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1. We investigated optokinetic eye movements in 3 species of stomatopod crustaceans (Odontodactylus scyllarus, Pseudosquilla ciliata, and Gonodactylus oer stedii), all of which are members of the superfamily Gonodactyloidea, by making video recordings of their behavior when placed at the center of a rotating striped drum. Results from these species were sufficiently similar to permit a general description of optokinesis in gono dactyloid stomatopods. 2. Within the range of drum speeds tested (0.40 to 33.6° s-1), the eyes frequently moved smoothly in the direction of the drum's rotation. The movements of the 2 eyes were only weakly coordinated, and optokinesis occurred with an irregular and intermittent time course. 3. Closed-loop gains varied with the drum's speed of rotation, ranging from 0.4 to near 1.0. The gain did not depend on the orientation of the eye in space, remaining relatively constant as the eye swung on its point of at tachment to the anterior end of the animal or rotated on the eyestalk axis. 4. In O. scyllarus (the only species tested), optokinetic eye movements in the animal's vertical, dorsoventral plane occurred with characteristics similar to those in the horizontal plane.

Summary. Odontodactylus scyllarus makes discrete spontaneous eye-movements at a maximum rate of 3/s. These movements are unpredictable in direction and timing, and there is no detectable co-ordination between the two eyes. The eye-movements were measured with a computer-aided video method, and from 208 of these the following picture of a typical movement emerges. It has roughly equal horizontal and vertical components of 78 ~ taking the eye-stalk axis about 12 ~ around a great circle, and also a rotational component of about 8 ~ The 3 components can occur independently of each other and are thus separately driven by the brain (Fig. 6). The average duration is 300 ms, and average velocity is 40 ~ s (Fig. 5). Most movements are made in a direction approximately at right angles to the orientation of the specialised central band. It is shown that the slow speed of the eye-movements is compatible with scanning, that is, the uptake of visual information during the movement rather than its exclusion as in conventional saccades. Mantis shrimps also make target-acquiring and tracking eye-movements which tend to be somewhat larger and faster than other spontaneous movements. Rotating a striped drum around the animal induces a typical optokinetic nystagmus whose slow phases are smooth, unlike target tracking which is jerky (Fig. 7). Eye-movements may therefore be conveniently grouped into 3 classes: targetting/tracking, scanning, and optokinetic.

Stomatopods locate prey, within a short range of distances, with one eye and strike it within a few milliseconds. We developed a model based on the complex input patterns of the eye transferred to a matrix of neural integrators called T2 and T3 fibers. In the integrators graded potentials are summed and generate spikes if the sum reaches threshold. Histograms of instantaneous frequencies were simulated on a PC for the T2 and for the T3 fibers for motion of a luminous point parallel to the T2 fibers and for approach of the point towards the eye. Position, size, speed of motion and distance of the target could be extracted from the frequency-pattern-coded output of the integrators in our model. A critical region in front of the center of the eye could be defined. This region is elliptical in shape and adapted to the size of the animal (respectively to the size of its raptorial appendages). We assume that prey is hit when it is in the critical zone. Histological and electrophysiological results seem to confirm our model.

On the distal lamina surface of stomatoped eyes a matrix of horizontal and vertical nerve fibers processes the complex input patterns. The output of these integrating fibers is a spike discharge pattern correlated to the input pattern. Here we introduce a ± neuron which either subtracts or sums the outputs from the set of horizontal and vertical fibers activated at that moment. The output pattern of spike frequencies of the ± neuron locates a target in space. Over a parallel channel outputs from the vertical fibers pass a bandpass filter and constitute one of the inputs for a decision neuron. The other input derives from specialized ommatidia at the center of the eye. If both inputs arrive within a short time interval, they sum, the threshold is reached and the decision neuron fires. Spikes from the decision neuron are the final cue for the muscles of the raptorial appendages. The appendages shoot forward and hit the prey with high precision.

Like all photoreceptor organs, crustacean compound eyes produce pigments that interact with the light impinging upon them. Here, the term “pigment” refers to molecules that absorb light in the visual range, at wavelengths between about 330 and 700 nm. The two major classes of pigments in crustacean eyes are first the visual pigments, the photosensitive molecules that capture light and set in motion the complicated processes that signal its presence, and second the photostable pigments that must be present to regulate the light within the eye.

