A new species of harpacticoid copepod, Ectinosoma mexicanum (Harpacticoida: Ectinosomatidae), is described from a coastal lagoon in northwestern Mexico (Sinaloa state). Ectinosoma mexicanum appears to be allied to E. porosum (Wells, 1967) by sharing a robust endopod on P2 and P4 and a strong setae on the first and second endopodal segment of P2 and P4. The new Mexican ectinosomatid also has the seta next to the outermost seta of exopod of P5 barely longer than the exopod inner edge as in E. porosum and E. mediterraneum Kunz, 1975

Gómez, S.

Seifried, S.

Open Marine Archive

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114(1):207-218. 200L
A new species of Ectinosoma Boeck, 1865 (Copepoda: Harpacticoida:
Ectinosomatidae) from northwestern Mexico
Samuel Gomez and Sybille Seifried
(SG) Institute de Ciencias del Mar y Limnologia, Unidad Academica Mazatlan, Universidad
Nacional Autonoma de Mexico, Joel Monies Camarena s/n, Ap. Postal 811, Mazatlan 82040,
Sinaloa, Mexico, Limburgs Universitair Centrum, Dept. SBG, Researchgroup Zoology,
Universitaire Campus Building D, B-3610, Diepenbeek, Belgium (SS) FB7/AG Zoosystematic
and Morphologie, University of Oldenburg, 26111 Oldenburg, Germany
Abstract.—A new species of harpacticoid copepod, Ectinosoma mexicanum
(Harpacticoida: Ectinosomatidae), is described from a coastal lagoon in north-
western Mexico (Sinaloa state). Ectinosoma mexicanum appears to be allied to
E. porosum (Wells, 1967) by sharing a robust endopod on P2 and P4 and a
strong setae on the first and second endopodal segment of P2 and P4. The new
Mexican ectinosomatid also has the seta next to the outermost seta of exopod
of P5 barely longer than the exopod inner edge as in E. porosum and E.
mediterraneum Kunz, 1975.
In 1991 a one-year study on the impact
of organic enrichment on the distribution
and abundance of meiofauna in a coastal
lagoon in the southeastern Gulf of Califor-
nia (Mexico) was undertaken (G6mez-No-
guera & Hendrickx, 1997). During this
study 63 harpacticoid taxa were identified,
most of which turned out to be new to sci-
ence. Ectinosomatidae was by far the most
abundant family throughout the study pe-
riod (39.4%), and was represented by spe-
cies of Halectinosoma Lang, 1965, Hastig-
erella Nicholls, 1935, Pseudectinosoma
Kunz, 1935 and Ectinosoma Boeck, 1865.
This contribution deals with the description
of the only species of Ectinosoma found in
the sediment samples taken in Ensenada del
Pabellon lagoon (northwestern Mexico).
Materials and Methods
Quantitative triplicate sediment samples
were taken in Ensenada del Pabellon lagoon
(Sinaloa, northwestern Mexico). The sam-
ple strategy was described in G6mez-No-
guera & Hendrickx (1997). Harpacticoids
were stored in 70% ethanol prior to further
investigation. Observations and drawings
were made from the whole and then dis-
sected specimen mounted in glycerin, at
1250X using a Leitz Periplan phase con-
trast light microscope equipped with a
drawing tube. The terminology proposed by
Huys & Boxshall (1991) for the general
morphological description, Koomen (1992)
and Seifried & Durbaum (2000) for U-
pores, Seifried (1997) and Seifried & Diir-
baum (2000) for the somitic ornamentation
(palisades), and Moore (1976) for hyaline
frill, were adopted. Abbreviations used in
the text and tables: P1-P6, first to sixth leg;
EXO, exopod; END, endopod; ae, aesthe-
tasc.
Family Ectinosomatidae Sars, 1903
Genus Ectinosoma Boeck, 1865
Ectinosoma mexicanum, new species
Figs. 1-6
Type material.—A single dissected female
(holotype) catalogued EMUCOP-020591-17,
deposited in the collection of the Institute of
Marine Sciences and Limnology, Mazatlan
Marine Station.
208 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
Type locality.—Ensenada del Pabellon
lagoon (24°19'-24°35'N, 107°28'-
107°45'W). Leg. S. Gomez, May 1991.
