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A previously unknown species of giant fairy shrimp is described. Branchinecta raptor n. sp. is highly adapted to a predatory mode of life. In both sexes, the first four pairs of thoracopods bear elongated, curved, heavily chitinized endopods, which are modified for grasping prey. Both sexes have elongated, “whip-like” cercopods nearly as long as the abdomen that are used for detecting prey. This new species appears most closely related to B. gigasLynch 1937. Both species are large in size, have small eyes and sensory papillae, and share similar habitats and food preferences. However, B. raptor has some unusual predatory behaviors that differ from B. gigas. B. raptor is separated from all other Branchinecta by the unique form of the second antennae, the form of the cercopods, and the male genitalia. Large branchiopod records from Idaho are also discussed.
Two new species of commensal leucothoid amphipods, Leucothoe ashleyae and Leucothoe kensleyi, are described with detailed host and ecological data. Although leucothoid amphipods are common endocommensals in sponges, tunicates, and bivalve mollusks, few authors have detailed specific host associations. Information on specific leucothoid host associations will further refine taxonomic and ecological studies within Leucothoidae. The convoluted taxonomic history of leucothoids necessitates the development and application of more precise taxonomic methodologies to enable comparative analyses among taxa. Persistent taxonomic constraints within Leucothoidae [sensu lato] include numerous cryptic species groups, most notably the problematic Leucothoe spinicarpa “complex.”
This paper is concerned primarily with the taxonomy of two species of the copepod genus Botryllophilus (Ascidicolidae: Botryllophilinae) collected from compound ascidian hosts in Golfo di Napoli (= the Gulf of Naples). Both copepods belong to subgroup 2 of female morphotype A of the genus. The female of B. banyulensisBrément, 1909, living in the type host Parascidia areolata (Delle Chiaie), is redescribed, and the male is described for the first time. In the case of B. neapolitanus n. sp., living in Aplidium sp., the female is described. In subgroup 2, consisting of four species including the new species, the leg armature formulas are of pattern II, in which additional armature elements (setae, spines, etc.) are found on most legs; this differs from the armature formula of pattern I. Six species of subgroup 1 of morphotype A have pattern I. In this paper, it is shown that the four species of subgroup 2 exhibit four different formulas of pattern II; B. banyulensis has pattern II–1, and B. neapolitanus has pattern II–3. The original concept of morphotype A is revised in order to accommodate all the species of subgroups 1 and 2.
The study of the population structure of A. armillatus was based on monthly collections (March 2000–February 2002) from two tidal flats—São Francisco Beach (SF), São Sebastião County, and Engenho d'Água Beach (EA), Ilhabela County—located at the northern portion of the State of São Paulo coast and separated by the 6 km wide São Sebastião Channel. Carapace length (CL) was measured to the nearest 0.01 mm. The proportion of ovigerous females and the embryonic development stage of eggs were recorded. The Von Bertalanffy growth equation was fit to modes of the temporal sequence of frequency distributions of CL classes (SF data). The same sampling effort yielded 547 males and 566 females at SF and 145 males and 150 females at EA. Proportions of ovigerous females were higher than 60% throughout the year in both sites. The temporal trend of percentage of late eggs indicated three annual hatching periods. Growth patterns of males and females were similar, with the former tending to grow more rapidly (K = 2.28) and to attain smaller size (L∞ = 13.90) than females (K = 1.90; L∞ = 14.90). The estimated longevity of males and females was 1.20 years (14.4 months) and 1.29 years (15.5 months), respectively.
Little is known of the growth of the sculptured shrimp Sclerocrangon boreas, a remarkable member of arctic and subarctic marine shelf communities. We determined the length-weight relationship, abdomen allometry, and size structure of shrimp in a population of the Gulf of Saint Lawrence, eastern Canada. We also reared shrimp for up to 3.5 years to measure their growth. The presence of very small immature females in the wild population indicates that the sculptured shrimp is not obligatorily a protandric hermaphrodite, if at all. Females grow faster, reach a greater size, and live longer than males. Males may be ≥ 4 years old at 17 mm cephalothorax length (CL) and females ≥ 6 years old at 29 mm CL. Ovigerous females have a broader abdomen with longer pleopod setae than similarly-sized immature females. After releasing their progeny, some females may molt and grow in length but revert to a condition of narrow abdomen and short pleopod setae, and then molt again to a condition of broad abdomen with long pleopod setae. This finding and demographic data suggest that some females are alternate-year spawners. Other females did not molt for ≥ 2 years and may spawn in successive years.
