Leucothoe kawesqari, a new amphipod from Bernardo O’Higgins National Park (Chile), with remarks on the genus in the Magellan Region (Crustacea, Peracarida)

Abstract Although the genus Leucothoe has been reported repeatedly in the Magellan Region, the citations in the Channels and Fjords Ecoregion were either unidentified or attributed to the previously considered cosmopolitan Leucothoe spinicarpa. In this work, Leucothoe kawesqari sp. n. is described, which can be distinguished from other species of the genus in the Southern Ocean by having eyes present, epimeral plates with no setae, anterior coxae not acutely produced or excavate, coxa 5 slightly bilobed, accessory flagellum present, mandibular palp article 3 shorter than ½ article 2, pereopods 5–7 basis expanded, ovoid, posterior margin weakly crenulate and telson apex irregularly truncated. The new species was found in hard substrates, both unvegetated and with macroalgae, mainly in kelp forest of Macrocystis pyrifera.


Introduction
Leucothoe Leach, 1814 is a speciose amphipod genus that currently comprises 132 species (WoRMS 2015). Species of Leucothoe are widespread in all oceans and inhabit a variety of benthic environments from the intertidal zone to -3570 m although most of them live in shallow waters in association with other invertebrates such as in ascidians, sponges, and bivalve mollusks, or free living in algae or coral rubble (White 2011).
The genus Leucothoe has been reported repeatedly in the Magellan Region, defined as the Patagonian shelf south of about 41°S on both the Pacific and Atlantic sides, assigned to the wrongly considered cosmopolitan species Leucothoe spinicarpa (Abildgaard, 1789) (see De Broyer et al. 2007, White 2011. Krapp-Schickel and De Broyer (2014) revised the Leucothoe in the Southern Ocean, and clarified the citation of Holman and Watling (1983) from Tierra de Fuego by describing the species Leucothoe weddellensis Krapp-Schickel & De Broyer, 2014. The rest of the records of the genus in the region do not provide descriptions, hence the specimens cannot be attributed to any described species. In this work, a new species found in the channels and fjords of Bernardo O'Higgins National Park (henceforward BONP) is described.

Materials and methods
BONP is placed in the Chilean geopolitical regions of Aysén and Magallanes, between 48.0-51.6°S and 73.3-75.8°W (Aravena et al. 2011). Its coastal line consists of countless channels and fjords along more than 400 linear kilometers of the southeastern Pacific , which house a variety of habitats.
Between January and March 2010 two cruises were carried out onboard the vessel MV Nueva Galicia with the objective of sampling the rocky sublittoral bottoms of the channels and fjords of BONP. A total of 23 sites was sampled with SCUBA: five samples were taken manually at both 5 and 15 m depth at each site (10 samples at each site), harvesting squares of 25×25 cm (0.063 m 2 ) by scraping off all the organisms (including fauna and smaller algae), but not the kelps. Samples were fixed in 5% buffered formalin and subsequently sorted, preserved in 70% alcohol and identified. Illustrations were performed using a camera lucida connected to a compound microscope.
Terminology used in the description follows Krapp-Schickel and De Broyer (2014). Body length is measured from dorsodistal extreme of pereon to frontal tip of head. Specimens with no penile process or marsupium are considered neuters. Type material is lodged in the collections of the Museo Nacional de Historia Natural, Chile (MNHNCL) and the Museo Nacional de Ciencias Naturales de Madrid (MNCN), Spain. Diagnosis. Head anterior margin rounded, mid-cephalic keel quadrate but not prominent. Eyes present. Epimeral plates with no setae, epimeron 3 posterior margin excavate, postero-ventral corner blunt, with right angle. Coxae 1-3 not acutely produced, nor excavated, coxa 3 longer than broad, coxa 5 slightly bilobed. Antenna 1 main flagellum of 11-12 articles, accessory flagellum present, minute, of two unequal segments. Antenna 2 flagellum of 6 articles. Mandibular palp article 3 shorter than ½ of article 2. Ganthopod 1 propodus palm with minute serrations. Dactylus reaching 0.4 of propodus length. Gnathopod 2 basis posterior margin smooth, carpus smooth, without tooth or process, setose, reaching 0.3 of propodus length, propodus with short, blunt distal prolongation and three medial rows of setae. Pereopods 5-7 bases expanded, ovoid, posterior margin weakly crenulate. Telson apex irregularly truncated.

