Category: Taxonomy

Two new bivalves from chemosynthetic ecosystems

In two new lead-authored publications in Venus (Journal of the Malacological Society of Japan), we described two new bivalves from chemosynthetic ecosystems of the Western Pacific. One of them is a large vesicomyid clam ‘Calyptogena‘ marissinica Chen, Okutani, Liang & Qiu, 2018 from a methane seep in the South China Sea, and the other is Thermomya sulcata Chen, Okutani, Watanabe & Kojima from a vent in southern Mariana Trough, which is the first cuspidariid found in any chemosynthetic ecosystems.

The two new species:

‘Calyptogena’ marissinica Chen, Okutani, Liang & Qiu, 2018
VESICOMYIDAE
-1372m, Taken by ROV Haima, From ‘Haima’ methane seep, Off southern Hainan Island, Northern sector of the South China Sea, 146.9mm, Paratype #1 (NSMT-Mo 79001)
Known only from the ‘Haima’ hydrocarbon seep in the South China Sea, ‘Calyptogena’ marissinica is a large vesicomyid clam with an average shell length of about 150mm and the largest specimens exceeding 210 mm. It probably relies on endosymbiotic bacteria living inside cells of its much enlarged gills like other vesicomyids, although this warrants further research to confirm. It lives in clusters or colonies and is usually positioned half-buried in mud. Like all large vesicomyid clams, the periostracum is lighter in colouration and more glossy in young individuals. Although a little-varied species, the proportional position of umbo varies slightly among individuals even from the same colony, and the radial ridge running from the umbo to the postero-ventral corner is stronger in younger individuals. It seems to be closely related to ‘Calyptogena’ similaris from the Nankai Trough, Japan, which is far more elongate and with a more concave ventral margin. Calyptogena nanshaensis Xu & Shen 1991 is the only other large vesicomyid reported from the South China Sea, but it clearly differs from ‘C.’ marissinica in hinge morphology as well as having a straight dorsal margin, a bluntly acute posterior end, and also being much smaller in size (only up to 70 mm shell length).

Thermomya sulcata Chen, Okutani, Watanabe & Kojima, 2018
CUSPIDARIIDAE
-2849m, Snail site (12°57.189’N 143°37.166’E), Southern Mariana Trough, Leg. Shigeaki Kojima during DSV Shinkai 6500 Dive #1228 on-board R/V Yokosuka cruise YK10-11, 2010/ix/14, 8.1mm, Holotype (NSMT-Mo 78997)
Thermomya sulcata is the first ever Recent cuspidariid bivalve to be recovered from deep-sea hydrothermal vents or any chemosynthetic ecosystems, and is a handsome species characterised by a compressed, blunt rostrum and sharply raised commarginal ribs on the shell discs. Such upturned and sharp commarginal ribs are unusual among cuspidariids, and the monotypic genus Thermomya was erected to house this species. Furthermore, it is also the first member of the superorder Anomalodesmata to be found at deep-sea vents. So far only known from two specimens taken by the manned submersible DSV Shinkai 6500 from the 2849 m deep Snail hydrothermal site in the Southern Mariana Trough, but it is likely more widely distributed in the periphery of western Pacific vents where small burrowing animals are easily overlooked. It is most likely a carnivorous bivalve like other cuspidariids, using internally generated suction forces to hunt small crustaceans. The two known specimens are 8.1 mm (holotype) and 5.5 mm (paratype) in shell length. Prof. Okutani gave it an elegant Japanese name: “Yume-no-syakushi-gai”, literally meaning “Ladle Shell From Dreams”. This is in reference to the Japanese name, “Yume-Hamaguri” (= “Dream Clam”), of the famously beautiful and rare deep-water venerid clam Circomphalus hiraseanus (Kuroda, 1930) which is also characterised by sharply upturned commarginal ribs and a relatively small size within its family.

