Research Article |
Corresponding author: Juliana Lopes Segadilha ( julianasegadilha@gmail.com ) Academic editor: Luiz F. Andrade
© 2023 Juliana Lopes Segadilha, Graham Bird, Marcos Tavares.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Segadilha JL, Bird GJ, Tavares M (2023) Stenotanais (Crustacea, Tanaidacea) from the Santos Basin: the first described species of the family Akanthophoreidae off the Brazilian coast. Zoosystematics and Evolution 99(2): 423-437. https://doi.org/10.3897/zse.99.103003
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Benthic samples collected from depths ranging between 686 and 2410 m along the Brazilian continental upper slope from Rio de Janeiro State to Santa Catarina State (23°S to 27°S) yielded a wealth of tanaidacean material, including two new species of Stenotanais. This is the first described species of the family Akanthophoreidae from Brazilian waters. Stenotanais leonardoi sp. nov. has a combination of unique characters including the uropod basal article longer than the pleotelson and the exopod somewhat wider than the endopod, longer than the endopod article-1 (0.7 times endopod length) and supporting two flat and wide terminal setae. Stenotanais uropedon sp. nov. is recognisable by its oar-shaped uropod endopod, with article-2 large, broad and flattened and the short exopod, only 0.3 times the endopod length. An identification key to the species of Stenotanais is given. These two species bring the total number of described akanthophoreids to 56 species and that of all tanaidaceans in Brazilian waters to 66 species.
continental margin, Peracarida, south-western Atlantic, Tanaidomorpha, taxonomy, upper slope
The family Akanthophoreidae Sieg, 1986 currently includes 54 species classified into ten genera (
Amongst this family, the genus Stenotanais Bird & Holdich, 1984 was erected by Bird & Holdich to distinguish these species from all other leptognathiid genera (as then defined) mainly by the extreme length of the pereonites 1–5, a very robust cheliped carpus and propodus with strong ventral spines and the presence of very robust uropodal setae. Currently, it is included in the family Akanthophoreidae after the
Amongst the akanthophoreid material obtained from the Santos Basin, off the south-eastern coast of Brazil, collected during the Santos Project – Santos Basin Environmental Characterization (Brazil), coordinated by PETROBRAS/CENPES, was a wealth of specimens of Stenotanais belonging to two undescribed species. Both species are described and illustrated herein and a key to all Stenotanais species is provided. These two new species bring the total diversity of tanaidaceans in Brazilian waters to 66 species.
A total of 277 akanthophoreids was collected along the Brazilian continental margin (between 23°S and 27°S) of the SW Atlantic, during the scientific expedition Santos Project (PCR-BS) – Santos Basin Environmental Characterization (Brazil), coordinated by PETROBRAS/CENPES, in 2019 on board the R/V Ocean Stalwart. A list of the sampling stations is given in the Suppl. material
Sediment samples were taken using a box corer, with three replicate samples at each station (stn) and subsequently stratified into three sediment layers, 0–2, 2–6 and 6–10 cm. Samples were washed through a 300-µm-mesh sieve. The material retained was fixed in 4% borax-buffered formalin (making molecular data unfeasible) and subsequently preserved in 70% ethanol and then tanaidaceans were sorted and identified.
Selected specimens were dissected using chemically-sharpened tungsten-wire needles and appendages, mounted on slides using glycerine and then sealed. Careful examination and drawings of external morphology of the studied material was performed using a microscope Zeiss, equipped with a camera lucida and then digitalised with WACOM Tablet using the graphic programme Adobe Illustrator CC 2017 for producing taxonomic plates. The morphological terminology follows the literature related to the family Akanthophoreidae (
Total body length (TBL) was measured from the tip of the rostrum to the tip of the pleotelson and pereonite width at the broadest part on whole specimens. The length/width ratio was calculated from the measurement made at mid-length and width of an article. To simplify species descriptions, the expression ‘Nx’ replaces ‘N times as long as’. The diagnostic characters to distinguish between species are given in Table
Diagnostic characters of Stenotanais species. Abbreviations: A1 = antennule; Car. = carpus; Che. = cheliped; Endo. = endopod; Exo. = exopod; Mer. = merus; P = pereopod; Prop. = propodus; Uro. = uropod.
