Additional Molts Research Articles

Biological Studies on the Cotton Mealybug Phenacoccus solenopsis Tinsley, (Hemiptera: Pseudococcidae) under the Laboratory Condition

The cotton mealybug Phenacoccus solenopsis Tinsley (1989) (Hemiptera: Pseudococcidae) is one of the invasive species recently introduced to Egypt and nowadays it is wide spread among various parts of the country. The aim of this study shed light on certain biological aspects of the cotton mealybug and the effect of three host plant species i.e. (“potato”, “tomato” and “cotton”) as food source on certain biological aspects under the laboratory conditions. The results showed that the female and male of the cotton mealybug are not equal in numbers of moulting and nymphal duration. The life cycle of cotton mealybug was greater for males compared to females may be due to the additional moult and the pupal stage in the male, and it was significantly affected by different host plants, the females lasted 24.2±2.7, 22.1±3.1 and 20.0±2.7 days on potato, tomato and cotton plants leaves, respectively, while the males life cycle lasted 25.2±2.6, 22.9±3.1 and 21.4±2.9 days on potato, tomato and cotton plants leaves, respectively. Adult females lived longer than males, the female longevity lasted 31.2±2.5, 26.8±3.6 and 23.1±3.2 days on potato, tomato and cotton plants leaves, respectively, while males lived 3.1±1.3, 2.1±0.9 and 2.0±1.0 days on potato, tomato and cotton plants leaves, respectively. The cotton mealybug fecundity was significantly affected by different host plants; the females laid 163.3±48.5, 212.8±55.1 and 265.8±57.7 Eggs/female when adults reared on potato, tomato and cotton plants leaves, respectively. Sex ratio between females and males of P. solenopsis reared on potato, tomato and cotton plants leaves are not affected by the host plant. From the motioned results, it could be concluded that the cotton mealybug, P. solenopsis preferred cotton plant than the other two host plants. Key words: Cotton mealybug, Phenacoccus solenopsis, biological studies, Egypt.

First description of epimorphic development in Antarctic Pallenopsidae (Arthropoda, Pycnogonida) with insights into the evolution of the four-articled sea spider cheliphore

BackgroundSea spiders (Pycnogonida) are an abundant faunal element of the Southern Ocean (SO). Several recent phylogeographical studies focused on the remarkably diverse SO pycnogonid fauna, resulting in the identification of new species in previously ill-defined species complexes, insights into their genetic population substructures, and hypotheses on glacial refugia and recolonization events after the last ice age. However, knowledge on the life history of many SO pycnogonids is fragmentary, and early ontogenetic stages often remain poorly documented. This impedes assessing the impact of different developmental pathways on pycnogonid dispersal and distributions and also hinders pycnogonid-wide comparison of developmental features from a phylogenetic-evolutionary angle.ResultsUsing scanning electron microscopy (SEM) and fluorescent nuclear staining, we studied embryonic stages and postembryonic instars of three SO representatives of the taxon Pallenopsidae (Pallenopsis villosa, P. hodgsoni, P. vanhoeffeni), the development of which being largely unknown. The eggs are large and yolk-rich, and the hatching stage is an advanced lecithotrophic instar that stays attached to the father for additional molts. The first free-living instar is deduced to possess at least three functional walking leg pairs. Despite gross morphological similarities between the congeners, each instar can be reliably assigned to a species based on body size, shape of ocular tubercle and proboscis, structure of the attachment gland processes, and seta patterns on cheliphore and walking legs.ConclusionsWe encourage combination of SEM with fluorescent markers in developmental studies on ethanol-preserved and/or long term-stored pycnogonid material, as this reveals internal differentiation processes in addition to external morphology. Using this approach, we describe the first known cases of pallenopsid development with epimorphic tendencies, which stand in contrast to the small hatching larvae in other Pallenopsidae. Evaluation against current phylogenetic hypotheses indicates multiple gains of epimorphic development within Pycnogonida. Further, we suggest that the type of development may impact pycnogonid distribution ranges, since free-living larvae potentially have a better dispersal capability than lecithotrophic attaching instars. Finally, we discuss the bearing of pycnogonid cheliphore development on the evolution of the raptorial first limb pair in Chelicerata and support a multi-articled adult limb as the plesiomorphic state of the chelicerate crown group, arising ontogenetically via postembryonic segmentation of a three-articled embryonic limb.

