Larval development of Austinixa bragantina (Crustacea: Brachyura: Pinnotheridae) reared in the laboratory

MORPHOLOGY AND PHYSIOLOGY

Larval development of Austinixa bragantina (Crustacea: Brachyura: Pinnotheridae) reared in the laboratory

Jô de Farias Lima

Embrapa Amapá. Rodovia Juscelino Kubitschek, km 5, Caixa Postal 10, 68903-000 Macapá, Amapá, Brasil. E-mail: [e-mail]; [e-mail]

ABSTRACT

The zoeal and megalopal stages of Austinixa bragantina Coelho, 2005, a small pinnotherid crab found in association with ghost shrimps Callichirus major (Say, 1818) and Lepidophthalmus siriboia Felder & Rodrigues, 1993 in the northeastern region of the state of Pará, Brazil, were reared in the laboratory from hatching to the megalopal stage. The duration of the larval period from hatching to megalopa was 28 days and the mean of duration for each larval stage was 6, 5, 5, 6, and 6 days, respectively. In the present study, the zoeal and megalopal stages are described and illustrated in detail.

Key words: Larval stages; larval description; Pará; Pinnotherid crab.

Members of Pinnotheridae are known to spend most or all of their post-planktonic life in symbiosis with other invertebrates, such as mollusks, polychaetes, annelids, ascidians, echinoderms, and other crustaceans (WILLIAMS 1984). According to NG et al. (2008) the family is currently subdivided in two subfamilies: Pinnotheriliinae and Pinnotherinae, as well as several insertae sedis species. According to BEZERRA et al. (2006), in the coast of Brazil, this family is represented by 22 species distributed across the 11 genera.

Austinixa Heard & Manning (1997) is represented by A. aidae (Righi, 1967) from Amapá to Rio Grande do Sul, A. leptodactyla (Coelho, 1997) from Pará to Sergipe, A. patagoniensis (Rathbun, 1918) from Rio de Janeiro to Rio Grande do Sul, and A. bragantina Coelho, 2005 from Pará to Ceará, always living in symbiosis with both thallassinidean shrimps of the Callichirus major (Say, 1818) complex, and a few ecologically equivalent thallassinidean species. In addition, it has been reported in association with the genus Pinnixa White, 1846 by LIMA et al. (2006).

Larval descriptions of Pinnotheridae crabs are available for 46 species among 15 genera. However, descriptions of the complete larval development has been published for 26 species. The remaining publications provide only partial information, being mostly restricted to the first zoea (MARQUES & POHLE 1996a). Currently, most studies focus on Dissodactylus Smith, 1870, Pinnixa and Tunicotheres Campos, 1996 (FAXON 1879, SEKIGUCHI 1978, BOUSQUETTE 1980, MARQUES & POHLE 1996a,b, LIMA et al. 2006). No larval description has hitherto been provided for Austinixa.

In the present paper, the larval stages of A. bragantina, a small pinnotherid crab found in association with ghost shrimps Callichirus major (Say, 1818) and Lepidophthalmus siriboia Felder & Rodrigues, 1993 are described and illustrated in detail from larvae reared in the laboratory. These results are briefly compared with other descriptions reported on pinnotherid larvae from Brazil.

MATERIAL AND METHODS

Six egg-bearing females were obtained from Ajuruteua beaches, northeastern state of Pará, Brazil. In the laboratory, all females were cleaned and monitored until hatching occurred in a five liters aquarium with constant aeration.

After hatching, larvae were transferred to glass containers of 500 ml capacity (approximately 30 larvae per container) filled with filtered seawater and kept at room temperature in the laboratory (~27ºC). Salinity was maintained at 30‰ and pH 8.1. Water and food were changed daily. The larval and postlarval stages were fed with rotifers (Brachionus sp.). Cultured diatoms (Thalassiosira sp.) were added to the culture. Survival was recorded daily and intermolt periods were inferred using mean of occurrence of exuviae for each stage.