Indian Ocean vent stalked barnacle gets a name

A new co-authored paper published in Royal Society Open Science led by Hiromi Kayama Watanabe describes a new species of deep-sea stalked barnacle from Indian Ocean hydrothermal vents: Neolepas marisindica Watanabe, Chen & Chan in Watanabe et al., 2018. Furthermore, we also carried out phylogeographic investigation of deep-sea eolepadid stalked barnacles, leading to a better understanding of their evolution and biogeography. The paper is Open Access and available here: http://rsos.royalsocietypublishing.org/content/5/4/172408

 Abstract
Phylogeography of animals provides clues to processes governing their evolution and diversification. The Indian Ocean has been hypothesized as a ‘dispersal corridor’ connecting hydrothermal vent fauna of Atlantic and Pacific oceans. Stalked barnacles of the family Eolepadidae are common associates of deep-sea vents in Southern, Pacific and Indian oceans, and the family is an ideal group for testing this hypothesis. Here, we describe Neolepas marisindica sp. nov. from the Indian Ocean, distinguished from N. zevinae and N. rapanuii by having a tridentoid mandible in which the second tooth lacks small elongated teeth. Morphological variations suggest that environmental differences result in phenotypic plasticity in the capitulum and scales on the peduncle in eolepadids. We suggest that diagnostic characters in Eolepadidae should be based mainly on more reliable arthropodal characters and DNA barcoding, while the plate arrangement should be used carefully with their intraspecific variation in mind. We show morphologically that Neolepas specimens collected from the South West Indian Ridge, the South East Indian Ridge and the Central Indian Ridge belong to the new species. Molecular phylogeny and fossil evidence indicated that Neolepas migrated from the southern Pacific to the Indian Ocean through the Southern Ocean, providing key evidence against the ‘dispersal corridor’ hypothesis. Exploration of the South East Indian Ridge is urgently required to understand vent biogeography in the Indian Ocean.

Neolepas marisindica, Paratype specimens and in situ photographs

  • Watanabe HK*, Chen C, Marie DP, Takai K, Fujikura K, Chan BKK* (2018). Phylogeography of hydrothermal vent stalked barnacles: a new species fills a gap in the Indian Ocean ‘dispersal corridor’ hypothesis. Royal Society Open Science, 5: 172408. DOI: 10.1098/rsos.172408

New shrimps from hydrothermal vents

A co-author paper of mine, led by Dr. Tomoyuki Komai from Chiba Natural History Museum and Institute, has been published in the journal Zootaxa. In this paper, we described two new species of shrimps in the genus Metacrangon (Caridea: Crangonidae) from hydrothermally influenced areas in Okinawa Trough, Japan.  http://www.mapress.com/j/zt/article/view/zootaxa.4410.1.5

Abstract

Two new species of the crangonid shrimp genus Metacrangon Zarenkov, 1965, are described and illustrated on the basis of materials collected from the Okinawa Trough, Ryukyu Islands, southern Japan, during diving operations of remotely operated vehicles (ROVs): M. ryukyu n. sp. from off Iheya Island, at depth of 986 m; and Metacrangon kaiko n. sp. from NE of Yonaguni Island, at depth of 2205 m. The two new species resemble members of the M. munita (Dana, 1852) species group, but are both characteristic in having setose dactyli on pereopods 4 and 5. Some minor differences in morphology and genetic analysis using partial sequences of the barcoding mitochondrial COI gene support the recognition of the two new species. Holotypes of the two new species were collected from hydrothermally influenced areas, representing a previously unknown habitat for species of Metacrangon.

  • Komai T*, Chen C, Watanabe HK (2018). Two new species of the crangonid genus Metacrangon Zarenkov, 1965 (Crustacea: Decapoda: Caridea) from the Okinawa Trough, Japan. Zootaxa, 4410(1): 97-112. DOI: 10.11646/zootaxa.4410.1.5

New scale worms from hydrothermal vents named

Co-authored paper describing hydrothermal vent scale worms (Polychaeta: Polynoidae) has been just published in Frontiers in Marine Science (sorry its not molluscs this time)! It is Open Access and free for all to read here: http://www.frontiersin.org/articles/10.3389/fmars.2018.00112/

In this paper, we described two new vent polynoides including Levensteiniella undomarginata Zhang, Chen & Qiu, 2018 and Branchinotogluma elytropapillata Zhang, Chen & Qiu, 2018; and also redescribed Lepidonotopodium okinawae Sui & Li, 2017 and Branchinotogluma japonicus Miura & Hashimoto, 1991 to include both sex forms. These scale worms are highly sexually dimorphic and in many cases the two sexes have been described as separate species or even genera, highlighting the importance of describing morphological characteristics of both sexes.