Carapace ontogeny of the bromeliad dwelling ostracod Elpidium bromeliarum Müller, 1880 (Crustacea: Ostracoda)

ABSTRACTOstracods have discontinuous development, marked by ecdyses, and determinate growth. Ontogenetic studies have suggested a pattern of nine postembryonic stages (eight juvenile phases and the adult) for the main freshwater ostracod superfamilies Cypridoidea, Cytheroidea and Darwinuloidea. However, cases of a supposed extra moult in the adult stage have been proposed for some ostracod species, which would amount to 10 postembryonic growth stages. One such example is Elpidium bromeliarum Müller, 1880, a cytheroidean that inhabits tank-bromeliads. The present study is aimed at investigating the ontogenetic development of E. bromeliarum using width and length measurements, as well as carapace and appendage morphology in order to test the existing hypothesis of an additional growth stage in adults of this species. Our results revealed nine postembryonic growth stages (eight juvenile and the adult), with sexual dimorphism beginning its expression in the last juvenile stage. Thus, the ontogenetic development of E. bromeliarum agrees with the overall pattern observed for podocopid ostracods and the hypothesis of 10 postembryonic growth stages was not corroborated. We argue that the inability to differentiate juveniles from adults, or different species from one another, may have misled to the assumption of an additional moult in E. bromeliarum.

Role of accelerated developmental pathway and limited nurturing capacity on soldier developmental instability in subterranean termite incipient colonies

In the subterranean termite Coptotermes gestroi (Wasmann), soldiers developing in incipient colonies display strong fluctuating asymmetry when compared with soldiers developing in mature colonies. This strong asymmetry may arise from two different types of stress factors on individuals. First, the accelerated development of nanitic (small) soldiers may impose a direct physiological stress as Coptotermes soldiers produced in incipient colonies have two less molting events than soldiers produced in mature colonies. Second, the environmental conditions in incipient colonies present a major constraint with limited access to resources and small numbers of workers to care for the developing brood. In this study, 459 soldiers from 73 incipient colonies (6-month-old) displaying only nanitic soldiers were investigated in a range of nurturing capacity scenarios. Nanitic soldiers developing in incipient colonies with high nurturing capacity displayed more symmetrical traits than the ones developing in colonies with low nurturing capacity. In addition, the first soldiers to emerge in the colony were the most asymmetrical individuals, showing that as the conditions improve rapidly with the growth of the colony, newly produced nanitic soldiers manifest the lessening of stress in normalization of their morphology. However, the nurturing capacity of the colony only partially explained the developmental instability variability, implying that the accelerated development of nanitic soldiers remains an important stress factor in incipient colonies, in comparison with soldiers developing in mature colonies with two additional molts and homeostatic environmental conditions.

Growth and Enzyme Production in Blue Crabs (Callinectes sapidus) Fed Cellulose and Chitin Supplemented Diets

The blue crab [Callinectes sapidus (Rathbun, 1896)] is a benthic decapod with a varied diet. The diet includes invertebrates and detrital material that can have relatively large amounts of chitin and cellulose, both of which can be difficult to digest for many organisms and often require the aid of specific bacteria in the gut microbiome. In this study, juvenile blue crabs were fed an optimized defined pelleted diet with a 20% replacement of wheat flour filler with either chitin, cellulose, or a 14%/6% mix of both, followed by a diet switch to the opposing ingredient. Crabs had increasing growth performance with increasing amounts of cellulose in the diet versus chitin and had an additional molt in most cases. This occurred during the initial phase and following the switch, indicating that performance can be recovered. Subsequently, cellulose and chitin digestion assays were used to show that the foregut, midgut, and hindgut were all able to significantly digest more cellulose than chitin with the majority of activity in the foregut and midgut. Implications for rearing and diet formulations as well as the role of cellulose and chitin digestion in the natural diet are discussed.

