Research Article |
Corresponding author: Kyuhee Cho ( chokh@kiost.ac.kr ) Corresponding author: Ruth Böttger-Schnack ( dschnack@ifm-geomar.de ) Academic editor: Danielle Defaye
© 2021 Kyuhee Cho, Chailinn Park, Ruth Böttger-Schnack.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Cho K, Park C, Böttger-Schnack R (2021) Taxonomy of three species of the genus Spinoncaea (Copepoda, Oncaeidae) in the North Pacific Ocean with focus on morphological variability. ZooKeys 1043: 147-191. https://doi.org/10.3897/zookeys.1043.64438
|
Three species of Spinoncaea Böttger-Schnack, 2003 are newly recorded in three locations of the equatorial and temperate Pacific Ocean collected by using a net of 60 μm mesh size. For all three species, morphological characters and patterns of ornamentation were analyzed in detail and illustrations of both sexes, also including form variants of the females, are provided. For the first time, information about the variability of various continuous (morphometric) characters are given, such as the spine lengths on the rami of the swimming legs or the proportions of urosomites. The complementary morphological descriptions of the Pacific specimens focus on similarities or modifications of characters as compared to earlier descriptions of these species from the type locality and various other localities. For S. ivlevi (Shmeleva, 1966), originally but insufficiently described from the Adriatic Sea, the Pacific material is similar in most aspects to the comprehensive redescription of the species from the Red Sea and from the type locality, except for a difference in the morphometry of the distal endopod segment on the antenna, which is discussed here. For S. tenuis Böttger-Schnack, 2003, and S. humesi Böttger-Schnack, 2003, the Pacific material mostly coincides with the characteristic features as described in the original account from the Red Sea. For all three species, differences and/or additions in ornamentation details were found in Pacific specimens (e.g., on the intercoxal sclerite of the first swimming leg or on the genital somite of the male) and females with aberrant morphology were detected. Genetic analyses based on 12S srRNA revealed for two species, S. ivlevi and S. humesi, little or no differences in genetic sequences between Pacific specimens and those recorded from the Mediterranean Sea, thus demonstrating that specimens from both locations are conspecific. For S. tenuis, for which no comparable genetic data are available, 12S srRNA amplification was unsuccessful as was the amplification of mitochondrial COI (barcoding) for all three species. The applicability of using COI amplification for barcoding of oncaeid copepods is discussed.
Molecular, morphological modification, Pacific, taxonomy, zooplankton
Species of Oncaeidae Giesbrecht, 1893 [1892] are abundant in marine ecosystems of temperate, tropical, and polar regions and in the whole water column (
The genus Spinoncaea was established by
Recently, a taxonomic study of the family Oncaeidae has been performed in the NE equatorial Pacific Ocean and one species of Spinoncaea identified as S. ivlevi was reported (
As a part of a new and ongoing taxonomical study on the oncaeid copepods in the temperate and tropical Pacific, we obtained new copepod material of Spinoncaea from the northeastern and northwestern equatorial Pacific as a supplement to the copepod material sampled earlier (
The copepod material was collected in three different regions and years in the Pacific Ocean, in the tropical northeastern (EP-1; 21 August 2009, EP-2; 19 March 2019) and northwestern (WP-1; 27 March 2016, WP-2; 4 April 2016) Pacific, and in the Korea Strait (KS; 7 October 2008) (Fig.
Sample locations for species of Spinoncaea in the equatorial and temperate Pacific Ocean.
Region | Station | Date | Geographical position | Sampling depth (m) |
---|---|---|---|---|
Northeastern Pacific | EP-1 | 21 August 2009 | 10°23'N, 131°20'W | 100 |
EP-2 | 19 March 2019 | 9°52'1.38"N, 131°45'38.28"W | 200 | |
Northwestern Pacific | WP-1 | 27 March 2016 | 13°23'46.44"N, 143°55'0.6"E | 150 |
WP-2 | 4 April 2016 | 13°20'3.42"N, 144°20'2.7"E | 150 | |
Korea Strait | KS | 7 October 2008 | 33°44'50.50"N, 128°15'39.02"E | 110 |
The morphological terminology used in the text and figures was adopted from
Al antennule;
A2 antenna;
ae aesthetasc;
P1–P6 first to sixth thoracopod;
exp exopod;
enp endopod;
exp (enp)-1 (2, 3) to denote the proximal (middle, distal) segment of a three-segmented ramus.
