Extension of geographical range and first record of Trizocarcinus Rathbun, 1914 (Brachyura: Euryplacidae) from the Western Tropical South Atlantic

30AC47DC-8661-4CFB-B30A-BB995F8AB0BB Here, we report the first occurrence of Trizocarcinus Rathbun, 1914 (Brachyura: Euryplacidae) from the South Atlantic (Brazil). Trizocarcinus tacitus Chace, 1940 was collected in the upper continental slope of the Potiguar Basin, northeastern Brazil. The new record expands by 3000 km the southern distribution of the species in the Western Atlantic.


Trizocarcinus from South Atlantic
Nauplius, 28: e2020022 inTroduCTion The family Euryplacidae Stimpson, 1871 is composed of marine crabs and its taxonomy was most recently revised by Castro and Ng (2010).The family currently comprises 15 genera found globally with a total of 32 recognized species (Castro and Ng, 2010;Ng et al., 2019).Members of this family occur on mud or gravel substrates between the continental shelf and the continental slope in depths from intertidal to 552 m (Castro and Ng, 2010).
Although the family has a widespread distribution in the Indo-West Pacific, Tropical and Eastern Pacific, and Western and Eastern Atlantic regions, only six species are known from the Western Atlantic (Castro and Ng, 2010), including members of the genus Trizocarcinus Rathbun, 1914, which is endemic to the Americas (Atlantic and Pacific Oceans), comprising only two species Trizocarcinus dentatus (Rathbun, 1893) and T. tacitus Chace, 1940.Trizocarcinus dentatus is endemic to the tropical Eastern Pacific, occurring at depths between 36-126 m, whereas T. tacitus is known from the Gulf of Mexico and Caribbean Sea in the Western Atlantic, in depths between 187-462 m (Chace, 1940;Castro and Ng, 2010).We report the first occurrence of Trizocarcinus from the South Atlantic (Brazilian Waters), based on specimens of T. tacitus collected in the upper continental slope of the Potiguar Basin, northeast Brazil.

MaTerial and MeThods
The specimens of Trizocarcinus tacitus were collected in the Northeast region of Brazil, between the states of Ceará (CE) and Rio Grande do Norte (RN) (Potiguar Basin) during the research project entitled "Avaliação da biota bentônica e planctônica da Bacia Potiguar e Ceará (Bpot)", developed by the Brazilian Oil Company "Petróleo Brasileiro S/A (Petrobras)" onboard the R/V Seward Johnson.The material was collected in May 2011 from bottom trawls conducted on the continental slope using a semi-balloon otter trawl with 50 mm mesh size and 18 m of mouth opening for 30 minutes between the depths of 150-2068 m.Water temperature and salinity were recorded.

Trizocarcinus from South Atlantic
Nauplius, 28: e2020022 Remarks.The present specimens of T. tacitus agree very well with the original description provided by Chace (1940) and subsequently revised by Castro and Ng (2010); their specimens from the Gulf of Mexico and Caribbean Sea.Trizocarcinus tacitus can easily be distinguished from its congener T. dentatus, which is from Tropical Eastern Pacific, by the following characteristics (in parentheses for T. dentatus): carapace with dorsal and ventral margin smooth (Fig. 1A) (vs.granular); outer orbital tooth conspicuous and well developed (Fig. 1A) (vs.outer orbital tooth reduced); stridulating ridge absent on pterygostomial region (Fig. 1B, C) (vs.granular stridulating ridge on pterygostomial region); ambulatory propodus and dactylus with anterior margin densely setose (Fig. 1D) (vs.structure densely setose along entire length); and G1 apex not particularly long (Fig. 2A, B) (vs.G1 apex prominently elongate) (cf.Castro and Ng, 2010).
Trizocarcinus has long being considered as an endemic of the Gulf of Mexico and Caribbean Sea (Chace, 1940).As observed in this paper, we reported the first occurrence of T. tacitus from Potiguar Basin

Trizocarcinus from South Atlantic
Nauplius, 28: e2020022 (Brazilian waters) in the South Atlantic.This is a significant range extension of about 3000 km from its previous range.Trizocarcinus tacitus is probably more abundant and widely spread than is documented here along the Brazilian coast.The general lack of sampling on the upper continental slope in the Southwestern Atlantic will therefore need to be addressed in the future.As previously discussed by Mantelatto et al. (2018), the reasons for the increasing new records and/ or extension of distributions reported for decapod species in Brazilian waters during the last decade are almost certainly related to the increase in larger research programs with laboratories more focused on marine biodiversity.In this sense, we argue in favor of continuity and new investments in biodiversity research programs in order to increase the knowledge of the biota of less explored regions.

Figure 3 .
Figure 3. Geographic distribution of Trizocarcinus tacitus Chace, 1940 in the Western Atlantic.Black circles = Previous records; Black star = Present new record.