glands and stylet sacs (see dubia ), whereas tsurugensis has two glands and two sacs. Finally, Valdés (2001)) used the number of accessory glands and stylet sacs and the radular formula to distinguish tsurugensis from both araneosa and imperfecta . The problem is that one of the paratypes of araneosa has two accessory glands and two stylet sacs, and should thus be identified as tsurugensis .

These authors have not pointed out that the anatomical information we have about tsurugensis is based on a single specimen. I certainly do not pretend that animals collected from the Canary Islands, the north-western coasts of Japan, and deep water off New Caledonia are all part of the same species. However, I argue that our lack of knowledge of character variation prevents us from answering this critical question: can morphology alone (i.e. without geographical data) help us identify unequivocally species such as tsurugensis , araneosa , and indecora ? However, the fact that tsurugensis was collected from temperate Japanese waters suggests that it may be distinct from the Paradoris species found in the tropical Indo-West Pacific and from species from other biogeographical regions, such as the Mediterranean. In summary, I still regard tsurugensis as a valid species name, but the reader needs to remember that this is only a decision by default.

Figures

Figure 56. Paradoris tsurugensis. A, dorsal view, after Baba (1986: fig. 1A). B, accessory glands and stylet sacs, after Baba (1986: fig. 3B), holotype, OMNH-Mo 34831, scale = 0.5 mm. C, reproductive system, after Baba (1986: fig. 3A), holotype, OMNH-Mo 34831, scale = 1.8 mm.