Mandibular Gnathobase Research Articles

A new species of Breviconia Conroy-Dalton & Huys, 2000 (Copepoda: Harpacticoida: Ancorabolidae Sars) from the Bering Sea, northern Pacific Ocean (Russia)

The finding of Breviconia andrei sp. nov. in the Russian Bering Sea enabled the clear-cut phylogenetic characterization of the former monotypic genus Breviconia Conroy-Dalton & Huys, 2000 as a monophylum. Comparison of the new species with B. australis (George, 1998) and other members of the subfamily Ancorabolinae Sars, 1909 yielded four autapomorphies that unambiguously support the monophyletic state of Breviconia: (1) an elongated and approximately 90°-curved mandibular gnathobase, (2) reduction of the maxillar endopod, (3) maxillar endites carrying 2 instead of 3 setae, and (4) loss of the minute seta on the maxillipedal claw. For B. andrei sp. nov., two autapomorphies could be detected, namely, (1) the development of dorsal tubercles on the P5-bearing body somite and (2) the remarkable elongation of the first endopodal segment of the first swimming leg that is twice as long as the whole exopod. Of particular interest is the presence of a 3-segmented endopod in the third swimming leg of the male of B. andrei sp. nov. It disproves the current assumption that the Ancorabolinae are characterized by (among others) the derived presence of an only 2-segmented endopod in the male’s third swimming leg.

A new species of Bestiolina (Copepoda, Calanoida, Paracalanidae) and complementary description of B. similis (Sewell, 1914) from the Nansei Islands, Japan.

Two species of the calanoid copepod genus Bestiolina occurred in estuarine/coastal waters of the Nansei Islands, southernmost Japan. One of them is described herein as Bestiolina okinawae sp. nov., which is distinguished from known congeners by a combination of the following characteristics: 1) fifth pedigerous somite bearing groups of tiny spinules on the posterior end, 2) female mandible bearing a rod-shaped first gnathal tooth, 3) male left leg 5 with short apical spine on long terminal segment, and 4) legs 23 with endopodal segment 2 lacking spinules. The new species was the dominant zooplankter in oligohaline waters. The other species is morphologically identifiable to Bestiolina similis (Sewell, 1914). Genetic analysis using COI revealed that the two species differed by 9.910.0%, in contrast to small intra-specific genetic variation (0.01.5%). The two species were spatially segregated in low-salinity (230) estuaries and high-salinity (2536) coastal waters, respectively, but co-occurred in some samples. Their body length decreased from the winter (around 20°C) to the summer (around 30°C) by 9.518.1%, depending on the species and sex. In both species, adult males, which lack mandibular gnathobase, were larger than the adult females.

Morphology of the mandibular gnathobases of the copepods Calanus australis and Calanoides carinatus: Evidence of omnivory

In spite of the worldwide ecological relevance of Calanus australis and Calanoides carinatus, little is known on the morphology of their mandibular gnathobase edges (MGEs). Thus, in order to further learn about the relationship between MGEs and diet, adults and copepodites of C. australis and C. carinatus collected from northern Patagonian coasts, Argentina, were morphologically analyzed using confocal laser scanning microscopy in transmission mode and scanning electron microscopy. In C. australis males as well as in C. australis and C. carinatus females, MGEs were found to end in one dorsal seta and to have one ventral tooth, four central teeth and three dorsal teeth. In contrast, in C. carinatus males, MGEs were observed to be rudimentary and with no dorsal seta, and −contrary to published data− they were found to have three cone-shaped, short and small tooth-like structures and three-four tooth-like structures that were long and pointed. The main differences between MGEs from copepodites and adults of C. australis and C. carinatus females lied in the number of cuspids observed on the different teeth and the presence of a short inner lateral peak found only in C. australis ventral tooth. Overall, the evidence gathered from our study leads us to classify C. australis and C. carinatus as omnivores.