Diagnosis.—Ectinosomatidae. Rostrum
relatively large and fused to cephalothorax.
Antennule six-segmented. Armature for-
mula of P1-P4 (EXO/END): 0.1.123/
1.1.221; 1.1.223/1.1.221; 1.1.323/1.1.221;
1.1.323/1.1.221. First and second endopo-
dal segment of P2-P4 with one strong spi-
nulose seta. Endopod of P2-P4 robust, first
endopodal segment of P2 and P3 as long as
wide, first endopodal segment of P4 wider
than long. Seta next to the outermost seta
of exopod of P5 barely longer than inner
edge of exopod. Setae I and VI of caudal
rami spine-like.
Description.—Habitus (Fig. lA-B, 2A-
C), fusiform. Length 773 |xm including ros-
trum and caudal rami. Rostrum (Fig. lA)
relatively large, fused with cephalothorax.
The latter about Vs of total body length, with
denticulate hyaline frill and sensilla; integ-
ument ornamented with tiny depressions ar-
ranged longitudinally and perforated by U-
pores. Surface of third to fifth thoracic so-
mites with tiny depressions arranged as in
cephalothorax; U-pores present. Third tho-
racic somite without palisades, fourth and
fifth thoracic somites with 2 and 4 trans-
verse rows of palisades, respectively; third
to fifth thoracic somites with denticulate
hyaline frill, that of the fifth one deeper
than that of the third and fourth thoracic
somites. Fifth thoracic somite with 1 trans-
verse row of small palisades and 3 trans-
verse rows of long palisades. P5 bearing-
somite (sixth thoracic somite) ornamented
with 3 transverse rows of small palisades
and 1 row of long palisades, and with even-
ly distributed tiny depressions (possibly
pores) and U-pores; with denticulate hya-
line frill. W:L ratio of genital double-so-
mite, 1.19 (width measured in the proximal
wider part of seventh thoracic somite); dor-
sal surface with remains of ancestral sub-
division between seventh thoracic somite
and first post genital abdominal somite (in-
dicated in Fig. lA-B) and ornamented with
transverse rows of palisades and evenly dis-
tributed depressions and U-pores; ventral
surface plain, with U-pores; P6 represented
by 2 setae, genital pore located in proximal
half; hyaline frill of first post genital ab-
dominal somite as in sixth thoracic somite.
Second and third post genital abdominal
somites ornamented with 3 and 4 rows of
palisades; second post genital abdominal
somite with U-pores and with denticulate
hyaline frill; third post genital abdominal
somite without U-pores, with protruded
pseudoperculum dorsally, reaching to distal
third of anal segment, with entire striated
hyaline frill ventrally (Fig. 2C). Anal seg-
ment (fourth post genital abdominal somite)
with palisades and U-pores. Caudal rami
about 1.5 times longer than broad, with 7
elements. Posterior dorsal edge of caudal
rami terminating as an acuminate lappet;
rami with 1 ventral proximal row of small
palisades, and 2 sets of ventrolateral spi-
nules at base of elements I and II; setae I
and VI developed as spines.
Antennule (Fig. 3A), six-segmented. Sur-
face of segments smooth. Armature formula
1.10.3+ae.0.3.3+ae.
Antenna (Fig. 3B): basis massive, with 2
inner long elements (indicated in Fig. 3B).
Endopod two-segmented; first segment
bare; second segment ornamented with
strong and short proximal spinules and with
longer spinules at base of 2 inner lateral
spines; with 6 distal spines. Exopod three
segmented; first segment as long as third
and about 2.3 times longer than second one,
with one seta; second segment with 1 spine;
third segment with 2 spines and ornamented
with subapical set of spinules, one of them
markedly stronger.
Mandible (Fig. 3C): gnathobase of coxa
with a strong spinulose distal spine on cut-
ting edge, 1 strong and 4 smaller teeth; ba-
sis large with 2 long and slender inner setae
and 1 thickened and spinulose inner ele-
ment. Endopod one-segmented, with 8 se-
tae, 2 each of distal 4 fused at base forming
2 pairs of elements. Exopod one-segment-
ed, small, with 1 lateral and 2 distal setae.