  • Zhang Y, Chen C, Qiu J-W* (2018). Sexually dimorphic scale worms (Annelida: Polynoidae) from deep-sea hydrothermal vents in the Okinawa Trough: Two new species and two new sex morphs. Frontiers in Marine Science, 5: 112. DOI: 10.3389/fmars.2018.00112

Three new muricids from Western Pacific

A co-authored paper describing three new muricid gastropods from the western Pacific, has been published in the peer-reviewed journal The Nautilus!

Of the three muricids described in this paper, one is a Chicomurex from the Philippines and Kwajalein Atoll – Chicomurex excelsus Houart, Moe & Chen, 2017. With live-taken specimens known from 150~200 m deep (dead shells have been collected as shallow as 60 m), this species is characterised by a long siphonal canal which carries intricately webbed fronds but lacks in strong recurved spines. This unique siphonal canal sculpture, as well as a lower spire and a more angular final teleoconch whorl, separate it from C. gloriosus (Shikama, 1977), the closest congener which it co-occurs with.

Chicomurex excelsus Houart, Moe & Chen, 2017, Holotype (7-9) and Paratype CM (10-11)

The other two species described are from Fiji and in the genus Chicoreus (Triplex) – Chicoreus kaitomoei Houart, Moe & Chen, 2017 and Chicoreus aquilus Houart, Moe & Chen, 2017, both being small-sized (<40 mm) for the genus. Although C. kaitomoei has been confused with C. aculeatus (Lamarck, 1822) and C. nobilis Shikama, 1977, these two species have multispiral protoconchs implying planktotrophic development unlike C. kaitomoei which has a pausispiral protoconch implying lecithotrophic development. The teleoconch of C. kaitomoei is by very short variceal spines (except those from P1-3) and a siphonal canal with three abapically bent spines concentrated on the anterior half. This species inhabit shallow waters around 9~30 m deep and is named after Kaito Moe, son of Chris Moe.

Chicomurex kaitomoei Houart, Moe & Chen, 2017, Holotype (21-23) and Paratype CM (24-25)

Finally, C. aquilus which is only known from the holotype taken from 31~40 m deep in Fiji, is a highly distinctive species closest to C. rubescens (Broderip, 1833) and a few other species belonging to Chicoreus “group 2” (sensu Houart, 1992) but easily distinguished by differences in varice and aperture characteristics.

Chicoreus aquilus Houart, Moe & Chen, 2017, Holotype

Houart R*, Moe C, Chen C (2017). Description of three new muricids (Gastropoda: Muricidae: Muricinae) from the Philippines and Fiji. The Nautilus, 131(4): 207-216.

First Columbellidae snail from deep-sea vent

Lead-authored paper published in Zootaxa today! This paper describes Astyris thermophilus Chen, Watanabe, Araya, 2017, the first Columbellidae species discovered from deep-sea hydrothermal vent ecosystems. Its Japanese name literally means “columbellid from the underworld”. It was found at the Natsu site, Iheya North hydrothermal field, Okinawa Trough, just shy of 1100m depth. http://www.mapress.com/j/zt/article/view/zootaxa.4363.4.13

Astyris thermophilus. A–D. Holotype (UMUT RM32644). E. Paratype #1 (NSMT Mo 78990). F. Paratype #2(UMUT RM32645), periostracum removed to show spiral striae. G. Protoconch of paratype #6, a juvenile specimen (UMUT RM32646). H. Operculum of paratype #2 (UMUT RM32645). I. Radula of paratype #2, UMUT RM32645). Scale bars = 2 mm (A–F),500 μm (G, H), 20 μm (I).

