Rony Huys

Sexual dimorphism in calanoid copepods: morphology and function

Mate location and recognition are essentially asymmetrical processes in the reproductive biology of calanoid copepods with the active partner (the male) locating and catching the largely passive partner (the female). This behavioural asymmetry has led to the evolution of sexual dimorphism in copepods, playing many pivotal roles during the various successive phases of copulatory and post-copulatory behaviour. Sexually dimorphic appendages and structures are engaged in (1) mate recognition by the male; (2) capture of the female by the male; (3) transfer and attachment of a spermatophore to the female by the male; (4) removal of discharged spermatophore(s) by the female; and (5) fertilization and release of the eggs by the female. In many male calanoids, the antennulary chemosensory system is enhanced at the final moult and this enhancement appears to be strongly linked to their mate-locating role, i.e. detection of sex pheromones released by the female. It can be extreme in calanoids inhabiting oceanic waters, taking the form of a doubling in the number of aesthetascs on almost every segment, and is less expressed in forms residing in turbulent, neritic waters. Mate recognition is a process where chemoreception and mechanoreception presumably work in conjunction. The less elaborate male chemosensory system in the Centropagoidea is counterbalanced by females playing a more active role in generating hydromechanical cues. This is reflected in females in the shape of the posterior prosomal margin, the complexity of urosomal morphology and the size of the caudal setae. Visual mate recognition may be important in the Pontellidae, which typically show sexual dimorphism in eye design. The most distinctive sexual dimorphism is the atrophy of the mouthparts of non-feeding males, illustrating how copepod detection systems can be shifted to a new modality at the final moult. In the next phase, the male captures the female using the geniculate antennule and/or other appendages. Three types of antennulary geniculations are recognized, and their detailed morphology suggests that they have originated independently. Grasping efficiency can be enhanced by the development of supplemental hinges. The scanty data on capture mechanisms in males lacking geniculate antennules are reviewed. It is suggested that the loss of the antennulary geniculation in many non-centropagoidean calanoids has evolved in response to increasing predator pressure imposed on pairs in amplexus. Spermatophore transfer and placement are generally accomplished by the modified leg 5 of the male. In some males, leg 5 consists of both a chelate grasping leg and a spermatophore-transferring leg, whereas in others, only the latter is developed. Tufts of fine setules/spinules and/or sclerotized elements on the terminal portion of the leg are involved in the transfer and attachment of the spermatophore. The configuration of gonopores, copulatory pores and their connecting ducts in the female genital double-somite is diversified in the early calanoid offshoots such as Arietellidae and Metridinidae, whereas in more derived groups, it is constant and invariable, with paired gonopores and copulatory pores located beneath a single genital operculum. The absence of seminal receptacles in most Centropagoidea limits the females ability to store sufficient sperm for multiple egg batches, suggesting that repeated mating is necessary for sustained egg production. Discharged spermatophores are usually removed by the female leg 5 and/or specialized elements on other legs. In Tortanus (Atortus) Ohtsuka, which has rudimentary fifth legs in the female and complex coupling devices in the male, a spermatophore supposedly remains on the female urosome, since eggs appear to be released from a ventral opening of the spermatophore. The type of sexual dimorphism is closely related to habitat and biology. Some hyperbenthic families never show multiplication of aesthetascs on the male antennule, whereas families of the open pelagic realm such as the Aetideidae always have non-feeding males exhibiting secondary multiplication of antennulary aesthetascs. The various aspects and diversity of calanoid sexual dimorphism are herein considered in an evolutionary context.

