Metamorphosis in balanomorphan, pedunculated, and parasitic barnacles:a video-based analysis

Cypris metamorphosis was followed using video microscopy in four species of cirripeds representing the suspension-feeding pedunculated and sessile Thoracica and the parasitic Rhizocephala. Cirripede metamorphosis involves one or more highly complex molts that mark the change from a free cypris larva to an attached suspension feeder (Thoracica) or an endoparasite (Rhizocephala). The cyprids and juveniles are so different in morphology that they are functionally incompatible. The drastic reorganization of the body implicated in the process can therefore only commence after the cyprid has irreversibly cemented itself to a substratum. In both Megabalanus rosa and Lepas, the settled cyprid first passes through a quiescent period of tissue reorganization, in which the body is raised into a position vertical to the substratum. In Lepas, this is followed by extension of the peduncle. In both Lepas and M. rosa, the juvenile must free itself from the cypris cuticle by an active process before it can extend the cirri for suspension feeding. In M. rosa, the juvenile performs intensely pulsating movements that result in shedding of the cypris carapace ∼8 h after settlement. Lepas sp. sheds the cypris cuticle ∼2 days after settlement due to contractile movements of the peduncle. In Lepas anserifera, the juvenile actively breaks through the cypris carapace, which can thereafter remain for several days without impeding cirral feeding. Formation of the shell plates begins after 1-2 days under the cyprid carapace in Lepas. In M. rosa, the free juvenile retains its very thin cuticle and flexible shape for some time, and shell plates do not appear until sometime after shedding of the cypris cuticles. In Sacculina carcini, the cypris settles at the base of a seta on the host crab and remains quiescent and aligned at an angle of ∼60° to the crab’s cuticle. The metamorphosis involves two molts, resulting in the formation of an elongated kentrogon stage with a hollow injection stylet. Due to the orientation of the cyprid, the stylet points directly towards the base of the crab’s seta. Approximately 60 h after settlement the stylet penetrates down one of the cyprid antennules and into the crab. Almost immediately afterwards the unsegmented vermigon stage, preformed in the kentrogon, passes down through the hollow stylet and into the crab’s hemocoel in a process lasting only 30 s. In S. carcini, the carapace can remain around the metamorphosing individual without impeding the process

Integrative taxonomy of crustacean y-larvae (Thecostraca: Facetotecta) using laboratory-rearing and molecular analyses of single specimens, with the description of a new vermiform species

Facetotecta, the taxon established for 'y-larvae', is the last major crustacean group for which the adult stage remains unknown. With only 14 described nominal species, all in the genus Hansenocaris, their incompletely known life cycle, small size and dearth of molecular data have hampered assessments of their true species diversity. Based on field studies during which > 11 000 y-larvae were sampled, a new integrative approach for studying the taxonomy of y-larvae is outlined. It focuses on last-stage nauplii and y-cyprids and includes methods for rearing lecithotrophic y-larvae for documenting the morphology of specimens with live photomicroscopy and scanning electron microscopy (SEM) and for obtaining molecular systematic data. This new and integrated approach, whereby each single specimen provides multiple kinds of information, was implemented to describe Hansenocaris demodex sp. nov., a unique y-larval form with semi-vermiform nauplii that occurs in the waters of Okinawa (southern Japan) and Taiwan. A preliminary Facetotecta phylogeny shows remarkable congruence between the morphology of all newly sequenced y-larvae and molecular data (18S rDNA). Four independent clades are formed by H. demodex and three other types/species of y-larvae, together being the sister-group to a smaller clade including H. itoi and unnamed species from GenBank

High thermal stress responses of Echinolittorina snails at their range edge predict population vulnerability to future warming

Populations at the edge of their species' distribution ranges are typically living at the physiological extreme of the environmental conditions they can tolerate. As a species' response to global change is likely to be largely determined by its physiological performance, subsequent changes in environmental conditions can profoundly influence populations at range edges, resulting in range extensions or retractions. To understand the differential physiological performance among populations at their distribution range edge and center, we measured levels of mRNA for heat shock protein 70 (hsp70) as an indicator of temperature sensitivity in two high-shore littorinid snails, Echinolittorina malaccana and E. radiata, between 1°N to 36°N along the NW Pacific coast. These Echinolittorina snails are extremely heat-tolerant and frequently experience environmental temperatures in excess of 55°C when emersed. It was assumed that animals exhibiting high temperature sensitivity will synthesize higher levels of mRNA, which will thus lead to higher energetic costs for thermal defense. Populations showed significant geographic variation in temperature sensitivity along their range. Snails at the northern range edge of E. malaccana and southern range edge of E. radiata exhibited higher levels of hsp70 expression than individuals collected from populations at the center of their respective ranges. The high levels of hsp70 mRNA in populations at the edge of a species' distribution range may serve as an adaptive response to locally stressful thermal environments, suggesting populations at the edge of their distribution range are potentially more sensitive to future global warming

Molecular phylogeography reveals multiple Pleistocene divergence events in estuarine crabs from the tropical West Pacific