  • Chen C*, Watanabe HK, Araya JF (2017). First columbellid species (Gastropoda: Buccinoidea) from deep-sea hydrothermal vents discovered in Okinawa Trough, Japan. Zootaxa, 4363(4): 592-596. DOI: 10.11646/zootaxa.4363.4.13

Two new vent snails from 2.8km deep in the Indian Ocean!

New lead-authored paper, announcing the discovery of two new peltospirid vent snails, has been published in the peer-reviewed Open Access journal Frontiers in Marine Science! Read for free here: https://doi.org/10.3389/fmars.2017.00392

This paper describes two new species of small gastropods, belonging to the hydrothermal vent endemic family Peltospiridae, from the Longqi hydrothermal vent field (~2785 m deep) on the Southwestern Indian Ridge, Indian Ocean; a new genus was erected to house one of them. The descriptions are based on shell (protoconch, teleoconch, periostracum, shell microstructure), radula, as well as anatomical characters.

Lirapex politus Chen et al., 2017 (~4.5 mm shell height) is the first Indian Ocean representative of genus Lirapex which is also known from eastern Pacific and mid-Atalantic vents, and differs from the other known congeners by its lack of obvious axial sculpture (hence ‘politus’, smooth), as well as a narrower umbilicus and the final 0.5 whorl of the teleoconch being less detached.

Lirapex politus n. sp., scale bars = 1 mm.

Dracogyra subfuscus Chen et al., 2017 (~7 mm shell diameter) is a depressed, globular, coiled peltospirid with a dark periostracum; the genus Dracogyra Chen et al., 2017 was established for this species. It is most similar to Depressigyra globulus Warén & Bouchet, 1989 known from the eastern Pacific, but easily separated from it by a lack of basal notch in the aperture and a more depressed shell with narrower umbilicus. Furthermore, the radula of D. subfuscus is highly characteristic with the central tooth being very wide and compressed.

Dracogyra subfuscus n. gen., n. sp., scale bars = 1 mm.

A Bayesian phylogeny using the mitochondrial COI barcoding gene confirmed the placement of the two new species in clade Neomphalina and family Peltospiridae. The two new species co-occur with two giant holobiont peltospirids including the scaly-foot Chrysomallon squamiferum Chen et al., 2015 and Gigantopelta aegis Chen et al., 2015, and are sometimes found on their body surface. The two new species do not host endosymbiotic bacteria and gut contents suggest that they probably feed on microbial film on chimney surfaces, as well as epibionts of the two larger peltospirids.

  • Chen C*, Zhou Y, Wang C, Copley JT (2017). Two new hot-vent peltospirid snails (Gastropoda: Neomphalina) from Longqi hydrothermal field, Southwest Indian Ridge. Frontiers in Marine Science, 4: 392. DOI: 10.3389/fmars.2017.00392

Two rare gastropods from two new vents!

Lead-authored paper reporting the unexpected discovery of two very rare snails in two new hydrothermal vent sites is now published in the peer-reviewed Open Access journal PeerJ! Read for free at: https://peerj.com/articles/4121/

In this paper, we report the discovery of two very rare gastropods – the calliostomatid Otukaia ikukoae Sakurai, 1994 and the muricid Abyssotrophon soyoae (Okutani, 1959) in newly located hydrothermal vent sites in the Okinawa Trough, Japan. One of the two new sites is named the “Fukai” site after the poisonous forest of the same name in the Studio Ghibli film “Nausicaä of the Valley of the Wind” (1984)! The discovery of these snails represent the second record of Calliostomatidae and the third Muricidae from vents, and also represent range extensions of both species to the southwest, by about 700 km in the case of O. ikukoae. Based on radular characteristics, O. ikukoae is returned to genus Otukaia from Tristichotrochus.