Body sizes of individuals were measured laterally from the anterior margin of the prosome to the posterior margin of the caudal rami, not considering the various degrees of telescoping of somites. The length to width ratio of the caudal rami, the anal somite, and the genital (double-)segment was measured in dorsal view. The variability of individual spine lengths on the exo- and endopod segments of the swimming legs was examined by calculating (1) on the exopods of P2–P4 (1a) the length of the distal exopod segment in relation to the length of the distal spine; (1b) the length of the outer spine on the proximal exopod segment in relation the outer spine on the middle exopod segment; (1c) the length ratio of the outer spine on the proximal exopod segment compared to the length of the outer spines on the distal exopod segment; (2) on the endopods of P2–P4, the length of the outer subdistal and/or outer distal spine on the distal segment in relation to the length of the distal spine. If possible, both the left and right sides of the swimming legs were measured for each specimen. Scale bars in the figures are indicated in micrometers (μm).
Total genomic DNA was extracted from presorted single individuals with DNeasy Blood & Tissue Kit (Qiagen, Hilden, Germany) following the protocol of
DNA sequences were compared against known species from the NCBI GenBank nucleotide database using BLASTn. All sequences were edited using BioEdit 7.0.5.3 software (
Order Cyclopoida Burmeister, 1834
Genus Spinoncaea Böttger-Schnack, 2003
The morphology of the three Spinoncaea species from the Pacific agrees in general with the (re)-description of these species from the Red Sea (
Oncaea ivlevi Shmeleva, 1966: 932–933, figs 1.1–1.11 (Adriatic).
Oncaea ivlevi:
Oncaea ivlevi:
Spinoncaea ivlevi:
1. Robust form. (1) Northwestern Pacific (a) 13°23'46.44"N, 143°55'0.60"E (WP-1), 27 March 2016: Five females and four males dissected on several slides, respectively. Four dissected females (NIBRIV0000882743–882746) and four dissected males (NIBRIV0000882747–882750) were deposited in the
2. Elongate form. (1) Northwestern Pacific, 13°23'46.44"N, 143°55'0.60"E (WP-1), 27 March 2016: One female (NIBRIV0000882776) dissected on two slides. This specimen was deposited in
Female (robust form, Figs
Prosome 1.9 × length of urosome, excluding caudal rami, 1.6 × urosome length, including caudal rami (Fig.
Spinoncaea ivlevi (Shmeleva, 1966), female, robust form (northwestern equatorial Pacific) A habitus, dorsal (caudal seta V on right side missing) B habitus, lateral C urosome, dorsal, setae on caudal rami are numbered using Roman numerals (seta V on right side missing) D urosome, lateral (seta V on right side missing) E urosome, ventral F leg 5, lateral G caudal setae IV–VI shown separately. Scale bars in μm.
P5-bearing somite with paired row of midventral spinous processes (Fig.
Posterior margin of genital double-somite and postgenital somites with undulate hyaline frill (Fig.
Genital double-somite (Figs
Anal somite approximately as wide as long, with insignificant variation in length to width ratio (Table
Caudal ramus (Fig.
Antennule 6-segmented (Fig.
Spinoncaea ivlevi (Shmeleva, 1966), female, robust form (northwestern equatorial Pacific) A antennule (separated between segments 3 and 4) B antenna, distal elements on distal endopod segment numbered using capital letters, lateral elements indicated by Roman numerals C mandible, individual elements indicated by capital letters D maxillule E maxilla, arrow indicating spinules on syncoxa, F maxilliped, posterior, syncoxa missing G labrum, anterior H labrum, posterior. Scale bars in μm.
Antenna 3-segmented, armature as for Red Sea specimens, including the absence of seta IV on the lateral armature of the distal endopod segment (Fig.
Labrum (Figs
Mandible (Fig.
Maxillule (Figs
Maxilla (Fig.
Maxilliped (Fig.
Swimming legs 1–4 (Fig.
Swimming legs armature formula. Roman numerals indicate spines, Arabic numerals represent setae. Differences in spine count are marked in bold. (a) S. ivlevi and S. tenuis, (b) S. humesi.
Leg | Coxa | Basis | Exopod | Endopod |
---|---|---|---|---|
P1 | 0–0 | 1–I | I-0; I-1; III,I,4 | 0–1; 0–1; 0,I,5 |
P2 | 0–0 | 1–0 | I-0; I-1; III(a)/II(b),I,5 | 0–1; 0–2; 0,II,3 |
P3 | 0–0 | 1–0 | I-0; I-1; II,I,5 | 0–1; 0–2; I,II,2 |
P4 | 0–0 | 1–0 | I-0; I-1; II,I,5 | 0–1; 0–2; I,II,1 |
Spinoncaea ivlevi (Shmeleva, 1966), female, robust form (northwestern equatorial Pacific) A P1, anterior [a: ornamentation on intercoxal sclerite of another specimen, b: second endopod segment shown separately, strong setules on inner margin arrowed] B P2, posterior C P3, anterior D P4, anterior, seta on basis figured separately. Scale bars in μm.
