Research Article |
Corresponding author: Fang Chen ( zhchenfang66@21cn.com ) Academic editor: Matthias Glaubrecht
© 2025 Cong Wu, Fang Chen, Ying Tian, Kazutaka Amano, Xin Su.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Wu C, Chen F, Tian Y, Amano K, Su X (2025) A new species of genus Provanna (Gastropoda, Abyssochrysoidea) from gas hydrate-bearing sediments of the northern South China Sea. Zoosystematics and Evolution 101(1): 45-54. https://doi.org/10.3897/zse.101.137176
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The genus Provanna (belonging to Superfamily Abyssochrysoidea) is a group of globally distributed gastropods commonly discovered in the deep-sea chemosynthetic environments. To date it is composed of 29 extant and nine fossil species and all of them seem to be endemic to vents, seeps or organic falls. Despite the increasing interest in cold seeps in South China Sea in recent decades, how this genus is distributed in this area is largely unknown. A new fossil species, Provanna dongshaensis sp. nov., collected from the hydrate-bearing sediments in the cold seep area of northern SCS, was studied. A basic morphological description together with the observation of shell microstructures was made, and a brief comparison to known Provanna species was summarized. The occurrence depths of this new species are consistent with the remarkable negative carbon isotope of carbonate layers, which mutually supports the relationship to the ancient seep. Such sedimentary samples from drilling cores may be potentially better materials for systematic research of deep-sea gastropods and other chemosynthesis fauna.
Ancient seep, fossil, Provanna, South China Sea
Provanna is a genus of small gastropods found in deep-sea chemosynthetic communities such as hydrothermal vents, hydrocarbon seeps, and organic falls like sunken wood and whale falls. They are known to primarily feed on bacterial mats and detritus, functioning as both deposit feeders and grazers (
The genus Provanna is considered the most diverse among the superfamily Abyssochrysoidea (
Global distribution of genus Provanna displayed as type locations of known species and location of this study (GMGS2-07B and GMGS2-09B). orange circle: active hydrothermal vents, hydrocarbon seeps where extant Provanna species are discovered; blue circle: seep deposits or organic falls that yield fossil Provanna.
In the South China Sea (SCS), a marginal sea of the Pacific Ocean, seep carbonates were first discovered in the northern SCS in 2004 (
During China’s second gas hydrate drilling expedition (GMGS-2) in the east of the Pearl River Mouth Basin, SCS, long drilling core sediments containing carbonate deposits were obtained. This acquisition gave a chance to investigate the local chemosynthetic community with a special emphasis on animals that have carbonate shells. Several specimens of the provannid genus were fortunately retrieved from the hydrate-bearing layers and have been identified as a new type within the genus Provanna. In this study, we give a formal description of the specimens, together with observations of their shell microstructures. Additionally, we undertake some brief comparisons with other Provanna species, and explain the geological significance of this newly found species.
Specimens of the new fossil Provanna were discovered in two drilling sites, GMGS2-07B and GMGS2-09B, at a water depth of 791 m and 664 m respectively, located in Dongsha area, northern part of SCS (Fig.
The individual gastropods were collected after the treatment of sediment sample by soaking and screening, a similar laboratorial processing of the coarse fraction analysis. 16 to 40 grams of dried sediment for each sample was soaked for 2 days in the beaker without any chemical dispersing agent until completely dispersed. It was then washed through a 250-mesh copper screen (pore size = 0.063mm), until each sample was guaranteed to be clean. For each specimen, the sampling procedure is as follows: (1) Sectioning is performed along the axis from the apex to the umbilicus of the shell. This results in two cross-sections of the shell; (2) Sampling is conducted at intervals of 1cm from the apex, with each sample measuring approximately 1 cm×1 cm; (3) The sectioned shells are polished on sandpapers with grit sizes of 220, 600, 800, 1200, 2000, and 3000 for a duration of 3 minutes each; (4) After each polishing step, the specimens are cleaned in an ultrasonic cleaner for 15 seconds; (5) The polished samples are then immersed in an EDTA solution buffered with ammonia to a pH of approximately 7–8, with a small amount of formaldehyde added, for a period of 10 minutes; (6) The samples, after immersion, are cleaned in an ultrasonic cleaner for two cycles of 20 seconds each; (7) The samples are then air-dried in a cool, dry place for 48 hours; (8) The shell quality structure is initially observed under a microscope to assess clarity; if the structure is clearly visible, the process proceeds to the next step, otherwise, steps (3)-(8) are repeated. Morphological observation and morphometric measurements of the shell were carried out under a Zeiss Discovery V20 stereo microscope. Scanning electron microscopy (SEM) of these specimens were carried out uncoated at 15 kV in a Hitachi TM3030 SEM provided by Guangzhou Marine Geological Survey (GMGS).