Description of a new species of Neoargestes Drzycimski, 1967 (Copepoda, Harpacticoida, Argestidae) from the Clarion Clipperton Fracture Zone (Pacific Ocean), with remarks on the systematics of the genus

Neoargestes laevis sp. nov. (Copepoda, Harpacticoida, Argestidae), the third species of the genus, is described from the Clarion Clipperton Fracture Zone (Pacific Ocean), and a re-description of the holotype of Neoargestes incertus Becker, 1979 is provided. The generic diagnosis of Neoargestes Drzycimski, 1967 is amended and its allocation to Argestidae is confirmed. The monophyly of Neoargestes is recognized by six autapomorphies: transformation of the mandibular gnathobase into a strong masticating apparatus with a broad front, reduction in size of the first endopodal segment in P2–P4, and reduction in size of the P5 baseoendopod and exopod. The presence of 3-segmented endopods in P2–P4 in Neoargestes points to a rather basal position of the genus within Argestidae. Its affinities to Argestinae, Bodinia George, 2004 and Odiliacletodes Soyer, 1964 as well as its intrageneric systematics are briefly discussed.

A New Indobathynella Species from an Indian Cave. The First Cavernicolous Bathynellidae (Syncarida: Bathynellacea) from South-eastern India.

Indobathynella socrates n. sp. is described from Karaiguda Cave in the Visakhapatnam District of Andhra Pradesh state, south-eastern India. This is the first cavernicolous species of Indobathynella, which is incidentally the most reduced genus in the family Bathynellidae as a whole. The type species of this genus, Indobathynella prehensilis, is from a farm bore. The new species fulfils all the principal generic criteria of Indobathynella, but is distinctly different from I. prehensilis in several essential features: absence of subapical seta on antennary exopod; 4 claws on distal maxillulary endite; 6 teeth on mandibular gnathobase, and uropodal exopod without ventro-medial seta. These and all other salient differences between the two species are tabulated. Besides providing brief notes on conservation and biogeography of the new species, a key to all the known Indian taxa of Bathynellidae is given for the first time.

Convergent evolution of mouthparts morphology between Siphonostomatoida and a new genus of deep-sea Aegisthidae Giesbrecht, 1893 (Copepoda: Harpacticoida)

A great diversity of the basal harpacticoid family Aegisthidae Giesbrecht, 1893 is found in the deep-sea benthic and hyperbenthic environments. Some members of this family have developed adaptations to dig into the sediment, while others have colonized hyperbenthic waters; however, no aegisthid associated with a vertebrate or an invertebrate host has yet been reported. During a sampling campaign aimed at evaluating the abyssal copepod fauna of the polymetallic province in the North East Pacific, we discovered a striking new genus of Aegisthidae which exhibits convergent evolution of mouthpart morphology with that of siphonostomatoid copepods. Siphonis gen. nov. has a labrum modified into a long oral cone similar to that found in ectoparasitic species of the primitive siphonostomatoid family, Asterocheridae Giesbrecht, 1899. The mandible, maxillule and maxilla of Siphonis gen. nov. are also modified into siphonostomatoid-like structures; however, some ground pattern characters of the family Aegisthidae are retained. The new genus is discussed and compared with members of the derived taxon Palinarthra, Seifried, 2003 which comprises all those harpacticoid families with an incipient oral cone and a slightly elongated mandibular gnathobase. Two species of the new genus are described herein and were verified by molecular evidence. Siphonis gen. nov. is placed within the subfamily Cerviniopseinae Brotskaya, 1963 and represents a third major shift in the lifestyle of aegisthid copepods, from benthic and hyperbenthic to associated forms (probably with sponges or cnidarians).

A new parasitic deep-sea copepod from the Angola Basin (southeast Atlantic Ocean): Abyssotaurus vermiambatus gen. et sp. nov. (Copepoda: Cyclopoida: Serpulidicolidae Stock, 1979), with remarks on serpulidicolid systematics and a key to the species

A new parasitic copepod, Abyssotaurus vermiambatus gen. et sp. nov. of the family Serpulidicolidae Stock (Copepoda, Cyclopoida), was discovered during the RV Meteor cruise M48/1 (DIVA 1) in the deep sea of the southeast Atlantic Ocean. Despite the doubtless affiliation of A. vermiambatus gen. et sp. nov. to Serpulidicolidae, the new species cannot be allocated into one of the currently known genera. It presents three autapomorphies: (i) fusion of the cephalosome with the remaining body somites, (ii) development of a derived labrum, and (iii) modification of the mandibular gnathobase into a strong masticatory apparatus. In addition to a detailed species description, a comprehensive phylogenetic evaluation of Serpulidicolidae using 52 morphological characters was realized. It confirms the monophyly of Serpulidicolidae, whose family diagnosis had to be amended, and reveals its closest relation to Nereicolidae Claus. Furthermore, some brief remarks on the biology of Serpulidicolidae, including an updated species checklist, are provided.

