Distribution, structure and importance of the cephalic dorsal hump, a new sensory organ in calanoid copepods

University of Tokyo
Marine Biology (Impact Factor: 2.39). 01/1989; 101(2):173-185. DOI: 10.1007/BF00391456


The occurrence, external morphology and internal ultrastructure of a cephalic integumental organ in calanoid copepods were studied, using the specimens from the Pacific, Indian and Atlantic Oceans. This organ is located on the dorsoanterior surface of the cephalosome, and a name, cephalic dorsal hump (CDH) is proposed. Externally, it usually has two pores, anterior and apical, a dorsal plate, and a thin cuticle along the sides. CDH is found only in the male of Calanidae, Megacalanidae, Mecynoceridae and Paracalanidae, and showed some variation between species or species groups both in size and shape. Transmission electron microscopy (TEM) on the specimens from Sagami Bay, Central Japan, revealed that the CDH of Paracalanus parvus and Calanus sinicus consists of two dermal glands and a receptor, which is assumed to be chemosensory. A comparison of the distributions of CDH and prehensile fifth legs of male calanoid copepods suggests that it plays an important role in mate recognition.

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    • "Its presence in other species of copepods is, however, unclear. Besides the cephalic organ described by Elofsson (Elofsson, 1971), Nishida (Nishida, 1989) described a " cephalic dorsal hump " on the cephalosome of Paracalanus parvus, which is only found in males. The author suggests that it is involved in chemosensory identification of potential partners due to the sexual dimorphism and morphological similarities with chemosensory structures. "
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    ABSTRACT: An increasing number of studies show the importance of chemical interactions in the aquatic environment. Our understanding of the role of chemical cues and signals in larger crustaceans has advanced in the last decades. However, for copepods, the most abundant metazoan zooplankton and essential for the functioning of the marine food web, much is still unknown. We synthesize current knowledge about chemical ecology of copepods including foraging, survival and reproduction. We also compile information on the sensory apparatus and new analytical approaches that may facilitate the identification of signal molecules. The review illustrates the importance of chemical interactions in many aspects of copepod ecology and identifies gaps in our knowledge, such as the lack of identified infochemicals and electrophysiological studies to confirm the function of sensory structures. We suggest approaches that are likely to further our understanding of the role of chemical interactions in the pelagic ecosystem.
    Full-text · Article · Jul 2014 · Journal of Plankton Research
    • "The function of this organ is not known. The cephalic dorsal hump is present in the outgroup and genera other than the tropical genera (Canthocalanus, Cosmocalanus, Undinula, and Nannocalanus ) from which it is absent (Nishida 1989) (char. 1). "
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    ABSTRACT: Cladistic analysis of Calanidae recovered two major clades: a tropical epipelagic clade composed of species without ontogenetic vertical migration (Canthocalanus + Cosmocalanus + Nannocalanus + Undinula); and a clade of ontogenetically migrating genera (Neocalanus + Calanoides + Calanus + Mesocalanus). The latter clade is least well supported although its Calanoides and Neocalanus lineages are well supported. Morphology-based topologies are largely congruent with published molecular trees, differing chiefly in the positions of Mesocalanus and Calanus. Independent homoplasious trends in character states in the male leg 5 include: reduction in segmentation and number of setae, increasing asymmetry as well as the probable retention of larval characteristics. The monophyly of Calanoides, Neocalanus and Calanus is well supported. It is postulated that Calanidae radiated during the mid to late Triassic from a bathypelagic megacalanid which was adapted to low oxygen conditions. High latitude locations may have been the first epipelagic environments to be recolonized.
    No preview · Article · Feb 2010 · Journal of Natural History
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    • "It is also called an intercoxal sclerite or coupler by Huys and Boxshall (1991). Nucal organ: according to Nishida (1989), a modified region adjacent to the suture of cephalosome, at the dorsal region, that seems to be depressed, similar to an integumental window. It can be well defined or not, and with at least two different forms: broader than long (rectangular transverse or rectangularis vel oblongus) "
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