Species | Stenotanais leonardoi sp. nov. | S. uropedon sp. nov. | S. arenasi Larsen, 2011 | S. crassiseta Bird & Holdich, 1984 | S. hamicauda Bird & Holdich, 1984 | S. macrodactylus Larsen, 2005 |
---|---|---|---|---|---|---|
Type locality | Brazil (SW Atlantic) | Brazil (SW Atlantic) | Manganese Nodule Province (Central Pacific) | Rockall Trough (NE Atlantic) | Feni Ridge (NE Atlantic) | Gulf of Mexico (NW Atlantic) |
Depth (m) | 686–2410 | 991–1974 | 4954 | 2070–2916 | 1600–4829 | 1320–2387 |
Holotype sex | female | female | male | female | female | female |
A1 length/ cephalothorax length | 0.6× | 0.6× | 0.7× | 0.6× | 0.6× | 0.8× |
Che. basis (L:W) | 3.6× | 3.9× | 2.4× | 2.9× | 3.8× | 2.5× |
Che. carpal shield | present | present | absent | present | present | present |
Che. fixed finger, cutting edge setation | two simple setae | two simple setae and one spine | three robust setae | three simple setae | three simple setae | two robust setae |
P1–6 mer. and carp. ventral spines type | simple spines | serrate spines | simple spines (= spiniform setae) | simple spines | simple spines | simple and bi-serrate (P5) spines |
P2–3 carp. spine length/ prop. length | long spine (longer than half) | long spine (longer than half) | long spine (longer than half) | short spine (about one third) | long spine (about half) | long spine (P2: longer than half; P3: about half) |
P2–3 prop. inferior margin | convex | convex | straight | convex | convex | straight |
P2–3 prop. ventral setation | spine, microtrichia and spinules | spine, microtrichia and spinules | spine (= spiniform seta) and setules (= microtrichia) | spine and spinules | spine and spinules | spine |
P1 dactylus length/ unguis length | 1.0× | 1.3× | 0.9× | 0.8× | 0.9× | 1.3× |
P2 dactylus length/ unguis length | 0.7× | 1.1× | 0.9× | 0.8× | 0.9× | > 2.0× |
P3 dactylus length/ unguis length | - | 1.4× | 0.7× | 0.9× | 1.0× | 1.4× |
P4–6 carp. bone-shaped seta | absent | absent | present | absent | absent | absent |
Uro. basis length/ pleotelson length | longer than (1.1×) | shorter than (0.6×) | shorter than (0.5×) | shorter than ( |
shorter than (0.4×) | longer than (1.4×) |
Uro. exo. length/ endo. article-1 length | longer than (1.8×) | as long as | shorter than (0.8×) | as long as | longer than (1.7×) | longer than (2.2×) |
Uro. exo. length/ endo. length | long, 0.7× | short, 0.3× | short, 0.4× | short, 0.4× | long, about 0.8× | long, about 0.8× |
Uro. endo. shape | subparallel margins | oar-shaped (article-2 broad and flattened) | subparallel margins | subparallel margins | subparallel margins | subparallel margins |
Uro. exo. shape | somewhat wider than endopod | subparallel margins | subparallel margins | subparallel margins | oar-shaped (broader distally) | subparallel margins |
Uro. endo. seta type | simple setae | simple setae | simple setae | one flat and wide distal seta | one flat and wide distal seta | simple setae |
Uro. exo. seta type | two flat and wide distal setae | two flat and wide distal setae | one specialised distal seta with flat and wide basis | simple setae | simple setae | one flat and wide medial seta and two articulated wide distal setae |
Holotypes were chosen from the best-preserved individuals. The type-material is deposited at Museu de Zoologia, Universidade de São Paulo (
Order Tanaidacea Dana, 1849
Suborder Tanaidomorpha Sieg, 1980
Superfamily Paratanaoidea Lang, 1949
Family Akanthophoreidae Sieg, 1986
(Modified from
Male. Immature (preparatory) male with antennule thicker than in female, functional mouthparts present (see remarks on genus). Sexually mature ‘swimming’ type: cephalothorax as long as first three pereonites; pereon shorter than in female; pleon well developed, as long as pereon, caudally pointed; multi-articulate antennule with multiple aesthetascs, distal article longer than preceding article; no functional mouthparts; uropod biramous, endopod and exopod two-articled.
Stenotanais crassiseta Bird & Holdich, 1984, by original designation. Gender: feminine.
Stenotanais arenasi Larsen, 2011; S. crassiseta Bird & Holdich, 1984; S. hamicauda Bird & Holdich, 1984; S. macrodactylus Larsen, 2005; S. leonardoi sp. nov.; S. uropedon sp. nov.