Crustaceans from bitumen clast in Carboniferous glacial diamictite extend fossil record of copepods

Copepod crustaceans are extremely abundant but, because of their small size and fragility, they fossilize poorly. Their fossil record consists of one Cretaceous (c. 115 Ma) parasite and a few Miocene (c. 14 Ma) fossils. In this paper, we describe abundant crustacean fragments, including copepods, from a single bitumen clast in a glacial diamictite of late Carboniferous age (c. 303 Ma) from eastern Oman. Geochemistry identifies the source of the bitumen as an oilfield some 100-300 km to the southwest, which is consistent with an ice flow direction from glacial striae. The bitumen likely originated as an oil seep into a subglacial lake. This find extends the fossil record of copepods by some 188 Ma, and of free-living forms by 289 Ma. The copepods include evidence of the extant family Canthocamptidae, believed to have colonized fresh water in Pangaea during Carboniferous times.

New tantulocarid, Stygotantulus stocki, parasitic on harpacticoid copepods, with an analysis of the phylogenetic relationships within the Maxillopoda.

ABSTRACT A new genus of Tantulocarida, Stygotantulus, is described based on material from an anchialine pool on Lanzarote, Canary Islands. It is the most primitive tantulocarid known and is ectoparasitic on representatives of at least two families of harpacticoid copepods. It is distinguished by the presence of 7 abdominal somites in the tantulus larva. The musculature of the penis on trunk somite 7 of the male suggests that it is derived by modification of the seventh thoracopods. The importance of trunk somite numbers in maxillopodan systematics is reexamined and an attempt is made to apply the concept of homology to the developmental processes determining somite numbers. The classification of the Crustacea, including the Tantulocarida, proposed by Starobogatov (1986), is criticized and the validity of the developmental-functional concept of the prototagma, as used by Starobogatov, is refuted. A new scheme of phylogenetic relationships among seven major maxillopodan groups is presented.

The Tantulocaridan Life Cycle: the Circle Closed?

ABSTRACT The discovery of a new stage in the life cycle of the Tantulocarida is reported. A sexual female, collected from a deep-sea harpacticoid copepod host, was removed from the trunk sac of the preceding tantulus larva. This female is a free-living and nonfeeding stage which presumably mates with the free-swimming adult male previously described. The female comprises a cephalothorax, probably incorporating 2 limbless thoracic somites, 2 free pedigerous trunk somites, and 3 limbless trunk somites. It also possesses paired antennules, the only well-defined cephalic appendages present at any stage in tantulocaridan life history. There is a median genital aperture, the copulatory pore, located ventrally on the cephalothorax at about the level of the incorporated first thoracic somite. This is interpreted as further evidence of a sister-group relationship between the Tantulocarida and the Thecostraca. The known life-cycle stages of the Tantulocarida are now interpreted as forming two cycles, one sexual, the other parthenogenetic.

A redescription of the presumed associated Caligopsyllus primus Kunz, 1975 (Harpacticoida, Paramesochridae) with emphasis on its phylogenetic affinity with Apodopsyllus Kunz, 1962

Caligopsyllus primus Kunz, 1975, reported from tidal pools near East London (South Africa), is redescribed and figured on the basis of type material. An amended diagnosis of the genus Caligopsyllus Kunz, 1975 is presented. Cladistic analysis falsified the hypothesis of a close relationship between Caligopsyllus and Kliopsyllus Kunz, 1962, favouring instead a link with Apodopsyllus Kunz, 1962. The morphological modifications are discussed within the context of a possible ecto-associated life-style. Finally, a standard format of abbreviations and terminology is proposed for the paramesochrid caudal ramus.

Taxonomy of Oncaeidae (Copepoda, Poecilostomatoida) from the Red Sea. III. Morphology and phylogenetic position of Oncaea subtilis Giesbrecht, 1892

Both sexes of Oncaea subtilis Giesbrecht, 1892, a small oncaeid species commonly occurring in temperate and tropical regions, are redescribed on the basis of material from the Red Sea. It is placed in a new monotypic genus, Monothula, on the basis of the loss of the outer spine on the third segment of the endopod of legs 2–4, and the presence of a single dorsal egg-sac, which is attached medially to the genital double-somite. The latter character is unique among oncaeids. The geographical distribution of M. subtilis comb. nov. is reviewed, and additional taxonomic data based on material from the eastern Mediterranean, the Arabian Sea and the eastern Indian Ocean are presented. The phylogenetic relationships of M. subtilis within the Oncaeidae are discussed.

