Research Article |
Corresponding author: Eduardo Suárez-Morales ( esuarez@ecosur.mx ) Academic editor: Danielle Defaye
© 2017 Eduardo Suárez-Morales, Martha A. Gutiérrez-Aguirre, Adrián Cervantes-Martínez, Thomas M. Illife.
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:
Suárez-Morales E, Gutiérrez-Aguirre MA, Cervantes-Martínez A, Iliffe TM (2017) A new anchialine Stephos Scott from the Yucatan Peninsula with notes on the biogeography and diversity of the genus (Copepoda, Calanoida, Stephidae). ZooKeys 671: 1-17. https://doi.org/10.3897/zookeys.671.12052
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Surveys of the anchialine crustacean fauna of the Yucatan Peninsula (YP), Mexico, have revealed the occurrence of calanoid copepods. The genus Stephos Scott, 1892, belonging to the family Stephidae is among the most frequent and widely distributed groups in anchialine caves but has not been hitherto recorded from the YP. Recent collections from an anchialine cave in an island off the northern coast of the YP yielded many specimens of a new species of Stephos. The new taxon, S. fernandoi sp. n., is described here based on male and female specimens. The new species is clearly distinguished from its congeners by the following characters: male left fifth leg with three terminal lamellae plus subdistal process, right leg with distal row of peg-like elements; female fifth leg with single long, acute apical process; genital double-somite with two rows each of 4 long spinules adjacent to operculum; legs 2-4 with articulated setae. The diversity of the genus shows regional differences; the Australia-Western Pacific region is the most diverse (eleven species), followed by the Mediterranean (seven species) and the Northeastern Atlantic (six species); only four species are known from the Northwestern Tropical Atlantic (NWTA). The morphology of the female fifth leg was examined to explore possible biogeographic trends in the genus; patterns suggest multiple colonization events in the highly diverse regions and a relatively recent radiation in the NWTA, characterized by anchialine forms. The introduction of stephid copepods in the region may be a relatively recent event derived from colonization of benthopelagic ancestral forms and subsequent invasion onto cave habitats. The new species appears to be linked to the strictly anchialine Miostephos.
Calanoid copepods, stygobionts, cave-dwelling fauna, biogeography, taxonomy
The primitive calanoid copepod families Epacteriscidae and Ridgewayiidae are the most representative and diverse copepods in anchialine and subterranean environments worldwide (
The anchialine crustacean fauna of the Yucatan Peninsula (YP) of Mexico is widely recognized as highly interesting, with many endemic species (
Specimens were collected on 6 July 2014 during a biological survey of an anchialine cave, Cenote Tres Potrillos, on Cozumel Island at 20°27'3.2"N, 86°59'14.4"W, Quintana Roo, Mexico. From a small pool at the cave entrance, a vertical shaft opens into a very large chamber with a halocline at 11 m. Beneath the halocline, sulfidic, fully marine water reaches a maximum depth of 38 m. A 40 m long passage at 12 m depth extends off the side of the main chamber (
Holotype. One adult ♀, collected on 6 July 2014 from the anchialine cave of Cenote Tres Potrillos, Cozumel Island (20°27'3.2"N, 86°59'14.4"W), Quintana Roo, Mexico. Specimen dissected on slide deposited in the collection of Zooplankton of El Colegio de la Frontera Sur (
Female. Mean length of prosome: 0.343 mm (n = 13); total length including caudal rami = 0.475 mm (n = 13). Body with typical calanoid shape, relatively robust in lateral and dorsal views, prosome 5-segmented, widest at first pedigerous somite (Figs
Stephos fernandoi sp. n., adult female from Cozumel, Mexico. A habitus, lateral view B antennule, segments 1–16 C antennule segments 17–24 D antennule segment 24 showing apical process E antenna F mandibular palp G gnathal base H maxillule I maxilla. Scale bars: A 100 μm; D 10 μm; B, C, E–I 20 μm.
Caudal rami subrectangular, symmetrical, length/width ratio = 1.6–1.7, armed with 6 caudal setae (II-VII) (Fig.
Antennule (Fig.
Antenna (Fig.
Mandible (Fig.
Maxillule (Fig.
Maxilla (Fig.
Maxilliped (Fig.
Legs 1-4 (Fig.
Stephos fernandoi sp. n., adult female from Cozumel, Mexico. A maxilliped B leg 1 C leg 2 D leg 3 E leg 4 F leg 1 exopod, another specimen showing reduced outermost apical spine (arrow) G leg 1 endopod, another specimen H male leg 1 I female leg 5, anterior view J fifth pedigerous somite and urosome, lateral view. Scale bars: A–I 20 μm; J 50 μm.
Fifth legs (Fig.
Male. Body slightly longer than female, average total length: 0.493 mm (n =10); length of prosome: 0.31 mm (Fig.
Left and right antennules 24-segmented, lacking geniculation, slightly longer than in female when extended posteriorly; antennulary armature as in female. Mouthparts and swimming legs 1–4 as in female.
