Lyonsiella illaesa Machado & Sigwart, 2024
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publication ID |
https://doi.org/ 10.3897/BDJ.12.e128431 |
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publication LSID |
lsid:zoobank.org:pub:568D735E-05A9-4BA3-BAB5-A4765ABD2D71 |
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persistent identifier |
https://treatment.plazi.org/id/60E51ACC-06CA-5320-8447-26D5EF5FC449 |
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treatment provided by |
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scientific name |
Lyonsiella illaesa Machado & Sigwart |
| status |
sp. nov. |
Lyonsiella illaesa Machado & Sigwart sp. nov.
Materials
Type status: Holotype. Occurrence: catalogNumber: SMF 373402 ; recordedBy: AleutBio Expedition; individualCount: 1; occurrenceID: B722383F-07E8-577F-BB10-3F6DC87E2366; Taxon: scientificName: Lyonsiella illaesa Machado & Sigwart ; kingdom: Animalia; phylum: Mollusca; class: Bivalvia; order: Poromyida ; family: Lyonsiellidae ; genus: Lyonsiella ; specificEpithet: illaesa ; scientificNameAuthorship: Machado & Sigwart; nomenclaturalCode: ICZN; Location: higherGeography: Pacific Ocean; waterBody: U. S. Exclusive Economic Zone, Alaska Region, Aleutian Trench area; country: USA; locality: station 6-4 ; verbatimDepth: 5261-5318; verbatimLatitude: 50 ° 37.959 ' N; verbatimLongitude: 169 ° 44.368 ' W; Event: samplingProtocol: Epibenthic sledge (EBS); eventDate: 07 / 08 / 2022; Record Level: institutionCode: SMF; basisOfRecord: PreservedSpecimen GoogleMaps
Type status: Paratype. Occurrence: catalogNumber: SMF 374320 ; recordedBy: AleutBio Expedition; individualCount: 1; occurrenceID: 1AF2E5B8-C43B-5541-82FB-61C0C8BCD0AD; Taxon: scientificName: Lyonsiella illaesa Machado & Sigwart ; kingdom: Animalia; phylum: Mollusca; class: Bivalvia; order: Poromyida ; family: Lyonsiellidae ; genus: Lyonsiella ; specificEpithet: illaesa ; scientificNameAuthorship: Machado & Sigwart; nomenclaturalCode: ICZN; Location: higherGeography: Pacific Ocean; waterBody: U. S. Exclusive Economic Zone, Alaska Region, Aleutian Trench area; country: USA; locality: station 6-4 ; verbatimDepth: 5100-5170; verbatimLatitude: 51 ° 41.711 ' N; verbatimLongitude: 166 ° 28.024 ' W; Event: samplingProtocol: Epibenthic sledge (EBS); eventDate: 20 / 08 / 2022; Record Level: institutionCode: SMF; basisOfRecord: PreservedSpecimen GoogleMaps
Description
Holotype: SMF 373402, one whole individual with soft parts. Dimensions: Length: 2.7 mm; Height: 1.8 mm; Width: 1.6 mm (Fig. 8 View Figure 8 A-C).
Paratype: SMF 374320, one whole individual with soft parts. Dimensions: Length: 3.1 mm; Height: 2 mm; Width: 1.8 mm (Fig. 8 View Figure 8 D – M). This individual presents a natural deformity (nd) at the shell margin with subsequent repairs and a permanent opening (po) on the posteroventral margin, both probably caused by a teratological process during embryonic development. Similar deformities have already been observed in other species of verticordiid, such as Policordia uschakovi (Gorbunov, 1946) , Policordia lisbetae Knudsen, 1970 , Policordia ochotica Scarlato, 1981 and Lyonsiella subquadrata (Jeffreys, 1882) (see Knudsen (1970), fig. 89, Allen and Turner (1974), fig. 26 b, Safonova and Krylova (2020), figs. 3 and 4 b).
Shell: small (up to 3.1 mm in length), whitish to translucent, inflated, inequilateral; subrectangular, anterior margin rounded, posterior margin slightly truncate, ventral margin sinuous (svm / white arrows); inequivalve; umbones inflated, slightly prosogyrate; prodissoconch (200 ± 5 μm, n = 2), circular, smooth, preserved in the two individuals analysed (Fig. 8 View Figure 8 C, pr). Shell surface spiked (Fig. 8 View Figure 8 C, D and J, sp), densely occupied by series of long and pointed projections (= spikes) extending over all margins; small pustules or granules (= pustule-shaped spikes) in umbones and central part of shell, sometimes arranged radially; indistinct radial threads and concentric growth lines. Right valve overlapping left valve on dorsal and antero-posterior margins (Fig. 8 View Figure 8 B and C); lunule absent; shallow escutcheon (Fig. 8 View Figure 8 C, es); hinge edentulous; with lithodesma (Fig. 8 View Figure 8 L, li).
