(Copepoda: Siphonostomatoida: Lernaeopodidae) a parasite from the olfactory sacs of Bathyraja scaphiops (Norman, 1937) in the South Western Atlantic

: During a parasitological survey of the olfactory sacs of 21 species of Rajiformes (Chondrichthyes) from the Southwestern Atlantic Ocean, copepods referable to Dendrapta Kabata (1964) (Siphonostomatoida: Lernaeopodidae) were found parasitizing the cuphead skate Bathyraja scaphiops (Rajiformes: Arhynchobatidae). Morphological analyses using both light and electron microscopy revealed that they belong to a new species. It can be easily distinguished from its congeners by the ratio between lengths of posterior process and trunk (1:0.8), the large to width ratio of trunk (1:0.7) and the armature of the antennule (1, 1, 5 + 1 aesthete). Dendrapta cameroni longiclavata is raised to full specifi c status, as Dendrapta longiclavata n. comb. Kabata & Gusev, 1966.


INTRODUCTION
Dendrapta Kabata, 1964 is a monotypic genus of lernaeopodid copepods parasites of rajid fi shes from the Northern Hemisphere. This genus was erected by Kabata (1964) to accommodate D. cameroni (Heller 1949), originally described as Charopinus cameroni Heller, 1949 from the external surface, near the fi n bases, of Amblyraja radiata (Donovan, 1808) (as Raja scabrata Garman, 1913) from the coasts of Quebec, Canadian Atlantic. Later on, Kabata & Gusev (1966) described the subspecies D. cameroni longiclavata Kabata & Gusev, 1966 from the skin of the ocellate spot skate Okamejei kenojei (Müller & Henle, 1841), Bathyraja smirnovi (Soldatov & Pavlenko, 1915) (as Raja kenojei and R. smirnovi, respectively) and of an unidentifi ed species of the same genus from the Kamchatkan Peninsula and Sakhalin Island, Russia. This subspecies was successively reported on Raja inornata Jordan & Gilbert, 1880 from British Columbia and in the Canadian Pacifi c (Kabata 1970). To the best of our knowledge, the last report of a member of this copepod genus was that of D. cameroni on its type host, from the Canadian Atlantic (Khan et al. 1980).
During parasitological studies on the parasites of the olfactory sacs of 21 species of Rajiformes from the Argentinian continental shelf, Southwestern Atlantic, parasitic copepods referable to Dendrapta were found only on Bathyraja scaphiops (Norman, 1937). They were found to be representatives of an undescribed species of Dendrapta, which is herein described.
The prevalence and mean intensity were calculated following Bush et al. (1997). Sterne's exact 95% confidence limits (CL) were calculated for prevalence using Quantitative Parasitology 3.0 software (QP3.0) (Reiczigel & Rózsa 2001, Reiczigel 2003. Skates were examined fresh or kept frozen at -20°C until examination. Olfactory sacs were excised and examined using a stereo microscope. In order to isolate copepods from host tissues, the entire attachment section was removed and the host remaining tissues, surrounding the holdfast, were degraded by enzymatic digestion with pepsin. Fifteen female copepods were fixed in 4% formalin for storage before being studied and measured. Two specimens were cleared in lactic acid; appendages were dissected and examined using a light microscope. Measurements are indicated in millimetres as mean ± standard deviation, with ranges and number of specimens measured in parentheses. Anatomical terminology followed Boxshall & Halsey (2004), terminology of appendages armature and segmentation follows Kabata (1979).
For scanning electron microscopy (SEM), two specimens were dehydrated using a graded series of ethanol washed up to 100%, then dried by evaporation with hexamethyldisilazane, sputter-coated with gold palladium and examined using a JEOL JSM 6460LV SEM (JEOL, Tokyo, Japan).

Bathyraja scaphiops was the only rajiform s p e c i e s p a ra s i t i z e d b y D e n d ra p t a
Adult male not found. Etymology: The specific name refers to the microhabitat of the parasite, the olfactory sacs in nasal cavities of its hosts.
ZooBank registration: This work and the nomenclatural acts it contains have been registered in ZooBank, the online registration system for the International Commission on Zoological Nomenclature (ICZN). The Life Science Identifier (LSID) for Dendrapta nasicola n. sp. is: urn:lsid:zoobank. org:act:E3E43B22-6237-4CB8-8E3C-30957C951ECB.

