Key to the identification and ecology of Cyclopoida (Crustacea, Copepoda) of North America (north of Mexico)

By Leszek Bledzki

This key provides an overview of Cyclopoida species known from North America, north of Mexico. The species description is limited to the few key characters, which allow for proper species identification. Keys are arranged into plates with easy-to-use pictorial guide. Each key provides all relevant characters (the written description and drawings) important for family, genus, and species identification, which include distinction from similar group or species. The species ecology chapter has all species to be organized in the alphabetical order, which is very practical and allows for faster search for desired information. Described also are recent changes (up to the December of 2023) in the taxonomy status of species and higher taxonomy levels up to the Cyclopoida order and fixed are several errors in the previously published keys, where one of them were repeated for around 100 years. This should be the most recent update of the taxonomy status of all Cyclopoida species known from North America, north of Mexico, with the modern approach in which the cosmopolitanism paradigm is replaced by the ideas of twin species or superspecies which unite closely related but isolated populations of morphologically similar forms. Progress on frontier research and applied environmental protection heavily depends on correct species identification. An unclear taxonomic status of any Copepoda species, the absence of reliable characters to discriminate specimens of the similar taxa, the lack of inclusion of many newest and valid species in the published papers, as well as the use of very old keys listing species that are no longer valid result in biased data interpretation in ecological publications. Therefore, this key should be of great help to overcome the above obstacles. The key presents 115 species reported from North America, described on 182 pages with 115 maps, 740 b/w illustration, all based on 770 primary reference papers.

• Language: English
• Publisher: Lulu.com
• Release date: Jan 7, 2024
• ISBN: 9781304734662

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Preface

This key provides an overview of Cyclopoida species known from North America, north of Mexico. This work is not intendent to be a monograph with detailed and exhaustive description of species morphology. Such information has been provided by monographs and papers listed in the reference section for each species. The species description is limited to the few key characters, which allow for proper species identification. Keys are arranged into plates with easy-to-use pictorial guide. Each key provides all relevant characters (the written description and drawings) important for family, genus, and species identification, which include distinction from similar group or species. The identification should always start from the beginning of the key. Otherways, a single character missed during the identification may lead to a wrong result. The species ecology chapter has all species to be organized in the alphabetical order, which is very practical and allows for faster search for desired information. Described also are recent changes (up to the December of 2023) in the taxonomy status of species and higher taxonomy levels up to the Cyclopoida order and fixed are several errors in the previously published keys, where one of them were repeated for around 100 years. This should be the most recent update of the taxonomy status of all Cyclopoida species known from North America, north of Mexico, with the modern approach in which the cosmopolitanism paradigm is replaced by the noncosmopolitanism paradigm, where the ideas of twin species or superspecies (semi-species), which unite closely related but isolated populations of morphologically similar forms (Kiefer, 1981; Xu et al., 2009; Mallet, 2021). Many researchers have been using outdated Cyclopoida species names, using the half-century or older keys, during their ecological research, which slows down the progress of the field, as such ecological research based on not valid species names may be doubtful and confusing. A good example of the misleading identification of Copepoda species based on the reference to the old keys is the example provided by Robertson (2014), where after 44 years which passed since his original publication from 1970 based on the old key-reference from 1959, author learned that in fact his specimen represents the undescribed species (Wilson and Yeatman, 1959; Robertson, 1970; Robertson, 2014). Progress on research in community and ecosystem ecology, an environmental monitoring, water quality or biodiversity assessment relies on an accurate enumeration of coexisting species, and this in turn requires that the specimens collected in the field must be properly identified to the species, the finest taxonomic level (Gotelli, 2004; Feio et al., 2006; Farnsworth et al., 2013). Therefore, progress on frontier research and applied environmental protection heavily depends on correct species identification. An unclear taxonomic status of any Copepoda species, the absence of reliable characters to discriminate specimens of the similar taxa, the lack of inclusion of many newest and valid species in the published papers, as well as the use of very old keys listing species that are no longer valid result in biased data interpretation in ecological publications. Therefore, this key should be of great help to overcome the above obstacles. The key presents 115 species reported from North America, described on 182 pages with 115 maps, 740 b/w illustration, all based on 770 primary reference papers.

