Abbreviated larval development of Macrobrachium inpa Kensley and Walker , 1982 ( Crustacea : Decapoda : Palaemonidae ) from an Amazon Basin forest stream , Brazil , reared in the laboratory

Th is paper brings the description and illustrations of the abbreviated larval development of the Amazonian freshwater palaemonid shrimp, Macrobrachium inpa Kensley and Walker, 1982. Th e study was based on ovigerous females (mean total body length of 27.0 ± 1.64 mm) collected in a small forest stream in the Reserva Florestal Ducke, near Manaus, Brazil, of which four released their larvae in the laboratory. Th e females carried 8 to 19 eliptical (2.39 ± 0.10 X 1.67 ± 0.08 mm), yolk-rich eggs. Th e larval period consists of three benthic, lecithotrophic larval stages, and lasts 10–11 days. Th e newly-hatched larvae bear very advanced morphological features such as antenna with several marginal plumose seta on scaphocerite and long, multiarticulated fl agellum; fully developed, functional uniramous pereiopods 3–5 (walking legs) and biramous pleopods. Th e morphology of the carapace, all appendages of the cephalothorax and pleon, and the tail fan are described in detail and illustrated. Th e larval form was considered to be a decapodid because of the benthic behavior and due to the fact that functional walking legs and pleopods are the main structures for displacement and propulsion. Th e larval development of M. inpa is compared with those of the so-called “continental” group of the caridean shrimps from the Amazon River basin. 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.

ZOOBANK htt p://zoobank.org/urn:lsid:zoobank.org:pub:1FE8E095-5586-4A09-BD42-91ED8BB53DF8 aBstract Th is paper brings the description and illustrations of the abbreviated larval development of the Amazonian freshwater palaemonid shrimp, Macrobrachium inpa Kensley and Walker, 1982.Th e study was based on ovigerous females (mean total body length of 27.0 ± 1.64 mm) collected in a small forest stream in the Reserva Florestal Ducke, near Manaus, Brazil, of which four released their larvae in the laboratory.Th e females carried 8 to 19 eliptical (2.39 ± 0.10 X 1.67 ± 0.08 mm), yolk-rich eggs.Th e larval period consists of three benthic, lecithotrophic larval stages, and lasts 10-11 days.Th e newly-hatched larvae bear very advanced morphological features such as antenna with several marginal plumose seta on scaphocerite and long, multiarticulated fl agellum; fully developed, functional uniramous pereiopods 3-5 (walking legs) and biramous pleopods.Th e morphology of the carapace, all appendages of the cephalothorax and pleon, and the tail fan are described in detail and illustrated.Th e larval form was considered to be a decapodid because of the benthic behavior and due to the fact that functional walking legs and pleopods are the main structures for displacement and propulsion.Th e larval development of M. inpa is compared with those of the so-called "continental" group of the caridean shrimps from the Amazon River basin.

Nauplius
BraZIlIan crustacean socIety

BraZIlIan crustacean socIety 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.

IntroductIon
The freshwater palaemonid shrimp Macrobrachium inpa Kensley and Walker, 1982 is so far known from some tributaries of the lower Rio Negro basin, in the state of Amazonas, Brazil, where it occurs in small, shadowed forest streams with very acidic, plankton-poor black waters (Kensley and Walker, 1982;Magalhães, 2009).
The specimens usually inhabit the submerged leaf litter or can be found in holes and fissures of submerged logs and branches (Walker and Ferreira, 1985).
In addition to M. inpa, at least three other taxa pertaining to the continental species of Macrobrachium with short rostrum are distributed in the lower Rio Negro basin (Kensley and Walker, 1982;Magalhães and Pereira, 2007): Macrobrachium brasiliense (Heller, 1862), Macrobrachium ferreirai Kensley and Walker, 1982, and Macrobrachium nattereri.All four are very similar and phylogenetically closely related (Pileggi and Mantelatto, 2010).The study of their larval development can add new characters, thus contributing to the study of the taxonomy and systematics of this group.The purpose of this paper is to provide morphological descriptions and illustrations of the three larval and first juvenile stages of M. inpa reared in the laboratory.