High and Low Throughput Screens with Root-knot Nematodes <em>Meloidogyne spp.</em>

Root-knot nematodes (genus Meloidogyne) are obligate plant parasites. They are extremely polyphagous and considered one of the most economically important plant parasitic nematodes. The microscopic second-stage juvenile (J2), molted once in the egg, is the infective stage. The J2s hatch from the eggs, move freely in the soil within a film of water, and locate root tips of suitable plant species. After penetrating the plant root, they migrate towards the vascular cylinder where they establish a feeding site and initiate feeding using their stylets. The multicellular feeding site is comprised of several enlarged multinuclear cells called 'giant cells' which are formed from cells that underwent karyokinesis (repeated mitosis) without cytokinesis. Neighboring pericycle cells divide and enlarge in size giving rise to a typical gall or root knot, the characteristic symptom of root-knot nematode infection. Once feeding is initiated, J2s become sedentary and undergo three additional molts to become adults. The adult female lays 150-250 eggs in a gelatinous matrix on or below the surface of the root. From the eggs new infective J2s hatch and start a new cycle. The root-knot nematode life cycle is completed in 4-6 weeks at 26-28°C. Here we present the traditional protocol to infect plants, grown in pots, with root-knot nematodes and two methods for high-throughput assays. The first high-throughput method is used for plants with small seeds such as tomato while the second is for plants with large seeds such as cowpea and common bean. Large seeds support extended seedling growth with minimal nutrient supplement. The first high throughput assay utilizes seedlings grown in sand in trays while in the second assay plants are grown in pouches in the absence of soil. The seedling growth pouch is made of a 15.5 x 12.5cm paper wick, folded at the top to form a 2-cm-deep trough in which the seed or seedling is placed. The paper wick is contained inside a transparent plastic pouch. These growth pouches allow direct observation of nematode infection symptoms, galling of roots and egg mass production, under the surface of a transparent pouch. Both methods allow the use of the screened plants, after phenotyping, for crossing or seed production. An additional advantage of the use of growth pouches is the small space requirement because pouches are stored in plastic hanging folders arranged in racks.

High and Low Throughput Screens with Root-knot Nematodes <em>Meloidogyne spp.</em>

Root-knot nematodes (genus Meloidogyne) are obligate plant parasites. They are extremely polyphagous and considered one of the most economically important plant parasitic nematodes. The microscopic second-stage juvenile (J2), molted once in the egg, is the infective stage. The J2s hatch from the eggs, move freely in the soil within a film of water, and locate root tips of suitable plant species. After penetrating the plant root, they migrate towards the vascular cylinder where they establish a feeding site and initiate feeding using their stylets. The multicellular feeding site is comprised of several enlarged multinuclear cells called 'giant cells' which are formed from cells that underwent karyokinesis (repeated mitosis) without cytokinesis. Neighboring pericycle cells divide and enlarge in size giving rise to a typical gall or root knot, the characteristic symptom of root-knot nematode infection. Once feeding is initiated, J2s become sedentary and undergo three additional molts to become adults. The adult female lays 150-250 eggs in a gelatinous matrix on or below the surface of the root. From the eggs new infective J2s hatch and start a new cycle. The root-knot nematode life cycle is completed in 4-6 weeks at 26-28°C. Here we present the traditional protocol to infect plants, grown in pots, with root-knot nematodes and two methods for high-throughput assays. The first high-throughput method is used for plants with small seeds such as tomato while the second is for plants with large seeds such as cowpea and common bean. Large seeds support extended seedling growth with minimal nutrient supplement. The first high throughput assay utilizes seedlings grown in sand in trays while in the second assay plants are grown in pouches in the absence of soil. The seedling growth pouch is made of a 15.5 x 12.5cm paper wick, folded at the top to form a 2-cm-deep trough in which the seed or seedling is placed. The paper wick is contained inside a transparent plastic pouch. These growth pouches allow direct observation of nematode infection symptoms, galling of roots and egg mass production, under the surface of a transparent pouch. Both methods allow the use of the screened plants, after phenotyping, for crossing or seed production. An additional advantage of the use of growth pouches is the small space requirement because pouches are stored in plastic hanging folders arranged in racks.