Exuviae, some zoeal larvae, and a megalopa were preserved in ethanol 70% + glycerine 10% (1:1) solution. The larvae were dissected with fine needles, measured and illustrated using an ocular micrometer coupled with binocular microscope. Carapace length was measured using the distance from the anterior portion of ocular orbit to posterodorsal margin of the carapace.

The terminology used in the description followed SEKIGUCHI (1978), BOUSQUETTE (1980), PEREYRA LAGO (1987, 1989), MARQUES & POHLE (1996a,b), MAGALHÃES & MEDEIROS (1998), BOLAÑOS et al. (2004, 2005), LIMA & ABRUNHOSA (2006), LIMA et al. (2006).

RESULTS

The larval development of A. bragantina consisted of five zoeal stages and one megalopa. The intermolt period of each larval stage and survival rate are presented in the table I. Morphological differences between zoea I of A. bragantina and Brazilian pinnotherids are provided in the table II. The first stage of A. bragantina is described in detail. Only main morphological changes were described for stages following the first zoea.

Zoea I

Carapace length 0.26 mm (0.25-0.28 mm), bearing one dorsal, one rostral, and two lateral spines (Fig.1). Lateral margin with one small simple setae. Eyes sessile. Antennule uniramous, unsegmented, smooth and conical, with two long and one short terminal aesthetascs (Fig. 7). Antenna uniramous, elongate, presented antennal flagellum spinulose with one simple (Fig. 8) Basial seta. Mandible symmetrical, with two distal incisor process (Fig. 9). Molar region circular, more or less serrated. Cuticle distally brown. Palp absent. Maxillule coxal endite supporting four plumose setae (Fig. 10). Basial endite with three cuspidate and two plumose setae. Endopod 2-segmented, proximal segment without setae, distal segment with four long plumose setae. Protopod absent. Exopod and epipod seta absent. Maxilla coxal endite with proximal and distal lobes almost fused with five plumodenticulate setae (Fig. 11). Basial endite with proximal and distal lobes fused bearing eight plumodenticulate setae. Endopod unsegmented with 2+1 long plumose setae. Scaphognathite with three or four plumose setae along anterior margin and one conical terminal process supporting microtrichia in the posterior margin. First Maxilliped basipod with internal margin bearing 2, 3, 1, 2 setae (Fig. 12). Endopod 5-segmented with 2, 2, 1, 2, 4 setae, respectively. Exopod unsegmented, with four plumo-natatory setae. Second maxilliped basipod with three to four setae (Fig. 13). Endopod 2segmented with 0 and (4+1) simple setae, respectively. Exopod unsegmented with four plumo-natatory setae. Third maxilliped absent. Pereiopods absent. Abdomen and telsonwith five abdominal somites, 2^th and 3^th with a pair of acute spines projecting sidelong, somite 5 expanded laterally into two lobes, which extend backward on each side of the terminal segment overlap the telson (Fig. 14). Telson bifurcated with two long lateral plumose spines. Internal margin with six (3+3) plumose setae of the asymmetric size separated for a triangular median projection.

Zoea II

Carapace length 0.35 mm (0.33-0.36 mm) (Fig. 2). Lateral margin with three simple setae. Eyes stalked. Antennule uniramous, unsegmented and conical with four long and one short terminal aesthetascs (Fig. 15). Antenna as illustrated (Fig. 16). Mandible as illustrated (Fig. 17). Maxillule coxal endite as illustrated (Fig. 18). Basial endite with two additional cuspidate setae. Protopodite with one long plumose seta. Maxilla coxal endite with proximal and distal lobes almost fused with six plumose setae (Fig. 19). Basial endite with 5+3 plumose setae. Scaphognathite with 4+3 marginal densely plumose setae. First maxillipedbasipod and endopod as illustrated (Fig. 20). Distal portion of the endopod with five simple setae. Exopod with six plumo-natatory setae. Second maxillipedexopod with six plumo-natatory setae (Fig. 21). Third maxilliped absent. Pereiopods absent. Pleopods absent. Abdomen and telson as illustrated (Fig. 22). External margin of telson with a pair of small spines projecting laterally.