Specimens of the two gastropods collected from hydrothermally influenced areas.(A–D) Tristichotrochus ikukoae from Fukai site, Higashi-Ensei. (E–J) Abyssotrophon soyoae from Crane site, Tarama Hill; (E–H) Specimen #1, (I, J) Specimen #2. Scale bars: (A–D) 1 cm, (E–J) 0.5 cm.

Although this is the first time either species are observed in their natural habitat, both are considered to be occasional invaders of vent ecosystems from surrounding regular sea bottom and not vent endemics given their other records from non-vent environment as well as the fact that they were found in weak diffuse flow venting areas and not focused venting areas. Nevertheless, it is clear that they are able to tolerate, to a certain extent, environmental stresses associated with vents (e.g., raised heavy metal and hydrogen sulfide concentrations). This enables them to access to rich food supplies supported by chemosynthesis primary production, and suggest that vent periphery likely play a key role in the evolution of biological adaptation to hydrothermal vent environment.

The Fukai site (above) and the Crane site (below).

  • Chen C*, Watanabe HK, Miyazaki J, Kawagucci S (2017). Unanticipated discovery of two rare gastropod molluscs from recently located hydrothermally influenced areas in the Okinawa Trough. PeerJ, 5: e4121. http://dx.doi.org/10.7717/peerj.4121/

New paper on diversity of Mollusca at a shallow vent

Lead-authored paper on shallow water hydrothermal vent molluscs published in journal Marine Biodiversity! Read online for free here: http://rdcu.be/wKVR

Mar Biodiv, doi:10.1007/s12526-017-0804-2

This paper reports diversity of molluscs inhabiting shallow water (10-30m deep only!) hydrothermal vent ecosystem off Kueishan Island, Taiwan. Unlike deep-sea hydrothermal vents no endemic molluscs were found, and the species present were a subset of species present in surrounding areas that are apprently able to tolerate the ‘extreme’ environment. We report a total of 13 core species including 12 gastropods and one chiton, and discuss their ecology at the shallow vents.

Representative specimens of the 13 mollusc species collected from shallow hydrothermal vents off Kueishan Island, Taiwan

New paper on a chiton ‘cryptic species complex’ published!

New paper dealing with a ‘cryptic species complex’ of polyplacophoran molluscs (chitons) published in Marine Biodiversity! Open access, please read here: http://bit.ly/2okQQ56

In this work, we present a case study of a total-evidence approach to resolving difficult and perplexing ‘cryptic species complexes’. A Pacific shallow water chiton Leptochiton rugatus (Carpenter in Pilsbry, 1892) is supposed to have a very wide range from Japan to Baja California, but has been previously suggested to comprise several cryptic species. Our genetic haplotype network using specimens across the range revealed four discrete clusters. Most strikingly, the haplotype of L. rugatus sensu stricto (California to Baja California) was very different in structure from that of the cluster ranging from the panhandle of Alaska to Oregon. The latter was found to have extremely high side fidelity and patchy distribution, and we present evidence that it is likely a brooder. The difference in life-history strategies between these two clusters account for the differences in their genetic structure. Although morphological differences were observed, these were minor and insufficient to guarantee each as species-level lineages alone. Only with the difference in life-history strategy could they be confidently recognised as separate species, the latter we described as L. cascadiensis sp. nov. after the Cascadia costal bioregion which it inhabits.

L. cascadiensis harbouring putative eggs in the pallial cavity

Things without names are difficult to rationalise, and are difficult to conserve; assigning names to species is therefore critical to understanding and conserving biodiversity. This study shows that combining evidence from molecules, morphology, and importantly life-history, is key to untangling ‘cryptic species complexes’ which have become increasingly discovered in the recent years. The take-home message: if you want to solve cryptic species problems, don’t forget to look at their way of life!

This is my first time getting involved with describing a chiton, yay! Chitons are awesome.

Sigwart JD, Chen C (2017). Brooding behaviour explains patchy distribution in a shallow-water invertebrate (Mollusca: Polyplacophora: Lepidopleurida). Marine Biodiversity, First Online, DOI: 10.1007/s12526-017-0688-1