Additional moults into ‘elongatus’ males in laboratory-reared Polydesmus angustus Latzel, 1884 (Diplopoda, Polydesmida, Polydesmidae) – implications for taxonomy

The number of stadia during post-embryonic development is supposed to be fixed in most species of the millipede order Polydesmida. For the first time since 1928, additional moults were observed in two males of Polydesmus angustus Latzel, 1884 reared in the laboratory. These ‘elongatus’ males sensu Verhoeff reached stadium IX instead of stadium VIII, with addition of a further podous ring (32 pairs of legs). One male had well-developed gonopods at stadium VIII, which regressed at stadium IX; the other had no gonopods at stadium VIII, which developed at stadium IX. The two cases correspond to the ‘regressionis’ and ‘progressionis’ forms described by Verhoeff in Polydesmus complanatus (Linnaeus, 1761), which confirms entirely his results. Additional moults appear to be associated with small body sizes and possible underlying mechanisms are discussed. Comparisons between millipede orders indicate that post-embryonic development is less strictly canalized in Polydesmida than in Chordeumatida. This implies that the adult number of body rings is of limited taxonomic value in Polydesmida and should not be viewed as a character of generic importance.

Two new species and taxonomic notes on the Neotropical spiny orb-weaving spi-ders Micrathena and Chaetacis (Araneae: Araneidae), with remarks on the development of Micrathena excavata IVAN L. F. MAGALHÃES & ADALBERTO J. SANTOS (Brazil)

In this paper, M. yanomami n. sp., from Brazilian Amazonia, Chaetacis bandeirante n. sp., from Central Brazil, and the males of M. gaujoni Simon, 1897 and M. ruschii (Mello-Leitão, 1945) n. comb. , respectively from Ecuador and Brazil, are described and illustrated for the first time. An ontogenetic series of the last development stages of both sexes of Micrathena excavata (C. L. Koch, 1836) is illustrated and briefly described. Adult females are larger and have longer legs and larger abdomens than adult males. Probably females undergo at least one additional moult before adulthood, compared to males. Micrathena ornata Mello-Leitão, 1932 is considered a junior synonym of M. plana (C. L. Koch, 1836), and M. mastonota Mello-Leitão 1940 is synonymized with M. horrida (Taczanowski, 1873). Acrosoma ruschii Mello-Leitão, 1945 is revalidated, transferred to Micrathena and considered a senior synonym of M. cicuta Gonzaga & Santos, 2004. Chaetacis necopinata (Chickering, 1960) is recorded for Brazil for the first time. Chaetacis incisa (Walckenaer, 1841) is considered a nomen dubium.

Control of larval–pupal-adult molt in the moth Sesamia nonagrioides by juvenile hormone and ecdysteroids

Sesamia nonagrioides (Lepidoptera: Noctuidae) larvae reared under long day (LD; 16L:8D) conditions pupate after 5 or 6 larval instars, whereas under short day (SD; 12L:12D) conditions they undergo up to 12 additional molts before pupating. This extended period of repeated molting is maintained by high levels of juvenile hormone (JH). Previous work demonstrated that both LD and SD larvae decapitated in the 6th instar pupate but further development is halted. By contrast, about one-third of SD larvae from which only the brain has been removed, undergo first a larval molt, then pupate and subsequently developed to the adult stage. Debrained LD larvae molt to larvae exceptionally but regularly pupate and produce adults. Implanted brains may induce several larval molts in debrained recipient larvae irrespectively of the photoperiodic conditions. The results of present work demonstrate that the prothoracic glands (PGs) and the corpora allata (CA) of debrained larvae continue to produce ecdysteroids and JHs, respectively. PGs are active also in the decapitated larvae that lack JH, consistent with the paradigm that CA, which are absent in the decapitated larvae, are the only source of this hormone. Completion of the pupal-adult transformation in both LD and SD debrained insects demonstrates that brain is not crucial for the development of S. nonagrioides but is required for diapause maintenance. Application of JH to headless pupae induces molting, presumably by activating their PGs. It is likely that JH plays this role also in the induction of pupal-adult transformation in debrained insects. Application of the ecdysteroid agonist RH 2485 (methoxyfenozide) to headless pupae also elicits molting: newly secreted cuticle is in some cases thin and indifferent, in other cases it bears distinct pupal or adult features.