Acknowledgments

Author is grateful to many colleagues who provided their published papers over the years, some of them hardly accessible, several of older published papers related to Copepods were provided by Chad Walter from the Smithsonian Institute, Washington D.C. I am also grateful to Janet W. Reid for providing her published papers for many years, and for the resolving problem with contradictory descriptions of Stolonicyclops heggiensis, and Joe Connolly for his comments related to the North American records of C. vicinus. Both, the Mount Holyoke College Library and Five College Library Depository staff helped with great resources over many years. The World Register of Marine Species (WoRMS) – The World of Copepods database website provided valuable, especially the older published papers. I would like to thank my wife Maria for her long-term support and tolerance for my time spent working on this book. Thank you all!

Seattle & Lynnwood, Washington, December 2023                                                                            Leszek A. Błędzki

Abbreviations

The general morphology, abbreviations and numerations are adopted after Schminke (1976), Huys and Boxshall, (1991), Dussart and Defaye (200), Alekseev (2002), Ueda and Reid (2003), Alekseev et al. (2006), Mercado-Salas and Suarez-Morales (2021). Caudal ramus setae numeration adopted after Huys (1988) and Huys and Boxshall (1991), where the new nomenclature system for the setation elements of caudal rami was established for 7 caudal setae for Copepods.

Morphological abbreviations

A1 – antennule

A2 – antenna

Ae – aestetascs

Bsp – basipodite

C1-C5 – first to fifth copepodites, larval stages

Cph – cephalothorax

Coxa – coxopodite

CR – Caudal rami

Enp – endopodite

Enp1-3 – first to third segments of the endopodite

Exp – exopodite

Exp1-3 – first to third segments of the exopodite

Fs – caudal ramus setae (on furca each ramus carries 7 setae)

Fs I-VII – first to seventh caudal ramus setae

Fs I – anterolateral accessory caudal ramus seta (usually missing or reduced in most Cyclopidae species)

Fs II – anterolateral caudal ramus seta (Me – marginal external seta)

Fs III – posterolateral outer external caudal ramus seta (Te – terminal external seta)

Fs IV – long outer terminal caudal ramus seta (Tme – terminal median external seta)

Fs V – long inner terminal caudal ramus seta (Tmi – terminal median internal seta)

Fs VI –terminal internal caudal ramus seta (Ti – terminal internal seta)

Fs VII – dorsal caudal ramus seta (Ds – dorsal caudal seta)

Fu – furca, caudal rami

Go – genital operculum

GS – genital double-somite

L – left

La – labrum

L/W ratio – Length to Width ratio

Md – mandible

Mx – maxilla

Mxl – maxillule

Mxp – maxilliped

N1-N6 – first to sixth naupliar stages

P1-4 – first to forth thoracic appendages, paired swimming legs, pediger 1 to 4

P5 – swimming leg 5, pediger 5

P6 – swimming leg 6, pediger 6

R – right

Ro – rostrum

RS – receptaculum seminis (seminal receptacle)

Serra – longitudinal row of spines on furcal rami

sp. – species

spp. – species plural, several species

Th3, Th4, Th5 – Thorax segment 5, pedigerous somite 5, somite 5 bearing a pair of legs (P5)

Ur – urosome

Ecological abbreviations

C:N:P = Carbon : Nitrogen : Phosphorus ratio

DOC – Dissolved Organic Carbon

DVM – Diel Vertical Migration

DW – Dry Weight

GRR – Gross Reproductive Rate it is an average number of offspring if female would survive all her reproductive period

ICZN – International Commission on Zoological Nomenclature

MYA – Million Years Ago

NRR – Net Reproductive Rate it is the sum of all offspring produces by female during her lifespan