A new species of the genusHalectinosoma(Copepoda, Harpacticoida, Ectinosomatidae) from Korea

Abstract A new species of harpacticoid copepod, Halectinosoma foveolata, was described from sandy sediments on several intertidal areas of Korea. This new species is mostly similar to H. dimorphum Coull, 1970, but differs from the latter by the following characteristics combined: (1) the third segment of antennule is longest; (2) the first exopodal segment of antenna has a row of spinules; (3) the mandibular gnathobase is composed of chitinous teeth without dorsal seta; (4) the female P5 has an incomplete boundary between the exopod and the baseoendopod; (5) the female P5 baseoendopod has two rows of spinules. We also discuss the state of H. arenicola sensu Ito (1973), reported from the Japanese coast, which is considered here a synonym with the new species.

Features of the fine structure and Si content of the mandibular gnathobase of four freshwater species of Epischura (Copepoda: Calanoida)

The cutting edge of the mandibular gnathobase in many marine and some freshwater copepods is fortified with opal crowns for holding and grinding food. There is evidence of silica in these opal crowns for only seven species of freshwater copepods. Distinguishing characteristics of the structure and silicon (Si) content of the mandible’s cutting edge were analysed in four species of Calanoida of one genus from two lakes in Russia ( Epischura chankensis and E. baicalensis ) and two lakes in North America ( E. lacustris and E. nevadensis ). The morphology of the mandibular gnathobase is described in detail for each species. Differences in the mandible characteristics and the level of crown silicification are observed within the genus Epischura . The highest content of silica is recorded in the crowns of E. baicalensis , which feeds on diatoms with thick frustules in Lake Baikal.

A new genus, Peniculoides (Copepoda, Calanoida), from deep waters of the North Atlantic with notes on the definition of Clausocalanidae

A new calanoid copepodPeniculoides secundusgen. et sp. nov. is described from a female specimen collected in the northern Atlantic from abyssal waters close to the sea bed during the German expedition DIVA 3 in 2009.Peniculoidesgen. nov. is a representative of the superfamily Clausocalanoidea with a heavily sclerotized mandibular gnathobase and maxillular praecoxal arthrite, the maxillular coxal epipodite lacking setae and the maxilla with coxal to basal endites flat and round distally, their surfaces densely covered by short, brush-like spinules. The new genus,Peniculoidesis provisionally placed in the Clausocalanidae. A combination of characters is proposed to distinguish between the families Clausocalanidae and Aetideidae. The generic composition of Clausocalanidae is revised.

Towards a revision of the genusHalectinosoma(Copepoda, Harpacticoida, Ectinosomatidae): new species from the North Atlantic and Arctic regions

This paper contributes to a revision of the genus Halectinosoma. Four new species are described, based on examination of ectinosomatid material from localities in western Europe, eastern Canada and the Arctic. Halectinosoma mandibularis sp. nov. is distinguishable from other species by the reduced setation of the mouthparts and enlarged mandibular gnathobase. Halectinosoma latisetifera sp. nov. bears an affinity with H. cooperatum but is easily distinguished by the shape of the setae on the female fifth leg. A species previously erroneously ascribed to H. finmarchicum (Scott) by several authors is described here as Halectinosoma kliei sp. nov.Halectinosoma gothiceps (Giesbrecht) is redescribed and the closely related Halectinosoma paragothiceps sp. nov. is described and distinguished from H. gothiceps. It is considered likely that some previous records of H. gothiceps are in error. © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society, 2007, 149, 453–475.