Characterization of an additional molt inhibiting hormone-like neuropeptide from the shrimp Metapenaeus ensis

We have identified a second form of the type-II neuropeptide encoding a molt inhibiting hormone-like (MeeMIH-B) neuropeptide. MeeMIH-B showed only a 70% amino acid identity to the MIH-A (formerly MIH) isolated from the same species, suggesting a possible different function of the deduced neuropeptide. Like other neuropeptide members of the CHH family, the MIH-B gene consists of three exons separated by two introns. The levels of MIH-B mRNA transcript in the eyestalk decrease in the initial phase of gonad maturation and increase towards the end of maturation. The drop in MIH-B level suggests an inhibitory role for this neuropeptide in the initiation of vitellogenesis. MIH-B transcripts can also be detected in the brain, thoracic ganglion and ventral nerve cord. Together with the CHH-B peptide that we have previously described, this is the second peptide of the CHH family that can also be identified in the ventral nerve cord and in the XOSG complex. A recombinant MIH-B was produced and a polyclonal antibody against rMIH-B was subsequently generated. Specific anti-rMIH-B antiserum recognized the presence of MIH-B in the sinus gland, X-organs, as well as a giant neuron of the ventral nerve cord. Injection of rMIH-B delayed the molting cycle of the maturing female. Taken together, the results of this study suggest that a drop in MIH-B level may be required for the delay in the molting of the maturing females.

POST-MATURATION MOLT FOUND IN A WOLF SPIDER, PARDOSA ASTRIGERA (ARANEAE, LYCOSIDAE)

Abstract An adult female Pardosa astrigera (Araneae, Lycosidae) died failing to finish an additional molt in the laboratory. Its maturity was morphologically ascertained by SEM examination.

Ecological correlates in the evolution of moult strategies in Western Palearctic passerines

Moult is an important process in the life cycle of birds. Passerines differ widely in the number, seasonality and extension of moult episodes, but the incidence of birds ecology on this variation remains largely uninvestigated. We analysed the patterns of moult in European passerines in relation to their distribution, migration and sexual dichromatism. Longer migrations and southern wintering quarters were characteristic of species with complete moults in summer and an additional moult in winter. The main moult in species with larger seasonal changes in sexual dimorphism tended to be scheduled just before the start of the breeding season, suggesting a link between sexual selection and the timing of moult. These patterns strongly support the importance of migration and dichromatism on the evolution of moult strategies.

Photoperiodic control of larval diapause in the yellow‐spotted longicorn beetle, Psacothea hilaris: analysis by photoperiod manipulation

AbstractThe photoperiodic control of diapause induction in the larvae of the yellow‐spotted longicorn beetle, Psacothea hilaris (Pascoe), was investigated using a west Japan‐type population collected from Ino, Kochi Prefecture, Japan. In this population, the larvae expressed a long‐day photoperiodic response with a critical daylength between 13.5 and 14 h at 25 °C; under a long daylength, the larvae pupated after the 4th or 5th instar, while the larvae entered diapause under a short daylength after 2.3 additional molts on average. When the photoperiod was changed from a short (L12:D12) to a long (L15:D9) daylength, pupation occurred in most of the individuals irrespective of the time of the change. When the photoperiod was changed from long to short at 1 or 2 weeks after hatching, all of the larvae entered diapause, whereas when the photoperiod was changed at 5 weeks after hatching or later, most of the larvae pupated. The 2 weeks exposures to a long daylength against a ‘background’ of a short daylength at various times revealed that the larvae of this insect are most sensitive to the photoperiod from 4 to 6 weeks after hatching.