Superfamily Abyssochrysoidea Tomlin, 1927
Family Provannidae Warén & Ponder, 1991
Trichotropis (Provanna) lomana Dall, 1918; Magdalena Bay, USA, Recent.
This new species is the only appearance of genus Provanna in SCS to date . We use the specific epithet “dongsha” to present the place where it is discovered.
Holotype : GMGS2-09B-C15-2. Paratype: GMGS2-07B-A1.
Site GMGS2-07B, GMGS2-09B, Dongsha area, northern SCS (Fig.
3.50, 3.60, 6.07 mbsf (meter below sea floor) at core GMGS2-09B, 33.85 mbsf at core GMGS2-07B; Carbonate layers, Late Pleistocene (Table
General information of specimens found in the Site GMGS2-07B and GMGS2-09B.
Specimens No. | Type | Measurements (mm) | Protoconch | Surface preservation | Depth (mbsf) | Sampling core | Ages (a.B.P.) |
---|---|---|---|---|---|---|---|
GMGS2-09B-C15-2 (Fig. |
holotype | shell height: 7.80; diameter of the last whorl: 5.02; apertural height: 3.66; shell thickness of the last whorl: 0.58 | broken | slightly eroded | 6.07 | 09B-4 | 16230 ± 50 * |
GMGS2-07B-A1 (Fig. |
paratype | shell height: >10.89; diameter of the last whorl: 7.13; apertural height: 6.77; shell thickness of the last whorl: 0.41 | unknown | strongly eroded | 33.85 | 07B-2H-2A | 91693** |
GMGS2-09B-C15-1 (Fig. |
(fragment) | broken | eroded | 3.50 | 09B-2M-1A | 15120 ± 50* | |
GMGS2-09B-C14 (Fig. |
(fragment) | unknown | strongly eroded | 6.07 | 09B-4 | 16230 ± 50* | |
GMGS2-09B-C13 (Fig. |
(fragment) | broken | eroded | 3.60 | 09B-2M-1A | 15120 ± 50* |
Type material and other fragment specimens. All specimens are deposited in China Deep Sea Drilling Core Repository, Guangzhou City, China.
Holotype is approximately 7.80 mm in height and 5.02 mm in width of the whole whorl, 3.66 mm in apertural height and up to 0.58 mm thick at the apertural wall. Apical angle of approximately 54° reaching at least 3.66 mm in height and 3.02 mm in width.
A medium-sized Provanna, sturdy, shell with prominent, angular whorls with nodes at intersection of the axial and spiral ribs.
Protoconch: at least one whorl, but poor preservation in all specimens; maximum diameter about 0.58 mm (Fig.
Provanna dongshaensis sp. nov., from a late Pleistocene seep site in the northern SCS. A–C. (Holotype, GMGS2-09B-C15-2). Specimen from core 09B-4, shell height: 7.8mm; D–F. (Paratype, GMGS2-07B-A1). Specimen from core 07B-2H-2A with the protoconch almost lost, shell height: 10.89mm; G–I. Incomplete specimen GMGS2-09B-C15-1 from core 09B-2M-1A; J–L. Incomplete specimen GMGS2-09B-C14 from core 09B-4. M-O. Incomplete specimen GMGS2-09B-C13 from core 09B-2M-1A. Scale bar: 5 mm.
(Table
Spatial distribution, geological time, and survival depth (extant species) of all known species of genus Provanna, associated with their morphological comparisons to the Provanna dongshaensis sp. nov. described in this study.
