Bull. Tohoku Univ. Museum. No. 23, pp. 23‒34, 2024
© by The Tohoku University Museum

A new species of Parisicaris (Microcarididae, Thylacocephala)from the upper Olenekian (Lower Triassic) Osawa Formationin the South Kitakami Belt, Northeast Japan
Masayuki Ehiro* and Harumasa Kano
The Tohoku University Museum, Sendai 980-8578 Japan,*Corresponding author (e-mail: masayuki.ehiro.d4@tohoku.ac.jp)
Abstract: A new thylacocephalan species of the microcarid genus Parisicaris, Parisicaris naoyai, is
described from the upper Olenekian (Lower Triassic) Osawa Formation in the South Kitakami Belt,
Northeast Japan. It belongs to family Microcarididae and is associated with the thylacocephalan
fauna, comprising the genera Ankitokazocaris, Concavicaris, Kitakamicaris, Miyagicaris andParaostenia. The generic classification of family Microcarididae and the species composition of
genus Parisicaris are also discussed.

Introduction
Thylacocephala is a class commonly considered tobelong to subphylum Crustacea (e.g. Lange et al., 2001).
Although it has a long stratigraphic record ranging from the
Silurian (or Cambrian) to the Cretaceous and has a wide
geographic distribution, only approximately 30 genera havebeen described at present (Schram, 2014; Ehiro et al., 2015,2019). Before the mid-2010s, Triassic thylacocephalans
had been reported mainly from various localities in southern
Europe of Austria, Italy, Spain and Slovenia, whereas theoccurrences of other regions are rare only from Madagascar
and South China. In particular, the Early Triassic records arelimited to Madagascar (Ehiro et al., 2015). However, overthe past decade, information of Triassic thylacocephalans
has increased markedly, and new occurrences from theLower Triassic have been reported from Northeast Japan(Ehiro et al., 2015, 2019), Western Australia (Haig etal., 2015), southern China (Ji et al., 2017, 2021), Idaho,
USA (Brayard et al., 2017, Charbonnier et al., 2019 andLaville et al., 2021), as well as Middle Triassic strata fromsouthern China (Feldmann et al., 2015) and northern Italy(Teruzzi and Muscio, 2018). These informations suggestthat thylacocephalans were already diversified and widelydistributed in low- to mid-latitude areas worldwide during the
Early Triassic (Ehiro et al., 2019).
Family Microcarididae is a major component of theTriassic thylacocephalan fauna; this family was present
throughout the Triassic, and broadly distributed worldwide.
In this study, we describe a new species of the microcarid
genus Parisicaris, Parisicaris naoyai, from the Lower

Triassic (upper Olenekian) Osawa Formation distributed in
the South Kitakami Belt of Northeast Japan, and discuss thegeneric classification of family Microcarididae and species
composition of genus Parisicaris.
.

Geological setting and materials
Among the Japanese Islands, thylacocephalans have beenreported only from the Lower Triassic Osawa Formation,
distributed in the Minami-sanriku area (Miyagi Prefecture) of
the South Kitakami Belt. The Osawa Formation is 250–350
m thick, and mainly composed of laminated mudstone. The
late Olenekian ammonoids are abundant from the lower toupper parts (e.g. Bando and Shimoyama, 1974; Ehiro et al.,2016; Shigeta, 2022) and uppermost part of the formation(Ehiro, 2022). Thylacocephalans have been collectedfrom three localities (Motoyoshi, Tatezaki A and Tatezaki
B; Figure 1) in the lower to middle parts of the formation(Ehiro et al., 2015, 2019). However, most samples havebeen obtained from the Tatezaki B locality, with very few
derived from other two localities. The fossil horizon of the
Tatezaki B locality is considered to represent middle partof the Osawa Formation, and six species belonging to fivegenera have been described from an interval 2 to 4 m above
the base of the sequence in this locality (Ehiro et al., 2019):
Ankitokazocaris bandoi Ehiro and Kato (Ehiro et al., 2015),
Ankitokazocaris tatensis Ehiro et al., 2019, Concavicaris
parva Ehiro et al., 2019, Kitakamicaris utatsuensis Ehiro
and Kato (Ehiro et al., 2015), Miyagicaris costata Ehiro etal., 2019 and Ostenocaris sp. In this fauna, K. utatsuensis isdominant, comprising more than 90% of the collection. The

24

Masayuki Ehiro and Harumasa Kano

stratigraphy and fossil assemblages of the Osawa Formation
have been described in detail in the previous researches(Ehiro et al., 2015, 2016 and 2019).

naoyai and Paraostenia sp.

Figure 2. Morphological terminology and dimensions
for the carapace in lateral view. Aav, angle (degree) of
anteroventral process; am, anterior margin; dm, dorsal
midline; H, Ha, Hp, maximum, anterior and posterior
carapace height (mm), respectively; L, carapace length(mm); pm, posterior margin; vm, ventral margin.