Remarks
At present, D. cameroni, the only species in the genus, is represented by two subspecies, D. c. cameroni andD. c. longiclavata (Dippenaar et al. 2004, Walter &Boxshall 2018). They differ in the proportions of the trunk, in the length of the posterior processes and the mode of branching of the attachment organ (Kabata & Gusev 1966). Indeed, based on averaged measurements, the trunk of D. c. cameroni is much wider than long, whereas that of D. c. longiclavata is only slightly wider than long; the posterior processes of the former are about half length of the trunk, but more than twice as long as the trunk in the later; additionally, the attachment organ of D. c. longiclavata is much more profuse and more finely divided than in C. c. cameroni (Kabata & Gusev 1966, Kabata 1988. Despite these differences, normally used as diagnostic specific characters in other species of lernaeopodids (Boxshall & Halsey 2004), Kabata & Gusev (1966) avoided erecting a new species after observing that, in both forms, females become wider and posterior processes increase in length as individuals grow. Because of the low number of specimens measured at that time, the authors considered that the differences between the Figure. 2 Dendrapta nasicola n. sp. (adult female) from Bathyraja scaphiops (Arhynchobatidae), stereo microscope photographs. a general habitus (lateral view). b cephalothorax and proximal portion of maxilla detail. c posterior part of body (lateral view). Scale bars: a = 2.5 mm; b = 1 mm; c = 2 mm. two forms could be attributed to developmental variation, not justifying the erection of a different species for the Pacific form; suggesting that their formation must have been caused by recent geographical isolation of their closely related hosts of the genus Raja.
The specimens from B. scaphiops differ from both subspecies of Dendrapta in having a longer, but narrower trunk (trunk length:width= 1:0.7, vs 1:1.4 and 1:1.1 for D. c. cameroni and D. c. longiclavata, respectively). The new species also attains a larger size, but its posterior processes are larger than in D. c. cameroni and notably shorter than in D. c. longiclavata (see also Dippenaar et al. 2004). These differences in morphometric relationships indicates that they are not due to intraspecific variability as a consequence of allometric growth (the larger the specimens, the larger the posterior processes), but they are actual interspecific differences. Indeed, the relative size of posterior processes is considered as a reliable diagnostic character for species of Schistobrachia Kabata, 1964(Dippenaar 2016, a genus closely related to Dendrapta (Dippenaar et al. 2004). Additionally, the armature of the antennule of the new species differs from that of its congeners by having a non-bifid tip of aesthete. Base on the An Acad Bras Cienc (2020) 92(Suppl. 2) e20180933 7 | 8 observed differences, a new species, Dendrapta nasicola sp. n. is proposed.
Most lernaeopodids are host-and sitespecific (Piasecki et al. 2010), therefore the host species and the microhabitat (olfactory bulbs) of the present material, along with the geographic region or origin (Southwestern Atlantic), support the erection of a new species of Dendrapta. For the same reasons, the former subspecies D. c. longiclavata is raised to full specific status and should be correctly known as Dendrapta longiclavata n. comb. Kabata & Gusev, 1966.

DISCUSSION
All previous records of the genus Dendrapta are restricted to the Northern Hemisphere. This is the first record of a new member of Dendrapta from the Southern Ocean, which expands the distribution range for the genus.
Even though 21 skate species were sampled, most of them represented by more than ten individuals, only B. scaphiops was found to be parasitized by Dendrapta nasicola n. sp., evidencing its high host specificity, a feature shared only with D. cameroni, since D. longiclavata is known from three host species. The only related lernaeopodid species found in the region, Brianella corniger, has been recorded parasitizing seven of the skate species herein examined (Irigoitia et al. 2016).
At present D. nasicola n. sp. is the first copepod species recorded parasitzing the cuphead skate B. scaphiops. In the study region, only four other copepod species have been found infesting some of the skates species examined in the present work (Irigoitia et al. 2016(Irigoitia et al. , 2017, demonstrating the fragmentary nature of the extant information on parasitic copepods in the Southwestern Atlantic. Further studies, including other groups of elasmobranchs, will surely render new taxonomic and biogeographic data about this group of parasites in a geographical region characterized by a high diversity of elasmobranchs (Menni & Lucifora 2007, Lucifora et al. 2012) and high levels of endemism (Ebert & Compagno 2007, Figueroa et al. 2013.