The rather infrequently-recorded Stenotanais is similar to akanthophoreid genera such as Pseudakanthophoreus Lubinevsky, Tom & Bird, 2022 and Parakanthophoreus Larsen & Araújo-Silva, 2014, by having chelipeds without extensive surface ornamentation and the absence of spurs on pleonite-5, pleotelson and the uropod basal article or endopod article-1. However, Stenotanais can be distinguished mainly by having the basis of pereopods 1–3 thicker than the basis of pereopods 4–6 and the presence of specialised setae with a wide and flat basal attachment on the uropod (
The single available specimen of S. arenasi may be a preparatory male, based on characters of the antennule articles 1–2 (as suggested by
Another character in the original generic diagnosis of
Holotype
: Brazil – Santa Catarina State • neuter, length 1.9 mm; stn A8 R2, 0–2 cm;
Paratypes
: Brazil – São Paulo State • 1 neuter (dissected), length 2.1 mm; stn E8 R3, 5–10 cm;
Neuter. Cheliped fixed finger with two simple setae on cutting edge. Pereopods 2–3 carpus with long spine, longer than half length of propodus. Uropod basal article longer than pleotelson; exopod and endopod with subparallel margins; exopod slightly wider than endopod, longer than endopod article-1 (0.7× endopod), with two flat and wide terminal setae.
The species is dedicated to the first author’s life partner, Leonardo Santos de Souza, who has supported and encouraged this author in her academic career.
Based on neuter holotype (
Antennule
(Fig.
Stenotanais leonardoi sp. nov. Paratype, neuter dissected (
Labrum
(Fig.
Maxilliped
(Fig.
Cheliped
(Fig.
Pereopod-1
(Fig.
Pereopod-2
(Fig.
Pereopod-3
(Fig.
Pereopod-4
(Fig.
Pereopod-5
(Fig.
Pereopod-6
(Fig.
Pleopod
(Fig.
Uropod
(Fig.
Male (Figs
Santa Catarina State, Brazil; stn A8 R2, -27,29679714, -46,62516071 (1045 m).
Brazil: Santos Basin (Rio de Janeiro, São Paulo, Paraná and Santa Catarina States). Occurring on the lower slope and the São Paulo Plateau area, ranging from depths of 686 to 2410 m. This species was the most abundant (51 individuals), with 71% of the specimens found at 2–5 cm sediment layer (i.e. up to 25× their body length).
This new species is similar to S. crassiseta from the NE Atlantic in having the propodus of pereopods 1–3 with a convex inferior margin bearing many spinules and the general shape of the uropod endopod, but is distinguished by: (1) the cheliped basis more slender 3.6× L:W (2.9× in S. crassiseta); (2) the cheliped fixed finger with two simple setae on cutting edge (three in S. crassiseta); (3) the pereopod-1 dactylus as long as unguis (0.8× in S. crassiseta); (4) the pereopods 2–3 carpus with long spine, longer than half length of propodus (about one third in S. crassiseta); and (5) the uropod exopod one-articled and much longer than endopod article-1, 0.7× endopod (exopod two-articled and as long as endopod article-1, 0.4× in S. crassiseta).
Stenotanais leonardoi sp. nov. also resembles S. macrodactylus from the Gulf of Mexico (NW Atlantic) mainly by the shape of uropod; however, it differs by a combination of characters including: (1) antennule 0.6× cephalothorax (slightly shorter 0.8× in S. macrodactylus); (2) cheliped fixed finger with two simple setae on cutting edge (two ‘spiniform setae’ in S. macrodactylus); (3) pereopod-2 dactylus 0.7× unguis (more than twice in S. macrodactylus); and (4) pereopods 2–3 propodus with convex inferior margin with ventrodistal spine, microtrichia and spinules (only with ventrodistal spine in S. macrodactylus). The new species has the cheliped fixed finger with strong serrate spines ventrally, which could have been overlooked by other authors (e.g. as ‘strong spines’,
The male is of the ‘swimming’ type with no functional mouthparts, shortened pereon and multi-articulate antennule with multiple aesthetascs. This specimen was found in the same sample as an individual of S. leonardoi (a neuter) and was identified as this species by chelipedal features, such as the basis with a long posterior lobe, a carpal shield and well-developed fixed finger with two strong serrate ventral spines and uropod rami with subparallel margins (not oar-shaped as in S. uropedon sp. nov.). Only one male specimen was sampled while 50 neuters were collected, demonstrating how “unbalanced” the sexual ratio can be in tanaidacean species. However, as with all ‘swimming males’ and the rare matching of sexes, only with a molecular analysis can conspecificity be absolutely confirmed (
Holotype
: Brazil – São Paulo State • neuter, length 1.7 mm; stn D10 R3, 5–10 cm;
Paratypes
: Brazil – Rio de Janeiro State • 1 neuter (dissected), length 1.7 mm; stn P10 R3, 5–10 cm;
Neuter. Cheliped fixed finger with two simple setae and one spine on cutting edge and a nearby spine on the distolateral margin of the propodal palm. Pereopods 2–3 carpus with long spine, longer than half length of propodus. Uropod endopod oar-shaped, with article-2 broad and flattened; exopod short, 0.3× of endopod length; both rami without specialised articulated setae.