Effects of Short- and Long-Day Photoperiods on Growth and Development of Sesamia nonagrioides (Lepidoptera: Noctuidae)

The effects of 2 photoperiods, a diapause-inducing (10:14 [L:D] h) and a nondiapause inducing one (16:8 [L:D] h) at 25°C on the growth and development of larvae of the corn stalk borer, Sesamia nonagrioides , were investigated. Under a long-day photoperiod, larvae completed their development and pupated after 6 molts, whereas under a diapauseinducing short-day photoperiod, several additional molts and considerable delay of pupation were recorded. Duration of 1st to 5th instars was about the same in diapause and nondiapause destined insects, but the duration of the 6th instar was significantly longer in diapause larvae. Similarly, head capsule widths of the larvae were about the same under both photoperiods until the 5th instar. The head capsule width of all instars, under both photoperiods, is described by the logistic model. Dyar's rule, implying a geometric model, was not found appropriate for our data. Larval weights were greater under long-day photoperiod up to 5th instar, but the reverse was true for 6th instar. Only 36% of the initial number of larvae reached pupation under short-day photoperiod, whereas 74% reached pupation under long-day photoperiod. Larval mortality gradually increased, for ≈ about 150 d under short-day photoperiod, whereas under long-day photoperiod, larval mortality occurred mainly during the first few days. Mean pupal weights for diapause and nondiapause insects were 202.8 mg and 168.1 mg, respectively. Under both photoperiods, female larvae tended to pupate later and the pupae were heavier.

Starvation Effects on the Endocrine Control of Metamorphosis in the Small Wax Moth, Galleria mellonella

Effects of starvation on late larval development was studied in Galleria mellonella (Linnaeus 1758). 48 h of feeding is required by the last instar larva (L 7 ) to induce pupation. Starvation of day-1 L 7 followed by refeeding delayed metamorphosis and resulted in occasional appearance of supernumerary larval moults or permanent larvae. When applied to chilled or hydroprene treated larvae, additional moults were merely delayed. Starvation to prior such treatments extended the period of sensitivity to both of them. Starvation of day-1 larvae resulted in an increased titre of juvenile hormone, refeeding in a decrease. Possible causal relationships with brain allatotropic activity and juvenile hormone degradation by specific esterases were evidenced and discussed.

Regeneration and molting effects on a proprioceptor organ in the Dungeness crab, Cancer magister.

Decapoda Crustacea molt in order to grow; some species, such as the Dungeness crab Cancer magister, achieve a very large size. Does sensory neuron hyperplasia in internal proprioceptors accompany this growth? To determine this, neurons in propodite-dactylopodite (PD) chordotonal organs were counted in first walking legs of juvenile (5th through 9th instar) and adult (10th through 13th instar) C. magister. We found that the PD organs of J5 crabs have about 56 neurons; the number increases to about 61 neurons in J6 crabs. Significant hyperplasia now occurs because an average of 79 neurons are found in the PD organs of J7 crabs. Little to no hyperplasia accompanies the several succeeding juvenile and adult molts (ca. 82-86 neurons are present). Because autotomized limbs are regenerated upon molting, we also examined how the number of PD organ neurons in regenerated legs compares with those of pristine legs. Newly regenerated legs (termed 1st stage regenerates) have fewer sensory neurons than do their contralateral pristine partners (65 vs 81); larger regenerated legs which have attained nearly normal size as a result of additional molts (2nd stage regenerates) still have fewer neurons than their pristine partners (69 vs 81). Additionally, in contrast to those of pristine walking legs, the elastic strand of PD organs from 1st stage regenerates in a misshapen sheet containing a cluster of small neurons with no obvious functional organization. Nonetheless, neurophysiological recordings indicate that all the receptor types typical for pristine legs (movement and position cells) are represented. The PD organs of 2nd stage regenerates differentiate to the shape and neuronal organization of pristine legs.

Laboratory studies on the larval growth and development of Nyctiphanes capensis (Euphausiacea)

Larvae of Nyctiphanes capensis Hansen were reared in the laboratory under different trophic conditions (i.e., algal, animal and mixed diets) from the second calyptopis stage to the first juvenile stage. It is demonstrated that diet is important in determining growth rates and development of the larvae. The highest growth rates were achieved on diets of Artemia nauplii mixed with either the flagellate Tetraselmis or Pseudodiaptomus nauplii. Poorer dietary conditions such as with the diatom Phaeodactylum yielded slower growth rates where additional moults were needed to complete furcilia development. Under favourable trophic conditions the intermoult period was 4–6 days and was not age dependent. Three dominant pathways of pleopod development were found in healthy individuals.