Figure 1. Index map showing the fossil locality (Tatezaki
B locality) in the Utatsu area of the southern part of theSouthern Kitakami Massif (South Kitakami Belt), Northeast
Japan. NDB: Nedamo Belt; NKB: North Kitakami Belt; SKB:South Kitakami Belt.
Recently Laville et al. (2021) suggested that there isconfusion between genus Ostenocaris Arduini et al., 1984
(originally described as Ostenia by Arduini et al., 1980)and Paraostenia Secrétan, 1985, stemming from the reportof Arduini et al. (1980), in which some specimens withquite different morphology from Ostenocaris and more
likely belonging to Paraostenia, were classified as Ostenia
cypriformis. Therefore, Laville et al. (2021) suggested thatsome taxa attributed to Ostenocaris, including Ostenocaris
sp. from the Osawa Formation, should be ascribed toParaostenia. We agree that Ostenocaris sp. from the Osawa
Formation belong to the genus Paraostenia. Laville et al.
(2021) also raised questions concerning the taxonomy
of some genera and species from the Osawa Formation,
including C. parva, K. utatsuensis and M. costata. However,
we do not agree with this latter proposal, as discussed laterin this study.
The present specimens of Thylacocephala, describedas P. naoyai sp. nov., were collected from the Tatezaki
B locality in association with the thylacocepalan species,
mentioned above. Therefore, the Osawa thylacocephalan
fauna comprises seven species belonging to six genera: A.
bandoi, A. tatensis, C. parva, K. utatsuensis, M. costata, P.

The morphological terminology, dimensions and theirabbreviations follow Ehiro et al. (2015; Figure 2), but using
the term “dorsal midline” instead of “dorsal margin” following
the observation and advocacy of Laville et al. (2021) that thethylacocephalan carapace (“shield” in Laville et al., 2021) is
univalve, and not bivalve. Arduini (1988) reported that thecarapace of Thylacocephala is univalve, as there is no hinge
between the both sides of the carapace of “Atropicaris” indorsal view (butterfly position), as also described by Lavilleet al. (2021). We agree with them because we also havesome thylacocephalan specimens in butterfly position orequivalent to it, the dorsal midlines of them are only carinate
without hinge lines (Figure 3); therefore, we used the terms“left side” and “right side” (of the carapace) rather than “leftvalve” and “right valve” (Ehiro et al., 2015, 2019).

Systematic description
The specimens described in this study are held in theInstitute of Geology and Paleontology, Tohoku University,
Sendai (IGPS; Tohoku University Museum) and the Utatsu
Ichthyosaur Museum (UIM; Educational Committee of
Minamisanriku Town, Miyagi Prefecture).
Class Thylacocephala Pinna, Arduini, Pesarini and Teruzzi,
1982
Family Microcarididae Schram, 2014
Included genera.— Ferrecaris Calzada and Mañé, 1993,
Kitakamicaris Ehiro and Kato (Ehiro et al., 2015), Microcaris
Pinna, 1974, Miyagicaris Ehiro et al., 2019 and Parisicaris
Charbonnier (Charbonnier et al., 2019).
Discussion.— Schram (2014) proposed the new family
Microcarididae, as part of a working set of hypotheses

A new species of Parisicaris (Triassic Thylacocephala) from Japan

Figure 3. Dorsal views (in butterfly position) of
thylacocephalan specimens from the Tatezaki B locality
showing univalve nature of carapaces.
1, Ankitokazocaris cf. bandoi Ehiro and Kato in Ehiro etal., 2015, IGPS coll. cat. no. 112846; 1a, dorsal view; 1b,
enlarged view of the dorsal midline of 1a; 2, Kitakamicaris
utatsuensis Ehiro and Kato in Ehiro et al., 2015, IGPS coll.
cat. no. 111456; 2a, dorsal view; 2b, enlarged view of thedorsal midline of 2a. dm, dorsal midline.
on the taxonomic subdivision of Thylacocephala, which
included the Triassic genera Atropicaris Arduini and Brasca,
1984, Ferrecaris and Microcaris, and the Cretaceous
genus Thylacocephalus Lange et al., 2001. The diagnostic
characters listed by Schram (2014) are as follows: small
to modest in size; thin pointed rostrum, anteriorly directed;
carapace surface with rugations or terraces.
Hegna et al. (2014) compared the Cretaceous genus
Polzia Hegna et al., 2014 with Microcaris. However, with theproposal of the new microcarid genus Kitakamicaris from theTriassic of Northeast Japan, Ehiro et al. (2015) claimed that25

