Morphology of the first zoeal stages of eleven Sesarmidae (Crustacea,Brachyura, Thoracotremata) from the Indo-West Pacific,with a summary of familial larval characters

Summary

The first zoeal stages of eleven species of Sesarmidae from the Indo-West Pacific were obtained from ovigerous females. Those of Labuanium scandens, L. rotundatum, L. trapezoideum, L. politum, Metasesarma aubryi, Pseudosesarma crassimanum, Stelgistra stormi, and Sesarmops impressum, are described for the first time, while the first zoeal stages of Clistocoeloma merguiense, Metasesarma obesum and Sesarmops intermedium are re-described. Larval characters of all these species are compared with previously described ones for the family and morphological features are re-evaluated. Minute spines on the telson of the zoeae are described as a new larval character in Sesarmidae and their presence or absence in other grapsoid groups is discussed. The results demonstrate that a recurrent combination of reliable larval characters distinguishes zoeae and megalopae of the examined sesarmids from the rest of the Grapsoidea. This appears to be consistent with recent studies that redefine the Sesarmidae.     

The zoeal development of Platymaia wyvillethomsoni Miers, 1886 (Crustacea: Decapoda: Majoidea: Inachidae) described from laboratory reared material

The spider crab Platymaia wyvillethomsoni was reared in the laboratory, from hatching to the megalopal stage at 20°C. The larval development comprises two zoeal stages and a megalopa. The zoeal stages are described for the first time and compared with those of the four known species of the family Inachidae from the northern Pacific. The zoeal characters (carapace spines, antenna, mouthpart appendages, pleon and telson fork) of P. wyvillethomsoni are significantly different from those of two Achaeus species from northern Pacific and other inachid genera (Inachus and Macropodia) from the Atlantic. Therefore, this species should not be placed in the family Inachidae based on zoeal morphology. A provisional key for the identification of known zoeae of the family from the northern Pacific is provided.     

Studies on the larval development of northeastern Atlantic and Mediterranean Procellanidae (Decapoda,Anomura). I — Redescription of the larval stages ofPorcellana platycheles (Pennant, 1777) reared under laboratory conditions

The complete larval development is described forPorcellana platycheles (Pennant) reared under laboratory conditions. The development consists of two zoeal stages and one megalopa. At 20°C and 35‰ salinity, the megalopa appeared 17–18 days after hatching. Survival was 56% from hatching to the megalopa stage. The morphological features of the zoeal and megalopa stages ofP. platycheles are compared with those of other species ofPorcellana, and a key of the known zoeal stages of the genus is given.     

The larval development of Petrolisthes politus (Gray, 1831) (Crustacea: Decapoda: Porcellanidae) under laboratory conditions

The complete larval development of the shallow-water Caribbean porcellanid crab, Petrolisthes politus (Gray, 1831), is described and illustrated from specimens reared in the laboratory. Petrolisthes politus hatches as a prezoea, which persist for less than 90 minutes, and then molts through two subsequent zoeal stages, which are completed in 6 to 7 and 14 to 16 days, respectively, before the megalopal stage is reached. From a total of about 2000 zoeae that were cultured, only two reached the megalopal stage. The two megalopae survived for up to 5 days but did not molt to the first crab stage. The zoeae of P. politus are compared with those of Petrolisthes rufescens (Heller, 1861), Petrolisthes lamarckii (Leach, 1820), Petrolisthes carinipes (Heller, 1861), Petrolisthes coccineus (Owen 1839) and Petrolisthes pubescens (Stimpson, 1858), which were hitherto the only species having bifid lateral spines on the telson of the first zoeal stage.     

Partitioning and utilization of energy during the larval development of the xanthid crab, Rhithropanopeus harrisii (Gould)

An energy budget is constructed for the larval development of the crab Rhithropanopeus harrisii (Gould) fed nauplii of the brine shrimp Artemia salina (L.). Between the first zoeal instar and the megalopa, there is a 5.4-fold increase in caloric consumption and a 13.2-fold increase in dry weight. Weight specific energy content increases through the zoeal stages and drops at the megalopa. Rate of oxygen consumption increases steadily throughout development. Assimilation, gross growth, and net growth efficiencies increase steadily through zoeal development and drop at the megalopa. Calories put into tissue production exceed those expended via respiration in zoeal stages II–IV; the reverse is true in zoeal stage I and the megalopa.

A total energy budget has been calculated and the partitioning of energy is discussed in relation to other physiological studies on this species.     

Occurrence of additional Zoea-VI larvae in the mud crab, Scylla paramamosain (Estampador), reared in the laboratory

Mud crabs, Scylla spp. , are commercially important in many Indo-Pacific countries. The larval development of mud crabs has been reported previously as five zoeal and one megalopal stages. This paper reports larval rearing experiments that revealed variability in larval developmental stages in the mud crab Scylla paramamosain, one of four mud crab species. In addition to normal five zoeal stages, an alternative pathway of developing through six zoeal stages was observed for the crab. There were evidences suggested that the appearance of the additional Zoea-VI larvae was associated with unfavourable dietary conditions, including poor quality of diet, inadequate quantity of dietary supply and a period of starvation for newly hatched larvae. Based on exuviae and larval specimens, the morphology of the additional Zoea-VI larvae was described.     