Species of Provanna | Distribution and Environment | Buried/survival depth (m) | Ocean/Area* | Age | Morphological comparison to P. dongshaensis sp. nov. |
---|---|---|---|---|---|
†P. alexi Amano & Little, 2014 | Shosanbetsu Village, northwestern Hokkaido, Japan, Chikubetsu Formation, whale-fall. | – | WP | Miocene | lack the strong angulation |
†P. antiqua Squires, 1995 | Washington State, USA, seep and wood-fall. | – | EP | Eocene to Oligocene | rounded whorls and lacks spines/tubercles |
†P. fortis Hybertsen & Kiel, 2018 | Satsop Weatherwax seep deposit, Washington State, USA. | – | EP | Eocene | the most similar,4–5 whorls, distinct angulation, 2 spiral ribs on the spiral base and up to 5 on the lowermost whorl, the same shelf-structure with new type, but less distinct strong axial structure, which make the new type a new species |
†P. hirokoae Amano & Little, 2014 | Joetsu City, Niigata, Japan, Ogaya Formation, seep. | – | WP | Miocene | lack the strong angulation |
†P. marshalli Saether, Little & Campbell, 2010 | East Coast Basin, North Island, New Zealand, Bexhaven and Ihungia Limestone Formation, seep. | – | WP | Miocene | similar to P. antiqua, lacks strong angulation but more spiral ribs on the whorls than P. dongshaensis sp. nov. |
†P. nakagawaensis Kaim, Jenkins & Hikida, 2009 | Nakagawa area, northwestern Hokkaido, Yezo Group, seep and wood-fall. | – | WP | Cretaceous | a distinct reticulate pattern, lacks the spines and does not have the shelf-structure made up by strong angulation |
†P. pelada |
Cerros El Pelado block 2, Talara Basin, Peru. | – | SA | Oligocene | – |
†P. tappuensis Kaim, Jenkins & Waren, 2008 | Tappu area, northwestern Hokkaido, Japan, Yezo Group, seep. | – | WP | Cretaceous | strong axial and spiral sculpture, but less spiral ribs on the body-whorl |
†P. urahoroensis Amano & Jenkins, 2013 | Urahoro, eastern Hokkaido, Japan, Nuibetsu Formation, seep. | – | WP | Oligocene | does not have the distinct reticulate pattern or anything resembling the spines |
P. dongshaensis sp. nov. (this study) | Dongsha area, northern South China Sea, seep. | – | WP | Late Pleistocene | – |
P. abyssalis Okutani & Fujikura, 2002 | Japan Trench, seep. | 5379 | WP | Recent | rounded whorls and lacks spines/tubercles |
P. admetoides Warén & Ponder, 1991 | Florida Escarpment, seep. | 624–631 | GM | Recent | more spiral keels on body-whorl, and also notably large number of axial ribs, up to 34–45 according to |
P. annae Nekhaev, 2023 | Plip Volcano, Bering Sea, vent. | 387–342 | NP | Recent | lack the strong angulation |
P. beebei |
Beebe Chimlets, Beebe Vent Field, Mid-Cayman Spreading Centre, vent. | 4956–4972 | CS | Recent | more number of spiral ribs and less strong axial ribs |
P. buccinoides Waren & Bouchet, 1993 | Hine Hina, Lau Basin; North Fiji Basin, vent. | 1900–2765 | WP | Recent | more angulation |
P. chevalieri Warén & Bouchet, 2009 | Regab site, West Africa, seep. | 3150 | WA | Recent | lack the shelf-structure |
P. cingulata Chen, Watanabe & Ohara, 2016 | the Shinkai Seep Field, Southern Mariana Forearc. | 5687 | WP | Recent | lacks angulation and axial sculpture, has an increasing number of spiral ribs |
P. clathrata |
Irabu Knoll and Hatoma Knoll, Okinawa Trough, Japan, vent. | 1647–1743 | WP | Recent | more angulation and spiny, no tubercles, and lacks the shelf-structure |