Exopods with general characteristics as for Red Sea specimens, including a reduced length of spine on middle segment (= exp-2) of P2 and P3 (Fig.
Endopods with length ranges of outer subdistal spine and outer distal spine relative to distal spine given in Table
P5 (Fig.
P6 (Fig.
Female (elongate form, Fig.
Variation in morphometric traits for three species of Spinoncaea (both sexes, including form variants of female S. ivlevi) from three locations in the Pacific Ocean (WP = western equatorial Pacific; EP = eastern equatorial Pacific; KS = Korea Strait; n = number of specimens examined) Abbreviations: A2 = antenna; AS = anal somite; CR = caudal ramus, for numbering of setae see Fig.
S. ivlevi | S. tenuis | S. humesi | ||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
female | male | female | male | female | male | |||||||||||
WP | EP | KS | WP | EP | KS | EP | KS | EP | KS | EP | WP | KS | ||||
robust | elongate | robust | elongate | robust | ||||||||||||
n | 11 | 1 | 6 | 4 | 3 | 4 | 4 | 1 | 8 | 1 | 3 | 1 | 3 | 2 | 1 | |
Total length (μm) | 327–360 | 305 | 318–373 | 330–345 | 343–344 | 306–329 | 307–331 | 298 | 320–355 | 329 | 310–325 | 292 | 344–348 | 285/295 | 292 | |
Pro:Uro including CR | 1.5–1.7 | 1.4 | 1.5–1.7 | 1.3 | 1.5–1.6 | 1.3–1.5 | 1.5–1.6 | 1.4 | 1.5–1.7 | 1.3 | 1.5 | 1.4 | 1.3–1.4 | 1.1/1.2 | 1.3 | |
AS L:W | 1.0–1.1 | 1.3 | 1.0–1.1 | 1.2–1.4 | 1.0–1.1 | 0.9–1.1 | 0.9–1.0 | 0.9 | 1.1–1.3 | 1.2 | 1.0 | 1.2 | 1.2–1.3 | 1.2 | 1.2 | |
CR | L:W (in) | 1.9–2.2 | 2.0 | 1.9–2.2 | 2.0–2.1 | 2.1 | 1.8–1.9 | 1.7–2.0 | 1.8 | 1.8–2.5 | 2.5 | 1.9–2.2 | 2.4 | 2.3–2.5 | 2.1/2.2 | 2.5 |
L:W (out) | 2.4–2.9 | 2.5 | 2.4–2.6 | 2.6–2.8 | 2.4 | 2.3–2.7 | 2.3–2.5 | 2.4 | 2.3–2.9 | 3.0 | 2.2–2.6 | 2.8 | 2.8–3.1 | 2.6/2.9 | 3.2 | |
Setae III:II | 1.5–1.9 | 2.0 | 1.3–1.7 | 1.6–2.0 | 1.3–1.6 | 1.6–1.9 | 1.2–1.9 | 1.4 | 1.0–1.5 | 1.1 | 1.2–1.5 | 1.2 | 1.6–1.7 | 1.6/1.8 | 1.3 | |
Setae IV:III | 1.2–1.8 | 1.7 | 1.5–1.7 | 1.2–1.3 | 1.8–1.9 | 1.3–1.5 | 1.2–2.0 | 1.8 | 1.4–2.3 | 2.2 | 1.7–1.9 | 2.0 | 1.2–1.6 | 1.4/1.5 | 1.6 | |
G(D)S (dorsal view) | L:W | 1.8–2.0 | 2.0 | 1.6–1.9 | 1.9–2.2 | 1.8 | 1.8–1.9 | 1.8–1.9 | 1.8 | 1.8–2.3 | 2.2 | 1.8–1.9 | 2.0 | 1.9–2.0 | 1.7/1.9 | 2.1 |
G(D)S L : PGS L | 1.4–1.5 | 1.7 | 1.7 | 1.4–1.5 | 1.6 | 2.3–2.5 | 2.0 | 2.1 | 1.5–2.1 | 1.9 | 2.6–2.7 | 2.4 | 1.4–1.5 | 2.1/2.2 | 2.3 | |
G(D)S Max W: Min W (posterior portion) | 1.2–1.5 | 1.5 | 1.4–1.5 | 1.4–1.6 | 1.3–1.5 | - | - | - | 1.5–2.1 | 1.8 | - | - | 1.7–2.0 | - | - | |
A2 DES L:W | 3.4–3.9 | 2.2 | 3.0–3.8 | 3.4–3.9 | 3.2–3.9 | 3.2–3.9 | 3.6–3.8 | - | 3.3–4.1 | 4.1 | 3.6–4.0 | 3.8 | 3.7–4.3 | 3.8–4.1 | 3.5 |
Prosome 1.3–1.4 × length of the urosome (incl. CR), smaller than in the robust form (1.5–1.7, Table
Genital double-somite with shape slightly different from robust form, degree of tapering being stronger (Fig.
