Chelorchestia darwini ( Müller, 1864 ), Muller, 1864

Serejo, Cristiana S., 2004, Talitridae (Amphipoda, Gammaridea) from the Brazilian coastline, Zootaxa 646, pp. 1-29 : 2-8

Chelorchestia darwini ( Müller, 1864) ( Figs 1–3 )

Orchestia darwini Müller, 1864: 16 , fig. 7; 1869: 25, fig. 7; Ruffo, 1956: 120, fig. 3. Talorchestia darwini — Stebbing, 1906a: 545.

Chelorchestia darwini — Bousfield, 1984: 203.

Material examined. Alagoas — Mundaú Lagoon, Maceió, AL, 2 males, A. Lemos de Castro col., 02/VIII/1978, MNRJ 19502. Bahia ­ Jacuruna river, BA, 1 male, 30/XI/1978, MNRJ 19504. Rio de Janeiro — Guapimirim Mangrove (APA), Guapi river, Guapimirim, RJ, 6 females, 2 male juveniles and 2 males, C. Serejo & A. de Souza col., 03/IV/2003, MNRJ 19508; Pedra de Guaratiba, RJ, mangrove, in Spartina sp., 2 females, 2 juveniles males and 1 male, Y. Wakabara col., VI/1997, MNRJ 19505; Gargaú mangrove, Campos, RJ, in Echornia sp., 1 male and 1 female, A. Bustamante col., 6–13/IX/2000, MNRJ 18745. São Paulo — Cananéia, Mangrove, 1 juvenile male, Y. Wakabara col., 14/IX/1981, MNRJ 15114; Cananéia Mangrove, A. S. Tararam col. VII/1988 to I/1989, 2 females, MNRJ 15075; 1 female, MNRJ 15076; 1 male and 4 females, MNRJ 15077; 1 juvenile male and 5 females, MNRJ 15079; 1 male, 3 juvenile males, and 10 females, MNRJ 15080; 1 juvenile male and 3 females, MNRJ 15082; 1 female, MNRJ 15083; 1 male and 2 females, MNRJ 15085; 1 female, MNRJ 15086. Paraná — Correias river, Paranaguá Bay, 25º31S 48º29W, PR, in mangrove, R. Bogrim, col., 1996, 1 female, MNRJ 17000; Boquerá river, Paranaguá Bay, 25º27S 48º32W, PR, 1 juvenile male, in mangrove, MNRJ 18744; Cachoeira river, Antonina Bay , 25º24S, 48º43W, PR, in mangrove, 1 male, MNRJ 19501; Cotinga Island, Paranaguá Bay, 25º32S, 48º26W, PR, 1 male juvenile, mangrove, MNRJ 19503; Corisco Island, Antonina Bay , 25º24S, 48º44W, PR, in mangrove, 1 female, MNRJ 19506; Guaramiranga de Dentro Island, Antonina Bay , 25º25S, 48º39W, mangrove, 1 female, MNRJ 19507.

Diagnosis. Antenna 2 reaching 2/5 of body length. Adult male gnathopod 2 chelate. Uropod 1, peduncle with inter­ramal robust seta; outer ramus lacking marginal setae.

Description. Male, 11.9 mm. Antenna 1 ( Fig. 1 A) reaching 2/3 of peduncle article 4 of antenna 2. Antenna 2 slender ( Fig. 1 A), reaching 2/5 of body length; article 5 of peduncle a little longer than article 4; first three articles of flagellum fused, flagellum with about 12 articles. Eyes large. Mandible with left lacinia mobilis 4­dentate, sometimes with minute fifth teeth; right lacinia bifid ( Fig. 1 B–C). Maxilla 1, inner plate with two distal plumose setae; outer plate with 9 dentate robust setae, palp reduced and 1­articulate. Maxilla 2, inner plate with several distal setae and two larger proximal plumose seta, being one seta larger than the other; outer plate a little larger than inner plate. Palp of maxilliped robust and 4­articulate, fourth article strongly reduced ( Fig. 1 D–E).

Gnathopod 1 ( Fig. 1 F), merus posteriorly produced into a pointed process; carpus and propodus with well developed posterior lobe. Gnathopod 2 ( Fig. 1 G), basis anterior margin with 0 to 3 tubercles, carpus fused with propodus, chelate in adult males. Pereopod 3 a little longer than pereopod 4, dactylus of pereopod 4 not thickened ( Fig. 1 H–L). Pereopod 5 shorter than pereopods 6–7 (Fig. 2A–C). Pereopod 7 (Fig. 2C), coxa with antero­distal corner forming a right angle. Dactylus of pereopods 3–7 simplidactylate.

Uropod 1 (Fig. 2D), peduncle with distal lateral robust seta, inner ramus with three marginal robust setae; outer ramus lacking marginal setae. Uropod 2 (Fig. 2E), peduncle and rami subequal in length, each ramus with 2 marginal robust setae. Uropod 3 (Fig. 2F), peduncle with a long, robust, sub­distal seta; ramus about half of peduncle. Telson long, medial line poorly observed, each side with one or two lateral robust setae and one distal robust setae.

