Research Article |
Corresponding author: Eduardo Suárez-Morales ( esuarez@ecosur.mx ) Academic editor: Kai Horst George
© 2019 Eduardo Suárez-Morales, Iván A. Castellanos-Osorio.
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, Castellanos-Osorio IA (2019) A new species of Monstrilla (Copepoda, Monstrilloida) from the plankton of a large coastal system of the northwestern Caribbean with a key to species. ZooKeys 876: 111-123. https://doi.org/10.3897/zookeys.876.38400
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The genus Monstrilla Dana, 1849 is the most diverse of the copepod order Monstrilloida. Monstrilloid copepods are endoparasites of benthic polychaetes and molluscs; adult individuals are free-living, non-feeding reproductive forms that briefly become part of the zooplankton community, where they are occasionally captured by plankton nets. Monstrilloid copepods are frequently found during routine plankton samplings of coastal and estuarine habitats, but they are rarely found in large numbers. The western sector of the Caribbean Sea is known to harbor a diverse monstrilloid fauna. The analysis of zooplankton samples obtained during nine years from Chetumal Bay, a large embayment of the Mexican Caribbean coast, yielded a male monstrilloid that was found to represent a new species. It is herein described following upgraded standards and compared with its congeners. A key to males and females of the Monstrilla species known from the northwestern Caribbean is also provided.
estuaries, crustaceans, parasitic copepods, taxonomy, tropical zooplankton
Monstrilloid copepods are protelean parasites of benthic invertebrates; most juvenile stages are endoparasitic and adult individuals are free-living, non-feeding reproductive forms that briefly become part of the zooplankton community, where they are occasionally captured by plankton nets (
At more than 2500 km2, Chetumal Bay is the largest estuarine lagoonal system of the Mexican Caribbean coast. It is a priority protection area for the conservation of the Caribbean manatee, both nationally and internationally (
A large set of 607 zooplankton samples was obtained over a period of nine years (1990–1997, 2015, 2016). Different zooplankton groups have been studied in Chetumal Bay, including medusae (
Zooplankton samples were obtained monthly in 1997 by performing daytime surface trawls at each of 13 sampling stations in Chetumal Bay on the southern coast of the Mexican Caribbean (Fig.
The new species is herein described in full following the current upgraded descriptive standards in monstrilloid taxonomy (
Order Monstrilloida Dana, 1849
Family Monstrillidae Dana, 1849
Genus Monstrilla Dana, 1849
Holotype adult male (ECO-CH-Z-10330), Chetumal Bay, near Mexico-Belize international border (18°26'54"N; 88°04'00"W) on 27 July 1997 by I. Castellanos-Osorio. Specimen partially dissected, cephalothorax and urosome in a vial, ethanol-preserved. Appendages including antennules and legs 1–4 mounted on semi-permanent slide with glycerine, sealed with acrylic varnish.
The epithet of the new species is a toponym that refers to Chetumal Bay, the type locality of this species.
Small-sized male Monstrilla (0.73 mm), with body divided in relatively short, robust prosome, pedigerous somites 2–4 tapering posteriorly, and slender urosome. Cephalothorax with low, rounded medial rostral projection, with both dorsal and ventral cuticular ornamentation. Antennule 5-segmented geniculate antennules. Geniculation between segments 4 and 5. Fifth pedigerous somite separated from preceding somite. Posterolateral margins produced and partially overlapping succeeding somite, visible in lateral and dorsal views. Somite with two small rounded ventral processes visible in lateral view. Legs 1–4 with outer sea on basis; exopods and endopods 3-segmented. Leg 5 absent. Genital somite with dorsal field of transverse striations; ventral genital complex represented by short shaft with distal laterally diverging lappets with rugose anterior surface, branches with dorsally directed apical spiniform processes, probably representing opercular flaps; lappets connected medially by dentate margin. Caudal rami with four subequally long caudal setae.
Body shape and tagmosis as usual in male Monstrilla (
Monstrilla chetumalensis sp. nov., male holotype A habitus dorsal view B habitus lateral view, arrow indicates medial ventral protuberance C urosome ventral view; arrow indicates ventral globular processes on fifth pedigerous somite D urosome lateral view; arrow indicates ventral globular processes on fifth pedigerous somite E genital complex with lappets, ventral view. Scale bars: 100 μm. (A–C)
Monstrilla chetumalensis sp. nov., male holotype (A–E, C) A anterior part of cephalosome ventral view; arrow indicates nipple-like processes; s = sensilla B antennule segments 1–4 in dorsal view showing setal elements (sensu
Armature of legs 1–4 including basis, exopods, and endopods. (Roman numerals indicate spiniform elements, Arabic numbers indicate setiform elements, set from inner to outer positions).