MaterIal and Methods
Some ovigerous females of Macrobrachium inpa were collected using dip net in the igarapé (an upland forest stream) Barro Branco, in the Reserva Florestal Ducke (2°55'48"S 59°58'28"W), near Manaus, in the state of Amazonas, in May and June 1994.The females were transported to the laboratory in a plastic container and kept in a 680x300x400 mm aquarium with some pieces of brick for shelter.Only four females carrying eggs with advanced embryos hatched their larvae and at least five specimens of each stage were used for observations and illustrations.Usually, two larvae of the first female to release its clutch were use for preparing the illustrations; at least one larva of the remainder females was used to verify any variability.Line drawings of the whole specimen in dorsal view were made with the aid of a stereoscopic microscope (Wild M8) equipped with a drawing tube and a light microscope (Leitz Laborlux S) with drawing tube was used for the line drawing of the dissected parts.Line drawings were scanned at 600 dpi and edited in Adobe Photoshop CS 2 software at 1200dpi.The plates were mounted in CorelDraw X3 software.The procedures for larval rearing and for taking measurements, dissections, preparing the line drawings, and morphological descriptions were made according to Magalhães (2000).The first larval stage is described in detail and only marked differences are mentioned in the morphological description of the respective structure in subsequent stages.

results
Ovigerous females with a mean total body length of 27.0 ± 1.64 mm (n = 11) carried 8 to 19 eliptical, yolkrich, dark red eggs measuring 2.39 ± 0.10 mm (long axis) and 1.67 ± 0.08 mm (short axis) (n = 44; 4 eggs randomly chosen from each of these 11 non hatching females were measured).It took two to three days for the females to release their entire clutch.Hatching was never observed during daytime.The species goes through three benthic larval stages without feeding.The duration of the whole larval period was ten to eleven days.
Cephalothorax (Figs. 1-2).Eyes sessile.Rostrum very short, unarmed, slightly overreaching anterior border of eyes, strongly curved downwards.Carapace with 1 small spine (antennal spine) always present on the anterolateral border, sometimes a minute spine present just ventrally to the antennal spine.
Maxilliped 2 (Fig. 21).Protopod segmented, epipod larger than that of the first larval stage.Endopod still rudimentary, segmentations distinct, except for incomplete segmentation between penultimate and ultimate segments.
Uropods (Fig. 25) only with posterior projection of protopod free, overreaching dorsally the proximal lateral margin of telson.
Antenna with 29 marginal plumose setae; otherwise similar to preceding stage.
Mandibles with cleft between incisor and molar processes more expanded; incisor process bearing 3 sharp teeth; molar process still rudimentary, but bearing 1 sharp tooth and some denticles.
Maxilliped 2 (Fig. 31).Coxa bearing 3 simple setae subdistally on inner margin, and large bilobed epipod.Endopod strongly curved inwards, 4-segmented, segmentations clearly distinct; penultimate and ultimate segments much broader than first and second ones; penultimate segment with 2 rudimentary simple setae subterminally on outer margin, 1 subterminally on inner margin; last segment with several short, simple and serrated setae terminally and subterminally along distal margin.
Telson (Fig. 35) subrectangular, narrower and longer than in preceding stage; lateral margins with distinct concavity on distal third on its length; distal margin strongly convex, bearing 11+11 plumose setae and 1 pair of small spine on laterodistal corner.
Pereiopods 1-2 with chela well developed, fully functional.Chela of pereiopod 1 (Fig. 45) with palm bearing 3 short, serrated plus 1 long, simple setae proximally on the lower margin, 2 simple setae distally on the upper margin; fixed and movable fingers tipped with tuft of simple setae, sets of simple plus serrated setae present medially on both fingers.Chela of pereiopod 2 (Fig. 46) with lower margin of palm smooth; upper margin with 1 median simple setae, 1 short plus 1 long simple setae distally; both fingers with sets of setae and tipped with tuft of simple setae.Pereiopod 2 longest, approximately 1.7 times the length of pereiopod 1.
Uropods (Fig. 47).Endopod fully developed, with several short, weakly plumose setae scattered along outer lateral margin and dorsal surface, 16-18 long, plumose setae along distal and inner lateral margins.Otherwise similar to preceding stage, except for exopod with number of setae slightly increased.