Female, 6.3 mm. Antenna 2 as in males, but flagellum without fused articles. Gnathopod 1 ( Fig. 3 A) distinctly subchelate. Gnathopod 2 ( Fig. 3 B), basis not expanded anteriorly; merus, carpus and propodus with tiny setae on posterior lobe, propodus oval. Oostegites 2–5 oval ( Fig. 3 C–F), oostegites 2–4 about 3.5 times longer than wide, oostegite 5 a little shorter than others, about 2.5 times longer than wide.

Variation on male gnathopod 2. This appendage shows a great variation during the development of the specimen, that can make confusion in the identification within the genus Chelorchestia . The basis show anteroproximal tubercles varying from 0 to 3 ( Figs. 1 G; 3G–H). Otherwise, the palm, which is transverse in early stages, has a medial strong concavity and the palmar corner develops into a process that will give a chelate appearance in adults male gnathopod 2 ( Fig. 1 G, 3H). In some specimens (8.5 mm) ( Fig. 3 G), there are two shallow concavities and the palmar process bears two rounded humps.

Remarks. Bousfield (1984) erected the genus Chelorchestia for one of the talitrid groups that inhabit mainly tropical mangrove and Spartina marshes or other low salinity habitats. Besides C. darwini , three other species of the genus are known: C. costaricana (Stebbing, 1906) from mangrove swamps of Costa Rica; C. vaggala ( Bowman, 1977) from the Galapagos Island; and the recently described C. forceps Smith & Heard, 2001 from southeastern coast of United States. Chelorchestia darwini was originally briefly described by Fritz Müller (1864) in his notable work in defense of Darwin evolutionary theory. Fritz Müller lived and worked in Desterro, nowadays Florianópolis, the capital of Santa Catarina state. In the time Müller was in Brazil (from 1852 until 1897) he also worked as a naturalist for the Museu Nacional, Rio de Janeiro. Unfortunately, no type material was deposited at the Museu Nacional, and there is no information where these types may be deposited. Taking this into account, C. darwini is herein redescribed and compared with other species of the genus. Ruffo (1956) also redescribed C. darwini with material from Cananéia, São Paulo, Brazil. However, Ruffo (1956) found only males with gnathopod 2 of type B ( Fig. 3 G), and suggested that these specimens could be possible juveniles of a latter mature male stage with gnathopod 2 of type A ( Fig. 3 H). Müller (1869) also noticed the same variations on male gnathopod 2 ( Fig. 3 I, J), and also concluded that both forms belong to the same species, as the females did not vary. In this study, I found samples with females and only males type A, even examining material from Cananéia, and never found sympatric males of both types. Besides the notable difference of the gnathopod 2, the antenna 2 is longer in specimens with gnathopod 2 type B, reaching half of body length, suggesting that these are two distinct species. However, I prefer wait to examine more material, especially females corresponding to male type B, before making changes to the species taxonomy.

Chelorchestia forceps is a similar species to C. darwini . Characters that could be useful to distinguish these species, as the number of tubercles on basis of male gnathopod 2, and the number of robust setae on the telson, showed variation in the examined specimens. The single clear distinction between C. forceps and C. darwini is the presence in the former of two robust setae, one dorsal and one ventral, at the articulation of propodus and dactylus of pereopods 3–4. Chelorchestia darwini has two long setae dorsally and one robust setae ventrally ( Fig. 1 I, L) in this position. Comparison between material of C. forceps and C. darwini would elucidate better the status of these taxa, which maybe synonyms.

The other two species of Chelorchestia , C. vaggala and C. costaricana are distinguished from C. darwini as follows: the male gnathopod 2 of C. vaggala is subchelate with a transverse palm ( Bowman, 1977) and C. costaricana has a long antenna 2, reaching more than half of body length and a longer propodus of male gnathopod 2, about twice as long as wide ( Stebbing, 1906b). For more comments on the genus see Smith and Heard (2001).

Type locality. Brazil, possibly Santa Catarina.

Distribution. Brazil: from Alagoas to Santa Catarina.

Ecology. Found in mangrove and estuarine areas, on mud or on the vegetation. In same areas this species lives in sympatry with Platorchestia monodi and the identification of the females may be confuse (see key).

Figures

FIGURE 1. Chelorchestia darwini (Müller, 1864), male 8.7 mm, MNRJ 19501. A, head; F, gnathopod 1; G, gnathopod 2; H, pereopod 3; I, pereopod 4. Female, 6.3 mm, MNRJ 17000. B, left mandible; C, right lacinia mobilis; D, maxilliped; E, detail of maxilliped. Scale bars: A, F – I, 0.5 mm; B – D, 0.1 mm; E, 0.05 mm.

FIGURE 3. Chelorchestia darwini (Müller, 1864), female, 6.3 mm, MNRJ 17000. A, gnathopod 1; B, gnathopod 2; C – F, oostegites 2 – 5 respectively. Male, 8.5 mm, MNRJ 19502. G, gnathopod 2. Male, 9.8 mm, MNRJ 19508. H, gnathopod 2. Male. I – J, gnathopod 2 (from Müller, 1869). Scale bars: A, 0.2 mm; B, 0.3 mm; C – H, 0.5 mm.