Anatomy:
Mantle margin: with two fused points, anteriorly forming short pedal gape and posteriorly forming siphonal apertures; posteroventrally, mantle margin fusion (Fig. 8 View Figure 8 J – M, mm) involving inner folds only (Type A) ( Yonge 1982); absence of fourth pallial aperture. No evidence of arenophilic glands (= radial mantle glands) and / or arenophilic secretions in outer surface of the shell. Perhaps functions of camouflage, strengthening thin shells and anchoring / stability in soft substrata, usually associated with such glands ( Prezant 1985, Machado et al. 2017, Morton and Machado 2019), are performed here by the thousands of spikes on the outer surface of the shell.
Siphons: Separated; inhalant siphon inverted (Fig. 8 View Figure 8 H, is), probably cone-shaped; both surrounded by small tentacles at base, ~ 8 in inhalant and ~ 3 in exhalant siphon, only a single row of tentacles was observed. Similar to other carnivorous anomalodesmatan, L. illaesa sp. nov. can be also characterised as ‘ lie-in-wait’ micro-predator ( Machado et al. 2017, Morton et al. 2019, Morton and Machado 2019), that is camouflaged within its habitat by detrital material attached to its shell by its thousands of spikes and capturing prey by eversion of the cone-shaped inhalant siphon.
Ctenidia: Reduced, non-plicate and horizontally aligned (Fig. 8 View Figure 8 H, J and K, ct); incomplete, with only inner demibranch, moderately shorter filaments in comparison with other lyonsiellids (e. g., Lyonsiella subquadrata , Lyonsiella fragilis Allen & J. F. Turner, 1974 ) and range in number from 8 to 10.
Labial palps: Non-lamellate, outer and inner palps short, unfused and elongated tips forming two wing-like lateral flaps (Fig. 8 View Figure 8 G, lp).
Musculature: Posterior and anterior adductor muscles present, isomyarian; with posterior and anterior pedal retractor muscle; posterior pedal retractor muscle bifurcated and dorsally attached to the shell close to the posterior adductor muscle (Fig. 8 View Figure 8 G, pprm); presence of taenioid muscle (= inhalant siphon retractor muscle) (Fig. 8 View Figure 8 G, tm).
Foot: Small, unpronounced heel (Fig. 8 View Figure 8 G and K, f); presence of a single byssal thread (Fig. 8 View Figure 8 K, bt).
Digestive system: Funnel-shaped mouth opening into a long oesophagus (Fig. 8 View Figure 8 M m, o) that enters into the anterodorsal portion of the stomach (Fig. 8 View Figure 8 L, st); stomach small, rounded, no crystalline style sac, no prey inside, surrounded dorsally, anteriorly and laterally by the gonads and the digestive gland; digestive diverticula with large gastric caecum (= blind ending tubules on both sides of the stomach walls) (Fig. 8 View Figure 8 L and M, dd / gc).
Organs of visceral mass: Pericardium / heart area well delimited (Fig. 8 View Figure 8 H, h / hs); paired kidneys restricted to the most posterior part of the body close to the posterior adductor muscle, posterior pedal retractor muscle and hind gut (Fig. 8 View Figure 8 H and J, k, pprm, hg). A lacunal system, formed by haemocoel spaces, is present in the posterior portion of the visceral mass, associated with the kidney and pericardium (Fig. 8 View Figure 8 H, h / hs). This system is commonly reported for members of Verticordioidea and appears to be an exclusive feature of this superfamily, having been associated with an important prey capture mechanism ( Morton 1984).
Reproductive system: Probably hermaphroditic, ovary well visible (> 30 mature oocytes counted, ~ 150 μm in diameter) (Fig. 8 View Figure 8 H, I, K and L, ov); at least two stages of gametogenesis observed, i. e. immature oocytes - small cells attached in the wall of the ovarian follicle and mature oocytes - larger and usually free in the ovarian lumen (Fig. 8 View Figure 8 H, I, K and L, io, mo); testis relatively small, oval and probably located in the anteroventral portion of visceral mass close to the ventral wall of the stomach (Fig. 8 View Figure 8 L, te?). It is also worth highlighting the possibility of L. illaesa sp. nov. having a brooding behaviour, since it presents some indirect evidence, for example, larval prodissoconch size, small dimensions of the body (miniaturisation) and the possibility of mature oocytes are, in fact, encapsulated oocytes (post-fertilisation). The brooding care has already been described for other anomalodesmatans, such as members of the Spheniopsidae ( Morton et al. 2016 a, Morton et al. 2016 b) and hypothesised for the verticordiid Trigonulina ornata d'Orbigny, 1853 ( Morton et al. 2019).