Copepodid Stages of Euryte Longicauda (Cyclopoida, Cyclopidae, Euryteinae) from the White Sea Associated with the Bryozoan Flustra Foliacea

Abstract The copepodid phase of development of Euryte longicauda Philippi, 1843, is described from six stages associated with the bryozoan Flustra foliacea Linnaeus, 1758 Distinctive character states of the species include: distal teeth of mandibular gnathobase perpendicular to proximal teeth; distal seta of maxillular praecoxa with multiple cusps is perpendicular to proximal setae with one cusp; coxa of maxillule as a gnathobase perpendicular to praecoxa; maxillular palp comprised of two setae; fluted setae medially on the distal segment complex of both rami of swimming legs 1–4. The segmental homologies of the maxilla of E. longicauda are an unarmed syncoxa, a basis with two setiferous lobes, and a ramus of three segments. A re-examination of type specimens of E. bellatula Humes, 1991, and E. verecunda Humes, 1992, revealed a 2-segmented protopod for leg 5, confirming their inclusion in Euryte. Euryte longicauda retains the ancestral state for development of swimming legs 1–4. Development of the maxilli...

Lipid deposition and sexual maturation in cohorts of Calanus finmarchicus (Gunnerus) originating from Bergen (60�N) and Troms� (69�N) reared in Troms�, Norway

Two cohorts of Calanus finmarchicus (Gunnerus), with habitats in Bergen (60°N) and Tromso (69°N), were reared from copepodite stage III (CIII) in mesocosms in Tromso from April 24 1998 to June 30 1998. The aim was to study whether the two cohorts diverged phenotypically with respect to indication of physiological preparation for diapause as opposed to initiating another generation. At the end of the experiment the fractions of the cohorts that had reached sexual maturation, based on observed stage shifts to adults, was ~45% within the Bergen cohort and ~35% for the Tromso cohort, within which males appeared before females. Examination of the mandibular gnathobase of copepodites at stage V (CV) revealed that 40% of the Tromso cohort were ready for ecdysis, eventually to become adults in the same year. The physiological expression of the range in individual maturity within the cohorts was revealed in individual carbon and nitrogen content. Both cohorts incorporated the storage lipids wax esters (WE) and triacylglycerols (TAG) rapidly, primarily during CV (0.16–0.21 μg total neutral lipid ind-1 day-1), with no significant difference. Lipid storage was incorporated from CIII and the maximum was reached at the CV stage. Presumably due to excess food, high WE, TAG and free fatty acid levels were observed in both cohorts. A relative decrease in neutral lipids was observed later in females from both cohorts. We suggest that part of the Bergen population, but also a fraction of the Tromso population, prepared for diapause in CV. A possible reason for the sexual maturation among the rest of the CV copepodites could be a shift in life "strategy" caused by an unusually high rise in temperature in the mesocosms during the last 10 days of the experiment.

Larval development of Japanese ‘conchostracans’: part 1, larval development of Eulimnadia braueriana (Crustacea, Branchiopoda, Spinicaudata, Limnadiidae) compared to that of other limnadiids