From the Greek ‘pedon’ (noun), meaning ‘oar, rudder’; alluding to the shape of uropod endopod. The name is a noun in apposition with the generic name.
Based on neuter holotype (
Antennule
(Fig.
Labrum
(Fig.
Maxilliped
(Fig.
Cheliped
(Fig.
Pereopod-1
(Fig.
Pereopod-2
(Fig.
Pereopod-3
(Fig.
Pereopod-4
(Fig.
Pereopod-5
(Fig.
Pereopod-6
(Fig.
Pleopod
(Fig.
Uropod
(Fig.
São Paulo State, Brazil; stn D10 R3, -25,94725395, -44,83425777 (1906 m).
Brazil: Santos Basin (Rio de Janeiro, São Paulo, Paraná and Santa Catarina States). Occurring on the lower slopes and the São Paulo Plateau area, ranging from depths of 991–1974 m. Twenty-two individuals of this species were collected, with 41% of them found in the 5–10 cm sediment layer (i.e. up to 50–60× their body length) and 32% at a depth of 2–5 cm.
This new species resembles S. hamicauda from the NE Atlantic by the oar-shaped uropod, but is different from it by: (1) cheliped fixed finger with two simple setae and one spine on cutting edge (three simple setae in S. hamicauda); (2) pereopods 1–3 dactylus 1.3× unguis (about as long as in S. hamicauda); (3) uropod endopod oar-shaped (in S. hamicauda the exopod is oar-shaped); and (4) exopod short, 0.3× endopod length (in S. hamicauda exopod reaching about 0.8× endopod length).
Stenotanais uropedon sp. nov. differs from S. leonardoi by its oar-shaped uropod endopod, with the article-2 broad and flattened (with short exopod, 0.3× endopod), whereas in S. leonardoi, the exopod is slightly wider than the endopod (0.7× endopod). Additionally, S. uropedon has pereopods with the merus and carpus having long serrate distoventral spines, which are different from those of S. leonardoi (with simple spines); however, these different forms could have been overlooked by previous authors in other congeneric species.
Modified from
1 | Cheliped carpus without large ventrodistal shield | S. arenasi |
– | Cheliped carpus with large ventrodistal shield | 2 |
2 | Uropod exopod or endopod distinctly oar-shaped (broader distally) | 3 |
– | Uropod exopod or endopod slender/subparallel-sided | 4 |
3 | Uropod exopod oar-shaped, reaching at least to 0.75× of entire endopod length; exopod with two specialised flattened setae | S. hamicauda |
– | Uropod endopod oar-shaped, with article-2 broad and flattened; exopod 0.3× of entire endopod length; exopod with two flat and wide setae | S. uropedon sp. nov. |
4 | Uropod basal article longer than pleotelson; exopod one-articled | 5 |
– | Uropod basal article shorter than pleotelson; endopod with one flat and wide seta distally; exopod two-articled without flat and wide setae | S. crassiseta |
5 | Uropod exopod with one flat and wide seta at mid-length and two articulated wide terminal setae | S. macrodactylus |
– | Uropod exopod with two flat and wide terminal setae | S. leonardoi sp. nov. |
This is the first Brazilian species described of the family Akanthophoreidae and the second record of the genus Stenotanais in the Southern Hemisphere. Stenotanais was first reported from the Southern Hemisphere on the continental slope of Magellan Region (Beagle Channel; 1279 m) (
The two new deep-burrowing species of Stenotanais described here bring the total number of akanthophoreids to 56 species and that of all tanaidaceans in Brazilian waters to 66 species. Although many papers on Tanaidacea off Brazilian waters have been published in recent years, we are still discovering new taxa in this region, with plenty of new species to be discovered in the future. Taxonomic works from understudied areas, such as the Brazilian deep-waters, provide a basis for future studies in fields such as biogeography, ecology and evolution and, although several papers have been published in the last decade, there is still much to be investigated regarding the tanaidaceans of Brazil.
The authors are grateful to the PETROBRAS/CENPES, which coordinated the fieldworks and made available the material examined. The first author also would like to thank Fundação de Apoio à Universidade de São Paulo (FUSP) for providing the postdoctoral fellowship (PIPD) during the course of this study. We also would like to thank the contribution of David Drumm and anonymous referees for their helpful comments and suggestions on the manuscript.
JLS and MT contributed to designing the study; JLS received funds for this work, identified the material, worked on illustrations, prepared the tables and wrote the manuscript; GB and MT reviewed the text; GB reviewed the English language. All authors read and approved the final manuscript and consent to publication.
Benthic samples with Stenotanais specimens obtained during Santos Project (PCR-BS) – Santos Basin Environmental Characterization (Brazil).
Data type: Table (word file).