Basis | Exopod | Endopod | |
Leg 1 | 1-0 | 0–I;0–1;2,2,I | 1-0;1-0;2,2,I |
Legs 2–4 | 1-0 | 0–I ;1-0;2,2,1, I | 1-0;1-0; 2,2,1, I |
Antennule relatively robust (Fig.
Legs 1–4 with smooth intercoxal sclerites of rectangular, smooth. Bases with straight inner margins; outer basal setal sparsely setulose on legs 1–4; on leg 3, outer basal seta about twice as long as and slightly thicker than in other legs. Endopods and exopods of triarticulated, outer margins of exopods smooth. All elements setiform and biserially plumose except for outer spines on first segments and outer apical spiniform seta on third exopodal segments displaying and third exopodal segments displaying sparsely spinulose inner margin and smooth outer margin (Fig.
Urosome consisting of fifth pedigerous, genital somite (carrying genital complex), two short, free postgenital somites divided by incomplete dorsal suture, and short anal somite (Fig.
The new species differs from the males of other known congeners in several respects. Firstly, there are only a few other male Monstrilla with divergent genital lappets that point backwards and end in a subtriangular or spiniform opercular process. The male of Monstrilla chetumalensis sp. nov. most closely resembles the Indian species Monstrilla lata Desai & Bal, 1962. Both have similar body proportions, cephalothorax ornamentation, and paired, divergent genital lappets, each with a short distal opercular structure. However, in M. chetumalensis, the lappets are strongly curved and have an inverted U-shape (
Also, we considered the resemblance of the described male with males of the recently described genus Caromiobenella Jeon, Lee & Soh, 2018, which is known from males only. It has been recognized (
In male Caromiobenella branched antennulary setae are absent from the fifth antennulary segment (
Currently, the are eight species of Monstrilla recorded from different coastal or reef areas of the Mexican Caribbean: M. reidae Suárez-Morales, 1993a (male) from Bahia de la Ascensión, M. mariaeugeniae Suárez-Morales and Islas-Landeros, 1993 (female) from off Puerto Morelos reef zone, M. ciqroi (Suárez-Morals, 1993b) (female) from Bahia de la Ascension, M. barbata Suárez-Morales & Gasca, 1992 (female) (see
1 | Antennules indistinctly segmented, slender or robust | 4 |
– | Antennules distinctly 4-segmented | 2 |
2 | With irregularly rugose medial rostral process | M. barbata Suárez-Morales & Gasca, 1992 |
– | Medial rostral process absent | 3 |
3 | A Fifth leg with small rounded protuberance adjacent to inner lobe |
M. ciqroi (Suárez-Morales, 1993b) |
– | Fifth leg with inner margin of fifth leg smooth | M. rebis Suárez-Morales, 1993b |
4 | Antennule with straight anterior and posterior margins; fifth leg with 1 lobe armed with 2 setae, inner margin smooth | M. elongata Suárez-Morales, 1994 |
– | Antennule with rounded protuberances along anterior and posterior margins; fifth leg with 1 lobe armed with 2 setae and with strong spiniform process on inner margin | M. mariaeugeniae Suárez-Morales and Islas-Landeros, 1993 |
1 | Fifth legs absent | 2 |
– | Fifth legs present, with 1 lobe armed with single seta |
M. elongata Suárez-Morales, 1994 |
2 | Genital complex with lappets directed backwards; fifth pedigerous somite with two small globular processes | M. chetumalensis sp. nov. |
– | Genital complex with lappets not directed backwards | 3 |
3 | Genital complex with inverted U-shaped lappets tapering into acute points | M. marioi Suárez-Morales, 2003 |
– | Genital complex with different structure, elongate, cylindrical, rod-like, with paired globular processes in terminal position | 4 |
4 | Fifth pedigerous somite with short digitiform ventral process; apical antennulary element 61 bifurcate | M. globosa Suárez-Morales, 2003 |
– | Fifth pedigerous somite lacking ventral process; apical antennulary element 61 not bifurcate | M. reidae Suárez-Morales, 1993a |
Most of the financial support to our zooplankton surveys in Chetumal Bay was provided by El Colegio de la Frontera Sur (