Re-establishment of Malletia sorror (Soot-Ryen, 1957), an endemic bathyal bivalve off Chile (Mollusca Bivalvia Nuculanoidea)

Abstract

Fresh material of a nuculanoid bivalve of the genus Malletia, collected during an expedition of the R/V SONNE off Chile in 2023, allows the re-establishment of Malletia sorror (Soot-Ryen, 1957), a species previously considered a synonym of M. peruviana Dall, 1908. The morphology and anatomy of the new material is described and the characteristics that justify a separation from M. peruviana Dall, 1908 are
worked out.

Full text

320
GAYANA
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Re-establishment of Mallea sorror (Soot-Ryen, 1957), an endemic
bathyal bivalve o Chile (Mollusca: Bivalvia: Nuculanoidea)
Restablecimiento de Mallea sorror (Soot-Ryen, 1957), un bivalvo baal endémico de las
costas de Chile (Mollusca: Bivalvia: Nuculanoidea)
Michael L. Zettler
Leibniz Institute for Baltic Sea Research (IOW), Warnemünde, Germany.
Corresponding author: michael.zeler@io-warnemuende.de
ABSTRACT
Fresh material of a nuculanoid bivalve of the genus Mallea, collected during an expedion of the R/V
SONNE o Chile in 2023, allows the re-establishment of Mallea sorror (Soot-Ryen, 1957), a species
previously considered a synonym of M. peruviana Dall, 1908. The morphology and anatomy of the new
material is described and the characteriscs that jusfy a separaon from M. peruviana Dall, 1908 are
worked out.
Keywords: Chile, Mallea, Malleidae, Mollusca, SE Pacic Ocean.
RESUMEN
Material fresco de un bivalvo nuculanoide del género Mallea, recogido durante una expedición del R/V
SONNE frente a las costas de Chile en 2023, permite restablecer Mallea sorror (Soot-Ryen, 1957), especie
considerada anteriormente sinónima de M. peruviana Dall, 1908. Se describen la morfología y la anatomía
del nuevo material y se elaboran las caracteríscas que juscan la separación de M. peruviana Dall, 1908.
Palabras clave: Chile, Mallea, Malleidae, Mollusca, Océano Pacíco SE.
INTRODUCTION
Members of the family Malleidae occur throughout the
Pacic, Indic and Atlanc Oceans with most records from
deep-waters (Sanders & Allen 1985; Huber 2010, 2015; Coan
& Valench-Sco 2012, Valench-Sco et al. 2020). Suárez-
Mozo et al. (2018, table 3) summarise the shell characteriscs
of all the Mallea species recorded in the eastern Pacic
Ocean. Only Mallea chilensis Des Moulins, 1832 and M.
sorror (Soot-Ryen, 1957) are missing. Not knowing why M.
chilensis was not menoned, the absence of M. sorror was
due to synonymisaon with M. peruviana by one of the co-
authors. Valench-Sco et al. (2020) examined the type
material of M. sorror and M. peruviana (at that me, only very
few specimens of the type localies were available) and found
that the dierences between these two species are minor and
synonymised the laer with M. peruviana. However, they also
predict a future analysis of this synonymy when addional
material is available. This nally leads to consideraon in
MolluscaBase (2024). To date, no new material has been
found for either M. sorror or M. peruviana. Only publicaons
are known of M. peruviana that always indicate the same
locality (holotype) in Peru (Dall 1908; Hertlein & Strong 1940;
Knudsen 1970; Alamo & Valdivieso 1997; Coan & Valench-
Sco 2012; Paredes et al. 2016; Valench-Sco et al. 2020).
The same is true for M. sorror in Chile (Soot-Ryen 1957, 1959;
Sco et al. 1990; Villarroel & Stuardo 1998).
By parcipang in the R/V SONNE expedion in January/
Gayana (2024) vol. 88, No. 2, 320-326
Original article