Asterocheres reginae, a new species of parasitic copepod (Siphonostomatoida: Asterocheridae) from a sponge in Belize

Asterocheres reginae n. sp., of the family Asterocheridae, is described from the spongeAgelas clathrodes (Schmidt) collected at Carrie Bow Cay, Belize. It inhabits the internal canal system of its sponge host. A detailed description of both sexes is presented, and emphasis has been placed on the recognition of homologies between the limb segments and armature elements in accordance with the new evolutionary scheme established by Huys & Boxshall (1991).

A new genus of groundwater Ameiridae (Copepoda, Harpacticoida) from boreholes in Western Australia and the artificial status of Stygonitocrella Petkovski, 1976

Examination of the copepod fauna inhabiting 50m deep production bores on Barrow Island (northwestern Australia), resulted in the discovery of an unusual ameirid which cannot be placed in any extant genus. Both sexes are characterized by a unisetose antennary exopod and extreme reduction in the swimming legs (particularly the endopods) and P5. Males lack a defined P6 closing off the single genital aperture and have an extraordinarily large spermatophore. Females similarly display a highly reduced genital field. The new species shows superficial similarities to both Psammonitocrella Rouch and Stygonitocrella Reid, Hunt & Stanley, however the combined presence of a sexually dimorphic inner basal spine on P1, a completely fused genital double-somite, reduced antennary exopod and vestigial P5 excludes it from either genus. Some problems in the current classification of freshwater Ameiridae are highlighted, with particular reference to the genus Stygonitocrella . A new genus Neonitocrella is proposed for Stygonitocrella insularis (Miura, 1962).

Size polymorphism in Oncaea venusta Philippi, 1843 and the validity of O. frosti Heron, 2002: a commentary

The morphological characters used to describe Oncaea frosti Heron, 2002 (Copepoda, Poecilostomatoida), an Atlantic medium-sized form variant of O. venusta Philippi, 1843, appear to be inadequate in view of the great polymorphism known for this ubiquitous species. Comparative analysis of published and newly collected length data of O. venusta variants worldwide demonstrates that O. frosti cannot be unequivocally delineated in the Indo-West Pacific. The validity of O. venella Farran sensu Heron (2002) is questioned and comments are given on Herons synonymization of O. venusta f.venella sensu Ferrari (1975) and sensu Böttger-Schnack (2001) with O. frosti. As long as the significance of the morphological characters used to separate O. venusta form variants is not substantiated by data emerging from alternative taxonomic methods, such as the analysis of gene sequences, the species names O. frosti and O. venella Farran sensu Heron (2002) are regarded as species inquirendae in the genus Oncaea.

Taxonomy, biology and phylogeny of Miraciidae (Copepoda: Harpacticoida)

Abstract The holoplanktonic family Miraciidae (Copepoda, Harpacticoida) is revised and a key to the four monotypic genera presented. Amended diagnoses are given for Miracia Dana, Oculosetella Dahl and Macrosetella A. Scott, based on complete redescriptions of their respective type species M. efferata Dana, 1849, O. gracilis (Dana, 1849) and M. gracilis (Dana, 1847). A fourth genus Distioculus gen. nov. is proposed to accommodate Miracia minor T. Scott, 1894. The occurrence of two size-morphs of M. gracilis in the Red Sea is discussed, and reliable distribution records of the problematic O. gracilis are compiled. The first nauplius of M. gracilis is described in detail and changes in the structure of the antennule, P2 endopod and caudal ramus during copepodid development are illustrated. Phylogenetic analysis revealed that Miracia is closest to the miraciid ancestor and placed Oculosetella-Macrosetella at the terminal branch of the cladogram. Various aspects of miraciid biology are reviewed, including repr...