[Figure][1] Peacock mantis shrimp are champion underwater boxers, wielding a pair of specialised club-shaped limbs to smash snail shells into smithereens. They are also surprisingly quick on the draw, and it turns out that this confers a rather unexpected advantage. Sheila Patek and Roy

Superman is alive and well in the warm, bright, shallow seas of the coral reef. He is faster than a speeding bullet, more powerful than a locomotive, and capable of seeing into a realm we cannot begin to understand. The mantis shrimp ( Odontodactylus scyallurus ), a misnamed stomatopod, is the captivating creature gracing this month’s cover, and he has an array of talents and stealth so impressive as to make him a decathlete of unprecedented prowess. For those interested in vision, this creature is truly world class, with few if any competitors. Eyes in these species should be considered the invertebrate equivalent of the avian eye in vertebrates—top of the line in the phylum. As can be seen from the arresting photograph on this page, the compound eyes of Odontodactylus scyallurus have a belt-like region that seems to divide the eye in half. This equatorial belt is called a mid-band and has six specialised rows of ommatidia, the individual units of every compound eye. An ommatidium contains eight separate retinular cells arranged in a petaloid fashion when seen in cross section. Each retinular cell provides microvilli with photopigments in its membranes. Each set of …

The distances of separation at which individuals of the territorial shrimp Gonodactylus oerstedii showed agonistic behaviors were measured in the laboratory. Sizes of interacting animals had no effect on distances at which behavior patterns were shown. Different acts occurred at significantly different distances. In the case of territorial G. oerstedii, most agonistic acts occurred just as an introduced animal crossed the gravel line marking the boundary of the territory. Actual distance separating animals was less important than location of an introduced shrimp in determining the probability of agonistic interactions. Overall, there was an inverse correlation between degree of site attachment in a species and the variance in its behavior‐distance values.

Mantis shrimp (Stomatopoda, Crustacea) that normally occupy holes in coral were presented with novel burrows (Erlenmeyer flasks painted black) in the laboratory. Individuals learn to recognize characteristics of the flask and enter, the burrow increasingly rapidly with repeated exposure to the flask. Individuals show consistently fast or slow learning curves, suggesting individual differences in learning ability. Three to seven days appears to be a critical period during which the stimulus must be re-encountered, or else the response is partially forgotten. However, a partial response remains after 14 days, and subsequent re-exposure to the stimulus is associated with more rapid re-acquisition of the entry behaviour than in naive animals. Field observations support the interpretation that individuals learn characteristics of their burrows and the environment. Further studies are needed to investigate the relationship of learning ability to the ritualized behaviour repertoire and to social interactions.

The crustacean cardiac pacemaker is a particularly useful experimental preparation for the investigation of neural control of rhythmic phenomena. In this paper a review of the experimental literature concerned with the pacemaker system of the mantis shrimp Squilla is given. It is pointed out that the anatomy and physiology of this animal are such that a very simple model may serve to describe the significant characteristics of its cardiac pacemaker control system. Such a model, relating muscle tension and length to pacemaker membrane potential, is derived. The applicability and use of the model are discussed.

A male and a female of Gonodactylus bredini collected off the coast of North Carolina were maintained in the laboratory for 16 months. Five clutches were spawned during a period of one year. Egg masses were pinkish orange, hollow spheres approximately 15 mm in diameter. Each egg mass consisted of 800-900 ovoid eggs ranging from 0.75-0.79 mm in length and 0.64-0.67 mm in width. The periodicity between emergences of pelagic larvae from the burrow ranged from 32-91 days, with a mean of 62 days. At 28°C developmental times were as follows: approximately 29-30 days from mating to the pelagic larval stage when brooding is no longer required, 20-21 days from spawning to the pelagic stage, and six days from the propelagic to the pelagic stage. The female appeared to sculpt a burrow in hard coral and then seal the burrow while larvae remained within. Only one molt was observed, during which time the stomatopod changed color before reverting to its normal hue. Larvae of G. bredini were reared to metamorphosis from the eggs spawned and hatched in the laboratory. Three propelagic, four pelagic, one supernumerary, and the first postlarval stage were described for G. bredini. The unequivocable existence of supernumerary instars has not been determined previously for any species of stomatopod. The duration of larval development is approximately 35-40 days at 25°C and 30 days at 30°C when larvae progress through seven stages before metamorphosing, and 40-50 days at 25°C and 36 days at 30°C for larvae metamorphosing after eight stages. Of the 454 larvae reared, only 4% metamorphosed successfully. Differences in color patterns, degree of aggressiveness, developmental times, and postlarval and adult characters between Bermudan and North Carolinian populations of G. bredini raise the possibility that the two populations may be distinct species.

