A new genus and species of Sternaspidae (Annelida: Polychaeta) from the deep eastern Atlantic

Based on specimens recently collected in sediments from 2700 m depth off Mauritania (Northwest Africa; type locality) and from 2700–4400 m depth off Angola (Southwest Africa), a new genus and species, Mauretanaspis longichaeta gen. et spec. nov., is described. The new genus and species are characterized by a unique combination of characters: ventro-caudal shield covered by firmly adhering sediment, lateral margins strongly bent and merging into integument; introvert hooks tapering; eight pre-shield segments; absence of peg chaetae; exceptionally long posteriormost lateral chaetae equaling body length; posterior shield chaetae equaling shield length. A comparative table of characters for all currently recognised sternaspid genera and a key to all species with ventro-caudal shield covered by firmly adhering sediment are provided.

Ontogenic allometry and sexual maturity of the hermit crab, Diogenes alias McLaughlin & Holthuis, 2001 (Decapoda, Anomura)

Growth studies on Anomura, especially hermit crabs, are relatively limited, due to the complexity in constructing generalized growth models as well as the heterogeneity of the group. Despite Diogenes alias being one of the most abundant species in the study area, there is a lack of information regarding its sexual dimorphism and maturity. The present study aims to evaluate its ontogenic allometry, using Jolicoeur’s multivariate allometric coefficient. The specimens were collected biweekly from trawl fishing grounds off the Mumbai coast for one year. Sexual dimorphism was patent at the larger cheliped width in males and the wider shield width in females, which was attributed to the differential energy allocation by both male and female. The size of morphological sexual maturity was established at 7.6 mm shield length for males, and at 6.2 mm in females.

Elevating the Precision of Plasma Probe Diagnostics by Elimination of Bare Probe Protective Shields’ Influence

Probe diagnostics of the low pressure inductive xenon plasma were conducted using classic cylindrical Langmuir probes with conventional protection of their circuits against radio frequency interferences by bare metal shields. The dimensions of their probetips were determined in the special experiment that provided negligible local plasma distortions. Accurate probe measurements were used to determine the spatial plasma parameter distributions in a gas discharge unit of an ion thruster model which helped to develop its ion-extracting grate. The subsequent analysis of probe measurements showed that in these experiments, the plasma electron energy distribution function (EEDF) was quite noticeably deviated from the Maxwell function depending on the main probe shield length that varied from maximum to zero. Use of an additional probe in the special position where its shield was rather long with zero shield length of the main probe showed that the additional shield lowered all plasma parameters. Comparison of both probes’ data identified the principled relationship between measurement errors and EEDF distortions caused by bare probe shield and this dependence was used to correct the initial probe measurements. Therefore plasma probe diagnostics became more precise due to the lowered influence of the bare probe protective shields. Its physical analysis based on previous authors’ works showed that this effect was caused by a shortcircuited double-probe phenomenon in the bare metal shields.

Population and reproductive characteristics of the hermit crab Pagurus proximus Komai, 2000 (Decapoda: Anomura: Paguridae) in the northern part of the species range

The population and reproductive characteristics of the hermit crab Pagurus proximus Komai, 2000 have been examined in the northern part of the species range (Vostok Bay, Peter the Great Bay, Sea of Japan). The average population density was 4–5 ind m−2 in winter and spring, 10 ind m−2 in summer and autumn; the biomass was 7–9 and 18–19 g m−2, respectively. Hermit crabs were found at a depth of 0 to 12 m but were most numerous at about 3 m depth with an average population density of up to 26 ± 7 ind m−2. The shield length of males varied from 1.3 to 7.8 mm and females from 1.2 to 6.7 mm. The male to female ratio was close to 1 but varied with size and season. Females attained sexual maturity at a shield length of more than 1.3 mm. Ovigerous females were found from December to August. The proportion of ovigerous females increased from 7% in December to 93% in late April; however, the embryos in clutches remained at early developmental stage until May. The mass release of larvae was observed at the beginning of June. A subsequent spawning probably took place in July. The main factors contributing to the high abundance of P. proximus in the investigated area are the presence of the embryonic diapause synchronizing the release of larvae at the most favourable time for their development, high fecundity, the presence of at least two egg clutches during the reproductive season, and total absence of parasites.

Has the land hermit crab Coenobita purpureus settled in Taiwan?

The land hermit crab, Coenobita purpureus Stimpson, 1858 (Anomura, Coenobitidae), is endemic to Japan. However, for the first time one light blue male land hermit crab, with a shield length of 1.51 cm, was collected on Dongji Island, South Penghu Marine National Park, in Taiwan. This paper describes the morphological characteristics of the collected individual and provides colour illustrations and photographs of the specimen. Because dispersal is one of the fundamental traits of all species, we herein also discuss hypotheses on the possible dispersal of C. purpureus to Dongji Island. Finally, this record is notably the southernmost report in the known global distribution of C. purpureus.

Allometric relationships and sexual dimorphism in three ubiquitous hermit crab species (Anomura, Diogenidae) from a tropical mangrove estuary

Shield length-weight relationship (LWR) and relative growth were studied in three tropical hermit crab species, Diogenes moosai Rahayu & Forest, 1995, Diogenes lopochir Morgan, 1989, and Clibanarius infraspinatus (Hilgendorf, 1869). Overall, the length exponent (b) for LWR ranged between 2.67 to 3.28 with males of both Diogenes species showing positive allometry () and females showing negative allometry (), whereas that of both sexes of C. infraspinatus showed negative allometry. Males had larger b values than females in all species, indicating that males are heavier than females of equal shield length. In all species, relative growth of cheliped and chela exhibited positive allometry () with distinct sexual dimorphism whereby males bear longer chelipeds and chelae compared to females of equal shield lengths. Intra- and interspecific variations in growth of body and cheliped among the three sympatric hermit crab species allow for the resource partitioning of their vital shell resources.

