Larvae of Rhizocephalans with a Kentrogonid Type of Development and their Significance in the Taxonomy and Phylogeny of Parasitic Crustaceans

This review is devoted to the pelagic larvae of rhizocephalan crustaceans with a kentrogonid type of development (Thecostraca: Cirripedia: Rhizocephala). These barnacles have undergone such a significant reduction of adult stages connected with the parasitic lifestyle that only the presence of a nauplius larva in their development indicates that this unique group belongs to crustaceans. The main attention is paid to the morphological characters of the larvae that can be used in the taxonomy and phylogeny of Rhizocephala. The differences between the larvae of peltogastrid and sacculinid types are discussed. The sexual dimorphism of cyprids associated with different functions of male and female larvae is analyzed.

What the Ur-crustacean Looked Like

Crustaceans are a paraphyletic assemblage within arthropods. Hexapoda (insects) are nested within crustaceans, with the Remipedia the most likely sister group to Hexapoda. Together, crustaceans and hexapods comprise the monophyletic Tetraconata (also called Pancrustacea). Herein, we “reconstruct” the last common ancestor of crown group Tetraconata, calling it the ur-crustacean. We base our reconstruction on knowledge of extant crustaceans. We tentatively suggest that the ur-crustacean displayed certain characters: The ur-crustacean was a free-living marine species with a distinct head and equipped with two pairs of sensory limbs (antennule and antenna), mandibles, and two more pairs of mouthparts (maxillule and maxilla). We suggest that no further segments were fused to the head and that no maxilliped was present. The ur-crustacean may or may not have possessed a carapace. Its brain was complex, with an extended olfactory system, possibly a central complex, and a lateral protocerebrum containing at least two optical neuropils. The protocerebrum was connected to a nauplius eye as well as to compound eyes. The ur-crustacean might have had a uniformly segmented trunk posterior to its five-segmented head or (less probably) may have possessed two tagmata, a limb-bearing thorax and a limb-less abdomen. It had a heart that might have extended right through the trunk independently of tagmatization. Its thoracopodal appendages were true arthropodal (consisting of podomeres) with a protopod (probably subdivided into coxa and basis), an exopod, and an endopod. Larval development started with a nauplius larva (probably an orthonauplius).

Abundance of Zooplankton in Ramsagar-Dighi, Dinajpur, Bangladesh

The present study was carried out from May, 2011 to March, 2012 which deals with the abundance of zooplankton in Ramsagardighi, Dinajpur, Bangladesh. A total of 27 species of 21 genera were recorded in which rotifers were more abundant with 9 genera and 12species followed by copepods with 6 genera and 7 species and cladocerans with 5 genera and 7 species from the study area. A crustacean, nauplius larva was also recorded from the study area. Monthly fluctuation of some physico-chemical parameters was also noted.Bangladesh J. Zool. 43(2): 303-312, 2015

On the use of experimental diets for physiological studies of hydrozoans

Recent studies of hydrozoans suggest that metabolic factors associated with the physiology of gastrovascular fluid transport play a role in regulating morphogenetic development of colonies. In that context, the objective of this study was to develop a system to experimentally control diets of hydrozoans in culture that could be used to test effects of specific compounds. This diet delivery system consisted of a known concentration of homogenate of brine shrimp nauplii that was solidified in a 1% agar block cut to the size of, and containing the equivalent of, a single, 2-day old brine shrimp nauplius larva. We tested the utility of this system by comparing the frequencies of ingestion, and rates of gastrovascular transport and growth following feeding, between polyps of Podocoryna carnea fed either a single brine shrimp nauplius (controls) or an agar cube including brine shrimp homogenate. Polyps fed experimental diets showed similar rates of gastrovascular transport (6 and 12 h after feeding) and growth (24 h after feeding) to those of polyps fed a brine shrimp nauplius suggesting that no significant artefacts existed associated with these response variables. However, the frequency of ingestion of experimental foods by polyps was much less than that by control polyps. These results imply that this system of delivery of experimental diets has potential as a means to manipulate physiological state and assay the effects on morphogenesis of hydrozoan colonies, but must first overcome limitations of low ingestion frequency.

Cleavage and gastrulation in the shrimp Sicyonia ingentis: invagination is accompanied by oriented cell division

Embryos of the penaeoidean shrimp Sicyonia ingentis were examined at intervals during cleavage and gastrulation using antibodies to beta-tubulin and DNA and laser scanning confocal microscopy. Cleavage occurred in a regular pattern within four domains corresponding to the 4-cell-stage blastomeres and resulted in two interlocking bands of cells, each with similar spindle orientations, around a central blastocoel. Right-left asymmetry was evident at the 32-cell-stage, and mirror-image embryos occurred in a 50:50 ratio. Gastrulation was initiated by invagination into the blastocoel at the 62-cell-stage of two mesendoderm cells, which arrested at the 32-cell-stage. Further invagination and expansion of the archenteron during gastrulation was accompanied by rapid and oriented cell division. The archenteron was composed of presumptive naupliar mesoderm and the blastopore was located at the site of the future anus of the nauplius larva. In order to trace cell lineages and determine axial relationships, single 2- and 4-cell-stage blastomeres were microinjected with rhodamine-dextran. The results showed that the mesendoderm cells which initiated gastrulation were derived from the vegetal 2-cell-stage blastomere, which could be distinguished by its slightly larger size and the location of the polar bodies. The mesendoderm cells descended from a single vegetal blastomere of the 4-cell-stage. This investigation provides the first evidence for oriented cell division during gastrulation in a simple invertebrate system. Oriented cell division has previously been discounted as a potential morphogenetic force, and may be a common mechanism of invagination in embryos that begin gastrulation with a relatively small number of cells.

The Feeding Apparatus of the Barnacle Nauplius Larva: A Scanning Electron Microscope Study

INTRODUCTIONThe nauplius stages of many barnacle species have been described at the light microscope level (Bassindale, 1936; Knight-Jones & Waugh, 1949; Costlow & Bookhout, 1957; Karande, 1974), including those of the British barnacles Balanus balanoides (L.) andBalanus hameri (Ascanius) (Crisp, 1962a, b). Although these studies have included full descriptions of limb structure, it is not possible with the light microscope to resolve the topographical relationship of the limbs and other structures associated with feeding. Attempts to describe the feeding process of barnacle nauplii (Lochhead, 1936; Norris & Crisp, 1953; Gauld, 1959; Moyse & Knight-Jones, 1967) have necessarily been limited for this reason.