Examination of the stomach contents of the Japanese mantis shrimp Oratosguilla oratoria showed that this species is a very intensive predator on the Macrura which is a principal component of the benthic megalofaunal community. Thus, the mantis shrimp, by feeding largely on the Macrura, may have a major influence on this community structure in Hakata Bay. The shrimp was also revealed to be an intensive predator on the Pelecypoda despite underestimation of preda-tion intensity, based on the stomach contents, because of its shell-smashing behaviour. Further-more, this study showed that many Macrura were captured during September and November by the mantis shrimp and that female shrimp of reproductive sizes also consume many Pelecypoda, As a prey species, mantis shrimp themselves were found infrequently in the digestive tracts of other predators.

The Japanese mantis shrimp Oratosquilla oratoria usually lives in the mud bottom. This species excavates a U-shaped tunnel with a sarge and a small opening on a tidal flat; the length of burrow is proportional to occupant size. Artificial burrows of various diameters and lengths were made of polyvinyl chloride pipes and used to study this selective habit in large aquaria. The results showed that the species had a significant preference on the basis of diameter of pipe, but not for pipe length above a lower limit. These facts and behaviour in the artificial burrow suggest that a normal life-cycle is dependent upon habitation of a burrow of compatible size. An artificial burrow of favourable size permits feeding, spawning, etc. and increases survival of mantis shrimp reared in the laboratory.

The mantis shrimp Gonodactylus festae lives in rock cavities which it must frequently defend against conspecifics. To determine if individual recognition is used to mediate these aggressive contests, adult intruders were matched sequentially against residents that were larger and smaller than themselves. Intruders were repulsed by large residents, but were able to evict small ones from their cavities. Later, each intruder was exposed once to a cavity containing the odour of the animal that deeated it and once to a cavity containing the odour of the animal it defeated. Intruders rapidly entered cavities containing the odour of the resident they defeated, but were hesitant to enter cavities containing the odour of the animal that had successfully defended against them. This demonstrates that G. festae can distinguish between the odours of two previously encountered opponents and suggests that this species is capable of individual recognition.

shrimp, Anchistus miersi (De Man), under the scanning electron microscope (Decapoda, Natan tia, Pontoniinae). Crustaceana, 29: 252-254. Grice, D. G. & T. J. Lawson, 1971. Use of the scanning electron microscope in morphological studies of copepods. Crustaceana, 21: 111-112. Guglielmo, L. & G. CosTANZO, 1977. Diagnostic value of the thelycum in euphausiids, II. Oceanic species. Genus Thysanopoda Milne Edwards, 1830. Crustaceana, 33: 275-283. Hindley, J. P. R. & C. G. Alexander, 1978. Structure and function of the chelate pereiopods of the banana prawn Penaeus merguiensis. Mar. Biol., 48: 153-160. Laughlin, R. B., Jr. & J. M. Neff, 1976. SEM observations on sensory structures of the zoea of Rhithropanopeus harrisii. American Zool., 16: 214 (Abstract 198). McLaughlin, P. A. & C. E. Lane, 1975. The morphology of unique structures on the spines of a deep-water Hawaiian hermit crab (Crustacea: Decapoda: Paguridae). Journ. Zool., London, 176: 519-526. Mauchline, J., Y. Aizawa, T. Ishimaru, S. Nishida & R. Marumo, 1977. Integumental sensilla of pelagic decapod crustaceans. Mar. Biol., 43: 149-155. Rainbow, P. S. & G. Walker, 1976. The feeding apparatus of the barnacle nauplius larvae: A scanning electron microscope study. Journ. mar. biol. Assoc. U. K., 56: 321-326. Sandberg, P. A., 1970. Scanning electron microscopy of freeze-dried Ostracoda (Crustacea). Trans. American microsc. Soc, 89: 113-124. Scotto, L. E., in press. Larval development of the Cuban stone crab, Menippe nodifrons (Brachyura Xanthidae), under laboratory conditions with notes on the status of the family Menippidae. Fish. Bull., U. S. Fish Wildl. Serv. Williams, A. B., 1978. Transfer to Pseudomedaeus of the xanthid crab Micropanope distinctus (Rathbun). Proc. biol. Soc. Washington, 91: 546-557.

