Table Of ContentZOOLOGICAL SCIENCE 9: 423-437 (1992) © 1992ZoologicalSocietyofJapan
Two New Species of the Genus Dicyema (Mesozoa) from Octopuses
of Japan with Notes on D. misakiense and D. acuticephalum
HlDETAKA FURUYA, KAZUHIKO TSUNEKI and YUTAKA KOSHIDA
Department ofBiology, College ofGeneral Education,
Osaka University, Toyonaka 560, Japan
—
ABSTRACT We examined dicyemid mesozoans from the renal sacs of both Octopus vulgaris and
Octopus minor, obtained off the coast ofJapan, and found two new species that belong to the genus
Dicyema.
Dicyemajaponicumsp. nov. from O. vulgaris, isamediumsizeddicyemid, rarelyexceeding 1500/um
inlength. Thenumberofperipheralcellsinthevermiformphasesisusually22. Thedisc-shapedcalotte
andparapolarcellsformthecephalicenlargement. Theaxialcelliscylindricalbutisroundedanteriorly,
anditextendsforwardtothebaseofpropolarcells. Infusoriformembryosconsistof37cells. Ineachof
the four urn cells, there are the cell's own nucleus and one germinal cell with its own nucleus.
Dicyema clavatum sp. nov. is a relatively small sized dicyemid, infrequently reaching 1000/urn in
length, anditisthefirstmesozoanspeciesdescribedfrom O. minor. Thenumberofperipheralcellsin
thevermiformphasesisusually22. The calotte iscap-shaped andsmoothly rounded. The axial cellis
enlarged and rounded in the calotte region, and it extends anteriorly to the base ofthe propolarcells.
Uropolarcellsoccasionallybecomeverruciform. Infusoriformembryosarecomposedof39cells. Each
ofthe urn cells contains two nuclei ofits own and one germinal cell with its own uncleus.
Furtherdetailsrelevanttothe description ofinfusoriformembryosofDicyemamisakienseNouvel et
Nakao are provided and a note to Dicyema acuticephalum Nouvel isgiven. The dicyemidfaunain the
two species ofoctopuses is briefly discussed.
octopuses caught off the coast of Japan, and we
INTRODUCTION
foundatleasttwonewdicyemidsthataredistinctly
Thefirst recordofdicyemid mesozoansinJapan different from each of the four species mentioned
was published in 1938 by Nouvel and Nakao [1]. above and from the other species so far described
Theyfound DicyemamisakienseNouvel et Nakao, in various regions outside Japan.
1938, in therenal sacofOctopus vulgaris, and also The present paper deals with these two new
Dicyema orientale Nouvel et Nakao, 1938, in dicyemid species: one obtained from Octopus vul-
Sepioteuthis lessoniana. Later, Nouvel [2] de- garis and the other from Octopus minor. In
scribed Dicyema acuticephalum Nouvel, 1947, addition, we give a detailed description of the
which was also obtained from Octopus vulgaris, infusoriform embryos of Dicyema misakiense
and identified another dicyemid from Sepia Nouvel et Nakao and further give an account of
esculenta as Pseudicyema truncatum Whitman, Dicyema acuticephalum Nouvel.
1883,whichhadbeenalreadydescribedinEurope.
All these host cephalopods were collected in the
MATERIALS AND METHODS
waters close to the Misaki Marine Biological Sta-
tion of the University of Tokyo. Since then no From April of 1989 to May of 1991, 23 indi-
reports on the dicyemid species from Japan have viduals of Octopus vulgaris and 19 of Octopus
been published. minor were obtained for detection of dicyemids.
We examined the dicyemids in the renal sacs of Mostofthemwere obtainedfromfish markets and
fishermen, but two were caught by the authors.
Accepted January 6, 1992 The size, sex, and source of each of these octo-
Received November 9, 1991 puses are given in Tables 1 and 2.