AbstractAs a part of a project to compare phylogenetically the larval or embryonic development of all major taxa of the Branchiopoda (Crustacea), the larval development of the Japanese spinicaudatan clam shrimp Eulimnadia braueriana Ishikawa, 1895, is described. Seven naupliar stages are recognized, based mainly on significant morphological differences between them, but in one case, on size alone. The seven stages range in length from 156 µm to 760 µm. Nauplius 1 is nonfeeding with incompletely developed and nonfunctional feeding structures. Nauplius 2 has apparently functional feeding structures, including a well‐developed mandibular gnathobase, setulate protopodal endites of the antennae, and setules on various setae involved in swimming and food manipulation. Nauplius 3 is morphologically identical to Nauplius 2, but more than 50% larger. In nauplius 4, the coxal endite (naupliar process) of the antennae develops a bifid tip. Nauplius 5 has a lateral pair of primordial carapace lobes, and the first 4–5 pairs of trunk limb buds are weakly developed, making the anterior part of the trunk wider than the posterior. In nauplius 6, five pairs of trunk limb buds are visible externally and a small carapace has appeared, reaching approximately to trunk limbs 2; also, the pair of large buds behind the mandibles in previous stages has become divided into a large, anterior, setose bud and two smaller, posterior buds. The identities of these structures as either paragnaths or maxillules/maxillae remain uncertain. In nauplius 7, about six pairs of trunk limb buds are visible externally. The general morphology of the nauplius larvae of E. braueriana is much like those of the well‐known Limnadia lenticularis (Linnaeus, 1758) and Eulimnadia texana Packard, 1871, including an elongate, lanceolate labrum; however, because of various heterochronies, the correspondence between the larval sequences of these species is not perfect. There is even less correspondence with the 5‐stage larval development reported for Limnadia stanleyana King, 1855, and the spatulate labra of that species and Jmnadia spp. are different from those of other known limnadiid nauplii. The larvae of E. braueriana possess many typical (and synapomorphic) branchiopod features, such as the general morphology of the appendages involved in feeding and the mode of trunk limb development, while the small buds of the first antennae and the exact number and development of the parts of the trunk limbs are typical for the Spinicaudata.

Specialized feeding mechanism in the pelagic copepod genus Heterorhabdus (Calanoida: Heterorhabdidae), with special reference to the mandibular tooth and labral glands

Scanning and transmission electron microscopy and gut-content analysis revealed the fine structure of the mandibular ventralmost tooth and labral glands of the carnivorous copepods Heterorhabdus spp. on the basis of the specimens collected in the waters near Nansei Islands, Southwestern Japan, in November 1993. The ventralmost tooth is hollow with a subterminal pore and a basal opening. The distal region of the tooth is like a hypodermic needle and is strengthened by opal layers. The tip of the tooth including the subterminal pore usually protrudes from between the labrum and the paragnath, while the basal region of the ventralmost tooth and the whole parts of the other teeth are semi-enclosed in the preoral food chamber formed by the labrum and the paragnath. There is a large glandular cell in the basal region of the mandibular gnathobase, but no direct connection exists between the gnathobasal cells and the tubular lumen of the ventralmost tooth. The posterior surface of the labrum carries a lateral pair of large glandular pores, which are located close to, and appear to fit exactly the basal openings of the ventralmost teeth. Each of these glands has two massive secretory cells, and the secretory materials from these cells appear to be mixed before discharge from the pore. A specialized feeding mechanism is proposed, wherein venom or anaesthetic is injected from the labral-gland pores into the tubular lumen of the mandibular ventralmost tooth, and then relcased into the prey from its subterminal pore immediately after capture using the stout maxillae of prey macrozooplankters such as copepodids and polychaetes.

Morphogenesis of opal teeth in calanoid copepods

Opal teeth of calanoid copepods develop early in the premolt phase of the molt cycle. They form in the apolysis space beneath the old tooth row on the mandibular gnathobase. We examined stages of tooth formation inNeocalanus spp. andCalanus pacificus. Apolysis occurs early in the distal gnathobase, then several epidermal cell types participate sequentially in formation of new teeth. Fibrous molds in the shapes of the new teeth are extruded onto the epidermal surface, then additional materials, probably proteinaceous, are secreted into them. Tooth molds next are linked to a gland in the proximal part of the gnathobase by ducts of an unusual type, “lamellar-walled ducts.” Silicification follows, apparently using highly osmiophilic material supplied by the proximal gland. Opal is laid down at the outer periphery of the mold then thickens toward the attachment of the mold to newly formed chitin at its base. During apolysis the epidermal cells move proximally without breaking ducts that connect small dermal glands with pores in the sides of the opal teeth. The molds for the new teeth form surrounding these ducts, and new pores result. The glands are like the ciliary exocrine glands seen in other Crustacea, with the duct deriving from fusion of the axonemes of a cilium. Presumably the glands secrete a substance into food newly broken by the teeth. This could be a toxin or a digestive enzyme.

Studies on the functional morphology and biology of the Notostraca (Crustacea: Branchiopoda)

Studies on the functional morphology and biology of the Notostraca (Crustacea: Branchiopoda)