Systematics
Derivatio nominis. Named after the Alacalufe people Kawésqar, whose ancestral territory extends through the Magellan Region, from the Gulf of Penas to the Strait of Magellan.
Description. Body (Fig. 1A) length 5-8 mm. Head (Fig. 1A) anterior margin rounded, anterodistal margin rounded. Mid cephalic keel quadrate but not prominent, eyes present, rounded. Antenna 1 (Fig. 1B) 0.4 times as long as body; peduncle article 1 2.3 times as long as broad; article 2 subequal in length, 4.3 times as long as broad; article 3 half as long as long article 2, 2.8 times as long as broad; accessory flagellum present, minute, about ½ as long as main flagellum article 1, biarticulated, first article about three times as long as second; main flagellum of 11 articles, about as long as peduncle article 1, aesthetascs present, flagellum article 1 as long as articles 2-3 and half of 4 together.
Uropods. Uropod 1 (Fig. 4F) peduncle 0.7 times as long as outer ramus; outer ramus with 5 spines; rami with marginal spines, inner ramus slightly shorter than outer. Uropod 2 (Fig. 4G) somewhat shorter than uropod 1, peduncle 1.6 times as long as outer ramus, with spines on distal half of outer margin; rami with marginal spines, inner ramus slightly shorter. Uropod 3 (Fig. 4H) 1.1 times as long as uropod 1, peduncle 1.2 times as long as outer ramus; outer ramus with marginal spines; the shorter one 0.8 times as long as the longer one, naked.
Telson (Fig. 4I) 3.3 times as long as broad, distal tip minutely, irregularly truncate. Remarks. As mentioned above, the only described species of Leucothoe found in the Magellan Region is L. weddellensis. Following Holman and Watling (1983), Krapp-Schickel and De Broyer (2014) divided the material of L. weddellensis in two groups, according to morphological differences, locations and size. The material from the Magellan Region (South of Tierra de Fuego) corresponds to the larger specimens (more than 14 mm long). From those, L. kawesqari differs (besides the length) in that the former lacks accessory flagellum, has a distinctively more slender gnathopod 1 propodus, coxa 5 is markedly bilobed, peropods 5-7 basis are pear-shaped oval (while in L. kawesqari are regularly oval) and more slender, the epimeron 1 is posteriorly serrate, the epimeron 2 has ventrodistal setae, and epimeron 3 as a posterodistal small prolongation. The smaller specimens differ in lacking accessory flagellum, having a longer mandibular palp article 3 (1/2 of the length of article 2), gnathopod 1 propodus anterior margin concave, gnathopod 2 basis more setose, pereopods 5-7 distinctly narrower, pereopods 5-6 with slightly concave hind margin.
Leucothoe tolkieni Vinogradov, 1990 is the only other species described from the Southeastern Pacific, although it was found well offshore. It differs from the species described here mainly in having the head anterior margin truncate with eyes that cover most of the head, gnathopod 1 basis anteroproximally expanded, and propodus curved, proximally inflated, gnathopod 2 carpus distally truncate, spoon-like, pereopods 5-7 bases narrowly expanded and telson apex rounded.
Although previous reports of L. spinicarpa in the Magellan Region are probably wrong (De Broyer et al. 2007, White 2011, it is worth mentioning the main differences with the present species. Based on the description provided by Crowe (2006), unlike L. kawesqari, L. spinicarpa has a gnathopod 1 propodus ventral margin with more than 10 spines, coxa 5 markedly bilobed, gnathopod 2 carpus scarcely setose with a subdistal cusp, epimeron 1 with anterodistal tuft of setae, and telson apex bidentate with a pair of distal setae.
Ecology. Leucothoe kawesqari was one of the dominant species of amphipod found in unvegetated hard substrates in the southernmost sampling site, where the amphipods Polycheria antarctica (Stebbing, 1875) and Orchestia spp., were also abundant. Towards the north of BONP, L. kawesqari was found in subtrates dominated by kelp forest of Macrocystis pyrifera, where Andaniopsis integripes (Bellan-Santini & Ledoyer, 1986) was dominant and it also co-occurred with the tanaid Zeuxoides troncosoi Esquete & Bamber, 2012 and juveniles of the isopod family Janiridae. High abundances of other benthic taxa were found co-occurring with L. kawesqari: the polychaetes Platynereis australis (Schmarda, 1861) and Perinereis gualpensis Jeldes, 1963, the bivalve Aulacomya atra (Molina, 1782) the decapod Halicarcinus planatus (Fabricius, 1775) and unidentified species of Echinodermata (Ophiuroidea and Psolidae), Porifera and Ascidiacea. These specimens of L. kawesqari were likely associated with or endocommensal associates of the Porifera and Ascidacea specimens withinin the sample, since the sampling method (scraping substrate) dislodges the samples and everything was sorted through at one time (White 2011, White andReimer 2012).  (1931) as Leucothoe spinicarpa which cannot be attributed to any known species (see text).

Discussion
The two species currently described for the Magellan Region have a well separated geographical distribution (Fig. 5): While the specimens of L. kawesqari come from the channels and fjords, L. weddellensis was found off shore, south of Tierra de Fuego and is distributed throughout the Antarctic seas (Krapp-Schickel and De Broyer 2014). Schellenberg (1931) reported Leucothoe in Cabo Valentina, Rio Seco, Strait of Magellan, Canal Beagle, and Isla Lennox. As mentioned above no illustration was provided, hence his records cannot be attributed to any described species. These locations lie between the distribution areas of the two known species. Otherwise, there are no more records of Leucothoe for the southeast coast of the Pacific. Further north, Leucothoe panpulco Barnard, 1961 is found in Acapulco and Panamá, and Leucothoe alata (Barnard, 1959) in California, with no overlap of distribution ranges of species of Leucothoe along the Pacific.
The geographical distribution of the species of Leucothoe studied by Krapp-Schickel and De Broyer (2014) and the data presented herein thus complete a latitudinal turnover of Leucothoe species along the west coast of the American continent, having from the north toward south, L. kawesqari, L. sp. and L. weddellensis. Nevertheless, large areas remain largely undersampled; future surveys in the East pacific including the Magellan region would reveal whether there are regions where species of the genus overlap, or a total latitudinal species turnover due to speciation through colonization.