the genera Thylacocephalus and Polzia should be excluded
from this family, because they have a distinct posterior
spine, which can be compared to those of Cretaceous
genera belonging to family Protozoeidae Schrum, 2014
(e.g. Protozoea Dames, 1886 and Pseuderichthus Dames,
1886). Charbonnier et al. (2017) added the Cretaceous
genus Keelicaris Charbonnier et al., 2017 and Jurassic
genus Rugocaris Tintori et al., 1986, together with
Thylacocephalus, to family Microcarididae on the grounds
that they have remarkable ribs on the carapace, which
are similar to other genera of Microcarididae. However, as
noted by Ji et al. (2021), there remains some confusion
about the classification of Keelicaris and Thylacocephalus.
Later, Charbonnier et al. (2019) proposed a new microcarid
genus, Parisicaris, from the Lower Triassic of Idaho, andexcluded Keelicaris, Rugocaris and Thylacocephalus from
the Microcarididae. Ehiro et al. (2019) added the new genus
Miyagicaris, associated with Kitakamicaris, from the Lower
Triassic of Northeast Japan.
Tintori et al. (1986) suggested that Atropicaris rostrata
Arduini and Brasca, 1984 could be considered a juniorsynonym of Microcaris minuta Pinna, 1974, as these
species have the same carapace outline and carapace
ornamentation, differing only in size. Arduini (1988) rejected
this view based mainly on the observations that Microcaris
bears a well-developed, strong and pointed rostrum,
whereas Atropicaris has a thin rostrum that ends in a spoonlike expansion; that the carapace of Microcaris is coveredby fine, irregularly developed, straight transverse ribs,
whereas Atropicaris shows strong, developed sigmoidal ribs;
and that Microcaris and Atropicaris differ in the variabilityof their forms, with Microcaris specimens showing wide
variability within a very small number of individuals, whereas
Atropicaris is characterized by the near-homogeneity of
its form. Tintori et al. (1986) reported that differences inornamentation between Atropicaris and Microcaris depend
exclusively on specimen size, but large specimens ofMicrocaris comparable to those of Atropicaris retained thesame characteristics as smaller individuals. Recently, Ji etal. (2021) suggested that morphological differences between
Microcaris and Atropicaris specified by Arduini (1988)
resulted from preservation and intraspecific variability, andconcluded that genus Atropicaris is a junior synonym ofgenus Microcaris, while accepting the specific validity of “A.”
rostrata (as Microcaris rostrata [Arduini and Brasca]).
Microcaris minuta specimens described by Pinna (1974,1976), Arduini (1988), and Dalla Vecchia and Muscio (1990)
showed broad “intraspecific” variability in the carapace
outline. Dalla Vecchia and Muscio (1990) divided these
into forms designated A–D. Form A resembles a paratypedescribed by Pinna (1974, p. 31, fig. 16), and has abroadly rounded anteroventral margin without a remarkable26

Masayuki Ehiro and Harumasa Kano

anteroventral process. Form B is characterized by a largely
obtuse anteroventral process and mountain-shaped convex
venter. Form C is similar to form B in the carapace outline,
but has somewhat sigmoidal ribs, similar to “Atropicaris.” The
carapace outline of form D is similar to that of the holotypeof Microcaris minuta, and has large, obtuse anteroventral
process and nearly flat to broadly convex venter (Figure 4).
There are some common elements in morphology among
the specimens belonging to Microcaris and “Atropicaris.”
The carapace height/length (H/L) ratio of all forms ofMicrocaris and “Atropicaris” are within the range of 0.4–0.5,
regardless of size (Figure 5A). The anteroventral processangles (Aav in Laville et al., 2021) are all large andobtuse, ranging from 100° to 140°, and become larger withincreasing carapace size (Figure 5B). Therefore, it is difficult
to discriminate M. minuta forms B and C and “A.” rostrata.
Furthermore, some specimens reported by Dalla Vecchia(1993) as Microcaris minuta have a thin rostrum ending in aspoon-like expansion and somewhat sigmoidal ribs, both ofwhich are characteristics shared by “Atropicaris.” Althoughsome problems remain to be resolved and it is difficult tojudge whether these morphological differences among theMicrocaris minuta specimens are the result of intraspecificvariability, we tentatively follow Ji et al. (2021) and treat“Atropicaris” rostrata as a species of genus Microcaris.
Genus Microcaris (including Atropicaris) is clearly
different from other genera of Microcarididae in having
the following characters (Figures 4 and 6): the base of therostrum is connected to the anterior margin of the carapace
by subangular (not circular) corners; the angle of theanteroventral process (Aav) is large and obtuse (100°–140°);and the posterior margin is concave, with sharply pointed
dorso- and ventroposterior processes. The holotype of
M. minuta with a broadly convex venter seems to havea narrowly rounded dorso- and ventroposterior process.
However, its posterior part is somewhat poorly preserved,
and a specimen reported by Arduini (1988, pl. 16, fig.
2) with nearly the same carapace outline has a pointed
dorsoposterior process (ventroposterior process is not wellpreserved).
The monotypic genus Ferrecaris, the type species of which
is Ferrecaris magransi Calzada and Mañé, 1993, describedfrom the Ladinian bed in Spain is distinguished from othergenera of Microcarididae by its acute posterior margin.