The mantis shrimpSquilla mantis responds to an electrical shock with a quick and violent flexure of its body (Fig. 1 and 2). The reaction time of this defensive response was measured for each experimental shrimp and the minimal current that elicited a reaction time equal to or lesser than 0.22 s was considered as its intensity threshold (Fig. 3). Different doses of morphine-HCl were injected and results showed that this drug produces a dose-related analgesia by increasing the intensity threshold. A concentration of morphine equal to 30.0 μg/mm of animal length (about 91.0 μg/g) causes a 50% inhibition in the sensitivity to the electrical stimulus, but the effect is fully blocked by naloxone (Table 2). The present study represents the first behavioral analysis of opiate effects in invertebrates. However, the effective dose reported in this experiment is far greater than that used with vertebrates. Some speculative arguments are mentioned in order to account for a such large difference.

1. 1. Rates of aquatic oxygen uptake ( V O 2 ) were determined for the burrowing stomatopod Helerosquilla tricarinata during routine ventilation and swimming activity over a range of environmental oxygen tensions ( P 1 O 2 ) at 15°C. 2. 2. Critical oxygen tensions ( P c ) were 80–90 mmHg (active animals) and 20–30 mmHg (routinely ventilating animals), 3. 3. Aerobic scope for activity (5.6 μl O 2 hr −1 /mg whole dry wt 07 ) and aerobic expansibility (x4.8) of Heterosquilla in air-saturated sea-water are maintained down to a P 1 O 2 of 80–90 mmHg; aerobic scope is 50% of the air-saturated value at P 1 O 2 , 45 mmHg and zero at P 1 O 2 , 10–15 mmHg. 4. 4. Some oxygen transport properties of Heterosquilla haemocyanin were determined ( P 50 = 21 mmHg; n = 4.5 at pH, 7.62/ P CO 2 1.75 mmHg; mean C max HcyO 2 = 1.29vol%). 5. 5. The aerobic metabolism of Heterosquitta tricarinata during environmental hypoxia is discussed with reference to the oxygen tensions which the animal experiences in its natural habitat.

Mean body lengths of age groups by sex of the Japanese mantis shrimp Oratosquilla oratoria in Tokyo Bay were determined by 2, 423 females and 2, 293 males using size-frequency analysis method. A growth curve was fitted to length at age data and the life span was examined. It was found that the recruitment period started in November with a body length around 5cm and com-pleted in June of the following year. The mode of age O group during the recruitment period was not used in further interpretations, because the continuous addition of newly recruited individuals was found to lower its value. After recruitment completion, it was found that the growth of the mantis shrimp has seasonal oscillation with the highest growth rate from late summer to late autumn. Females showed higher growth oscillation than males. Growth of the mantis shrimp was best expressed by the Pauly and Gaschutz equation as Lt=16.12{1-exp[-0.395(t+2.667)-(0.486/2π)sin 2π(t-0.323)]} for females and Lt=21.51{1-exp[-0.264(1+2.473)-(0.232/2π)sin 2π(t-0.281)]}for males, where Lt is body length in cm and t is age in months. It seems that most of the mantis shrimp in Tokyo Bay died during age 2.

Four different polypeptides all showing a molecular weight around 70 Kd have been detected by isofocusing electrophoresis in 8M urea and further characterized by SDS polycrylamide gels and by immunoelectrophoresis. On structural grounds they can be related to a common polypeptide family; the immunological analysis strongly correlating the two most represented subunits suggests their common origin from the same native polypeptide. Their difference is probably explained by subsequent processing.