Hydrozoan and protozoan epibionts on two decapod species, Liocarcinus depurator (Linnaeus, 1758) and Pilumnus hirtellus (Linnaeus, 1761), from Scotland

Crabs of the species Liocarcinus depurator and Pilumnus hirtellus, collected on the west coast of Scotland, showed hydrozoan and protozoan epibionts. The epibionts of Liocarcinus depurator were the protozoan Ephelota plana and the hydrozoans Clytia gracilis and Leuckartiara sp. The epibionts of Pilumnus hirtellus were the protozoans E. plana and Zoothamnium sp. For Liocarcinus depurator the number of Ephelota per crab fluctuated between 0 and 47 and the greatest number of suctorians were located on the chelipeds, carapace and anterior pereiopods. The hydrozoans, for Liocarcinus depurator, showed densities of 0-20 (Clytia gracilis on the second pereiopod) and 0-507 individuals per crab (Leuckartiara sp., principally on chelipeds, carapace and the fourth right pereiopod). For Pilumnus hirtellus, Ephelota plana showed densities between 3 and 56 individuals per crab, the greatest number of suctorians being located on the same areas as on Liocarcinus depurator. There was a density of 10-69 individuals per crab of Zoothamnium sp. on Pilumnus hirtellus (located on the carapace). Ephelota plana has not been observed previously as an epibiont on crustacea, nor had Zoothamnium sp. as an epibiont on Pilumnus hirtellus. Both hydrozoans, Leukartiara and Clytia, have not been previously described as epibionts on Liocarcinus depurator. Data about the morphological characteristics and distribution of these epibionts are included.     

Larval development ofMacrophthalmus erato De Man, 1887 (Brachyura ocypodidae)

The zoeal and megalopal stage ofMacrophthalmus erato were obtained under laboratory conditions and are described and figured. Five zoeal and one megalopal stages were reared at 25; salinity and temperature of 29°C. Their features are compared with those of known species of the genus.     

Complete larval development of the hermit crabs Clibanarius aequabilis and Clibanarius erythropus (Decapoda: Anomura: Diogenidae), under laboratory conditions, with a revision of the larval features of genus Clibanarius

The complete larval development (four zoeae and one megalopa) of Clibanarius aequabilis and C. erythropus, reared under laboratory conditions, is described and illustrated. The larval stages of the two northeastern Atlantic Clibanarius species cannot be easily differentiated. Their morphological characters are compared with those of other known Clibanarius larvae. The genus Clibanarius is very homogeneous with respect to larval characters. All Clibanarius zoeae display a broad and blunt rostrum, smooth abdominal segments and an antennal scale without a terminal spine. Beyond the second zoeal stage, the fourth telson process is present as a fused spine, and the uropods are biramous. In the fourth larval stage all species display a mandibular palp. The Clibanarius megalopa presents weakly developed or no ocular scales, symmetrical chelipeds, apically curved corneous dactylus in the second and third pereiopods, and 5–11 setae on the posterior margin of the telson. Apart from the number of zoeal stages, Clibanarius species may be separated, beyond the second zoeal stage, by the telson formula and the morphology of the fourth telson process.     

Morphology of the reflecting superposition eyes of larval oplophorid shrimps

The eyes of larval and juvenile oplophorid shrimps are described for the first time. Variations in eye development occur depending on whether the zoeal stages are lecithotrophic or planktotrophic. In those genera where the first free-living stage is planktonic, the eyes are of the transparent apposition type seen in other decapod zoeas. However, where the eggs hatch after completion of the lecithotrophic zoeal stages, the eyes are laready developing the superposition optics found in the adult. In Oplophorus spinosus the changeover from hexagonal to square facets, indicative of superposition optics, proceeds from anterior to posterior. In Systellaspis debilis the square facets appear first on the lateral face of the eye. Eventually, in both species, only the most dorsal ommatidia retain apposition optics. © 1995 Wiley-Liss, Inc.     

The complete larval development of Panopeus lacustris Desbonne 1867 (Brachyura: Panopeidae), from the Amazon region,reared in the laboratory

Larvae of the mud crab Panopeus lacustris were reared in laboratory from ovigerous females collected in the estuarine area of the Caeté River in the Amazonian region. The complete development of this species consisted of four zoeal and one megalopal stages, which were described and illustrated in detail. The results are compared with those of other previous studies on larval development of the species belonging to the genus Panopeus and then briefly discussed.     

Development and metamorphosis of the feeding apparatus of the stone crab,Menippe mercenaria (brachyura,xanthidae)

Analysis of the feeding apparatus of the stone crab, Menippe mercenaria (Brachyura, Xanthidae), has demonstrated that substantial internal and external morphological alterations occur at metamorphosis and suggests that the mastication of food shifts from the mandibles to the gastric mill at that time. These changes correspond to the changes in environment and diet that take place at metamorphosis, when the previously planktotrophic larvae begin benthic life. A detailed account of the structure and development of the mandibles is presented. The mandibles of all zoeal stages are similar: The incisor process has a series of teeth and denticles and the prominent molar process appears to be well adapted for grinding food. Megalopal mandibles are transitional but have the form that is typical of all subsequent stages: The expanded incisor process is rounded and toothless and the molar process is less prominent and has lost its grinding denticles. The cardiac stomach of the zoeal stages has no gastric mill; the medial and lateral teeth of the mill first appear in the megalopa. A very simple procedure is described for preparing larval mandibles for scanning electron microscopy using the molted exoskeletons from larval rearing experiments.