424 H. FURUYA, K. TSUNEKI AND Y. KOSHIDA
From every octopus, which was brought alive to paired renal sacs. Pieces of renal tissues were
the laboratory, the head and tentacleswere cut off smeared with the fluid from the renal sac on slide
just behind the eyes, without anesthetic. Then the glasses. Some preparations were used to confirm
visceral hump was placed, ventral side up, in a the occurrence of living dicyemids under the
tray, and the mantle was opened to expose the phase-contrast microscope, while others were
Table 1. Octopus vulgaris and parasite dicyemids
Hosts
Dicyemids
Dorsal mantle Body Date of
No. Sex Source*
length (cm) weight (g) examination
D. acuticephalum
I
VU12 7.2 350 M 1 06.21.1989 < D. japonicum
D. misakiense
\
D. japonicum
f
VU98 9.5 865 F 1 07.14.1990 I D. misakiense
D. sp. (A)
1
VU5 7.4 270 F 1 06.14.1989 '
VU16 5.4 78 M 2 07.06.198S
VU17 5.7 123 M 2 07.06.1989
VU18 6.5 - 1—48 M 2 07.06.1989
VU20 7.5 F 5 07.24.1989
—
VU28 9.5 M 3 08.04.1989
—
VU32 15.2 M 4 08.10.1989 D. japonicum
VU41 12.5 740 F 2 10.20.1989 D. misakiense
VU43 8.2 528 M 6 10.27.1989
VU44 9.7 738 M 6 10.27.1989
VU45 6.9 460 M 1 12.01.1989
VU83 13.5 465 M 1 05.11.1990
VU101 5.3 96 M 2 07.21.1990
VU102 6.6 218 F 2 07.21.1990
—
VU103 7.9 F 5 07.30.1990
VU104 7.8 508 M 2 05.08.1991 -
VU3 8.2 260 M 1 04.26.1989 N
VU4 11.4 770 F 1 05.30.1989 > D. acuticephalum
VU40 9.7 750 F 2 09.06.1989 .
VU105 9.2 550 M 1 05.27.1991 D. misakiense
VU15 4.0 70 F 2 07.06.1989 None
* Source numbers indicate the following:
(1) Commercially supplied from a fish market at Akashi (Hyogo Pref.) where fish dealers receive octopuses
caught mainly inside Osaka Bay and/or in the Sea of Harima (the eastern area of the Inland Sea).
(2) Commercially supplied from a fish market at Shounai (Toyonaka, Osaka Pref.). Locations of these
octopuses are presumably similar to those of octopuses bought at Akashi.
(3) Commercially supplied from a fish market at Shirahama (Wakayama Pref.). The octopus was probably
caught inside Tanabe Bay where it faces the Pacific Ocean.
(4) Commercially supplied from a fish market at Sakaiminato (Tottori Pref.). The octopus was possibly
obtained from the coast of the Sea of Japan near Sakaiminato.
(5) Caught byfishermen in Dozen, Oki Islands (Shimane Pref.), located in the SeaofJapan about50kmtothe
north of Sakaiminato.
(6) Collected by the authors in Maizuru Bay (Kyoto Pref.) where it is open to the Sea of Japan.
Dicyemid Mesozoans from Japan 425
Table2. Octopus minor and parasite dicyemids
Hosts
Dorsal mantle Body Date of Dicyemids
No. Sex Source*
length (cm) weight (g) examination
M
MI89 6.5 78 2 07.11.1990 ^
M
MI90 7.9 168 2 07.14.1990 > D. clavatum
M
MI91 8.3 204 2 07.14.1990 ' D. sp. (B)
M
MI92 8.8 239 2 07.14.1990 >
MI97 5.2 68 F 2 07.14.1990
MI93 8.2 126 F 2 07.14.1990
MI94 8.3 207 F 2 07.14.1990 > D. clavatum
MI95 8.3 194 F 2 07.14.1990
MI96 7.3 145 F 2 07.14.1990 J
MI63 7.2 105 F 04.10.1990
>|
M
MI64 8.7 175 04.10.1990
MI65 7.2 142 F 04.10.1990 > D. sp. (B)
MI69 7.3 110 F 04.10.1990
M
MI71 6.5 231 04.10.1990 >
M
MI84 6.4 124 2 07.11.1990 '
M
MI85 7.4 155 2 07.11.1990
M
MI86 6.5 192 2 07.11.1990 D. sp. (C)
M
MI87 6.9 111 2 07.11.1990
MI88 6.7 118 M 2 07.11.1990 ;
See explanations for Table 1
promptly fixed in Carnoy's fluid or in alcoholic Host: Octopus vulgaris Lamarck, Octopodidae.