STOMATOPOD crustaceans, commonly named mantis shrimps, have compound eyes of unique design. A central band composed of six parallel rows of ommatidia separates two peripheral ommatidial groups, and all three regions view the same area of visual space1–3. In the central bands of members of the stomatopod superfamily Gonodactyloidea, four of the ommatidial rows are built of tiers of photoreceptors; in two of these rows, the photoreceptors themselves contain coloured filters4. Such a design could in principle produce many spectral classes of photoreceptors using only a single visual pigment4,5. We measured the absorption spectra of the coloured filters and the visual pigments in frozen sections of retinae of a typical species, Pseudosquilla ciliata, using end-on microspectrophotometry. The retina contains not one, but as many as ten visual pigments, each in a distinct photoreceptor class, having maximum absorbances at wavelengths from 400 to 539 nm. Because of the unique anatomy of stomatopod eyes, ten or more spectral types of photoreceptors exist in this species.

Pairs of the mantis shrimp Gonodactylus festai fought in an open arena. Later, the dominant individual was placed in a cavity and defended it against the subordinate. Visual, tactile, and acoustical displays used during contents for cavities are here described. Fifteen minutes later the subordinate animal was placed in an arena with a cavity containing water from the aquarium of the animal that had just defeated it, water from the aquarium of a stomatopod it had never met, or water that had never contained a stomatopod. Animals readily entered cavities containing clean water, investigated and entered cavities containing strange stomatopod water, and avoided cavities containing water from the home aquarium of the animal that had previously defeated them.

The SDS-PAGE of Squilla mantis hemolymph reveals 16 major protein bands. Three of them, showing a molecular weight (MW) around 125 kdal, are female specific proteins (FSP) to be considered as vitellogenins because their amount increases with ovarian maturity. The MW of the hemocyanin subunit is confirmed around 70 kdal. Low MW proteins appear or intensify at molt. Hemolymph incubation with 35S-Methionine and subsequent autoradiography of SDS-PAGE slabs show that hemocyanin and vitellogenins are not synthesized by the circulating hemocytes, while some proteins connected with molt are heavily labeled by the tracer.

One of the constraints imposed upon arthropods by their protective exoskeleton is the necessity to molt. While the physiology and morphogenesis associated with the molt cycle in crustaceans has commanded a great deal of attention (e.g., Pas sano, 1960 ; Drach and Tchernigovtzeff, 1967 ; Stevenson, 1972 ; Aiken, 1973; Davis, Fyhn, and Fyhn, 1973 ; Reaka, 1975a) , few workers have examined the process of molting in an evolutionary perspective. This study examines the eco logical and evolutionary consequences of molting in stomatopod crustaceans. Mantis shrimp are primitive members of the Malacostraca ( Brooks, 1962; Siewing, 1963 ; Holthuis and Manning, 1969 ; Schrani, 1%9a, b, 1973 ; Burnett and Hessler, 1973 ; Reaka, 1975b) , but they possess a highly specialized life style which may be associated with unique molting and reproductive adaptations. Stomatopods frequently live in species assemblages where as many as five con generics occupy indistinguishable microhabitats in one tidepool (Reaka, 1972, and in preparation) and seven congenerics may occupy one tide flat (this study). Protection from predation is afforded by burrows or cavities in mud, sand, rocks or coral. Stomatopods employ intense and sometimes lethal agonistic behavior against conspecifics and congenerics while fighting to obtain or retain burrows and in addition are rapacious carnivores. All crustaceans are susceptible to conspecific or other predators when molting and often possess behavioral adaptations to minimize mortality at this time (Passano, 1960). This vulnerability is considerably magnified in molting stoma topods because of their behavior and frequent sympatry with closely related species; if not killed by another mantis shrimp, a stomatopod may be displaced from its hole and exposed to predation by fishes (Townsley, 1953; Camp, 1973). Large size is an obvious advantage for pursuit and overpowering of prey, defense against predators, conspecific and congeneric fighting, and reproduction (Reaka, 1974, 1975c), but carries the disadvantage of repeated molts. How, then, do stomatopods minimize the effects of molting while maintaining their tactics of predation and contest competition? Reclusive and submissive behavior, as well as sealing the entrance of the burrow, reduce vulnerability at the molt in stomatopods; the stages of morphogenesis associated with incapacitation and exuviation are abbreviated in several aggressive taxa of crustaceans but especially in stomatopods; and asym metrical stages of the molt cycle suggest that the early premolt may be a waiting period, whereupon initiation of the molt progresses rapidly following the correct cue (Reaka, 1975a). The present paper examines timing of molting and repro duction, and suggests that lunar and tidal synchrony of molting in the population 468