Abbreviated larval development of Macrobrachium inpa
Nauplius, 24: e2016009 dIscussIon The relatively short duration (10-11 days) of the larval period, the benthic behavior, and the advanced morphological features exhibited by lecithotropic larvae on hatching characterize Macrobrachium inpa as a species with an abbreviated type of larval development according to the categorizations made by Gore (1985), Rabalais and Gore (1985), Anger (2001), Jalihal et al. (1993), and by Guerao and Cuesta (2014).Gore (1985) and Rabalais and Gore (1985) further subdivided this category into "direct development" and "advanced development".Macrobrachium inpa can be categorized as pertaining to advanced type of development.In the much subdivided classification proposed by Jalihal et al. (1993), M. inpa can be included in the Type II-Ai-c.Although the newly-hatched larvae are not freeswimming and bear some quite advanced morphologic characters (antenna with several marginal plumose seta on scaphocerite and long, multi-articulated flagellum; fully developed, functional walking legs and pleopods; no trace of exopods in the pereiopods), they also exhibit some typical larval features (such as sessile eyes, unsegmented antennule, mostly rudimentary mouthparts -at least for the structures involved in feeding activities -, nonfunctional chelipeds, and absence of free uropods and spatulated telson).These structures gradually improve their morphology towards the basic adult shape, which is attained at the third molt.Additionally, in spite of the low number of observations, the developmental sequence can be considered as regular, both in terms of duration and number of ecdysis.
Several names for larval forms have been used in the decapod larval development literature.Williamson (1982), Gore (1985), Anger (2001), and Guerao and Cuesta (2014) thoroughly discussed this issue and offered slightly different definitions.They all used the criteria of functional morphology (particularly the situation of the locomotory appendages) to denominate the larval forms.According to the terminology proposed by Anger (2001), I considered M. inpa as exhibiting a decapodid type of larval form because the newly-hatched larvae use their already fully formed and functional walking legs (pereiopods 3-5) and pleopods as the main structures for displacement and propulsion.The features of larval stages given by

Abbreviated larval development of Macrobrachium inpa
Nauplius, 24: e2016009 Guerao and Cuesta (2014) are somewhat too general to adequately define the larval stages of M. inpa, which is apparently among the many exceptions as cautioned by the authors.
The number and size of the eggs carried by the females of M. inpa verified in the present study are very similar to those found by Gualberto et al. (2012).In their study, 18 similarly sized ovigerous females (25.8-32.8mm versus 27.0 ± 1.64 mm in this study) carried 6-21 eggs (versus 8-19) with a size of 2.46 X 1.70 mm (versus 2.39 X 1.67 mm).These similarities can be explained by the population's taxonomic identity or because the populations in both studies come from nearby locations in the same geographical area.
The molts during the larval phase of M. inpa do not imply significant changes in size and morphology (probably also in biomass, but this was not measured in this study), thus corroborating the typical larval trait of the decapodids seen in caridean shrimps as mentioned by Anger (2001).Similarly, transition from decapodid to the juvenile phases in M. inpa is very gradual as most of the morphological structures are already fully developed at the third decapodid stage.Only those structures involved primarily in feeding activities (mandibles, maxillule, inner parts of maxilla and maxillipeds, and chelae of pereipods 1 and 2) still bear incipient features in the third larval stage, as the larvae at this stage are still lecithotropic, but become fully developed and functional after the third molt, thus marking the end of the very abbreviated larval period.
When compared to other Amazonian palaemonid shrimps, the advanced larval development of M. inpa is more similar to that exhibited by Pseudopalaemon chryseus, Ps. amazonensis, and M. ferreirai.The larvae of those species also hatch as decapodid whose locomotion and propulsion are provided mainly by the fully developed, functional walking legs (pereiopods 3-5) and pleopods (Magalhães, 1986/87;Magalhães and Medeiros, 1998;C. Magalhães, unpubl. data).The other Amazonian species of Macrobrachium for which the abbreviated larval development have been described do not show a degree of abbreviation as high as that of M. inpa.The main differences among them are that in the first larval stage of M. nattereri (see Magalhães, 1989) the distal flagella of the antennule is partially fused and not separated from the peduncle (vs.flagella individualized and clearly separated from the peduncle in M. inpa); the antenna has a partially developed scaphocerite, with only a few plumose setae along the distal margin, and an unsegmented flagellum, only twice as long as the scale (vs.fully developed