Bouin's fluid (a 15 :5 :1 mixture ofsaturated picric Locality: Western Honshu, Japan. See "Source"
acid in absolute ethanol, formalin, and acetic in Table 1.
acid). Carnoy-fixed preparations were subjected Syntypes: A slide registered as NSMT-Me-1 was
to Feulgen or McMannus's periodic-acid Schiff deposited at the National Science Museum,
(PAS) procedures, and then they were stained Tokyo,Japan. ThisslidewaspreparedfromNo.
with Ehrlich's acid hematoxylin and light green. VU44 octopus (Table 1) and contains both
AlcoholicBouin-nxedpreparationsweresubjected nematogens and rhombogens. It includes D.
to the last two staining procedures only. Afterthe misakiense as well, but D. japonicum can be
staining, the preparations were dehydrated and clearly distinguished from D. misakiense in the
mounted in the usual fashion for observation of shape of the head as described below. Other
dicyemids under the light microscope. slides were numbered according to the host
Measurementsanddrawingswere madewiththe number in Table 1 and are in the authors'
aid of a micrometer and an image tracer, respec- collection.
tively. Etymology: The specific name "japonicum" was
given, because this species is common in Octo-
pus vulgaris caught off the coast ofJapan.
Dicyemidae van Beneden, 1882
Dicyema von Kolliker, 1849
Dicyemajaponicum sp. nov. Fumya et Tsuneki DESCRIPTION
[New Japanese name: Yamato-nihaityu]
Diagnosis: Body length up to 1800jum.
(Figs. 1-7, Tables 1, 3, and 4) Peripheral cell number of vermiform phases (ver-
426 H. FURUYA, K. TSUNEKI AND Y. KOSHIDA
miform embryo, nematogen, and rhombogen) PAS-positive, but negative after saliva test. Cells
usually 22:4 propolars, 4 metapolars, 14 trunk and nuclei ofpropolars, smaller, respectively, than
cells. Propolarandmetapolarcellsform adisc-like those of metapolars. Trunk mostly uniform in
head together with parapolar cells. Infusoriform width. Trunk cells, arranged in opposedpairs. No
embryosconsistof37cells. Nucleusnumberofurn verruciform cells. Axial cell, cylindrical and
cell, 1. Host, Octopus vulgaris. rounded anteriorly, extends forward to base of
Nematogens (Figs. 1-3): Body slender, 300 to propolar cells. Usually two sizes of axoblasts,
1800/um long; 40-75 /um wide. Peripheral cell standard and large; the latter often twice the size
number usually 22 (Table 3): 4 propolars, 4 of the former. In large individuals, about 80
metapolars, 2 parapolars, 10 diapolars, 2 uropo- vermiform embryos at most found in the axial cell,
lars. Calotte and parapolar cells form cephalic calotte occasionallyflower-like in shape, and afew
enlargement. Calotte becomes disc-shaped as in- accessory nuclei evident in both peripheral and
dividuals grow. Cilia covering calotte about 4.7 axial cell. In Carnoy-fixed large individuals, many
jum long, oriented forward, slightly shorter but fine granules found in peripheral cells.
denserthan cilia oftrunk cells. Cytoplasm ofboth Transitional individuals from nematogens to
propolar and metapolar cells, stained by hema- rhombogens enclose degenerating vermiform
toxylinmoreconspicuouslythanthatofothercells; embryos, proliferating infusorigens, and develop-
ing or full-grown infusoriform embryos, simul-
taneously, in the axial cell. Standard axoblasts
only, no large ones in these individuals.
Vermiform embryos (Fig. 4): Full-grownvermi-
form embryos, 40 to 70/um long, 8 to 12/um wide;
peripheral cell number fixed at constantly 22
(Table 3). The ratiooftotalbodylengthto calotte
length, 1:0.24 to 0.28. Anterior end of calotte
tapering slightly and pointed bluntly. Trunk cells,
arranged in opposed pairs. Axial cell tapering
anteriorly, sometimes pointed, extending forward
to base of propolar cells, as seen in nematogens.
Axial cell nucleus, usually located in center or in
anteriorhalfofaxial cell, always anteriortoone or
two standard-sized axoblasts.
Stem nematogens (Fig. 5): Two stem nema-
togenswere obtained. One ofthem, 221 /um long,
with three axial cells. Peripheral cell number: 23
(4propolars, 4metapolars, 2parapolars, 11 diapo-
lars, 2 uropolars). Vermiform embryos found in
both second and third axial cell but not in the first.
