A new species of Cymadusa Savigny , 1816 ( Crustacea : Amphipoda : Ampithoidae ) from northeastern Brazil

A new species of the amphipod family Ampithoidae Stebbing, 1899 is described from the northeastern Brazilian waters. The new described taxon is grouped in the genus Cymadusa Savigny, 1816, since it presents all the diagnostic characteristics of the genus. The examined material was collected by scuba diving in the Rocas Atoll, off Rio Grande do Norte state coast, Camamu Bay and Todos os Santos Bay, Bahia state. The new species described here is close to C. filosa Savigny, 1816, type species of the genus, by presenting anterior margin of gnathopod 1 poorly setose, male gnathopod 2 densely setose, with palmar corner not defined by a spine and dactylus subequal in length to palm, being considered part of the C. filosa complex. Among the species of this complex, the one which most resembles to the new taxon is C. imbroglio Rabindranath, 1972, which is distinguished by the absence of both the trapezoid process in the palm and spine at the palmar corner in the gnathopod 2. This is the second species of the genus Cymadusa recorded from Brazilian waters.


INTRODUCTION
The Amphipoda belong to the Superorder Peracarida, a crustacean group with direct development, incubating the eggs in a marsupium ventral to the thorax formed from thin plates called oostegites.Amphipoda includes, currently, about 7.000 species grouped into four suborders: Senticaudata, Gammaridea, Hyperiidea and Ingolfiellidea, according to Lowry and Myers (2013).
The amphipods from the family Ampithoidae Stebbing, 1899 are among the most abundant associated to the phytal substrates (Nelson 1979;Edgar 1983a, b;Duffy, 1990).Despite this, there are only six ampithoid species recorded until now from is recorded from Brazilian waters.Another species, Grubia sardenta Oliveira, 1953, described with material from Guanabara Bay, 1 m depth, was synonymized to C. filosa by Peart (2004), despite some morphological differences between the two species.The type series of this material is currently lost and the description and illustrations made by Oliveira (1953) are not well detailed.Thus, it is still necessary to analyze materials of collections from this species type locality, to confirm or not the validity of the species described by Oliveira.
The species of the genus Cymadusa, can be easily recognized among the other Ampithoidae, by presenting uropod 1 with long and sharp distoventral spike (spur), on the tip of the peduncle, between the basis of rami.According to Peart (2007), species of Cymadusa tend to be bigger, brighter and more colorful than other amphipods.Genus Cymadusa has accessory flagellum on antenna 1, as the easer way to distinguish this genus from all others.However, despite the abundance and size of individuals, the genus taxonomy remains ambiguous, because of inadequate definitions and descriptions.Peart (2004) defined a species complex around C. filosa, including six species with strongly setose antennae and gnathopods.However, some of these species do not present these appendages too much setose, as illustrated by the author herself.
In this paper, we describe a new species of Cymadusa, the second one recorded from Brazilian waters, and the first one known from the Rocas Atoll, as for the northeastern Brazilian coast.This species is part of the C. filosa complex since it presents antennae and posterior margin of merus, carpus and propodus, and palm of gnathopods 1 and 2, besides anterior margin of propodus of gnathopod 2 well setose.