VOLUME 1 14, NUMBER 1
209
100pm
Fig. 1. Ectinosoma mexicanum. new species. Holotype, female, EMUCOP-020591-17 A habitus dorsal-B, surface ornamentation of fourth to seventh thoracic somites and first post genital abdominal somite.'
210 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
B
100Mm
Fig. 2. Ectinosoma mexicanum, new species. Holotype, female, EMUCOP-020591-I7. A, urosome, ventral
(first urosomite omitted); B, urosome, lateral, (first urosomite omitted); C, part of anal segment and left caudal
ramus, ventral.
VOLUME 1 14, NUMBER 1 211
lOOMm 100pm
Fig. 3. Ectinosoma mexicanum, new species. Holotype female, EMUCOP-020591-17. A, antennule, third
segment separated from second and fourth; B, antenna; C, mandible; D, maxillule; E, maxilla; F, maxilliped
(endopodal setae lost during dissection).
212 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASfflNGTON
Fig. 4. Ectinosoma mexicanum, new species. Holotype female, EMUCOP-020591-17. A, PI, anterior; B,
P2, anterior.
VOLUME 1 14, NUMBER 1 213
Fig. 5. Ectinosoma mexicanum, new species. Holotype female, EMUCOP-020591-17. A, P3, anterior; B,
P4, anterior.
214 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
50 pm
Fig. 6. Ectinosoma mexicanum, new species. Holotype female, EMUCOP-02059I-17, Fifth leg, anterior.
Maxillule (Fig. 3D): arthrite of praecoxa
with 4 apical spines and 2 bare setae; coxa
and basis fused, the latter with 3 setae; ex-
opod and endopod not articulating at base;
exopod with 2 seta, endopod with 6 setae,
2 each fused at base to form 3 pairs of se-
tae.
Maxilla (Fig. 3E): syncoxa with 3 en-
VOLUME 1 14, NUMBER 1
215
50 Mm
6?8.4'2, Prrr:.L^~ ^^^"^' ''''' «°^°^^P^ ^-^^^ ^--^ ^--y Muscu. (London)-1967.8.4.21. Endopod of P4
216 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
Table 1.—Armature formula of swimming legs (Pl-
P4) of Ectinosoma mexicanum.
EXO END
PI I-O; I-l; in, II, 1 0-1; 0-1; I, n, 2
P2 I-l; I-l; III, II, 2 0-1; 0-1; I, II, 2
P3 I-l; I-l; III, II, 3 0-1; 0-1; L n, 2
P4 I-l; I-l; III, n, 3 0-1; 0-1; L n, 2
dites, proximal endite with 3, middle endite
with 2, distal one with 3 setae; allobasis
with 3 setae medially. Endopod one-seg-
mented, with 2 long spines and 5 setae.
Maxilliped (Fig. 3F): badly damaged; the
endopodal setae missing. Basis with 2 par-
allel rows of spinules.
PI (Fig. 4A), with massive coxa orna-
mented with distal spinules. Basis with out-
er seta and inner strong spine, with spinules
at base of exo- and endopod and close to
inner spine. Rami three-segmented, orna-
mented with strong spinules; exopod barely
reaching beyond second endopodal seg-
ment. Inner seta of second endopodal seg-
ment spinulose at tip. Armature formula as
in Table 1.
P2-P4 (Fig. 4B, 5A-B), with massive
coxa ornamented with row of spinules in
outer distal corner. Basis ornamented with
strong spinules at base of exopod and with
minute ones at base of endopod and in dis-
tal inner comer, the latter with dentiform
process. Rami three-segmented, ornament-
ed with spinules as in PI. Exopod of P2
barely reaching beyond second endopodal
segment, of P3 and P4 reaching middle of
third endopodal segment. Endopods robust;
first endopodal segment of P2 and P3 as
long as wide, of P4 wider than long; first
and second endopodal segment of P2-P4
with strong curved setae ornamented with
2 rows of spinules. Armature formula as in
Table 1.