The otherstemnematogen, 223/umlong, alsowith
three axial cells. Peripheral cell number: 26 (4
propolars, 4 metapolars, 3 parapolars, 14 diapo-
lars, 1 uropolar). Vermiform embryos foundin all
three axial cells. Only standard-sized axoblasts in
Fig. 1. Dicyemajaponicum sp. nov. Fourentire nema- both stem nematogens.
togens of various sizes are shown on the left and Rhombogens (Figs. 1-3): Slightly shorter and
three rhombogenson the right. Note the character- stockier than nematogens, otherwise generally
istic shape of the head. Bar represents 100/um.
Drawn from specimens prepared from No. VU44 similar in shape and proportion; body 300 to 1000
octopus. /um long; 40 to 75 /um wide. Peripheral cell num-
Dicyemid Mesozoans from Japan 427
PA
AC
AC
PA
#
I A- -
-*
D
IF-
4
AX
3 * b
Fig. 2. Anterior part of a nematogen (a) and a rhombogen (b) of D. japonicum. Photographs were taken after
alcoholicBouinfixation,whichwasfollowedbyEhrlich'sacidhematoxylinandlight-greenstaining. Notethatthe
calotte (C) isconspicuously stained and iscovered with a dense arrayofcilia. AX, axoblast; AC, axialcell; D,
diapolar cell; IF, infusoriform embryo; PA, parapolar cell; V, vermiform embryo. Bars represent 20//m. (a)
Prepared from No. VU103 octopus, (b) prepared from No. VU44 octopus.
ber, usually 22, sometimes lower (Table 3). spermatocytes, 3 to 19 (mode, 3). Fertilized eggs,
Cephalic enlargement, composed of calotte and 12.3/urn in diameter.
parapolarcellsasinnematogens. Calotte becomes Infusoriform embryos (Fig. 7): Ovoid, rounded
disc-shaped as individuals grow. Shape and tip bluntly to pointed posteriorly. Based on 100
position of axial cell, similar to those in nema- full-grown embryos, length (excludingcilia), 23.68
togens. Axial cell sometimes expanded at the ±1.98^m (mean+S.D.); length-width-height
region where infusorigens are included. One, ratio, 1 :0.80:0.73. Cilia at the posteriorend, 6to
sometimes two, and very rarely three infusorigens 7jum long. Refringent bodies, smaller than total
in the axial cell. Some accessory nuclei observed massoffoururncells, occupyanteriorone-thirdor
occasionally in both peripheral and axial cell. No so of embryo, when viewed from lateral side.
verruciform cells. Nuclei ofsecond ventral cells, small and pycnotic.
Infusorigens (Fig. 6): Medium-sized, sometimes Ventral internal cells project cilia to urn cavity.
relatively large. Axial cell usually irregular in Capsule cells with many large granules on side
shape. In 25 mature infusorigens examined: num- adjacent to urn. Granules, intensely stained by
ber of external cells including oocytes, 8 to 58 PASprocedure andstaining-resistantinsalivatest.
(mode, 15); number of internal cells including Full-grown infusoriform embryos consist of 37
428 H. FURUYA, K. TSUNEKI AND Y. KOSHIDA
Table3. Number of peripheral cells of Dicyema
japonicum sp. nov.
Number of individuals
No. of
V m
cells r Nematogens Rhombogens
em^ry°os
20 2 1
21 2 8
22 54 52 54
AC1
31
Fig. 3. Anterior part of three nematogens (top) and —
two rhombogens (bottom) of D. japonicum. Cilia AC2 i
are shown in optical section on the nematogen
depicted on the far right. Bar represents 50jum.
Drawn from specimens prepared from No. VU103
octopus.
©P
i
AC3
V
a
Fig 5. A stem nematogen of D. japonicum with three
axial cells. This individual has vermiform embryos
© inboththesecondandthethirdaxialcell;inthefirst
axial cell its nucleus is visible but no embryos are
seen. Photograph (a) was taken after alcoholic
Fig. 4. A vermiform embryo within the axial cell (the gBroeueinnsftiaxiantiinogn., EThhrleicthr'asciancgid(bh)emwaatsoxdyrlaiwnnafnrdomligthhte-
cell outline is omitted) ofa nematogen (on the left) photograph. AC1,firstaxialcell;AC2,secondaxial
jaanpdonaifcrueme-.liviBnagrvserrmeipfreosremntlar1v0aj(uomn.theDrriagwhtn)offrDo.m cPerlel;paArCe3d,frtohmirdNoa.xiValU1ce0ll3.ocBtaorpurse.presents 20//m.
specimens prepared from no. VU103 octopus.