POSTMARSUPIAL DEVELOPMENT AND GROWTH OF PAGURAPSEUDES LARGOENSIS MCSWEENY (CRUSTACEA, TANAIDACEA)

Postmarsupial development of the gastropod shell-inhabiting tanaidacean Pagurapseudes largoensis McSweeny is described and compared with that of Heterotanais oerstedii (Kr0yer) and Neotanais micromopher Gardiner. This is the first such study of an apseudomorphan based on experimentally reared animals. P. largoensis is gonochoristic; two manca instars are typical of all tanaidaceans so far investigated. In females, the mancas are followed by two or possibly three juvenile instars (=neutra), one or two preparatory instars characterized by rudimentary oostegites, and a copulatory stage with complete marsupium. Laboratory maintained animals pass through up to three copulatory stages, each separated by a preparatory stage of one or two instars. A preparatory instar, characterized by very small rudimentary oostegites often restricted to thoracopods VI, sometimes occurs between the juvenile and normal preparatory stages. The small number of such field-collected specimens suggests that it is an abnormality. Males develop either directly from the manca 2 instar or from the first juvenile instar. Pleopods and heterochelae either accompany initial appearance of genital cones or appear after one or two additional molts. Males retain a full set of mouthparts, feed, and molt throughout their lives. Variability in the pattern of instar succession may be construed as a primitive trait and supports the position of the Apseudomorpha as least derived of the three tanaidacean suborders. Males alone are heterochelous; the right chela is always major and its growth is allometric with respect to carapace length. Intermolt period increases with age, from a 2-week mean for mancas 1 to about 4 weeks for preparatory and copulatory females and 7 weeks for large males, although minimum intermolt periods are similar for all stages (11-29 days). Longevity is estimated at up to 15 months for males and 9 months for females. The sex ratio for field-collected specimens is about 1:1. Females bear 4-17 offspring per marsupium. Investigations into the development of the Tanaidacea have treated a very small percentage of the several hundred known species. Most are reconstructions of life histories based on preserved material. Biickle-Ramirez' (1965) experimental rearing of the tanaidomorph Heterotanais oerstedii (Kroyer) is the only detailed work based on live animals. The current investigation represents the first study of postmarsupial development of a member of the suborder Apseudomorpha to be based on live animals as well as preserved material. Pagurapseudes largoensis McSweeny, 1982, belongs to the family Pagurapseudidae Lang, 1970 (see also Gutu, 1972) and occupies vacant gastropod shells as do hermit crabs. It dwells in a variety of shallow, inshore, bottom communities in the Florida Keys but appears to prefer carpets of algae dominated by the red alga Laurencia poitei (Lamouroux) that occur in beds of turtle grass (Thalassia testudinum Konig). It is also frequently found clinging to the undersides of tussocks of the calcareous red alga Jania rubens (Linnaeus) and to bases of colonies of the inshore finger coral Porites divaricata Lesueur, both of which are found in Thalassia beds (Messing, 1979). This tanaidacean has both advantages and disadvantages as an experimental animal. It does not swim and can be kept in open dishes without becoming inextricably and fatally caught in the surface tension, a problem with tanaidaceans that can swim. It appears to be an unspecialized detritivore and is easily maintained in the laboratory. On the other hand, it occupies opaque or, at best, translucent shells that do not permit monitoring of ovarian maturation, egg deposition,

Ultrastructure of the envelopes of resistant and nonresistant Daphnia eggs

During early development, the nonresistant egg of Daphnia had an outer wall of [Formula: see text], and an inner wall approximately the thickness of the plasma membrane. In the same genus at a comparable developmental stage, resistant eggs were surrounded by a three-layered envelope, [Formula: see text] thick. Although the outer layer [Formula: see text] of the latter appeared similar to the outer wall of the nonresistant egg, the middle layer [Formula: see text] resembled the crustacean procuticle. The outer layer developed before the formation of the middle component, and both structures were absent after development resumed. This suggests that the resistant egg envelope is characterized by an additional embryonic cuticle and molt.