Figure 4. Sketched reconstructions of the carapaces of some species of Microcarididae.
Those of Microcaris and “Atropicaris” species were prepared from the figures of Arduini and Brasca (1984) and Arduini(1988); The posterior margin of Microcaris minuta form D was estimated from pl. 16, fig. 1 of Arduini (1988); those of
Parisicaris rectilineatus and Parisicaris triassica are from Ji et al. (2021) and Laville et al. (2021), respectively. Scale bar isfor all figures.

A new species of Parisicaris (Triassic Thylacocephala) from Japan

Figure 5. Plots of the (A) carapace height/length ratio (H/L-L) and (B) anteroventral process angle (Aav) to carapace
length (L) for Microcaris and “Atropicaris” species.
However, specimens of F. magransi are poorly preserved
and the outline of the posterior part is unclear (Calzada
and Mañé, 1993, fig. 1). With the exception of the posterior
end, the carapace outline and carapace ornamentation of
F. magransi are very close to those of M. rostrata (Arduini
and Brasca) and some specimens described as M. minuta
by Dalla Vecchia (1993). Therefore, there remain questions
about the validity of genus Ferrecaris.
Laville et al. (2021) claimed that the genera Kitakamicaris
Ehiro and Kato (Ehiro et al., 2015) and Parisicaris
Charbonnier (Charbonnier et al., 2019) are junior synonyms
of Ankitokazocaris Arduini, 1990, and that M. costata Ehiro
et al., 2019 may be a synonym of K. utatsuensis Ehiro andKato (Ehiro et al., 2015). Laville et al. (2021) stated that
Kitakamicaris and Parisicaris have a morphology diagnosticof Ankitokazocaris, and that the vertical ridges (ribs) thatcharacterize these genera (Kitakamicaris and Parisicaris)
may vary according to the sex, ontogeny or molting cycleof the organism, and can also be affected by the type ofpreservation.
However, there are obvious differences in carapace
morphology between Ankitokazocaris and KitakamicarisParisicaris. As noted in the emended diagnosis of genus
Ankitokazocaris (Laville et al., 2021, p. 78), Ankitokazocaris
has “a ventral margin subdivided into a sub-horizontal
anterior part and a posterior part steeply descending
anteroventrally,” whereas Kitakamicaris and Parisicaris (andother genera belonging to family Microcarididae) have amount-like convex ventral margin, the anterior part of which
is not sub-horizontal.

27

The bases for the second argument, outlined above,
which deny the validity of surface ornamentation as acriterion of thylacocephalan classification, are hypotheticaland lack reliable evidence. Laville et al. (2021, p. 80) statedonly that “the outer layer of the shield is formed of sinuous,
small and thin vertical ridges (Fig. 7E–G)” in the descriptionof the shield ornamentation of Ankitokazocaris acutirostris
Arduini, 1990. However, it is difficult to find any verticalridges or ribs in these figures. Moreover, they described that“no transversal ridges were found in A. acutirostris” (p. 88).
Likewise, they also stated that “with the reinterpretation of
Parisicaris as Ankitokazocaris, we show that specimens ofAnkitokazocaris can be preserved as a smooth shield, with
only few ridges or with a fully ornamented shield” (p. 79).
No specific evidence for these claims is provided, and theirfigure 10A–D for “Ankitokazocaris” triassica (p. 88) may be
the only case. This specimen is a very poorly preserved
Parisicaris, and there are no true Ankitokazocaris specimens
with vertical ribs (including poorly developed), nor Parisicaris
specimens originally having a smooth carapace.
For genus Kitakamicaris, we have more than 200
specimens of K. utatsuensis, including fragmental
specimens, ranging in size (carapace length) from ca. 19
to 38 mm, which are considered to represent rather wide
ontogenetic stages. The ratio of H/L ranges from 0.45 to
0.55, which show only a slight decreasing tendency withincreasing size (Figure 6A). The Aav concentrated around90°, mostly in the range of 87°–93°, and is also independentof size (Figure 6B). Kitakamicaris utatsuensis specimens
ranging in size from smallest (L = ca. 19 mm) to largest (L= ca. 38 mm) are shown in Figure 7. There are almost no
differences in carapace outline and rib pattern, except fora slight decreasing trend in the ratio of H/L with increasing
size. In addition, the number of vertical ribs of K. utatsuensis
specimens is constant throughout the ontogenetic
stages (Figure 6C), although the rib measurements
are rough estimates due to irregular rib bifurcation andpoor preservation. All fragmental specimens also show
remarkable ribbing; there are no smooth or poorly ribbed
specimens.
Therefore, the hypothesis of Laville et al. (2021) thatgenera Kitakamicaris and Parisicaris are junior synonyms
of Ankitokazocaris is unacceptable, and we consider both
Kitakamicaris and Parisicaris to be valid genera.
Miyagicaris costata Ehiro et al., 2019 has an acute (ca.
70°) Aav clearly different from that of Kitakamicaris. It isalso characterized by strong, dendritically branched ribsin the anterior third of the carapace. Laville et al. (2021)
suggested that the dendritic branching of ribs is ostensible,
caused by deformation and fracturing. It is true that theholotype specimen of M. costata suffered some fracturing in
its upper (dorsal) part and near posterior end; however, as28