Characterization of the occupied shells by the hermit crab Clibanarius vittatus (Decapoda, Diogenidae) at Baixio Mirim tideflat, Guaratuba Bay, southern Brazil

A characterization of the occupied shells by the hermit crab Clibanarius vittatus was carried out. Hermit crabs were collected in the intertidal zone, during the low spring tide monthly from April 2005 to March 2006. They were sexed and their cephalothoracic shield length (CL) was measured. Shells were identified, dried, weighed and the aperture length (AL) and width (AW) were measured. 1187 crabs were collected (949 males, 216 females and 22 intersexes), which occupied 12 species of gastropod shells. Stramonita haemastoma, Olivancillaria urceus and Dorsanum moniliferum made up 96.55% of the total shell species. Male hermit crabs attained significantly larger sizes than females; therefore, males occupied a wider spectrum of shells in size and weight. A stronger correlation ratio was obtained between CL and AW of S. haemastoma. Last whorl with a rounded shape and a spacious inner area is a common feature of all shell species most frequently occupied by this hermit crab where it occurs. The successful establishment of C. vittatus at Baixio Mirim is mainly due to the appropriately shaped and wide range of size of S. haemastoma shells that were most often occupied by the hermit crabs of the studied population.

Population biology and reproduction of the hermit crab Clibanarius vittatus (Decapoda: Anomura) in an estuarine region of southern Brazil

The population dynamics and reproduction of the hermit crab Clibanarius vittatus were evaluated on Pescadores Beach, located on the estuarine channel of São Vicente (São Paulo), Brazil. The hermit crabs were captured by hand during low tide, from May 2001 to April 2003. A total of 2554 hermit crabs were captured, of which 701 were males, 1741 non-ovigerous females, 48 ovigerous females and 64 intersex individuals. The size–frequency distribution of the males was represented by a platykurtic bell-shaped curve, which differed from the leptokurtic bell-shaped curve of the females. The smaller and intermediate classes were composed mainly of females (modal size 6.5–7.5 mm carapace shield length (CSL)), and the larger classes only by males (modal size 9.5–10.5 mm CSL). The overall sex-ratio was skewed toward females (0.39:1/M:F), differing significantly from the expected 1:1. A seasonal reproductive pattern was recorded for C. vittatus in this location, with more intensive reproductive activity in the warmer months. The absence of juveniles suggests that their recruitment area is different than the area inhabited by adults, possibly another area with more protection and specialized or different resources for young.

Growth of the hermit crab Clibanarius vittatus (Bosc, 1802) (Crustacea, Anomura, Diogenidae) at São Vicente, São Paulo, Brazil

The present study analyzed the growth of males and females of the hermit crab Clibanarius vittatus (Bosc, 1802), at São Vicente, São Paulo, Brazil. Monthly collections were made from May/2001 through April/2003, at the Pescadores Beach in São Vicente. The 2,501 crabs caught were identified and sexed and the carapace shield length (CSL) was measured. For the seasonal growth study, the population was divided into 5mm size classes (CSL) and analyzed by the Bertalanffy method, with the aid of the program Fisat II. The mean sizes of the 703 males and 1,798 females were 8.94±1.80 and 6.61±1.13 mm, respectively. A seasonal growth pattern was observed, with males reaching an asymptotic size (14.92 mm) larger than that of females (13.85 mm). Males began the growth process approximately five months before the females. This growth pattern probably helped to reduce intraspecific competition for the shells, because the males reached larger size and made the smaller shells available to the females.

Population and reproductive features of the western Atlantic hermit crab Pagurus criniticornis (Anomura, Paguridae) from Anchieta Island, southeastern Brazil

The population of the hermit crab Pagurus criniticornis (Dana, 1852) was studied based on seasonal abundance, size frequency distribution, sex ratio, reproductive period, fecundity and shell relationship. Specimens were collected monthly by SCUBA diving in the infralittoral area of Anchieta Island, Ubatuba. A total of 1,017 individuals was analyzed. Animal size (minimum and maximum shield length, respectively) was 0.7 and 2.9 mm for males, 0.6 and 2.8 mm for non-ovigerous females, and 1.0 and 2.5 mm for ovigerous females. The sex ratio was 1:1.29. Sexual dimorphism was recorded by the presence of males in the largest size classes. Ovigerous females were captured during all months along the year, with percentages varying from 8% (July) to 84.3% (February) in relation to the total females collected. Mean ± SD fecundity was 168 ± 125 eggs and tended to increase with increasing hermit size. Shells of four gastropod species [Cerithium atratum (Born, 1778), Morula nodulosa (Adams, 1845), Anachis lyrata (Sowerby, 1832) and Modulus modulus (Linnaeus, 1758)] were occupied by ovigerous females of P. criniticornis but fecundity was not significantly different in relation to the different shell types. The profile showed continuous and intense reproduction of P. criniticornis probably related to strategies developed to compensate for interspecific competition in the studied insular area.