Zoea III

Carapace length 0.42 mm (0.40-0.44 mm) (Fig. 3). Lateral margin with four small simple setae. Eyes peduncled and mobile. Antennule as illustrated (Fig. 23). Antenna showing endopod bud reaching in the medial portion of protopodite (Fig. 24). Basial seta present. Mandible as illustrated (Fig. 25). Maxillule coxal endite with five plumodenticulate setae (Fig. 26). Basial endite with five cuspidate and two simple setae. Protopodite as illustrated. Maxilla coxal endite with six plumose setae (Fig. 27). Basial endite with 5+5 plumodenticulate setae. caphognathite with 7+6 densely plumose setae. First maxilliped basipod with 1, 2, 1, 2, 1 and 3 simple setae, respectively (Fig. 28). Exopod with eight plumo-natatory setae. Second maxilliped exopod with eight plumo-natatory setae (Fig. 29). Third maxilliped absent. Pereiopods absent. Pleopods absent. Abdomen and telson as illustrated (Fig. 30).

Zoea IV

Carapace length 0.52 mm (0.52-0.53 mm) (Fig. 4). Lateral margin with six small simple setae. Antennule showing four terminal and one subterminal aesthetascs and one simple terminal seta (Fig. 31). Endopod bud present. Antenna endopod bud well developed with one small basial seta, flagellum as illustrated (Fig. 32). Mandible – with three distal incisor process. Molar region circular serrated with two small denticulettes (Fig. 33). Palp present as small bud. Maxillule coxal endite with one simple and five plumodenticulate setae (Fig. 34). Basial endite with eight plumodenticulate and three plumose setae. Protopodite with two plumose setae in external border. Maxilla coxal endite with proximal and distal lobes fused with eight plumodenticulate setae and one simple seta (Fig. 35). Basial endite with proximal and distal lobes fused showing 16 to 17 plumodenticulate setae. Scaphognathite with 14 + 7 densely plumose setae. First Maxilliped– basipod with 2, 1, 1, 3, 3 simple setae, as illustrated (Fig. 36). Exopod with 10 plumo-natatory setae. Second Maxilliped– Exopod with 10 plumo-natory setae (Fig. 37). Third maxilliped present as small bud. Pereiopods present as small bud. Pleopods present as four small bud (Fig. 4). Abdomen and telson as illustrated (Fig. 38).

Zoea V

Carapace length 0.73 mm (0.72-0.74 mm) (Fig. 5). Lateral margin with 10 small setae as illustrated. Antennule well developed with eight aesthetascs and one simple seta (Fig. 39). Endopod bud present. Antenna endopod well developed with size twice of the protopodite (Fig. 40). Mandible as illustrated (Fig. 41). Maxillule coxal endite with five plumodenticulate and three simple setae (Fig. 42). Basial endite with 30 plumodenticulate and five simple setae. Maxilla coxal endite with eleven plumodenticulate setae (Fig. 43). Basial endite with 14 plumodenticulate and six plumose setae. Scaphognathite with 33 plumose setae. First maxilliped as illustrated (Fig. 44). Second maxilliped as illustarted (Fig. 45).Third maxilliped with endopod and exopod buds visible (Fig. 46). Pereiopods longer, with sharply ponted tips, segmentation apparent and bifurcation of chelae clearly visible (Fig. 5). Pleopods longer, not yet segmented nor biramous (Fig. 5). Abdomen and telson as illustrated (Figs 5 and 47).