Masayuki Ehiro and Harumasa Kano

Figure 6. Plots of the (A) carapace height/length ratio (H/L-L) and (B) anteroventral process angle (Aav) to carapace
length (L) for some genera and species of the Microcarididae, and (C) the primary rib number to L for Kitakamicaris.
H, L and Aav data for Microcaris (including “Atropicaris”) were estimated from figures of Arduini and Brasca (1984)
and Arduini (1988). Those of Parisicaris triassica were obtained from Laville et al. (2021). H and L data for Parisicaris
rectilineatus were obtained from Ji et al. (2021) and Aav data were estimated from figures of Ji et al. (2021). Data for
Kitakamicaris utatsuensis and Parisicaris naoyai are provided in Appendices A and B, respectively.

A new species of Parisicaris (Triassic Thylacocephala) from Japan

29

Figure 7. Kitakamicaris utatsuensis specimens of various sizes, sampled from an outcrop in the middle part of theOsawa Formation at the Tatezaki B locality, Utatsu, Minamisanriku Town.
1, IGPS coll. cat. no. 112783 (largest specimen); 2, UIM 30604; 3, IGPS coll. cat. no. 112786; 4, IGPS coll. cat. no.
111448 (holotype); 5, IGPS coll. cat. no. 112796; 6, IGPS coll. cat. no. 111453; 7, IGPS coll. cat. no. 111481 (smallest
specimen). dm, dorsal midline; ls, left side; rs, right side. IGPS, Institute of Geology and Paleontology, Sendai; UIM, Utatsu
Ichthyosaur Museum. Scale bar is for all figures.

shown in photographs and line drawings (Ehiro et al., 2019,fig. 10A–10D), the dendritic branching in the anteroventral
region was clearly not affected by fracturing. This inferenceis supported by the smooth continuity of the lower part of theanterior margin and anterior half of the ventral margin.
Genus Parisicaris Charbonnier in Charbonnier, Brayard andthe Paris Biota Team, 2019
Type species.— Parisicaris triassica Charbonnier(Charbonnier et al., 2019)
Parisicaris Charbonnier (Charbonnier et al., 2019)
Microcaris (Parisicaris) Charbonnier (Charbonnier et al.,2019). Ji et al., 2021

Masayuki Ehiro and Harumasa Kano

30

Ank itokazocaris Arduini, 1990, Laville, Smith, Forel,
Brayard and Charbonnier, 2021
Included species.— Parisicaris naoyai sp. nov., P.
rectilineatus (Ji et al., 2021), P. triassica Charbonnier(Charbonnier et al., 2019).
Emended diagnosis.— The trapezoidal carapace has arelatively large, rounded optic notch, limited by a short thickrostrum, broadly fused with the carapace, and narrowly
rounded, remarkable anteroventral process. In side view,the dorsal midline is broadly convex and the ventral margin
is convex and mountain shape. The short, nearly straight
posterior part is slightly inclined backward to the verticalaxis, with narrowly rounded dorso- and ventroposterior
processes. The carapace surface is ornamented by oblique,widely spaced ribs.
Discussion.— Charbonnier et al. (2019) proposed a new
genus Parisicaris belonging to family Microcarididae, with P.
triassica as the type species. A distinctive ventral notch at
the anterior part of the ventral margin, which was deemed
to be a diagnostic feature of the new genus, was laterinterpreted as an artifact of preparation (Laville et al., 2021).
Ji et al. (2021) also pointed out that this feature was related
to preservation. We agree with these opinions, althoughspecimens of Parisicaris have other morphological featuresthat allow its taxonomic identification. Laville et al. (2021)
concluded that the genus Parisicaris is a junior synonym of
Ankitokazocaris Arduini, 1990, because these two genera
have the same morphological characteristics. As discussed
above, this inference is based on hypotheses unsupportedby specific evidence and erroneous identification, and is
unacceptable.
Ji et al. (2021) considered Parisicaris to be a subgenus
of Microcaris Pinna, 1974, and described a new speciesof Microcaris, Microcaris rectilineatus Ji et al., 2021, which
resembles P. triassica in carapace outline and carapace
ornamentation, from the late Olenekian of South China. They
stated that the carapace outline and surface ornamentationof P. triassica and “M.” rectilineatus are similar to thoseof genus Microcaris. However, as described above, thecarapace outline, particularly the angular shape of the optic
notch and pointed dorso- and ventroposterior processes,
and surface ornamentation characterized by dense, nearlyvertical sigmoidal ribs of genus Microcaris are strikingly
different from those of P. triassica and “M.” rectilineatus(Figure 4). We consider genus Parisicaris to be valid andthat “M.” rectilineatus should belong to genus Parisicaris
based on their similarities in carapace outline and surface
ornamentation.
Parisicaris naoyai sp. nov.
Figure 8.1–8.6