Dicyemid Mesozoans from Japan 429
cells: 33 somatic and 4 germinal cells (Table 4).
Cell terminology used here is that of Nouvel [3]
and Short and Damian [4]. Somatic cells are
composedofperipheralcellsthatcoveralargepart
of anterior and lateral surfaces of embryo (2
enveloping cells), peripheral cells with cilia on
external surfaces (2 paired dorsal cells, 1 median
dorsal cell, 2 dorsal caudal cells, 2 lateral caudal
cells, 1 ventral caudal cell, 2 lateral cells, 2 post-
eroventral lateral cells), peripheral cells with re-
fringent bodies (2 apical cells - cilia not clearly
Fig. 6. Infusorigen of D. japonicum. Around the in-
fusorigen, atwo-pronucleistageegg(E), afertilized
egg(F), andanaxialcellnucleus(N)arefound. Bar
represents10jum. Drawnfromaspecimenprepared
from No. VU103 octopus.
Fig. 7. Infusoriformembryoof.D.japonicum. Dorsalview(a),ventralview(b), sagittalsection (c), andhorizontal
section (d, ciliaoimtted) areshown. Envelopingcellsare ommitted. A, apicalcell; AL, anteriorlateralcell; C,
couvercle cell; CA, capsule cell; DC, dorsalcaudalcell; G, germinal cell; L, lateral cell; LC, lateralcaudal cell;
MD, mediandorsalcell; PD, paireddorsalcell;PVL,posteroventrallateralcell; R, refringentbody; U, urncell;
UC, urn cavity; VC, ventral caudal cell; VI, ventral internal cell, VI, first ventral cell; V2, second ventral cell.
Bar represents 10jum. Drawn from specimens prepared from No. VU103 octopus.
430 H. FURUYA, K. TSUNEKI AND Y. KOSHIDA
Table4. Number ofcells in infusoriform embryos
and the nucleus number of urn cells in four Dicyema misakiense Nouvel et Nakao, 1938
dicyemid species [Japanese name: Misaki-nihaityu]
No. of No. of nucleus (Fig. 8a, Tables4 and 5)
Species
cells* of urn cells* Materials examined: Slides were numbered
D. japonicum 37 1 according to the host numberin Table 1 and are
D. misakiense 37 1 in the authors' collection.
D. acuticephalum 37 2
D. clavatum 39 2 Diagnosis: Body length up to 1700jum.
Peripheral cell number22. Calotte consists oftwo
* These numberswere veryconstantinfourspecies
examined. tiers; thetierofpropolarsslightlysmallerthanthat
ofmetapolars and faintly constricted from the tier
visible onthese cells), peripheral cellswithoutcilia of metapolars. Infusoriform embryos, 37 cells.
(2 first ventral cells, 2 second ventral cells, 2 Nucleus number of urn cell, 1. Host, Octopus
anterior lateral cells, 1 couvercle cell), internal vulgaris.
cells with cilia (2 ventral internal cells), internal
cellswithout cilia (2 dorsal internal cells, 2 capsule Table5. Number of peripheral cells of Dicyema
cells, 4 urn cells). Each of the four urn cells misakiense
enclosesitsownnucleusandonegerminalcellwith Number of individuals
its one nucleus (Table 4). All somatic nuclei tend No. of
to become pycnotic as infusoriform embryos ma- cells Veermmbirfyoosrm Nematogens Rhombogens
ture.
21 1
Geographical variations: Not found either in
22 51 51 55
vermiform stages or infusoriforms.
P
M
M
:?—
V
PA
PA
AC AC
» -
N
IF
AX
D
Fig. 8. Anteriorpart oftwo rhombogensofD. misakiense (a) and anematogenofD. acuticephalum (b). Compare
the head shape of these species with that of D. japonicum (shown in Fig. 2). Photographs were taken after
alcoholic Bouin fixation, Ehrlich's acid hematoxylin and light-green staining. AC, axial cell; AX, axoblast; D,
diapolarcell; IF, infusoriform embryo; M, metapolarcell; N, axial cell nucleus; P, propolarcell; PA, parapolar
cell. Bar represents 20jum. (a) Prepared from No. VU44 octopus, (b) prepared from No. VU40 octopus.