Nervous system: Cerebro-pleural (Fig. 8 View Figure 8 M, ceg), visceral (Fig. 8 View Figure 8 H, vg) and pedal ganglia present; statocysts were not observed associated with the latter.
Diagnosis
Shell whitish to translucent, thin, inflated, subrectangular, ventral margin sinuous; outer surface ornamented by spikes (> 1000) covering entire shell surface, except for prodissoconch (pr); umbones inflated and slightly prosogyrate; radial lines absent; hinge edentate; posterior pedal retractor muscle bifurcated; presence of taenioid muscle; ctenidia reduced, with only inner demibranch, horizontally aligned; absence of crystalline style sac; paired kidney restricted to the most posterior part of the body; presence of a single byssal thread; probably hermaphrodite with large oocytes.
Etymology
Relative to the absence of any damage caused during the morphological description. The Latin word illaesa [in (“ non ”) + laesa (“ lesion ”, “ wounded ”, “ damaged ")]. For the first time, a new species of mollusc is described in detail (including shell and internal tissues) without the use of any invasive tool.
Distribution
Known only from the Aleutian Islands, off Alaska, North Pacific. Bathymetric range: 5,100 –5,318 m, a new record for the genus previously recorded at 4,429 m in the North Atlantic (see Poutiers and Bernard (1995)).
Taxon discussion
This species was compared with all morphologically similar species of the genus and differs from the other Pacific species, such as Lyonsiella quaylei F. R. Bernard 1969 ( Coan and Valentich-Scott 2012, plate 326), Lyonsiella magnifica Dall, 1913 (holotype USNM 266802), Lyonsiella pacifica Dall, 1908 (holotype USNM 110583), Lyonsiella quadrata Hedley, 1907 , Lyonsiella aotearoa Dell, 1995 and others in having an outline more rectangular, a ventral margin sinuous, absence of radial lines and umbones more inflated and central (= less prosogyrate). These same features were also used to differentiate it from the Atlantic species Lyonsiella frielei Allen & Turner 1974 (holotype MCZ 272672), Lyonsiella abyssicola ( Machado and Passos 2022, fig. 3 j, MCZ 272772), Lyonsiella subquadrata (syntype USNM 63238, MCZ 272774, 348035) and all its possible shell variations illustrated by Allen and Turner (1974), figs. 1–2, 26–27. Regarding anatomy of new species, some features, such as the number of ctenidia filaments and siphonal tentacles, posterior pedal retractor muscle bifurcated, a single byssal thread, absence of crystalline style sac, paired kidney restricted to the most posterior part of the body, can also be used to differentiate it from their congeners, although the first two may be associated with intraspecific variations in individual size and shape, perhaps related to age.
Notes
Methods
The two well-preserved specimens analysed here were collected in the eastern part of the Aleutian Trench, Alaska by SO- 293 AleutBio Expedition, using epibenthic sledge ( EBS). The new species individuals are part of a larger collection with more than 1,200 lots and 3,500 individuals of Mollusca collected between 2,500 and 7,500 m depth. Both were described using only non-invasive techniques / tools, such as photos by stereomicroscope (Nikon) and tomographic images using the micro-CT scanner TomoScope ® XS Plus (Werth). Only the paratype was scanned, for this purpose, it was previously immersed in a contrast solution containing 0.3 % phosphotungstic acid ( PTA at a concentration of 99.995 %) with 3 % dimethyl sulphoxide ( DMSO) in 95 % ethanol by 7 days (adapted from Machado et al. (2019)). Scanning parameters were as follows: source voltage = 140 kV, current = 140 µA, exposure time = 666 ms, ignore images = 0, image quality = 10, voxel size = 3.56 µm, number of images per revolution = 1770, CTsensor = Kurzer _ AAI _ Size _ 007 _ XL, filter = no, drift correction = on, time of acquision = 3 h 16 min. Images were reconstructed and analysed using the software WinWerth ® RAW Viewer, Viewer and 3 D Viewer available in https://www.werth.de/en/downloads.html. In addition, all the volumetric datasets are on-line available at the Harvard’s Dataverse under the link https://doi.org/10.7910/DVN/ARIDIS. The holotype and paratype are archived at Senckenberg mollusc collection in Frankfurt am Main ( SMF). Other museum lots were also analysed for comparison with the new species, most of them available on the websites of the respective institutions ( MCZ – Museum of Comparative Zoology, Harvard, https://mczbase.mcz.harvard.edu/SpecimenSearch.cfm?collection_id=1; USNM – Smithsonian National Museum of Natural History, https://collections.nmnh.si.edu/search/iz/).
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