Material examined.— Eight specimens, IGPS coll. cat.
nos. 1112810 (holotype) and 112811–112816, and UIM
30625.
Etymology.—The specific epithet is dedicated to Naoya
Takahashi, who collected and donated specimens of present
new species, including the holotype.
Diagnosis.— The small carapace is trapezoidal, with athick rostrum widely fused with the carapace. The height ofthe carapace is approximately half of its length. The concave
anterior margin is connected at an obtuse angle to theconvex, mountain-shaped ventral margin. Widely spaced,slightly convex ribs incline forward, and develop over theentire carapace surface. Some ribs penetrate into therostrum region, bending parallel to its extension direction.
Description.— Only the carapaces are preserved. The
carapace is trapezoidal in lateral view, with a small but
distinct, thick rostrum that is widely fused to it. The dorsal
midline is broadly convex. The broad anterior margin (optic
notch) is concave and composed of semicircular upper half
and nearly straight lower half. The ventral margin is convex
forming a mountain-shaped, nearly symmetrical, downwardbend. The anteroventral process is narrowly rounded,
forming an obtuse angle. The narrow posterior margin isnearly straight and inclined slightly backward, with narrowly
rounded ventroposterior and dorsoposterior processes.
The maximum height is at a position close to the center ofthe venter where it bends. The carapace size ranges fromca. 24 to 31 mm in length and 12 to 16 mm in height, andthe H/L ratio ranges from 0.47 to 0.52 (usually 0.51–0.52).
The Aav ranges from 100° to 114°.
The entire carapace surface is covered by widely spaced
fine ribs, many of which are single and run nearly in parallelfrom near the dorsal midline to the ventral margin; however,some ribs bifurcate, and some short ribs are intercalated
between the primary ribs, mainly in the ventral region. A few
ribs bifurcate at two or three points. Near the lower anterior
margin, the ribs are diagonal to the nearly vertical anterior
margin and run from the anterior margin to the venter. The
ribs are slightly convex, and inclined forward at an angleof 40°–50° to the horizontal axis of the carapace in themain part and nearly 70° near the anterior and posterior
margins. Near the base of the rostrum, three to five or moreribs bend parallel to the extending direction of the rostrum
and penetrate into the rostrum region (Figures 8.1d, 8.2c,
8.3c and 8.5b). Although it is difficult to accurately calculate
the number of primary ribs, because of their occasional
branching and poor state of preservation, it is assumed to
be 30–35, including short ribs near the anteroventral corner
crossing the anterior margin.
Discussion.— The newly described species, P. naoyai
resembles other species of the genus, i.e. P. triassica andA new species of Parisicaris (Triassic Thylacocephala) from Japan

31

Figure 8. Parisicaris naoyai sp. nov., from the Osawa Formation in the South Kitakami Belt, Northeast Japan. All
specimens were collected from the middle part of the formation at the Tatezaki B locality.
1, IGPS coll. cat. no. 112810 (holotype); 1a, left side view; 1b, interpretive drawing of 1a; 1c, counter part of 1a(fragmental); 1d, enlarged view of the rostrum of 1c; 2, IGPS coll. cat. no. 112814; 2a, right side view; 2b, interpretive
drawing of 2a; 2c, enlarged view of the rostrum of 2a; 3, IGPS coll. cat. no. 112811; 3a, right side view; 3b, interpretive
drawing of 3a; 3c, enlarged view of the rostrum of 3a; 4, UIM30625, left side view 5, IGPS coll. cat. no. 112813; 5a, outermold of right side; 5b, enlarged view of the rostrum of 5a; 6, IGPS coll. cat. no. 112815, dorsal view. Scale bars 1 cm,
unless otherwise indicated.

Masayuki Ehiro and Harumasa Kano

32

P. rectilineatus, in having widely spaced, oblique ribs on the
carapace. However, it is clearly distinguished from the latter
two in having large Aav (100°–114°), upwardly curved ribs
and ribs penetrating into the rostrum region.
Occurrence.— From an outcrop of the middle part of theOsawa Formation (upper Olenekian) to the north of Cape
Tatezaki (Tatezaki locality of Ehiro et al., 2015; Tatezaki B
locality of Ehiro et al., 2019), Utatsu, Minamisanriku Town,
Miyagi Prefecture, Northeast Japan.

Acknowledgments
The authors express their deep gratitude to the
Educational Committee of Minamisanriku Town and AbeiGumi Co. Ltd. for their support during fieldwork. We also
thank Naoya Takahashi for providing specimens including
the holotype, and the members of the Tohoku University
Museum for assistance in fieldwork. Hiroshi Nishi and an
anonymous reviewer provided constructive comments andsuggestions that helped us to improve the manuscript.