Abbreviated larval development of Macrobrachium inpa
Nauplius, 24: e2016009 scaphocerite and a long, multisegmented flagellum in M. inpa); pereiopods 3-5 are nonfunctional buds (vs.fully developed, functional in M. inpa); all pair of pleopods are smooth, not functional buds (vs.fully developed, setaceous and functional in M. inpa); the telson is similar in both species, but it is less setaceous in M. nattereri (7+7 marginal plumose setae) than in M. inpa (12+12).Other noteworthy differences in the second larval stage can be found in the antenna (scaphocerite still partially developed as in the first stage, in M. nattereri), pleopods (as buds a little more developed, but still not setaceous, in M. nattereri), and telson (outline of lateral margins clearly discontinued due to exopodal buds being partially protruded in M. nattereri vs. a continuous outline in M. inpa); in the third stage the larvae of both species are, in general, very similar.
The differences are even greater when the larval development of M. inpa is compared to that of M. jelskii (see Magalhães, 2000), which has a little less developed larval form on hatching due to features such as: antenna with a segmented flagellum only about 1.5 times longer than the scaphocerite; maxilla with outer margin of scaphognathite devoid of plumose setae; pereiopods 1-2 as biramous, chelate buds, with the exopod as a smooth, incipient bud; pereiopods 3-5 as uniramous buds; pleopods as biramous, smooth buds; and telson with 9+9 plumose setae.In the second and third larval stages, the cheliped buds still keep the exopod, but bearing distal plumose setae, and the pleopods are still glabrous, with incipient appendix interna.Moreover, the uropods are freed at the third stage, but the endopod is still rudimentary.Therefore, the biramous chelipeds and the underdeveloped, not fully functional pleopods throughout the larval period seem to be the most remarkable differences between the larval developments of these two species.
Unfortunately, comparison between the larval development of M. inpa and M. ferreirai cannot be properly made because Magalhães and Walker (1988) offered very brief information on the first larval stage of the latter species, mostly about the behavior of the newly-hatched larvae.However, their larval development must be very similar since the first larval stage of M. ferreirai also bears fully developed, functional walking legs and pleopods (C.Magalhães, unpubl. data).It would also be interesting to compare the larval development of M. inpa and Macrobrachium cortezi Rodríguez, 1982. Rodríguez (1982) described the latter species from the upper Orinoco River basin and it is suspected that it could be a senior synonym of M. inpa (G.Pereira, pers. comm.).

acKnowledgeMents
This paper is dedicated to Prof. Dr. Nilton José Hebling in appreciation for his remarkable role in the development of the Brazilian carcinology, as well as in gratitude for his support and encouragement during my early studies about the larval development of the Amazonian shrimps.I thank Dr. Klaus Anger and two anonymous reviewers for constructive comments on the manuscript, the Conselho Nacional de Desenvolvimento Científico e Tecnológico -CNPq for an ongoing research grant (proc.303837/2012-8), Dr. J. A. Cuesta, for kindly sending a copy of his paper, and Ms. Colleen L. Flanagan for the linguistic revision of the English text.

Abbreviated larval development of Macrobrachium inpa
The temperature of the water used for larval rearing ranged from 26 to 28 o C. The four female specimens used in this study are deposited in the Crustacean Collection