Dicyemid Mesozoans from Japan 431
Note: Nouvel and Nakao [1] reported that the (generally 18), andthe nucleusnumberofurncells
number of peripheral cells in vermiform phases was two. We confirmed his findings in our mate-
was usually 22, but was sometimes lower. How- rials, but the number of peripheral cells in the
ever, we found this number to be almost constant; vermiform embryos was constant and equal to 18
157 out of 158 vermiform individuals examined and no variation was detected (Table 6). We also
had 22 peripheral cells, but only one nematogen revealed that fully mature infusoriform embryos
had 21 cells (Table5). consist of 37 cells (Table4).
The original description of the infusoriform
Table6. Number of peripheral cells of Dicyema
embryos is brief: the embryos (excluding cilia) are acuticephalum
25jumlong, 20jumwide, and 18jumhigh; andeach
of the urn cells has its own nucleus and one "TNumber of individuals
germinal cell [1]. We confirmed in our materials Nceol.lsof Nema.ogens Rhombogens
that the nucleus number ofurn cells is one (Table
4). Additional details ofthe infusoriform embryos 16 2
are given, based on our observations. 17 1
Infusoriform embryos: Ovoid and rounded 18 62 56 58
bluntly to pointed posteriorly. Based on 100 19 1 2
full-grown embryos, length (excludingcilia), 24.67
±1.28^m (mean±S.D.); length-width-height
REMARKS
ratio, 1 :0.86:0.81. Cilia at the posteriorend, 6 to
7jum long. Refringent bodies, smaller than total The distinction between Dicyema japonicum
mass of four urn cells, occupy about 40% of and Dicyema acuticephalum is clear because of
anteriorpart ofembryo, when viewed from lateral differences in typical number ofperipheral cells in
side. Nuclei of second ventral cells, small and full-grown vermiform phases (22 vs. 18) as shown
pycnotic. Ventral internal cells with cilia project- in Tables 3 and 6, in calotte shape (disc type vs.
ing into urn cavity. Capsule cells contain many conical type), in position of the axial cell tip
large granules, which are located on side adjacent (extending to the base of propolar cells vs.
to urn. Full-grown infusoriform embryos com- metapolar cells), and in the number of somatic
posed of 37 cells (33 somatic and 4 germinal). nuclei in the urn cells of infusoriform embryos
Somatic cell composition same as in D. japonicum (one vs. two) as shown in Table 4.
(Table4). Somaticnuclei tendtoshowpycnosisas Both Dicyema japonicum and Dicyema mis-
embryos mature. akiense are similar in the average length of the
body and have, typically, 22 peripheral cells
(Tables3 and 5). In both species, the axial cell
Dicyema acuticephalum Nouvel, 1947
extends to the base ofpropolar cells in vermiform
[New Japanese name: Togari-nihaityu]
phases, and infusoriform embryos consist of 37
(Fig. 8b, Tables4 and 6) cells, whichincludeurncellsthatcontaintheirown
Materials examined: Slides were numbered singlenuclei (Table4). Nevertheless, wecanpoint
according to the host numberin Table 1 and are out the following differences between D. japoni-
in the authors' collection. cum and D. misakiense. (1) The calotte of D.
japonicum is a disc-shaped and forms the cephalic
Diagnosis: Bodylengthup to 800jum. Peripher- enlargement with parapolar cells (Figs. 2 and 3),
al cell number constantly 18. Calotte bell-like in whereas D. misakiense has a slender calotte (Fig.
shape. Infusoriformembryosconsistingof37cells. 8a). No individuals with a calotte that was in-
Nucleus number of urn cell, 2. Host, Octopus termediate in shape between those of the two
vulgaris. specieswere found. (2) Vermiform embryosofD.
