Morphological review of the freshwater fairy shrimp Dendrocephalus brasiliensis Pesta , 1921 ( Anostraca : Th amnocephalidae )

Information concerning the morphology of Dendrocephalus brasiliensis Pesta, 1921 is currently fragmented. Th is study reviewed the morphological structures described previously and new features (e.g., antenna-like structures and gonopod). We review the distribution of this species and also expand the geographic distribution of D. brasiliensis in the state of Alagoas. Th e specimens were obtained from fi sh-breeding tanks in Porto Real do Colégio, Alagoas, Brazil, in November 2012. Several morphological structures of D. orIgInal artIcle This article is part of the special series offered by the Brazilian Crustacean Society in honor to Nilton José Hebling in recognition of his dedication and contributions to the development of carcinology in Brazil.

In recent decades, a growing demand for alternative sources of food for aquaculture has attracted the interest of researchers to the genus Dendrocephalus (Cohen et al., 2014).Among the species that occur in Brazil, D. brasiliensis is notable for the increase in the number of published studies that address its use as a food source to replace Artemia Leach, 1819 (Yflaar andOlivera, 2003;Carneiro et al., 2004;Lopes et al., 2007).
Similar to other Anostraca, D. brasiliensis inhabits temporary pools, with resting eggs laid on the bottom of the pool (Brendonck et al., 2008).These eggs allow survival during the dry period but are also responsible for the dissemination of the species.To date, D. brasiliensis has been collected in natural and artificial Caatinga pools from the north of Minas Gerais to the north of Rio Grande do Norte and also in pools in Gran Chaco in northern Argentina.The species has also been collected in the more humid climate of coastal northeastern Brazil (Rabet and Thiéry, 1996).To date, the species has not been reported in the Cerrado biome.Dendrocephalus brasiliensis is found with several large branchiopods, such as D. orientalis in coastal Paraíba and D. cervicornis (Weltner, 1890) in northern Argentina (César, 1989;Rabet and Thiéry, 1996;César et al., 2004).Other large branchiopod species reported together with D. brasiliensis are Cyclestheria hislopi (Baird, 1859) (Lemos-de-Castro andLima, 1986), Eulimnadia colombiensis Roessler, 1989 and Eulimnadia magdalensis Roessler, 1990 (NR, pers. obs.).
The morphology of D. brasiliensis was first described by Pesta (1921) and Lutz (1929) and was subsequently revised by Pereira (1983), Lemos-de-Castro and Lima (1986) and Rabet and Thiéry (1996).Although different authors have investigated the morphology of D. brasiliensis, most descriptions (Pesta, 1921;Lutz, 1929) were performed without the standardization of morphological terminology proposed by Belk and Pereira (1982) and Pereira (1983).In addition, the description of some structures, such as branch 1V and branch 2A of the frontal appendage and thoracopods require some additional observations (see Pereira, 1983;Lemos-de-Castro and Lima, 1986;Rabet and Thiéry, 1996).Currently, information on the morphology of D. brasiliensis is fragmented into different studies, making it difficult to use.
Given the great potential of D. brasiliensis for aquaculture and the possible expansion of its distribution into other regions, the correct identification of the species becomes of great importance.Thus, the objective of this study is to provide a review of D. brasiliensis, to compile and expand the already existing knowledge of morphology and to describe structures for which there is little information to date (e.g., antenna-like structures and gonopod).Moreover, a new record of the geographical distribution was provided for this species.