Due to the lack of visible barriers to gene flow, it was a long-standing assumption that marine coastal species are widely distributed, until molecular studies revealed geographically structured intraspecific genetic differentiation in many taxa. Historical events of sea level changes during glacial periods are known to have triggered sequential disjunctions and genetic divergences among populations, especially of coastal organisms. The Parasesarma bidens species complex so far includes three named plus potentially cryptic species of estuarine brachyuran crabs, distributed along East to Southeast Asia. The aim of the present study is to address phylogeography and uncover real and hidden biological diversity within this complex, by revealing the underlying genetic structure of populations and species throughout their distribution ranges from Japan to West Papua, with a comparison of mitochondrial COX1 and 16S rRNA gene sequences. Our results reveal that the P. bidens species complex consists of at least five distinct clades, resulting from four main cladogenesis events during the mid to late Pleistocene. Among those clades, P. cricotum and P. sanguimanus are recovered as monophyletic taxa. Geographically restricted endemic clades are encountered in southeastern Indonesia, Japan and China respectively, whereas the Philippines and Taiwan share two clades. As individuals of the Japanese clade can also be found in Taiwan, we provide evidence of a third lineage and the occurrence of a potential cryptic species on this island. Ocean level retreats during Pleistocene ice ages and present oceanic currents appear to be the main triggers for the divergences of the five clades that are here addressed as the P. bidens complex. Secondary range expansions converted Taiwan into the point of maximal overlap, sharing populations with Japan and the Philippines, but not with mainland China

Ecology and Biodiversity of Rocky Intertidal Barnacles Along a Latitudinal Gradient; Japan, Taiwan and Hong Kong

The life cycle of barnacles is composed of a planktonic larval and a sessile adult stage. As a result the geographical distribution of barnacles is influenced by a combination of ocean currents, settlement success and subsequent recruitments. Barnacles show different geographical distributions along the, latitudinal gradient that connects the North West Pacific and South China Sea. On the Pacific coast of Honshu Japan the high shore was dominated by Chthamalus challengeri (>70 % cover). South of Honshu in Okinawa the high tide zone was populated by Nesochthamalus intertextus and Hexechamaesipho pilsbryi. In Taiwan the high tide zone was colonized by H. pilsbryi, Chthamalus malayensis and C. moro. In Hong Kong the high tide zone was occupied by C. malayensis (>60 % cover). The mid shores were all occupied by the genus Tetraclita. In the NW Pacific (Honshu, Okinawa and Taiwan), the common species were Tetraclita kuroshioensis, T. japonica japonica and T. j. formosana. In Hong Kong, only T. squamosa and T. j. japonica were recorded. The life history pattern of the barnacles in Hong Kong was seen to follow a seasonal trend not observed in the NW Pacific, in the warmer waters of Hong Kong early gonad development and settlement were followed by a regular summer die-off linked to heat and desiccation stress. Barnacles in Japan were found to have a shorter reproductive period and a longer life span than those in Hong Kong. Association with different ocean currents explains some of the difference in barnacle composition between Hong Kong and the NW Pacific, the rest is explained by the environmental and climatic changes along the latitudinal gradient and the ensuing differences of ecology and biodiversity found among the sites

Galkinius Perreault, 2014 or Darwiniella (Anderson, 1992)? A new coral-associated barnacle sharing characteristics of these two genera in Pacific waters (Crustacea, Cirripedia, Thoracica, Pyrgomatidae)

Volume: 719Start Page: 1End Page: 2

A new deep-sea scalpelliform barnacle, Vulcanolepas buckeridgei sp. nov. (Eolepadidae: Neolepadinae) from hydrothermal vents in the Lau Basin

Chan, Benny K.K., Chang, Yen-Wei (2018): A new deep-sea scalpelliform barnacle, Vulcanolepas buckeridgei sp. nov. (Eolepadidae: Neolepadinae) from hydrothermal vents in the Lau Basin. Zootaxa 4407 (1): 117-129, DOI: https://doi.org/10.11646/zootaxa.4407.1.

Tetraclita ehsani sp. n. (Cirripedia, Tetraclitidae), a common intertidal barnacle from the Gulf of Oman, Iran

A new species of intertidal acorn barnacle Tetraclita ehsani sp. n. was identified from the Iranian coast in the Gulf of Oman. T. ehsani sp. n. inhabits low exposed rocky shores and also attaches to shells of molluscs and the barnacle Megabalanus species. Parietes of T. ehsani ranged from white to pink which is different from T. serrata (in South African waters), which has green parietes. Morphology of the tergum and cirrus III of T. ehsani sp. n. is distinctive from other described West Indian Ocean species which have pink or white parietes (T. rufotincta, T. achituvi and T. reni). The tergum of T. ehsani is very narrow and the basal margin is slightly concave or straight, in contrast to T. rufotincta and T. reni, in which the tergum are board and with a very concave basal margin. Cirrus I anterior ramus of both T. ehsani and T. reni is antenniform and thus differing from the cirrus I of T. rufotincta (see Chan et al. 2009). Cirrus III of T. ehsani sp. n. is non-antenniform and lacks multicuspidate type setae, which is different from T. reni byan antenniform cirrus III and with multicuspidate setae