P. cooki |
East Scotia Ridge segment E9, Southern Ocean, vent. | 2394–2641 | SO | Recent | higher whorls and lacks tubercles |
P. exquisita Chen & Watanabe, 2022 | Eifuku Volcano, Mariana Arc, | 1606 | WP | Recent | more angulation to form spiral keels |
P. fenestrata Chen, Watanabe & Sasaki, 2019 | Crane site, Tarama Hill, Okinawa Trough, Japan, vent. | 1559 | WP | Recent | strong axial and spiral sculptures, raised and equally spaced |
P. glabra Okutani, Tsuchida & Fujikura, 1992 | off Hatsushima, Sagami Bay, Japan, seep. | 1110–1200 | WP | Recent | lack the strong angulation |
P. goniata Warén & Bouchet, 1986 | Guaymans Basin, seep. | 2000–2020 | EP | Recent | more angulation and spiny |
P. ios Warén & Bouchet, 1986 | East Pacific Rise 21°N–17°S, Galapagos Spreading Center, vent. | 2450–2620 | EP | Recent | more angulation, spiny, and higher spiral shell |
P. kuroshimensis |
Kuroshima Knoll, Okinawa, Japan, seep. | 644 | WP | Recent | lack the strong angulation |
P. laevis Warén & Ponder, 1991 | Gulf of California, Guaymas Basin, Oregon Margin, Juan de Fuca Ridge, vent and seep. | 500–2000 | EP | Recent | lack the strong angulation |
P. lomana Warén & Bouchet, 1986 | Oregon Margin, seep. | 450–1200 | EP | Recent | lack the strong angulation, and the spiral ribs on the body-whorl |
P. lucida |
Minami-Ensei Knoll, Okinawa Trough, Japan, vent. | 701 | WP | Recent | lack the strong angulation |
P. macleani Warén & Bouchet, 1989 | Oregon Margin, seep and sunken drift wood. | 2713–2750 | EP | Recent | more number of spiral ribs and less strong axial ribs |
P. muricata Warén & Bouchet, 1986 | East Pacific Rise 21°N, Galapagos Spreading Center, and North Fiji and Lau Back-Arc Basins, vent. | 2450–2615 | EP | Recent | more angulation and spiny |
P. nassariaeformis Okutani, 1990 | Mariana Back-Arc Basin, Manus Back-Arc Basins, vent. | 3670–3680 | WP | Recent | more number of axial ribs and lack the shelf-structure |
P. pacifica Warén & Bouchet, 1986 | Gulf of Panama; Oregon Margin; Costa Rica Margin | 1017–2750 | EP | Recent | more angulation and spiny |
P. reticulata Warén & Bouchet, 2009 | Regab, Guiness and MPS 1-Congo sites, West Africa, seep. | 750–3150 | WA | Recent | more angulation and spiny, more number of spiral ribs |
P. sculpta Warén & Ponder, 1991 | Louisiana Slope, seep. | 550 | GM | Recent | similar strong and swollen tubercles at the intersections between spiral and axial ribs, but lack the shelf-structure; and higher spiral shell |
P. segonzaci Warén & Ponder, 1991 | Lau Back-Arc Basin, vent. | 1750–1900 | WP | Recent | more angulation, spiny, and lack the shelf-structure |
P. shinkaiae Okutani & Fujikura, 2002 | Japan Trench, seep. | 5343 | WP | Recent | more angulation and spiny, higher spiral shell |
P. stephanos Chen, Watanabe & Sasaki, 2019 | ‘Off Hatsushima’ seep site, Sagami Bay, central Honshu, Japan, seep. | 908 | WP | Recent | major spines on the spiral ribs and more angulation to form spiral keels |
P. subglabra |
Okinawa Trough, Japan, vent. | 710–1632 | WP | Recent | lack the strong angulation |
P. variabilis Warén & Bouchet, 1986 | Juan de Fuca Ridge, Endeavour Segment, Gorda Ridge, Oregon Margin, vent, seep. | 675–2200 | EP | Recent | less strong axial ribs and lack the shelf-structure |
Only from the type locality and horizon.