1. 1. The disposition of ommatidia and optical axes in the eye of Gonodactylus is described. 2. 2. The matrix of horizontal and vertical fibers on the distal lamina surface presumably sub- serves integration of a complex input pattern and transmits signals for the strike to the raptorial appendages. 3. 3. The antennal scales contain two parallel nervous systems contributing apparently to the visual inputs for the strike. 4. 4. Some aspects of visual behavior correlated to the strike are reported. 5. 5. Computer simulations show the input patterns for points and segments moving around the eye in space. 6. 6. The patterns change with distance, size, speed and position of the target. 7. 7. It is hypothesized that the fiber matrix in the lamina integrates inputs and translates them into spike discharge patterns. The shape of the histograms, representing the patterns, contains the information necessary for catching a prey. 8. 8. The input pattern and its variations are correlated to the behavior, the histological results and the luminous habitat of the animals.

Summary Crustaceans showed considerable differential distribution in response to a variety of features. Portunid crabs may be responding to salinity gradients, peak abundance of shrimp may be associated with detritus from rivers flowing into the Gulf and mantis shrimp may be influenced by sediment type and biotic interactions. Because of the ecologic and economic value of crustaceans these findings are significant in terms of red tides (Hargraves and Viquez 1981) and potential perturbations in the Gulf of Nicoya. Differences between shallow tropical marine ecosystems and temperate counter-parts concern chemical and physical characteristics (temperature, light, rainfall, nutrients), community structure (species diversity, population density, biomass), and biological functions (primary productivity, growth rates, resource sharing) (Johannes and Betzer 1975). Spight (1977) posed some generalizations concerning differences between tropical marine and temperate communities. These generalizations included: (1) ...

Ecologically important members of the estuarine infauna may be missed by conventional surface-operated sampling gear. A bottom survey of Narragansett Bay (Rhode Island, U.S.A.) by direct observations using SCUBA revealed the previously unreported presence of large numbers (up to 7 m −2 ) of the stomatopod, Squilla empusa . These crustaceans live in large burrows which they excavate in the soft muddy bottom. Burrows are of two seasonal types: summer and winter. The summer burrow consists of two similar openings connected by a U-shaped tunnel, the horizontal member of which usually has two bends in plan. These burrows are 15–50 cm deep, have a diameter of 1–10 cm depending on the size of the occupant, and are up to 2 m long. Winter burrows have a single opening to a more or less straight vertical tube up to 4.1 m long, possibly with a lateral chamber. Dissolved oxygen decreases and temperature increases with depth in the winter burrow. It is hypothesized that such deep winter burrows, at the northern end of the geographical range of Squilla empusa , represent a behavioral adaptation to water temperatures too low for the animal's survival. High densities of large burrowers and their burrows may have significant effects on the stratigraphy and sediment-water exchanges in estuaries.