P5 (Fig. 6): baseoendopod with 2 inner
setae, innermost about 1.8 times longer than
outer one; inner expansion of baseoendo-
pod ornamented with fine spinules at base
of both setae, and with strong ones along
inner margin of posterior face; with 1 me-
dian anterior, and 1 distal and 1 median
posterior U-pore; inner baseoendopodal ex-
pansion reaching middle of exopod. Exo-
pod wider than long, basal limit only visible
on posterior face; with 4 marginal setae and
ornamented with row of long spinules in
the middle and at the base of the three larg-
est marginal elements; outermost seta about
3.5 times longer than adjacent one, the lat-
ter barely longer than inner edge of exopod;
seta adjacent to innermost seta about 1.8
times longer than innermost element, the
latter about 1 .2 times longer than outermost
seta of baseoendopod.
Remarks.—At present about 35 species
of Ectinosomatidae (apart from E. mexican-
um new species), have been attributed to
the genus Ectinosoma. The taxonomy and
phylogeny of this genus has been obscured
by poor descriptions that in most cases lack
sufficient detail. Moreover, no revisions of
the genus are available and nothing is
known about the phylogenetic relationships
of this taxon (Seifried, 1997; Seifried &
Diirbaum, 2000).
Ectinosoma mexicanum and E. porosum
(Wells, 1967), seem to be related by the fol-
lowing synapomorphies: strong spinulose
seta on the first and second endopodal seg-
ment of P2 and P4, and by the robust en-
dopod of P2 in which the first segment is
as long as wide. Unfortunately, Wells
(1967) illustrated only the third exopodal
segment of P3, and did not discuss the gen-
eral morphology of P4. In order to check
the general morphology of P3 and P4 of E.
porosum, the only material available (Ho-
lotype 1967.8.4.21) was borrowed from the
Natural History Museum (London). Unfor-
tunately, the only slide on which the dis-
sected holotype of E. porosum was mount-
ed was badly damaged during transit and
only the mouth parts, PI, P2, P4, P5 and
abdomen were successfully recovered.
The general morphology of P4 of E. po-
rosum (Fig. 7) showed that the robust rami
constitutes a synapomorphy for E. porosum
and E. mexicanum. On the other hand, the
general morphology of P2-P4 of E. mexi-
VOLUME 1 14, NUMBER 1 217
canum shows that the robust condition of
the rami and the strong spinulose seta of the
first and second endopodal segment is con-
stant in these three swimming legs. This is
the case also for P2 and P4 of E. porosum
and in all probability for the third swim-
ming leg.
Some Bradya Boeck, 1872, Pseudobrad-
ya Sars, 1904, and Halectinosoma Lang,
1965 species, exhibit more robust endopods
of P2—P4 than observed for most Ectino-
soma species, but E. mexicanum seems to
be unique within the genus Ectinosoma in
the following derived characters: endopod
of P2-P4 robust, first endopodal segment of
P2 and P3 as long as wide, and first endo-
podal segment of P4 wider than long; first
and second endopodal segment of P2-P4
with strong curved setae equipped with 2
characteristic rows of spinules; exopod of
P5 wider than long (not shared by any other
Bradya, Pseudobradya, Halectinosoma or
Ectinosoma species), and outermost but one
seta barely longer than inner edge of exo-
pod. The latter is shared with E. mediter-
raneum Kunz, 1974, and E. porosum. The
outermost but one seta of exopod of P5 is
much shorter than the inner edge of exopod
in E. obtusum Sars, 1920, and much longer
in all other Ectinosoma species.
Acknowledgements
The first author is indebted to Dr. Frank
Fiers of the Koninklijk Belgisch Instituut
voor Natuurwetenschappen and Dr. Ernest
Schockaert of the Limburgs Universitair
Centrum (Belgium) for their support during
my stay in Belgium (1995-1998). The sec-
ond author is very grateful to Professor H.
K. Schminke for the introduction in the
world of copepods and phylogenetic sys-
tematics. This paper is a contribution to
project G.0086.96 and was financed by the
Fund of Scientific Research-Flanders and
the Direccion General de Asuntos del Per-
sonal Academico of the National Autono-
mous University of Mexico. Also the sup-
port of the German Science Foundation
(project SCH 352/19-2) is gratefully ac-
knowledged.
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A new species of <i>Ectinosoma</i> Boeck, 1865 (Copepoda: Harpacticoida: Ectinosomatidae) from northwestern Mexico

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