P/B – production to biomass ratio

POM – Particulate Organic Matter

USNM – United States National Museum

WW – Wet Weight

Introduction

Copepods are one of the most abundant metazoans, and ecologically successful taxon, which colonized benthic and planktonic habitats of aquatic ecosystems with the global diversity of free-living (non-parasitic) copepods estimated to be around 2,814 freshwater species (out of over 14,800 mostly marine species), where from Nearctic area reported were only 347 species, which consists only 12% of all Copepoda species (Humes, 1994; Balian et al., 2008; Boxshall and Defaye, 2008; Williamson and Reid, 2009; Reid and Williamson, 2010; Vakati et al., 2023; Walter and Boxshall, 2023). Cyclopoid copepods make up a major portion of zooplankton, their biomass and productivity of aquatic ecosystems, and they also occupy an important intermediate position in the food chains as predators having substantial impact on their prey population, and importantly, they are reflecting trends of the ecological and environmental conditions by changes in their abundance, diversity patterns, life history, and reproductive strategies (Makarewicz and Likens, 1979; Williamson and Reid, 2009; Reid and Williamson, 2010; Błędzki and Rybak, 2016; Vakati et al., 2023). The worldwide conservation status of copepods was reviewed and 6 species are considered extinct and more than 220 species are considered under some degree of threat, this include the North American Cyclopoida related to Rheocyclops (endemic North American genus), where several species were represented by the collection of only several specimens, all from ephemeral waters which currently undergoes destruction (Reid et al., 2002a). Copepods have been used as a model or tools for the ecological studies (Hutchinson, 1951; Touratier et al., 1999; Fields and Weissburg, 2005). The summary of Copepoda ecological impacts and current research trends were provided by Vakati et al. (2023). In short, Copepoda are one of the most significant animal groups of aquatic ecosystems living in planktonic and benthic communities. They are the largest and most diverse group of crustaceans. Their total biomass in all waters makes them most abundant metazoan groups on Earth. They have high nutritional value in aquatic food webs, feed on primary producers (phytoplankton), bacteria, heterotrophic flagellates, organic matter (detritus) and they are also predators on many other small organisms, often including fish larvae and mosquito larvae. Several Cyclopoida genera feed on mosquito larvae have been using as biological control for mosquito-borne diseases. Many Copepoda species are sensitive to environmental change and are a good indicator of the assessment of the impact of climate changes and human activities (including oil spills, microplastic, chemical pollution, acidification). For example, Mesocyclops longisetus), is one of the main vectors in the transmission of cholera, where Vibrio cholerae Pacini, 1854 has been shown to be the natural inhabitant of riverine, estuarine, and coastal waters, and copepods are the most significant member of zooplankton community in such habitats (Suarez-Morales, 2015). Copepods in North America have been studied for around 150 years. One of the oldest Cyclopoida species (Cyclops thomasi Forbes, 1882, currently valid name is Diacyclops thomasi) was described from Lake Michigan (Forbes, 1882b), and one of the newest species (Cyclops divergens Lindberg, 1936) was reported in the year 2022 from Lake Eire (Connolly et al., 2022). At this point, it should be mentioned out, that non-professional taxonomists have been responsible for describing more than half of the animal species (Fontaine et al., 2010). Then, progress of combined molecular and morphometric phylogenetic methods allows for the distinction of many undescribed species, but there is still not resolved problem, namely determining at what point two groups of organisms are distant enough from each other to be separate species (Kunz, 2012; Mallet, 2021). The combined approach of genetic identification and morphological studies seems to be the best way, as it allows access to the level of phenotypic variation within and among populations necessary to identify taxonomically relevant traits (Billiones et al., 2004), but we should remember Kunz’s statement, that "It is not sufficient to identify two organisms belonging to two different species by their diagnostic traits. It is more scientific to be able to explain the reasons that the organisms belong to two different species" (Kunz, 2012). We should keep this statement in mind before we decide to describe a new species that only slightly differs from the already known pool, it could be thus common biological variability, and this approach may save us from the need of the future effort of synonymization of some species. Describing the new species, requires both, naming the species and an explicit statement of the species concept used in this description. For example, the morphological characters are affected by many factors, such as heritable polymorphisms, allometry, phenotypic plasticity (in response to seasonal, geographic, latitudinal, and climatic variation), and morphological stasis and the reader of a taxonomic paper might be interested in knowing whether the author accounted for these factors, and if so, how the potential problems were addressed (Dodson and Lee, 2006). For more detailed info about all those problems please refer to (Graybeal, 1995; Dodson and Lee, 2006; Kunz, 2012; Mallet, 2021). Species scientific names are essential in all kind of scientific research activity. For centuries, species specific morphology was at the basis of naming species (including copepods), but now the current trend shows an increase in etymologies related to geography and recognition of influential scientists in the field (Macêdo et al., 2023).