MaterIal and Methods
The specimens were obtained from fish-breeding tanks of the Centro Integrado de Recursos Pesqueiros e Morphology of the fairy shrimp D. brasiliensis Nauplius, 24: e2016008 Aquicultura (CERAQUA), which belongs to the Companhia de Desenvolvimento dos Vales do São Francisco e do Parnaíba -CODEVASF (10°12'07.70"S36°47'30.43"W),situated at an altitude of 10 m in the municipality of Porto Real do Colégio, Alagoas, in northeastern Brazil.The individuals were sampled with a plankton net (300-µm mesh size) on 23 November 2012.
Literature descriptions (Pesta, 1921;Lutz, 1929;Pereira, 1983;Lemos-de-Castro and Lima, 1986;Rabet and Thiéry, 1996) and identification keys (Rabet and Thiéry, 1996;Rabet, 2006;Chaves et al., 2011;Rogers et al., 2012;Hirose et al., 2015) were used for species identification.The present description was based on the observation of 60 individuals (40 males and 20 females).For detailed examinations, the specimens were dissected under a stereoscopic microscope and prepared on semi-permanent slides.Drawings of the appendages were made with an optical microscope (Axioskop 2, Zeiss) provided with a camera lucida.The specimens' total length was measured from the anterior margin of the head to the telson (excluding cercopods).The brood pouch was measured from the proximal portion (distal of postgenital abdominal segment IV) to the most distal portion.The resting eggs were measured as the largest diameter.The measurements were made with a stereomicroscope equipped with an imaging and measurement tool (Zeiss Stemi DV4, accuracy 0.1 mm).The terminology of branches and sub-branches is based on Pereira (1983).
The occurrence of D. brasiliensis in fish-breeding tanks in the Porto Real do Colégio represents the first record of this species in the state of Alagoas.Two main hypotheses should be considered for the current record of these populations in Alagoas: 1) associated with the natural distribution of the species, even if it is not found yet in natural ponds in this state; or 2) introduced by human action in connection with aquaculture.
Dendrocephalus brasiliensis is typically found in temporary ponds in the Caatinga biome and in a coastal area (at João Pessoa, Paraíba, see Rabet and Thiéry, 1996).The distribution of this species appears to be interrupted in Bahia state (Fig. 1).This apparent gap should be confirmed by a precise examination of many dendrocephalid populations, because Dendrocephalus orientalis is clearly dominant in the center of Bahia, but we cannot exclude a sympatric distribution of the second species.
In addition to its natural distribution, the expansion of the geographical distribution of D. brasiliensis might be associated with fish-breeding tanks.Dendrocephalus brasiliensis and D. orientalis were collected twice in fish tanks (Rabet and Thiéry, 1996;1998;this study), and this activity might have a major impact on the distribution of the species.Particularly, this can generate predictions of the rapid expansion of D. brasiliensis into other hydrographic basins, which might cause problems related to the introduction of exotic species (Rocha et al., 2005;Mai et al., 2008).
Gonopod (retracted state) with basal part short, with slightly curved triangular lateral projection containing small spines and surface protuberances, as well as pointed end portion.Distal end of retracted gonopod globose and nude, with small groove at tip (Fig. 6A).
Remarks.Some features have been described here for the first time, such as antenna-like structures and the gonopod (retracted state).Furthermore, some morphological characteristics that were previously described superficially were examined in more detail (e.g., the endopod of thoracopods, the number of spines on branch 1V and sub-branches I, II and III of branch 2D, the number of cell pads in branch 2V).
In branch 1V, the anterior sub-branch is longer than the posterior branch and the distal portion is swollen, as in D. affinis (see Cohen et al., 2014), D.
Branch 2V is typically bent at the tip and terminates in several well-defined cell pads (3-5), which are frequently found in the subgenus Dendrocephalus but differ in D. carajaensis (see Rogers et al., 2012) and D.

Morphology of the fairy shrimp D. brasiliensis
Nauplius, 24: e2016008 sarmentosus (see Pereira and Belk, 1987), which share only two cells pads in the distal portion.

dIscussIon
The morphology of Dendrocephalus brasiliensis has been completely revised in this study.Some of the structures that have been newly described here, such as eyes, first and second antenna, branches and sub-branches of the frontal appendage, thoracopod endopods 1-3 and eggs, are similar to previously described structures (Pesta, 1921;Lutz, 1929;Pereira, 1983;Lemos-de-Castro and Lima, 1986;Rabet and Thiéry, 1996).
Traditionally, the identification of D. brasiliensis was supported by the absence of spines on the anterior portion of the male frontal appendage arms (Rabet, 2006;Chaves et al., 2011).However, Hirose et al. (2015) demonstrated for Dendrocephalus orientalis that such morphological characteristics can vary among individuals of the same species, as was also verified for Dendrocephalus affinis by Cohen et al. (2014), reinforcing the need to use other morphological characteristics that can be used for species identification.According to Hirose et al. (2015), important morphological features for identification of D. brasiliensis are: 1) branch 2A podiform; 2) second thoracopod endopodite without basolateral spine; 3) first thoracopod endopodite without basolateral lobe; and 4) branch 1V anterior sub-branch with distal portion swollen.Therefore, the need of accurate morphological descriptions of Dendrocephalus species is evident, as well as a standardization of the descriptive process, so that the characteristics of diagnostic importance and its details can be adequately described, enabling interspecific comparisons.
Morphologically, the populations of D. brasiliensis studied appear to be relatively homogeneous in relation to the frontal appendage, the legs and the basal part of the gonopod.Nevertheless, D. brasiliensis is clearly more widely distributed than other dendrocephalid species and might be composed of several cryptic species.Particular attention should be focused in the future to understand the distribution of populations of these species, especially in Argentina.

acKnowledgMents
The authors dedicate this study to Dr. Nilton José Hebling, who had a crucial role in the NEBECC (Group of Studies on Crustacean Biology, Ecology and Culture) foundation, acting directly and indirectly in the education of several carcinologists in Brazil, including SPBA, DFRA, EABJ and GLH.The authors thank the Centro Integrado de Recursos Pesqueiros e Aquicultura (CERAQUA), belonging to the Companhia de Desenvolvimento dos Vales do São Francisco e do Parnaíba (CODEVASF), M.Sc.Sergio Antônio Medeiros Marinho and Dr. Marcelo Fulgêncio Guedes de Brito for kindly providing the animals used in this study.

Figure 6 .
Figure 6.Dendrocephalus brasiliensis Pesta, 1971 from Porto Real do Colégio, Alagoas, Brazil (CARCINO 104).A) non-everted gonopod lateral view; B) brood pouch; C) polyhedral resting eggs with rounded ridges.Scale bars = 0.2 mm.The arrow indicates the nude appearance, with a small groove at the tip of the distal end of the retracted gonopod.