Schram, F. R. (Dept. of Zool., Eastern Ill. U., Charleston, lll. 61920) 1974. Convergences between Late Paleozoic and modern caridoid Malacostraca. Syst. Zool. 23:323-332.-Study of the Middle Pennsylvanian, Mazon Creek, Essex fauna Crustacea (Johnson and Richardson, 1966; and Richardson and Johnson, 1971) of northeastern Illinois has prompted an examination of the entire Late Paleozoic radiation of caridoid malacostracans. Members of this radiation bear several gross anatomical similarities to Mesozoic-Cenozoic eucarid forms, yet are totally and completely distinct taxonomically from them. This convergent phenomenon affords a rare look at the evolution of a major taxonomic category extending over a period of some 300 million years. The comparison also bears on general theoretical considerations of diversity and convergence in evolutionary theory. [Convergence; Malacostraca; Diversity models.] The malacostracan crustaceans have been present in the fossil record since Cambrian time. The earliest and more primitive forms have been the Phyllocarida, forms with seven segments in their abdomens. In Devonian time a more advanced array of malacostracans apparently evolved from the phyllocarids. These forms, the Hoplocarida and the Eumalacostraca, are characterized by having six segments in the abdomen and a great variety of tagmatic and appendicular specializations that enabled them to more effectively dominate their environments. The Late Paleozoic radiation of advanced malacostracans was composed of hoplocaridans, syncaridans, and primitive eumalacostracans variously termed Eocarida (Brooks, 1962), caridoids, or schizopods. The Hoplocarida almost completely died out at the close of the Paleozoic except for the specialized Stomatopoda or "mantis shrimp." The caridoids persisted and formed the basis of the modern malacostracan radiation. The caridoids are all characterized by an array of features first elucidated by Calman (1909): two flagella on the first antenna, two segments in the thoracic protopod, five segments in the thoracic endopod, annulate and natatory thoracic exopods, thoracic epipodite gills, thorax and abdomien subequal, thorax containing viscera and covered by a carapace, abdomen developed with a special musculature for the distinctive backward-swimming caridoid escape reaction. These primitive caridoids gave rise to the groups which are the dominant malacostracans today, the Eucarida and Peracarida. The Peracarids have developed a brooding habit for protecting the young, and morphologically have a tendency to lose the carapace and greatly modify the body regions so as to diverge markedly from the caridoid morphotype. The evolution of the peracarids proper must remain the subject of another paper. The Eucarida have more closely retained the caridoid facies and are the dominant caridoid types today. The only living peracarids that can be termed "caridoid" are the Mysidacea. PERIPATETIC TAXONOMY The taxonomic affiliations of the Late Paleozoic caridoid malacostracans have been realigned several times. Huxley (1857) termed Pygocephalus cooperi an early form of decapod (Brooks, 1969, has since assigned this species to the genus Crangopsis). Huxley's designation influenced subsequent workers to categorize their fossil species as "macrurous decapods" as in Etheridge's (1877) description of some specimens of Anthrapalaemon and Wood

The influence of size on the aggressive behavior of Gonodactylus viridis was examined by matching large animals against others 50, 60, 70, 80, 90, and 100% their size. With size discrepancies of 10% or greater, the larger animals won significantly more of their fights. The smaller participants of a contest avoided more, attacked less, and threatened more than did their larger opponents. When the contestants were evenly matched, attack and avoid values were intermediate, but the animals threatened as often as did the smaller animals. These results are reviewed in light of recent game theory analyses which suggest that threat should be used by the smaller contestant or when the risk of escalation is great compared to the expected pay-off.

Spawning season of the Japanese mantis shrimp Oratosquilla oratoria in Tokyo Bay was ex-amined from seasonal changes in percentage occurrence of mature females and in female gonad index. A total of 15, 871 specimens was sampled in Tokyo Bay from April to December in 1982 and from August 1986 to September 1987. Analysis showed that spawning season lasted from April to August. Percentage occurrence of mature females during the spawning season showed two peaks, the first one from April to May, and the second from July to August. The first peak was caused by the maturation of females older than 2 years with body lengths above 10cm. In July or August, 1 year old females with body lengths above 8cm matured and contributed to the second peak. The result of the present study showed that the age of maturation of the mantis shrimp in recent years has become rather earlier compared with that in the 1950s in Tokyo Bay.