Fifth legs (Figs
The new species is named after the Mexican carcinologist Dr. Fernando Alvarez (Instituto de Biología,
The new species was included in the diverse stephid genus Stephos based on its possession of the following characters: 1) cephalosome and first pedigerous somite separate, pedigers 4–5 partially fused, 2) female urosome 4-segmented, male five-segmented; 3) caudal rami with 4 terminal setae (III–VI), dorsal caudal seta VII inserted on inner margin; 4) antennules 24-segmented in male and female, lacking geniculation in male; 5) female leg 5 uniramous, one or two-segmented, distal segment tapering, ornamented; 6) male fifth legs uniramous, strongly asymmetrical, modified into grasping organ, left leg five-segmented, with complex distal segment, right leg slender (
Based on the morphology of the male fifth legs,
Armature formula of swimming legs 1-4. Roman numerals indicate spines and Arabic numerals are setae.
coxa | basis | exopod | endopod | |
---|---|---|---|---|
leg 1 | 0-1 | 1-1 | 0-0; I-1; I,2,2 | 0,2,3 |
leg 2 | 0-1 | 0-0 | I-1; I-1; III,I,4 | 0-1; 0,2,2 |
leg 3 | 0-1 | 0-0 | I-1; I-1; III,I,4 | 0-1; 0-1; 0,2,2 |
leg 4 | 0-1 | 0-0 | I-1; I-1; III,I,4 | 0-1; 0-1; 0,2,2 |
The new species is the only one in this group with a right leg 5 ramus combining a distal segment (segment 4) with diverging processes set at right angles with acute tips plus a series of peg-like elements along the longest process (Fig.
Stephos fernandoi sp. n., from Cozumel, Mexico. SEM-processed specimens. Female. A habitus, semi-lateral view B same, lateral view, another specimen C rostrum, ventral view D antennule segments 9–13, spiniform seta on segment 12 arrowed E genital double-somite, ventral surface showing ornamentation (arrows) F caudal rami showing caudal setae II-VII, ventral view G distal segment of leg 5 H leg 5, ventral view. Male. I left leg 5 showing segmentation J same, detail of distal segment K right leg 5, distal segment, detail of apical end L right leg 5, distal segment. Scale bars A, B 100 μm; C, D, H, I 20 μm, E–G, L 10 μm; J, K 5 μm.
The female fifth leg of S. fernandoi differs from that known in most species of Stephos, which has a medial seta and/or a row of spinules on the distal segment. It most closely resembles the fifth legs of the two species of Miostephos, M. cubrobex from Cuba (
Geographic distribution of Stephos female fifth leg groups A–F. Group A lateral seta present, segment apically elongate B lateral seta present, segment not apically elongate, short C lateral seta absent, segment apically elongate D lateral seta present, segment elongate, with additional segmental processes, branched or bifurcate E lateral seta absent, segment elongate, with outer segmental processes F lateral seta absent, segment short, apically truncate or blunt, leg rami symmetrical or asymmetrical.
The distribution of primitive anchialine copepods (i.e., epacteriscids, misophrioids) in the Caribbean, Yucatan, the Canary Islands, and the tropical Pacific has been taken to indicate their Tethyan origin (
In terms of its known geographic distribution, the 32 known species of Stephos occur in different regions each harboring its own, distinctive diversity, as follows:
a) Australia-Western Pacific (eleven species): S. penthacanthos, S. morii, S. tropicus Mori, 1942, S. tsuyazakiensis, S. pacificus Ohtsuka & Hiromi, 1987, S. angulatus, S. robustus, S. kurilensis Kos, 1972, S. hastatus Bradford-Grieve, 1999, S. geojinensis, S. projectus Moon, Youn & Venmathi Maran, 2015.
b) Mediterranean (seven species): S. gyrans (Giesbrecht, 1893), S. margalefi Riera, Vives & Gili, 1991, S. vivesi, S. cryptospinosus Zagami, Campolmi & Costanzo, 2000, S. marsalensis, S. boettgerschnackae Kršinić, 2012, S. grieveae Kršinić, 2015.
c) Northeastern Atlantic (six species): S. canariensis Boxshall, Stock & Sánchez, 1990, S. rustadi, S. minor Scott, 1892, S. scotti Sars, 1902, S. fultoni Scott T. & A., 1898, S. lamellatus Sars, 1902.
d) Northwestern Tropical Atlantic (four species): S. deichmannae, S. exumensis, S. lucayensis, S. fernandoi.
e) Polar (three species): S. antarcticum Wolfenden, 1908, S. longipes Giesbrecht, 1902, S. arcticus Sars, 1909.
f) Indo-Pacific (one species): S. maculosus Andronov, 1974.
The genus is most diverse in the Australia-Western Pacific region, followed by the Northeastern Atlantic and the Mediterranean. There are no records of Stephos from the Southwestern and Southeastern Atlantic and the Eastern Pacific (Fig.
Stephids are in general benthopelagic or anchialine forms, strongly associated with the bottom communities, but some species are known from the plankton (
In Stephos, the male fifth legs show at least four different morphological patterns (
Pattern D was deemed as the most primitive group, followed by groups A and B, also with a lateral seta and an apically elongate or short segment, respectively. The derived patterns are those lacking a lateral seta (i.e., E, C, and F). The known distribution of records of these six groups is presented in Fig.
Support during SEM sessions was kindly provided by Luis Fernando Carrera-Parra (