Many undergraduate and graduate students are required to identify copepods during their research or lab projects, and they should learn to rely on the newest keys and monographs. Many of them, as well as some professionals, do not have the sufficient training in species identification, and do not have access to published monographs needed to achieve the proper species identification. Therefore, here proposed is a clear, easy-to-use, taxonomic dichotomous key for family, genera, and species identification. Keys are arranged into plates with an easy-to-use pictorial guide. In the subsequent chapter all species are listed in alphabetical order, along with subspecies names and a list of used synonyms, ecology, and taxonomical notes. Described also are recent changes in taxonomy status of the family, genera, or species. The key provides all relevant characters important for family, genera, and species identification as well as distinction from other similar groups or species. Provided are also written descriptions and drawings for most of the key-characters. The identification process always should start at the beginning of the key, otherwise a single character missed during the identification may lead to the wrong result. The next step after the proper species identification is data analysis within a framework provided by modern community ecology, hardly relying on analytical methods, please refer to several chapters of my other book for comprehensive detailed description (Błędzki and Rybak, 2016). For more information about copepods please refer to Huys and Boxshall (1991), Dussart and Defaye (2001), Boxshall and Halsey (2004), and Błędzki and Rybak (2016), but for the historical information about early Copepoda taxonomists please refer to Damkaer (2002). Papers relating to the taxonomy and ecology of North American copepods are scattered through the literature. Here presented is the comprehensive review of Cyclopoida papers related to North American cyclopoid copepods, their identification, ecology, and continental distribution.

Morphology

The detailed morphology of Copepods was described by many authors (Huys and Boxshall, 1991; Dussart and Defaye, 2001; Williamson and Reid, 2001; Ueda and Reid, 2003; Reid and Williamson, 2010; Błędzki and Rybak, 2016; Mercado-Salas et al., 2016; Suárez-Morales et al., 2020), and here adopted is from several authors (Wilson and Yeatman, 1959; Balcer et al., 1984; Van de Velde, 1984a; Van de Velde, 1984b; Huys and Boxshall, 1991; Einsle, 1993a; Einsle, 1996a; Karaytug, 1999; Dussart and Defaye, 2001; Ueda and Reid, 2003; Mercado-Salas et al., 2016; Suárez-Morales et al., 2020). The general morphology of copepods is presented on Figure 1. The morphology of antenna and its importance to the Cyclopidae systematics was described by Fiers and Van de Velde (1984). The antennulary development during the copepodid phase of the family Cyclopidae was elaborated by Karaytug and Boxshall (1999) and Schutze et al. (2000). Terms pediger denoting the swimming thoracal leg and pedigerous somite denoting the thorax segment, first time were used by Thomas E. Bowman (Reid and Ferrari, 1988). The morphological-evolutionary description of cyclopoid copepods oligomerization, the reduction of number of segments of the thoracic limbs and the first antenna was examined by Monchenko and von Vaupel Klein (1999). They showed that oligomerization in Cyclopoida is corelated with decrease of body length. The importance of the species-specific pattern of spines on the posterior (caudal) face of the coxa of the 4th pair of swimming legs (P4) was described by Einsle (1985), he proposed and described six groups of spines denoted by the letter A-F (Figure 2). Later, many researchers described useful microcharacters, such as the border ornamentation of the prosomal somites, the shape and ornamentation of the terminal spine on the endopod of P1, the presence and number of integumental pores on the terminal endopodal segment of P1, and details in the ornamentation of the middle caudal setae, pattern of spines on the caudal side of the coxa and intercoxal sclerite (coupler) ornamentation of P4 and A2 basipodite ornamentation. All of them are helpful in differentiation of species (da Rocha, 1998; Alekseev et al., 2006; Alekseev, 2023).

In Cyclopidae the sperm is stored in an internal seminal receptacle, the shape of which is used as a taxonomic character firstly established by Kiefer (1981) and Van de Velde (1984b), later described more detailed by Defaye et al. (2003).

The morphometric measurements are provided according to Koźmiński (1936), where the body length is the total length excluding caudal setae, measured in millimeters (mm) or micrometers