References
Arduini, P., 1988, Microcaris and Atropicaris, two genera of the class
Thylacocephala. Atti della Società Italiana di Scienze Naturali
e del Museo Civico di Storia Naturale di Milano, vol. 129, p.
159–163.
Arduini, P., 1990, Studies on Permo-Trias of Madagascar. 1.
Thylacocephala from lower Trias of Madagascar. Atti della
Società Italiana di Scienze Naturali e del Museo Civico di
Storia Naturale di Milano, vol. 131, p. 197–204.
Arduini, P. and Brasca, A., 1984, Atropicaris: Nuovo genere dellaclasse Thylacocephala. Atti della Società Italiana di Scienze
Naturali e del Museo Civico di Storia Naturale di Milano, vol.
125, p. 87–93.
Arduini, P., Pinna, G. and Teruzzi, G., 1980, A new and unusual
Lower Jurassic cirriped from Osteno in Lombardy: Ostenia
cypriformis n. g. n. sp. Atti della Società Italiana di Scienze
Naturali e del Museo Civico di Storia Naturale di Milano, vol.
121, p. 360–370.
Arduini, P., Pinna, G. and Teruzzi, G., 1984, Ostenocaris nom. nov.
pro Ostenia Arduini, Pinna and Teruzzi, 1980. Atti della Società
Italiana di Scienze Naturali e del Museo Civico di Storia
Naturale di Milano, vol. 125, p. 48.
Bando, Y. and Shimoyama, S., 1974, Late Schythian ammonoids
from the Kitakami Massif. Transactions and Proceedings of
the Palaeontogical Society of Japan, New Series, no. 94, p.
293–312.
Brayard, A., Krumenacker, L.J., Botting, J.P., Jenks, J.F., Bylund,K.G., Fara, E., Vennin, E., Olivier, N., Goudemand, N.,
Saucède, T., Charbonnier, S., Romano, C., Doguzhaeva,
L., Thuy, B., Hautmann, M., Stephen, D.A., Thomazo, C.
and Escarguel, G., 2017, Unexpected Early Triassic marine
ecosystem and the rise of the Modern evolutionary fauna.
Science Advances, vol. 3, e1602159.
Calzada, S. and Mañé, R., 1993, Primera cita de un Tilacocefalo(Crustacea) en el Ladininiense espanol. Trabajos del Museo

Geologico del Seminario, vol. 224, p. 13–17.
Charbonnier, S., Brayard, A. and the Paris Biota Team, 2019, New
thylacocephalans from the early Triassic Paris Biota (Bear Lake
County, Idaho, USA). Geobios, vol. 54, p. 37–43.
Charbonnier, S., Teruzzi, G., Audo, D., Lasseron, M., Haug, C. andHaug, J.T., 2017, New thylacocephalans from the Cretaceous
Lagerstätten of Lebanon. Bulletin de la Société Géologique deFrance, vol. 188, no. 19.
Dalla Vecchia, F.M., 1993, Segnalazion di crostacel Nell’unita Fonte
Santa (Triassico Sup.) presso Filettino (Lazio, Italia). Gortania- Atti del Museo Friulano di Storia Naturale, vol. 14 (1992), p.
59–69.
Dalla Vecchia, F.M. and Muscio, G., 1990, Occurrence of
Thylacocephala (Arthropoda, Crustacea) from the Upper
Triassic of Carnic Prealps (N. E. Italy). Bollettino della Societa
Paleontologica Italiana, vol. 29, p. 39–42.
D a m e s , W. , 1 8 8 6 , U e b e r e i n i g e C r u s t a c e e n a u s d e m
Kreideablagerungen des Libanon. Zeitschrift der Deutschen
Geologischen Gesellschaft, vol. 38, p. 551–575.
Ehiro, M., 2022, Latest Olenekian ammonoids from the uppermost
part of the Osawa Formation (Inai Group) in the South Kitakami
Belt, Northeast Japan. Paleontological Research, vol. 26, p.
137–157.
Ehiro, M., Sasaki, O., Kano, H., Nemoto, J. and Kato, H., 2015,
Thylacocephala (Arthropoda) from the Lower Triassic of
the South Kitakami Belt, Northeast Japan. PaleontologicalResearch, vol. 19, p. 269–282.
Ehiro, M., Sasaki, O. and Kano, H., 2016, Ammonoid fauna of theupper Olenekian Osawa Formation in the Utatsu area, South
Kitakami Belt, Northeast Japan. Paleontological Research, vol.
20, p. 90–104.
Ehiro, M., Sasaki, O., Kano, H. and Nagase, T., 2019, Additional
thylacocephalans (Arthropoda) from the Lower Triassic (upper
Olenekian) Osawa Formation of the South Kitakami Belt,
Northeast Japan. Palaeoworld, vol. 28, p. 320–333.
Feldmann, R.M., Schweitzer, C.E., Hu, S.X., Huang, J.Y., Zhou,
C.Y., Zhang, Q.Y., Wen, W., Xie, T. and Maguire, E., 2015,
Spatial distribution of Crustacea and associated organisms in
the Luoping Biota (Anisian, Middle Triassic), Yunnan Province,
China: evidence of periodic mass kills. Journal of Paleontology,
vol. 89, p. 1022–1037.
Haig, D.W., Martin, S.K., Mory, A.J., McLoughlin, S., Backhouse,
J., Berrell, R.W., Kear, B.P., Hall, R., Foster, C.B., Shi, G.R.
and Bevana, J.C., 2015, Early Triassic (early Olenekian) life in
the interior of East Gondwana: mixed marine–terrestrial biota
from the Kockatea Shale, Western Australia. Palaeogeography,
Palaeoclimatology, Palaeoecology, vol. 417, p. 511–533.
Hegna, T.A., Vega, F.J. and González-Rodríguez, K.A., 2014,
First Mesozoic thylacocephalans (Arthropoda, ?Crustacea;
Cretaceous) in the Western Hemisphere: new discoveries from
the Muhi Quarry Lagerstätte. Journal of Paleontology, vol. 88, p.
606–616.
Ji, C., Tintori, A., Jiang, D.Y. and Motani, R., 2017, New speciesof Thylacocephala (Arthropoda) from the Spathian (Lower
Triassic) of Chaohu, Anhui Province of China. PalZ, vol. 91, p.
171–184.
Ji, C., Tintori, A., Jiang, D., Motani, R. and Federico Confortini, F.,
2021, New Thylacocephala (Crustacea) assemblage fromthe Spathian (Lower Triassic) of Majiashan (Chaohu, Anhui
Province, South China). Journal of Paleontology, vol. 95, p.
305–319.
Lange, S., Hof, C.H. J., Schram, F.R. and Steeman, A., 2001, New