This study was planned to determine the neuromuscular basis of the very rapid strike movement, lasting only 5–10 ms, used by mantis shrimps to capture prey or defend themselves. The raptorial second thoracic append-ages which are responsible for the strike action are unfurled by four muscles in the merus, two extensors and two flexors. All were found to be specialized for slow not fast contraction. The largest extensor muscle has a twitch time of 400 ms, reaches peak tetanic tension in 700 ms and takes one second to relax completely from this. It receives two “slow” and one “fast” motor axons distributed uniformly throughout the muscle. An overshooting spike occurs in each muscle fiber from the first activation of a train in the fast axon, but many seconds must elapse before the first muscle fiber will again respond with a spike. The smaller, medial extensor receives one fast axon which may give rise to overshooting spikes and an inhibitor whose effects appear to be minor; its muscle fibers are only weakly electrically excitable. The contraction and relaxation rates are slow, as are those of the medial flexor which receives two slow axons. The lateral flexor is divisible into two parts; a proximal region comprised of electrically passive fibers innervated solely by a slow axon and a distal region of spiking fibers innervated by a fast axon. The rapid strike action is explained not in terms of the rapid contraction of these muscles but in their operation of a mechanical device in the form of a “click-joint,” described previously.

Two propelagic and nine pelagic larval stages of Squilla armata H. Milne Edwards, from New Zealand, are described and illustrated. A larval calendar showing monthly abundance and ratio of occurrence of pelagic larvae from the plankton in relation to the mean water temperature is given. Habits of the larvae are described.

Eyes of nineteen malacostracan crustaceans (sixteen from coastal, three from deep water) have been examined for purines and pteridines, with a view to determining their role as reflecting pigments. White shrimp, Penaeus setiferus , received most attention; other animals examined were one isopod, one stomatopod, eight penaeids, six brachyurans, and two anomurans. Methods used were paper chromatography, enzymatic assay or identification, UV spectrophotometry and fluorophotometric assays. Isoxanthopterin was the chief pteridine present in eyes of white shrimp, in amounts up to 250 μg per eye; xanthopterin and 2-amino-4-hydroxypteridine occurred in smaller quantities, in that order. Isoxanthopterin was generally present in the eyes of the malacostracans examined except for the scarlet prawn, Aristaeomorpha foliacea , which had only xanthopterin. In the white shrimp, pteridines are localized in the three reflecting layers of the eyes. Purines generally occur in small amounts (except one unidentified quenching substance); they include xanthine, hypoxanthine and guanine. Eyes of mantis shrimp contain much xanthine.

1. The electrocardiogram of the tubular heart of the mantis shrimp, Squilla oratoria de Haan, was studied. Structural findings are described which confirm Alexandrowicz's observation.2. The electrogram consists of rapid spike components and slow action potentials. The spikes originate from the median nervous system of this heart, and the slow potential from the muscle.3. The results of transection experiments on the nerve trunk support the view that the nerve cell of the thirteenth segment has a dominant role in the pacemaker activity of the heart contraction.

The ultrastructure of some muscle fibers of the five physiologically different motor units operating the strike of the mantis shrimp were studied by electron microscopy. The distal portion of the lateral flexor was found to have the shortest sarcomere length (4.3 μm), the densest, most complex sarcoplasmic reticulum, the largest number of dyads per unit cross-sectional area and the smallest filament cluster (“fibril”) size. The proximal portion of the same muscle differs from it mainly in having a less well-developed reticulum and a large filament cluster size. The remaining muscles have longer sarcomere lengths: 5.3 μm for the medial flexor, 7.8 μm for the lateral extensor, and 6.0–10.2 μm for the medial extensor, as well as a weakly-developed sarcoplasmic reticulum and fewer dyads per unit cross-sectional area. These data were compared with contraction and relaxation times of the units and showed that the rates of both contraction and relaxation are lower the greater the A band or true relaxed sarcomere length. For fibers of equal A band length, faster rates were found to be associated with a more extensive sarcoplasmic reticulum, giving reduced filament cluster size, as well as with a larger number of dyads.

1. Courtship and copulation are brief in G. bredini. Either sex can indicate courtship by approaching; after antennular palpation the male then grasps the female by the carapace and copulation takes place.2. Receptive females can be distinguished morphologically by darkened internal organs visible through the telson and behaviorally by their acceptance of a male's approach. Unreceptive females attack males immediately.3. Males share cavities with females during the few days prior to spawning. Following egg-laying females defend cavities against males. The eggs are kept in the cavity and frequently manipulated; the newly hatched larvae remain in the cavity with the female until they reach Stage IV.4. The form and duration of reproductive and maternal behavior in G. bredini are apparently a consequence of cavity living.