Note: Nouvel [2] reported that the number of japonicum often have two axoblasts within the
peripheralcellsinthisspeciesrangedfrom 16to 19 axialcell,while those ofD. misakienseconsistently
:
432 H. FURUYA, K. TSUNEKI AND Y. KOSHIDA
have only one axoblast [1]. (3) The length-width-
Dicyemidae van Beneden, 1882
height ratio ofinfusoriform embryos of D. japoni-
cum is different from that of D. misakiense (1 Dicyema von Kolliker, 1849
0.80:0.73 vs. 1:0.86:0.81). These differences Dicyema clavatum sp. nov. Furuya et Koshida
[New Japanese name: Konbou-nihaityu]
should be sufficient for establishing species in the
dicyemids and therefore we have identified D. (Figs. 9-14, Tables2, 4. and 7)
japonicum as a new species. In the paper by Host: Octopus minor (Sasaki), Octopodidae.
NouvelandNakao [1], the textinlines33-36onp. Locality: Western Honshu, Japan. See "Soruce"
74, in lines 1-5 on p. 75, and Figures6 and7 on p. in Table 2.
76 could be regarded as referring to D. japonicum Syntypes: A slide registered as NSMT-Me-2 was
and not to D. misakiense. deposited at the National Science Museum,
Dicyema aegira McConnaughey and Kritzler, Tokyo,Japan. ThisslidewaspreparedfromNo.
1952 [5], from Octopus vulgaris, has 22 peripheral MI95 octopus (Table 2) and contains nema-
cells as equal as D. japonicum, but the twospecies togens and rhombogens of D. clavatum exclu-
are easilydistinguishablefromthefollowingdiffer- sively. Otherslideswerenumberedaccordingto
ences. D. aegirahasacalottethatisslightlylonger the host number in Table2 and are in the
than the breadth of the anterior end of the trunk, authors' collection.
andthe axial cell ends atthe base ofthe metapolar Etymology: Thespecificname "clavatum" isgiven,
cells, unlike the arrangement in D. japonicum. because ofthe shape ofthebodyischaracteristi-
DicyemaorientaleNouveletNakao, 1938 [1] has cally clavate.
a calotte that is very similar in shape to that ofD.
japonicum, and it also has 22 peripheral cells. DESCRIPTION
However, at full-grown vermiform stages, D.
orientale is much larger than D. japonicum; the Diagnosis: Body length up to 1000jum.
number of axoblasts within vermiform embryos in Peripheralcell numberofvermiform phasesusual-
D. orientale is also larger than in D. japonicum (8 ly 22:4 propolars, 4 metapolars, 14 trunk cells.
vs. 1 or 2). The host cephalopod ofD. orientale is Propolar and metapolar cells flat and covering the
Sepioteuthis lessoniana, a decapod, not an octo- enlarged end of the axial cell. The infusoriform
pod. It seems reasonable, therefore, that these embryosconsistof39cells. Nucleusnumberofurn
two dicyemids should be considered members of cell, 2. Host, Octopus minor.
different species. Nematogens (Figs. 9-11): Body, pestle-like;
Dicyema benthoctopi Hochberg et Short, 1970 200to 1000jumlong; 60to 120jumwide. Peripher-
[6] is very similar to D. japonicum in the calotte al cell number usually 22; 4 propolars, 4 metapo-
shape and in the size ofvermiform stages, but the lars, 2parapolars, 10diapolars,2uropolars,diapo-
number of peripheral cells in D. benthoctopi is lars sometimes lower (Table7). Cephalic swelling
very variable. The host of D. benthoctopi is distinct. Calotte, smoothly rounded and cap-
Benthoctopus magellanicus, a deep-sea octopod shaped in most individuals, flattened and disc-
distributed in the Atlantic Ocean near the Falk- shaped in a few individuals. Cilia covering calotte
land Island, at about 500 km east of the Strait of about 6jum long, oriented forward, more densely
Magellan, the southern extremity of the South distributed than those on trunk cells. Trunk cells
American Continent. It is hard to conclude, arranged in opposed pairs. Uropolar cells occa-
therefore, that D. benthoctopi and D. japonicum sionally verruciform; their nuclei, often enlarged;
are the same species, even thoughinfusoriforms of their cytoplasm, stained intensely by hematoxylin.
D. benthoctopi have not yet been described. Axial cell extends anteriorly to base of propolar
cells, typically enlarged and rounded in calotte
regions. Rounded tip of axial cell is covered by a
cap of thin propolar cells and by metapolar cells
often arranged as a band. Large individuals en-