Megalopa

Carapace length 0.70 mm, almost hexagonal, wider than longer, base of rostrum rectangular, terminal portion short and triangular (Fig. 6). Eyes deeply lodged in the orbit. The cardiac area shows a small high carina almost straight line, extending without interruption. The lateral margin with numerous plumose setae. Antennule basial segment inflated showing three simple setae (Fig. 48). Peduncle 2-segmented without setae. Endopod uniramous with 3+1 setae. Exopod 4-segmented with 10 aesthetascs and one simple seta. Antenna antennal peduncle 3-segmented with each segment showing one simple seta (Fig. 49). Antennal flagellum 4-segmented. Segments 2 with four long terminal setae and two small simple setae. Segment 3 with one terminal simple seta. Last segment with three terminal setae. Mandible scoop-shaped process with smooth, thin cutting edge distally; with five to seven small denticulattes (Figs 55 and 56). Palp 2-segmented, proximal segment smooth, distal segment with 20 small simple and one plumose seta. Maxillule coxal endite with three plumodenticulate and five plumose setae (Fig. 50). Basial endite with 23 plumodenticulate setae. Endopod 2-segmented, proximal with two and distal segments with one simple terminal seta. Protopodite present. Maxilla coxal endite with 21 plumose setae (Fig. 51). Basial endite with 49 plumodenticulate setae. Endopod as illustrated. Scaphognathite with 71 plumose setae marginally and one simple seta subdistally in the anterior border. First Maxilliped basial and coxal endite with approximately 30 setae (Fig. 52). Endopod 2-segmented with two simple setae in each segment. Exopod 2-segmented, proximal and distal segment with one and five simple setae, respectively. Second maxilliped basial and coxal endites lacking setae (Fig. 53). Endopod 5-segmented, with 2, 4, 0, 14, 10 simple setae, respectively. Exopod 2-segmented, proximal segment with two spines and one simple seta, distal segment with five plumose setae. Third maxilliped well developd (Fig. 54). Endopod 4-segmented: basipod showing two small plumose setae, ischiomerus with six plumose setae and two simple setae, carpus with six small simple setae, propodus with 12 long plumose setae, dactylus with 12 long plumose setae. Exopod 2-segmented, proximal segment with five simple setae, distal segment with four plumose setae. Epipodite with 22 small basial and seven long terminal setae. Pereiopods developed and functional for walking, covered with numerous long plumose setae (Figs 59 and 63). Chelipeds symmetric bearing small setae with propodus longer than other segments. Pereiopods 2 and 3 similar in structure. Pereiopod 4 longer and stronger than others with numerous long plumose setae, as illustrated. Pereiopod 5 short with dorsal and ventral margin showing numerous long plumose setae. Pleopods progressing distally, pair 1-4 usually with 10, 8, 8 and 6 long plumose setae, respectively (Fig. 57). Abdomen and telson additional somite 6^th bearing 12 small simple setae (Figs 57 and 58). Telson semi-circular, wider than longer, with four small simple setae.

DISCUSSION

Descriptive studies of pinnotherid larvae have been carried out in recent yearsthus improving the classification of Pinnotheridae, mainly in morphological aspects. The number of zoeal stages within the Pinnotheridae varies from only one, in Epulotheres Manning, 1993 (GOODBODY 1960) to five stages in some genera, such as Asthenognathus Stimpson, 1858, Pinnaxodes Heller, 1865, Pinnixa White, 1846, Pinnotheres Latreille, 1802, Tumidotheres Campos, 1989 as reported by MARQUES & POHLE (1996a) and A. bragantina in the present study.

Based on morphological characters, it is straightforward to discriminate zoeae of Austinixa from the other Pinnotherid genera. Similar to what is observed in species of Fabia Dana, 1851, Pinnixa , and Parapinixa Holmes, 1894, the zoeal stages of A. bragantina showed a structural enlargement in the fifth abdominal segment. This appears to be a distinct characteristic of Fabia, Parapinixa, Pinnixa, and Austinixa, as observed in Fabia subquadrata (Dana, 1851) (IRVINE & COFFIN 1960), Parapinnixa affinis Holmes, 1900 (GLASSELL 1933), P. longipes (Lockington, 1877) (BOUSQUETTE 1980), P. rathbuni Sakai 1934 (SEKIGUCHI 1978), P. Gracilipes Coelho, 1997 (LIMA et al. 2006), P. chaetopterana Stimpson, 1860 (HYMAN 1925), as well as A. bragantina, in the present study. In agreement with HYMAN (1924), the first to fifth stage of P. chaetopterana showed an elongate deltoid extending in the middle of the furcal arch of the telson. This characteristic was also found in A. bragantina in the present study, Zaops ostreum (Say, 1817) by SANDOZ & HOPKINS (1947), Gemmotheres chamae Campos, 1996 by ROBERTS (1975) and absent in P. gracilipes by LIMA et al. (2006), P. longipes by BOUSQUETTE (1980) and P. rathbuni by SEKIGUCHI (1978). Other morphological difference among zoea I of A. bragantina and Brazilian pinnotherids are provided in the table II.