MATERIAL AND METHODS
The examined material was collected on sublittoral algae by scuba diving at the northeastern Brazilian coast.The type material is from the Rocas Atoll Biological Reserve (03º52'S / 033º48'W).The collections were made from October 2000 to November 2001, during the project Oceanic Islands Diversity -Rocas Atoll, coordinated by the Departamento de Invertebrados, Museu Nacional, Universidade Federal do Rio de Janeiro.This atoll is located at the peak of a seamount, about 150 km west of the Fernando de Noronha archipelago and 267 km northeast of the Rio Grande do Norte State.The algae samples were anesthetized with 5-10% ethanol and washed in a 0.5mm mesh sieve.Some paratypes were also collected using the same methodology at the Camamu Bay (13º56'S / 39º06'W) and Todos os Santos Bay (12°46'22"S / 38°33'32"W), both in the Bahia State coast.All the examined material for this study is preserved in 70% ethanol.For the taxonomic study, the appendages and mouthparts of the dissected specimens were mounted on glycerol gel slides and drawn under an optical microscope with camera lucida, Motic BA-310.Illustrations were digitalized in CorelDraw X5, using a Wacon Intuos 4 tablet.All the material is deposited at the Crustacea Collection of the Departamento de Zoologia, Universidade Federal do Rio de Janeiro (DZUFRJ), and the Crustacea Collection of Museu Nacional (MNRJ).
The setae classification used on this work follows the one proposed by Watling (1989) and the gnathopods 2 palm nomenclature was based on Poore and Lowry (1997).
Description: Based on holotype female (DZUFRJ 4937).Head, eyes present, well developed, round, lateral cephalic lobe, well developed, broadly rounded.Antenna 1, flagellum 52-articulate, longer than antenna 2, poorly setose; accessory flagellum 1-articulate.Antenna 2, flagellum 30-articulate.Upper lip rounded and apically setose.Lower lip apically notched with thin setose margin; inner lobe bigger than outer lobe; apically setose.Mandible molar triturative with long plumose accessory seta; incisor and lacinia mobilis multi-cuspidate; palp 3-articulate covered with small setules, article 1 about 2X longer than wide, article 2 about 3.2X longer than wide with a simple slender seta on its angle, article 3 about 2.7X longer than wide with seven long plumose setae at the apical margin.Maxilla 1 inner plate small and subtriangular with six slender plumose setae at the inner margin, without apical setae; outer plate with eight multi-cuspidate robust setae at the apical margin; palp 2-articulate, article 2 with nine stout plumose setae at the apical margin and four slender plumose facial setae.Maxilla 2 with outer plate 1.6X wider and slightly longer than inner plate; inner plate, marginal and facial rows of plumose setae present; outer plate with row of slender simple setae at the outer margin, plumose setal row at the apical and inner margin, subapical surface covered by small setules.Maxilliped, inner plate 1.8X longer than wide, with plumose setae at the inner and apical margin; outer plate 1.6X longer than wide, 1.5X longer than inner plate, with trifid robust setal row on the inner margin and plumose setae on the distal and outer margin; palp 4-articulate, 1.4X longer than outer plate, article 1 small and subrectangular, article 2 subtriangular with 2 small plumose setae and 4 bigger plumose setae on the outer margin, article 3 subrectangular, article 4 subrectangular with eight distally plumose setae, nail with three small plumose setae.
Epimeral plates 2 and 3 rounded, with small slender setae on the posterior margin.Uropod 1, peduncle with long and sharp distoventral spike (spur); peduncle about 2.3X longer than wide, with four stout setae with accessory seta on the dorsal margin, three stout setae with accessory seta on the dorsolateral margin and slender setal row on the ventral margin; outer ramus slightly longer than inner ramus, with seven stout setae with accessory seta on the dorsal margin, three simple setae and one stout seta with accessory seta on the dorsolateral margin, five stout setae on the apical margin; inner ramus with four stout setae with accessory seta and three simple setae on the dorsolateral margin and six stout setae with accessory setae on the ventral margin, two stout setae on the apical margin.Uropod 2 peduncle about 2X longer than wide, one stout seta with accessory seta on the dorsal margin, one stout seta with accessory seta on the dorsolateral margin; outer ramus slightly longer than inner ramus, six stout setae with accessory seta on the dorsal margin, five stout setae with accessory seta on the dorsolateral margin, three stout setae and two stout setae with accessory seta on the apical margin.Uropod 3, peduncle about 1.2X longer than wide, with seven stout setae and seven plumose setae; outer ramus 1.3X shorter than inner ramus; inner ramus with two proximal stout setae, four simple setae and small cover of slender setae on the dorsal margin, two stout setae on the extremity; outer ramus with two curved thick setae, four stout setae, four small setae on the ventral margin, nine long plumose setae on the apical extremity.Telson rounded and concave; two nodes at the apical extremity with one plumose seta; three long plumose setae on the apical margin; 11 plumose setae and two small simple setae on the lateral margins.
Geographic distribution: The species is known from the Rocas Atoll, its type locality (03º52'S / 033º48'W), and for the Bahia State coast (Camamu Bay and Todos os Santos Bay) (Fig. 5).