The shell-shape characteristics can be used for the rapid identification of Provanna, particularly in fossil materials that lack organic body. Certain characteristics unify all Provanna species and distinguish the genus. Their specimens are never wider than tall. Regardless of their size, the specimens typically feature no more than 2 to 3 unbroken shell whorls, thin periostracum, no umbilicus, and small, turbinate, dextral shells. Their apertures have a characteristic shape, rarely being circular or ovate.
Despite the absence of a radula in our material, the polytomous key for species identification by
To facilitate a more in-depth discussion of other complex structural varieties, particularly the differentiation of fossil species, additional essential points regarding the shell, including angulation, tubercles, spiral ribs, and shelf-structure, are consequently elaborated upon here as supplementary remarks to “Remarks.”
Two Miocene fossil species, P. alexi and P. hirokoae, inhabited the Japanese seep location described by
Especially the emergence of bead-like tubercles in P. dongshaensis sp. nov. seems to be a unique trait only shared with one extant species (P. sculpta) living in the Gulf of Mexico and Caribbean Sea, far from SCS. The new fossil species P. dongshaensis sp. nov. can therefore be quickly distinguished from other species that are angulate and spiny, such as P. goniata, P. ios, P. pacifica, P. muricata, P. reticulata, P. segonzaci, P. shinkaiae, and P. stephanos. Another similar species, Provanna fortis, shares some features with P. dongshaensis sp. nov., including pronounced angulation, 2 spiral ribs on the spiral base and up to 5 on the lowermost whorl, and a shelf-structure, etc. However, it features less robust axial structures on the body whorl with no indication of inflated tubercles or bead-like strings.
The observation of shell microstructures was used as supplemental evidences for elucidation of the fossil vent and seep gastropods since they lost the organic body. According to the important report of microstructure related to provannid gastropods by
In P. dongshaensis sp. nov., the central complex crossed lamellar layer is markedly found in the SEM and present at all sections of the shell (Fig.
Shell microstructures of Provanna dongshaensis sp. nov. observed in SEM. A. Marginal exposure of specimen GMGS2-09B-C13; B. Eroded surface of specimen GMGS2-09B-C13; C, D. Marginal exposure of specimen GMGS2-09B-C14. Abbreviations: oSPL = outer simple prismatic layer; CCL = complex crossed lamellar layer; iSPL = inner simple prismatic layer. Scale bar: 200 μm (A), 100 μm (B), 50 μm (C), 30 μm (D).
P. dongshaensis sp. nov. were yielded at the depth of 3.50, 3.60, 6.07 mbsf in GMGS2-09B and 33.85 mbsf in GMGS2-07B (Table
At the burial depths of the genus Provanna, a diverse assemblage of other gastropod species has also been identified. These species belong to the genus Pusia (Family Costellariidae), Canidia (Superfamily Buccinoidea), Epitonium (Family Epitoniidae) and Lissotesta (Family Skeneidae) (data to be published). The occurrence of these gastropod fossils is closely correlated to the distribution of carbonate nodules, validating the inference that the beddings containing carbonate nodules in the study area are indicative of paleo-seepage activity across different phases/epochs. These episodic paleo-seepage events had created environments that were conducive to the growth and development of benthic organisms, particularly gastropod species.
Considering the adaption and endemic distribution, the discovery of provannid gastropods and accurate identification of P. dongshaensis sp. nov. could be the biological evidence, and play an essential role in explaining the existence of the ancient seep in the northern SCS during the Pleistocene. To date, P. dongshaensis sp. nov. is the only known Provanna fossil record in this hydrate-yielded location and in the Pleistocene epoch, expanding the geological range of genus Provanna geographically and temporally. To further understand and interpret the evolutionary history of genus Provanna, additional real fossil specimens should be gathered and examined in the future.
Furthermore, the carbonate nodules creating carbonate layers have widespread appearance in the neighboring drilling cores of this area, (e.g., at least 13 unique carbonate layers were recognized in GMGS2-08,
I would like to thank Steffen Kiel, for discussion of shell structures and shell formation in gastropods, and two anonymous reviewers for their critical reading of the manuscript. This study was financially supported by the National Natural Science Foundation of China (grant No. U2344222).