Few differences were observed in abdomen and carapace of A. bragantina during zoeal stages. The first zoea stage shows telson with spines absent. However, similar to what is observed in P. gracilipes by LIMA et al. (2006), the 2^th to 5^th zoeal stages show a pair of small spines projected laterally on lateral margin of telson (Figs 22, 30, 38 and 47). These spines appear to be unique for A. bragantina and P. gracilipes, as they are not present in closely-related species, such as P. longipes by BOUSQUETTE (1980) and P. rathbuni by SEKIGUCHI (1978). Other changes include the increase in the number of setae in the feeding appendages, the appearance of the endopod in the antenna and antennule and appearance of the pleopods and pereiopods starting from the 4^th zoea, which are similar to those observed in other pinnotherids larvae (SANDOZ & HOPKINS 1947, SEKIGUCHI 1978, BOUSQUETTE 1980, LIMA et al. 2006). The number of zoeal stages was similar in A. bragantina, P. rathbuni, P. longipes and P. gracilipes.

The megalopa of A. bragantina can be easily distinguished from the other already described pinnotherids species known in Brazilian coast through the morphological features. The carapace in A. bragantina is smooth and semi-rounded similar to C. stebbingi (Rathbun, 1918) , Pinnixa gacilipes Coelho, 1997 and D. crinitichelis Moreira, 1901, Z. ostreum (SANDOZ & HOPKINS 1947) and Tumidotheres maculatus (Say, 1818) (COSTLOW & BOOKHOUT 1966). Carapace is wider than long in A. bragantina, P. gracilipes and T. maculatus contrary to what is observed in C. stebbingi and D. crinitichelis, in which the carapace is nearly as wide as long, and Z. ostreum by SANDOZ & HOPKINS (1947) with carapace longer than wide. The small triangular rostrum observed in A. bragantina was similar to the reported for P. gracilipes (LIMA et al. 2006) and clearly different of C. stebbingi (MARQUES & POHLE 1996b) with long and spine form rostrum, D. crinitichelis (POHLE & TELFORD 1981) with small and sub-triangular rostrum, T. maculatus (COSTLOW & BOOKHOUT 1966) with rostrum terminates as two rounded lateral and one slightly larger, median projection. The rostrum in Z. ostreum (SANDOZ & HOPKINS 1947) is represented by two small lobes, covered by small setae.

The megalopal stage of A. bragantina and T. maculatus are more easily identified among pinnotherids crabs from Brazil. Austinixa bragantina is distinct due to the presence of a fine carina that cuts every cardiac area, whereas T. maculatus shows dorsal to the rostrum; a pair of spines projecting anteriorly and laterally over the eyestalks and one dorsal spine arises from the carapace on the median line. The general morphological differences among megalopal stages of A. bragantina and Brazilian pinnotherids are summarized in the table III.

The descriptions in the present study are sufficient to distinguish A. bragantina from the described pinnotherid larvae from the Brazilian coast. However, further larval studies are needed to increase the understanding of this taxonomic group.

ACKNOWLEDGMENTS

Thanks are due to Maria I. Sampaio, Fernando A. Abrunhosa, Marcos A.B. Pires for providing logistic support to the present study. We also thank the Instituto do Milênio and Universidade Federal do Pará, Campus Avançado de Bragança, for the financial support destined to this research, and to Raimundo Pinheiro Lopes Filho, Embrapa Amapá for the preliminary revision of this paper.

LITERATURE CITED

Submitted: 14.VI.2008; Accepted: 02.III.2009.

Editorial responsibility: Maria Lúcia Negreiros-Fransozo

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Publication Dates

• Publication in this collection
  30 Apr 2009
• Date of issue
  Mar 2009

History

• Accepted
  02 Mar 2009
• Received
  14 June 2008