321
Re-establishment of Mallea sorror (Soot-Ryen, 1957): Zettler, M
February 2023 (SO296) o Chile, I had the opportunity to
obtain sample material from a transect 50 to 1850 metres.
At the deepest staon several Mallea individuals were
prominent, which were later determined as M. sorror, a
species synonymised with M. peruviana to this me. The
present study aims to rehabilitate M. sorror (Soot-Ryen, 1957)
as a good species.
MATERIAL AND METHODS
The material used in this study was taken o Chile during a
cruise with the research vessels SONNE (SO296). Sediment
samples were taken using a dredge. The samples were
sieved by washing retaining the fracons larger than 1 mm.
The residues were xed in ethanol and later sorted out and
determined in the laboratory.
Selected shells and specimens were colour-photographed
using a stereo Zeiss microscope Discovery.V8 in IOW. Digital
microphotographs were made using an AxioCam 105 color
(Carl Zeiss MicroImaging GmbH, Jena) and AxioVision soware
(Carl Zeiss Imaging Soluons GmbH, Jena). The resulng les
were imported into Adobe Illustrator 2023 (Adobe Systems
Incorporated) for further processing.
The material is deposited at the Chilean Naonal Museum
of Natural History in Sanago de Chile.
SYSTEMATIC RESULTS
Class: Bivalvia Linnaeus, 1758
Superfamily: Nuculanoidea H. Adams & A. Adams, 1858
(1854)
Family: Malleidae H. Adams & A. Adams, 1858 (1846)
Genus: Mallea Des Moulins1, 1832
Type species Mallea chilensis Des Moulins, 1832 (type by
monotypy).
Mallea sorror (Soot-Ryen, 1957)
(Figs 1A-J)
Malleella sorror Soot-Ryen, 1957: 2; Soot-Ryen (1959): 18,
pl. 1, gs. 4, 5; Villarroel & Stuardo (1998): 154, 182
Mallea sorror (Soot-Ryen, 1957): Sco et al. (1990): 9
1 Charles des Moulins, full name Charles Robert Alexandre des
Moulins (13 March 1798 – 23 December 1875) was a French
naturalist, a botanist and malacologist. The spelling Desmoulins can
also be found (e.g. in MolluscaBase 2024) (Further informaon at
hps://de.wikipedia.org/wiki/Charles_des_Moulins).
Material invesgated: Chile, 75 km o Concepción • 5
live collected specimens and 2 empty double valves; sta.
SO296/2-5; 36.3667°S, 73.8333°W; 1850 m; 22 Jan. 2023;
dredge. The material is kept at the Chilean Naonal Museum
of Natural History (Spanish: Museo Nacional de Historia
Natural or MNHN) under the collecon numbers MNHNCL
MOL 101636 and MNHNCL MOL 101637.
Compared photo material:
Malleella sorror Soot-Ryen, 1957: Holotype (USNM
606947), South-west coast o Chile, “Albatross” staon
2791; 38.1333°S, 75.8833°W; 1238 m; 14 Feb. 1888.
(hp://n2t.net/ark:/65665/m37c004327-7bba-452b-87a2-
5bf1b630a10b)
Mallea peruviana Dall, 1908: Syntype (USNM 110574),
Northern Peru, Aguja Point, “Albatross” staon 4654;
5.7667°S, -81.5333°W; 1895 m; 12 Nov. 1904. (hp://
n2t.net/ark:/65665/m34beaf136-d4cf-4a7b-a090-
fa96941c052b)
Descripon. See Figs. 1A-F. Shell equivalve, oblong oval,
moderately inated, a lile gaping antero and postero ventrally,
longer than high (length to height rao 1:0.6) (see Table 1),
inequilateral. Umbones broad and slightly protruding, located
about one-third of shell length from anterior end. Anterior
end rounded, posterior end truncated postero-ventrally.
Inner ventral margin smooth. Interior of valves smooth and
chalky-white. Pallial sinus very short but disnct (Fig. 1D, F).
Adductor muscle scars subequal. Exterior sculpture smooth-
glossy and with clear growth lines. Periostracum thin, glossy,
pale yellow to light brown. Hinge with 10 anterior V-shaped
teeth and 30 posterior teeth. Ligament long, external, narrow,
dark brown, extending nearly ¾ the length of posterodorsal
margin. Maximum length 19.5 mm, height 12 mm, width 8.5
mm.
Anatomy. See Fig. 1E. Foot massive, deeply cle medially;
digesve gland is prominent below the umbo; labial palp
around the middle of the animal, palp proboscis large with
disnct lamellae; lamellae of the gills relavely short, gills
range lile longer as the posterior hinge.
Habitat. Bathyal (1238 to 1850 m), so boom.
Distribuon. The species is currently only known from two
staons in the bathyal waters of central Chile (Fig. 3).

