Morphological features of the larvae of spider crab <Emphasis Type="Italic">Pugettia quadridens</Emphasis> (Decapoda: Majidae) from the Northwestern Sea of Japan

The entire cycle of larval development of the spider crab Pugettia quadridens (de Haan, 1850) (Decapoda: Majidae), widespread in Peter the Great Bay (Sea of Japan) is studied under the laboratory conditions. The development cycle of this species comprises prezoea, zoea I, zoea II, and megalopa. At a temperature of 18–20° C larval development took from 11 to 15 days. Zoea II is described in detail for the first time. Many morphological characters are found distinguishing zoea and megalopa of P. Quadridens in Russian waters from the larvae of this species in Japanese and Korean waters. Some characters of larvae are similar in P. Quadridens and the related species of the genus Pugettia. The larvae of P. Quadridens occur in the plankton of Vostok Bay from late June to late October with a density up to 5 ind/m³ at a surface water temperature of 13–21°C. They are easily distinguished from the other brachyuran larvae of this region by the absence of lateral spines on the carapace.Original Russian Text Copyright © 2004 by Biologiya Morya, Kornienko, Korn.     

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.     

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.     

Differential susceptibility of marine invertebrate larvae: Laboratory predation of sand dollar, Dendrasterexcentricus (Eschscholtz), embryos and larvae by zoeae of the red crab, Cancer productus Randall

Predation on eggs, embryos, and larvae of the sand dollar, Dendraster excentricus (Eschscholtz) was investigated in a series of laboratory feeding experiments. Dendraster susceptibility to predation by zoea larvae of the red crab, Cancer productus Randall was strongly dependent on developmental stage and ontogenetic differences in motility. Clearance rates by C. productus were highest for eggs and averaged 0.551·zoea⁻¹·day⁻¹. Embryos and prism larvae of Dendraster were consumed at an intermediate rate, while pluteus larvae were captured at a relatively low rate. Clearance rates decreased from 0.18 to 0.031·zoea⁻¹·day⁻¹ during the transition of prism larvae into echinoplutei. Differences in Dendraster susceptibility to predation cannot be attributed to increasing prey body size because dwarf plutei were captured at the same rate as normal plutei. Reduced capture rates by Cancer productus zoeae are dependent on the development of Dendraster swimming behavior. Periodic reversals in the direction of ciliary beating and backwards swimming effectively remove Dendraster plutei from the immediate capture sphere of Cancer productus. Reversed swimming appears to function as a post-contact encounter response that reduces the mortality rates of Dendraster plutei.     

Two New Species of Zeugmatothrips Priesner, 1925 (Thysanoptera: Phlaeothripidae: Idolothripinae) from Costa Rica with a Key to the Species

Two new species of Zeugmatothrips are described from Costa Rica. The species Z. verae n. sp. can be distinguished by the wide abdominal segments II–V and body length. On the other hand, Z. gerardoi n. sp. is characteristic by the length of the mid-dorsal setae on the head and the seta on antennal segment V. The key of Mound & Palmer modified for eighteen species is presented.     

Development of the sand dollar <Emphasis Type="Italic">Scaphechinus mirabilis</Emphasis>

Under laboratory conditions, the development of larvae of the sand dollar Scaphechinus mirabilis (Agassiz) took 28.5–29 days from fertilization to settling and the end of metamorphosis at a temperature 20°C and salinity 32.2–32.6‰ The cleavage divisions were completed in 12 hours after fertilization (AF) by the release of free swimming ciliary blastula from the egg membrane. The larvae attained pluteus I stage with one pair of arms at an age of 40 hours. In 4.5–5 days the pluteus II stage with three pairs of arms, and in 9 days the pluteus III stage with four pairs of arms were formed. On the 20–21st day AF the larvae developed a vestibule, in which the adult skeleton rudiments, spicules, plates and pedicellariae were formed on the 26–27th day AF. The size of the larvae at an age of 22.5 days was 1064.3 ± 44.7 μm. The settling of larvae was recorded on the 28–29th day of development. Most of the larvae completed their metamorphosis in 4.5–5 hours after settling.     

Habitat selection by grayling-II. Preliminary results on larval and juvenile daytime habitats

Larval grayling were found along the shoreline at velocities <20 cm s^-1 depths <40 cm, shear stress <2 dyn m^-2 and over sand and silt. Juveniles were found in the river channel at currents of 20-40 cm s^-1 depths of 40-60 cm and shear stresses of 2-4 dyn m^-2, over gravel and pebbles.