A single, well-preserved fossil specimen of a large macruran decapod from the Jurassic Redwater Shale Member of the Stump Formation in northeastern Utah forms the basis for description of a new species of Eryma von Meyer, 1840. The discovery documents only the third species of the genus, and one of very few decapods, to have been described from Jurassic rocks in North America.
Digging is a distinct form of locomotion that poses different mechanical problems than other locomotor modes that are commonly used by crustaceans, e.g., walking, swimming. I examined the mechanisms of digging by shovel nosed lobsters (Ibacus peronii), which spend most of the day underneath sand. Ibacus peronii were videotaped while digging. Ibacus peronii use a “wedge” strategy to submerge into sand. An individual penetrates the sand with the walking legs, then extends the abdomen to push sand backwards, then flexes the abdomen while pushing backward with the legs, which slowly drives the body into the sand. This basic sequence repeats for several minutes. Digging often ends with a short series of tailflips. Digging by “wedging” is substantially different from previously described mechanisms in more specialized digging species. When presented with a choice of substrates, I. peronii preferred to dig in sand over shell grit, but individuals showed no preference for different types of sand.
New decapod crustacean fossils collected from Eocene rocks of Algarrobo, Chile, have yielded a new genus and species of callianassid, Melipal chilensis. The large sample size makes it possible to recognize marked sexual dimorphism of the major cheliped and pronounced heterochely in the new taxon. Cretaceous fossils from Algarrobo are referred to Protocallianassa saetosa (Förster and Stinnesbeck, 1987) new combination. That genus is rather large and unwieldy as currently understood, but examination of type material will be necessary to revise it.
Fiddler crabs demonstrate a wide range of simple and complex behaviors in both mating strategies and defense mechanisms. During investigation, five species of fiddler crabs were observed engaging in immobility or catatonic behaviors after being turned upside down. While crabs were observed in a rigid, immobile posture for mean ranges of 45–171 seconds, several crabs were recorded to remain immobile for more than two hours. Fiddler crabs are often preyed upon by birds that use crab movement as a cue. Other crustacean species, such as lobsters, have been observed in this upside-down, immobile position after having their abdomens rubbed. Consequently, immobility may be an anti-predator strategy when escape is not feasible or a byproduct of tactile stimulation.
The diversity, abundance and spatial distribution of macro-epibionts colonizing the graceful crab, Cancer gracilis, the red rock crab, Cancer productus, and the Dungeness crab Cancer magister were examined. These three crab species were common in Barkley Sound, British Columbia, occurring sympatrically across much of their range. Twenty nine epibiont species, representing ten different phyla were found. Thirty three percent of Cancer gracilis, 49% of Cancer magister and 68% of Cancer productus possessed one or more epibiont species. Cancer gracilis was the least speciose, while Cancer productus exhibited the greatest diversity of epibiont species. Male crabs were larger than females and had a greater species richness and diversity of epibionts. Epibionts were largely absent on juvenile crabs; in adult crabs, occurrence increased with crab size. Barnacles were the most common epibiont; the majority were Balanus crenatus, which predominated on the dorsal surfaces of the cephalothorax of each crab species. Green, red and brown algae were also common, the majority of which (>80%) were found on the antennae of the crabs. Tube-dwelling polychaete worms were less abundant, showing a preference for the ventral surfaces of the crabs. Hydrozoan colonies were found on only 7% of all the crabs examined, mostly settling on the ventral surfaces and limbs. Bryozoans were only found on Cancer productus and Cancer magister. The majority were the encrusting Membranipora membranacea. Unlike the above taxa, bryozoans showed no clear preference for a specific area of the carapace. Organisms in the phyla Urochordata, Mollusca and Porifera were only found on a few individual Cancer magister and Cancer productus. The distribution of each epibiont species is discussed in relation to larval settlement patterns and ecological, morphological and behavioural differences among the three host species.
The responses of individuals of the crayfish Orconectes virilis to the same set of chemical cues were tested under flow (lotic) and non-flow (lentic) conditions. The cues presented to the crayfish were food cues, alarm (= crushed conspecifics) cues, and the combination of food alarm cues. Crayfish behavior (time in burrows) and posture (lowered posture) were significantly affected by the odor treatment, the flow environment, and an interaction of treatment and environment. While the general patterns of responses to odors (more time spent feeding when food cues were introduced, and more time spent in lowered posture and in burrow when alarm cues were introduced) were qualitatively similar in the two environments, responses were stronger (especially to food odors) in the environment with flow. However, the different strength of these responses seemed not to be related to the directional information provided by the flow but rather was probably the effect of a difference in crayfish behavior between lentic and lotic environments in the control (no added chemical cues). In flow, crayfish spent less time executing feeding movements and more time in the lowered posture and in the burrow than in no-flow conditions.