A new species of Parisicaris (Triassic Thylacocephala) from Japan
genus and species from the Cretaceous of Lebanon links theThylacocephala to the Crustacea. Palaeontology, vol. 44, p.
905–912.
Laville, T., Smith, C.P.A., Forel, M.-B., Brayard, A. and Charbonnier,S., 2021, Review of early Triassic Thylacocephala. Rivista
Italiana di Paleontologia e Stratigrafia, vol. 127, p. 73–101.
Pinna, G., 1974, I Crostacei della fauna Triassica di Cene in Val
Seriana (Bergamo). Atti Società italiana di Scienze naturali edel Museo civico di Storia naturale di Milano, vol. 21, p. 7–33.
Pinna, G., 1976, I crostacei Triassici dell’alta Valvestino (Brescia).
Natura Breaciana, vol. 13, p. 33–42.
Pinna, G., Arduini, P., Pesarini, C. and Teruzzi, G., 1982,
Thylacocephala: una nuova classe di crostacei fossili. Atti della
Società italiana di Scienze naturali e del Museo civico di Storia
naturale di Milano, vol. 123, p. 469–482.
S c h r a m , F. R . , 2 0 1 4 , F a m i l y l e v e l c l a s s i f i c a t i o n w i t h i nThylacocephala, with comments on their evolution and possible

33

relationships. Crustaceana, vol. 87, p. 340–363.
Secrétan, S., 1985, Conchyliocarida, a class of fossil crustaceans:relationships to malacostraca and postulated behavior.
Transactions of the Royal Society of Edinburgh: Earth
Sciences, vol. 76, p. 381–389.
Shigeta, Y., 2022, Revision of early Spathian (late Olenekian, Early
Triassic) ammonoids from the Osawa Formation at Akaushi
in the Motoyoshi area, South Kitakami Belt, Northeast Japan.
Paleontological Research, vol. 26, p. 405–419.
Teruzzi, G. and Muscio, G., 2018, Thylacocephalans from theAnisian (middle Triassic) of the Carnic Alps. Gortania, vol. 40, p.
49–55.
Tintori, A., Bigi, E., Crugnola, G. and Danini, G., 1986, A new
Jurassic Thylacocephala Rugocaris indunensis gen. n. sp.
n. and its paleoecological significance. Rivista Italiana diPaleontologia e Stratigrafia, vol. 92, p. 239–250.

Appendix A. Measurements of Kitakamicaris utatsuensis Ehiro and Kato (Ehiro et al., 2015), all collected from theOlenekian Osawa Formation at the Tatezaki B locality in the Utatsu area, South Kitakami Belt, Northeast Japan. IGPS,
Institute of Geology and Paleontology, Tohoku University, Sendai (Tohoku University Museum); UIM, Utatsu Ichthyosaur
Museum. Dimensional abbreviations are provided in Figure 2. Rib numbers are rough estimates.

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Masayuki Ehiro and Harumasa Kano
Appendix B. Measurements of Parisicaris naoyai sp.
nov. collected from the Olenekian Osawa Formation at the
Tatezaki B locality in the Utatsu area, South Kitakami Belt,
Northeast Japan. Rib numbers are rough estimates.