322
Gayana 88(2), 2024
Figure 1. Mallea sorror (Soot-Ryen, 1957), A-F: IOW-Material, Chile, o Concepción, Sta. SO296/2-5. A-D: length 18.5 mm; E: length
17.2 mm, (aa: anterior adductor muscle; dg: digesve gland; fo: foot; gi: gill; lp: labial palp; pb: palp proboscis; pm: posterior adductor
muscle; si: siphon) F: length 19.5 mm. G-J: Holotype (USNM 606947), Chile, o Lebu, Sta. Albatross 2791, length 18.3 mm. (The
holotype images G-J with authorisaon from the Department of Invertebrate Zoology, Naonal Museum of Natural History, Smithsonian
Instuon, Washington DC. Photo Credit: Marilyn Gaizband). / Mallea sorror (Soot-Ryen, 1957), A-F: IOW-Material, Chile, frente a
Concepción, Sta. SO296/2-5. A-D: longitud 18,5 mm; E: longitud 17,2 mm, (aa: músculo aductor anterior; dg: glándula digesva; fo:
pie; gi: branquia; lp: palpo labial; pb: probóscide palpebral; pm: músculo aductor posterior; si: sifón) F: longitud 19,5 mm. G-J: Holopo
(USNM 606947), Chile, frente a Lebu, Sta. Albatros 2791, longitud 18,3 mm. (Las imágenes del holopo G-J con autorización del
Department of Invertebrate Zoology, Naonal Museum of Natural History, Smithsonian Instuon, Washington DC. Crédito de la foto:
Marilyn Gaizband).

323
Re-establishment of Mallea sorror (Soot-Ryen, 1957): Zettler, M
Figure 2. Mallea peruviana Dall, 1908, A-D: Syntype (USNM 110574), Peru, Aguja Point, Sta. Albatross 4654, length 28 mm. (With
authorisaon from the Department of Invertebrate Zoology, Naonal Museum of Natural History, Smithsonian Instuon, Washington
DC. Photo Credit: Marilyn Gaizband). / Mallea peruviana Dall, 1908, A-D: Sinpo (USNM 110574), Perú, Punta Aguja, Sta. Albatros
4654, longitud 28 mm. (Con autorización del Department of Invertebrate Zoology, Naonal Museum of Natural History, Smithsonian
Instuon, Washington DC. Crédito de la foto: Marilyn Gaizband).
Table 1. Measurements of specimens of Mallea sorror from Chile o Concepción (Sta. SO296/2-5). / Medidas de ejemplares de
Mallea sorror de Chile frente a Concepción (Sta. SO296/2-5).
Specimens length
(mm)
height
(mm)
width
(mm)
length/
height
anterior
teeth
posterior
teeth
19.5 6.1 3.5 1.6 10 21
215.8 9.8 6.2 1.6 10 30
317 10.1 7 1.7 closed closed
417.5 10.5 7.8 1.7 10 32
518 11 7.9 1.6 closed closed
619 11.3 8.1 1.7 10 31
719.5 12 8.5 1.6 11 33

324
Gayana 88(2), 2024
Figure 3. Records of M. sorror (triangle) and M. peruviana (star) in waters o Chile and Peru (type = type locality; ps = present study). /
Registros de M. sorror (triángulo) y M. peruviana (estrella) en aguas de Chile y Perú (type = localidad po; ps = presente estudio).

325
Re-establishment of Mallea sorror (Soot-Ryen, 1957): Zettler, M
DISCUSSION
If we compare M. sorror with other Mallea species from the
Pacic using Table 3 of Suárez-Mozo et al. (2018) and the
monographic books by Coan & Valench-Sco (2012) and
Valench-Sco et al. (2020), the only similar species is M.
peruviana (see Table 2). All Mallea-species of SE Pacic (o
Peru and Chile), especially M. peruviana, have a very shallow
pallial sinus, whereas the sinus is more disnct in M. sorror. As
already stated by Soot-Ryen (1957, 1959) the most disnctly
feature of M. sorror is its broadly rounded anterior margin.
In contrast, Dall (1908) emphasised that the anterior margin
of M. peruviana is almost pointed, which can be clearly seen
when comparing Figures 1 and 2. Furthermore, the clear
dierence in size between M. sorror (maximum 19.5 mm) and
M. peruviana (28 mm) is striking. Based on the series of ve
individuals collected alive and two double valves, I assume
that I have recorded the size spectrum of M. sorror (see
Table 1). The holotype of M. sorror ts very well with a length
of 18.3 mm. Although only an indicaon for the separaon, the
distance between the type locality of M. sorror and our staon
is about 280 km, whereas it is about 3700 km compared to
the type locality of M. peruviana (Fig. 3). The maximum rao
of anterior to posterior teeth is 11/33 in M. sorror and 11 to
36 in M. peruviana. Although Soot-Ryen (1957, 1959) gives
10-11 anterior and 30-40 posterior teeth for the holotype of
M. sorror, it is not clear where this informaon comes from. At
that me only three specimens (two paratypes, one holotype)
were available (see Sco et al. 1990), and for the descripon
Soot-Ryen (1957) used the largest specimen, which has only
10 anterior to 30 posterior teeth.
Table 2. Summary of shell characters of Mallea peruviana and M. sorror from the Pacic Ocean. / Resumen de los caracteres de las
conchas de Mallea peruviana y M. sorror del Océano Pacíco.
Species Shape Type locality
Reported
depth
range (m)
Maximum
length
(mm)
Anterior
end
Pallial
sinus Hinge
Mallea
peruviana Dall,
1908
O Punta
Aguja,
Piura, northern
Peru
1900 28 pointed shallow
10–11 anterior
teeth; 33–36
posterior teeth
Mallea sorror
(Soot-Ryen,
1957)
South-west
coast o Chile,
“Albatross”
staon 2791
1230 -
1850 19.5 broadly
rounded disnct
10–11 anterior
teeth; 30-33
posterior teeth
CONCLUSION
In the end, the only conclusion that can be drawn is that
Mallea sorror (Soot-Ryen, 1957) is a separate species that
needs to be re-established. The material collected in the
present study certainly allows barcoding, but there is currently
no material available from M. peruviana that allows a genec
comparison.
ACKNOWLEDGEMENTS
We thank the crews and scienc stas of the cruise SO296
for their dedicaon during the sediment sampling. SO296
was part of the Mapuche project funded by the Federal
Ministry of Educaon and Research (grant no. 03G0296A).
Thanks to Frank Pohl and Mayya Gogina (Rostock) for helping
during the cruise. I would also like to thank the Department
of Invertebrate Zoology, Naonal Museum of Natural History,

326
Gayana 88(2), 2024
Smithsonian Instuon, Washington DC (Custodian John
Pfeier) for giving me the authorisaon to use the type
photographs.
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Received: 27.02.2024
Accepted: 03.09.2024
Editor: Fulgencio Lisón