Anal somite with length to width ratio larger in elongate form (1.2–1.4) than in robust form (1.0–1.1) (Table
Caudal ramus with ranges in length to width ratio overlapping between the two female form variants (Table
Antennule (not figured) 6-segmented. Armature formula as for S. ivlevi robust form.
Antenna (not figured) 3-segmented, armature as for S. ivlevi robust form. Distal endopod segment with variation of length to width (Table
Mandible, maxillule, maxilliped (not figured) similar to those of the robust form.
Swimming legs variable in proportional lengths of endopodal and exopodal spines on P2–P4 as given in Table
Variation in proportional spine lengths on P2–P4 for three species of Spinoncaea (both sexes, including form variants of female S. ivlevi) from three locations of the Pacific Ocean (WP = western equatorial Pacific; EP = eastern equatorial Pacific; KS = Korea Strait, n = number of specimens measured) Abbreviations: DS = distal spine; L = length; MS = middle spine; ODS = outer distal spine; OSDS = outer subdistal spine; PS = proximal spine; SP = spine; W = width.
S. ivlevi | S. tenuis | S. humesi | ||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
female | male | female | male | female | male | |||||||||||
WP | EP | KS | WP | EP | KS | EP | KS * | EP | KS * | EP | WP | KS * | ||||
robust | elongate* | robust | elongate | robust | ||||||||||||
n | 11 | 1 | 6 | 4 | 3 | 4 | 4 | 1 | 8 | 1 | 3 | 1 | 3 | 2 | 1 | |
P2 L ratio exp-3:DS | 1.03–1.38 | 1.13 | 1.19–1.32 | 1.03–1.20 | 1.1–1.29 | 1.07–1.28 | 1.20–1.30 | 1.19 | 0.92–1.09 | 0.98 | 1.02–1.07 | 1.0/1.03 | 1.04–1.12 | 1.04–1.23 | 1.13/1.16 | |
P3 L ratio exp-3:DS | 1.21–1.52 | 1.21 | 1.09–1.38 | 1.06–1.19 | 1.22–1.43 | 1.17–1.57 | 1.23–1.32 | 1.28 | 0.95–1.07 | 0.98 | 1.01–1.12 | 1.05/1.06 | 1.14–1.21 | 1.13–1.19 | 1.19/1.22 | |
P4 L ratio exp-3:DS | 1.26–1.49 | 1.26/1.60 | 1.31–1.41 | 1.20–1.30 | 1.26–1.43 | 1.23–1.52 | 1.33–1.49 | damaged | 0.96–1.13 | 0.97 | 1.00–1.04 | 0.99 | 1.11–1.20 | 1.06–1.28 | 1.28/1.48 | |
L ratio spines on P2 exp | SP exp-1:SP exp-2 | 1.24–1.57 | 1.46 | 1.33–1.63 | 1.32–1.43 | 1.43–1.74 | 1.44–1.77 | 1.31–1.55 | 1.39 | 1.29–1.47 | 1.27 | 1.36–1.52 | 1.21/1.33 | 1.31–1.42 | 1.25–1.32 | 1.25/1.26 |
SP exp-1:PS exp-3 | 1.36–1.76 | 1.46 | 1.36–1.79 | 1.46–1.72 | 1.43–1.64 | 1.53–1.83 | 1.42–1.57 | 1.45 | 1.28–1.72 | 1.32 | 1.40–1.70 | 1.33/1.45 | 1.13–1.26 | 1.04–1.15 | 1.13/1.19 | |
SP exp-1:MS exp-3 | 1.00–1.16 | 0.97 | 0.95–1.16 | 1.03–1.07 | 1.02–1.11 | 0.86–1.17 | 1.03–1.29 | 1.07 | 0.97–1.14 | 1.00 | 1.00–1.17 | 1.10/1.22 | ||||
SP exp-1:ODS exp-3 | 0.90–1.13 | 0.88 | 0.92–1.10 | 0.88–0.95 | 0.90–1.18 | 0.88–1.15 | 0.89–1.15 | 0.91 | 0.82–1.17 | 0.85 | 0.85–0.94 | 0.97/1.03 | 0.94–1.13 | 0.93–1.00 | 0.89/0.96 | |
L ratio spines on P3 exp | SP exp-1:SP exp-2 | 1.05–1.38 | 1.14 | 1.10–1.22 | 1.16–1.30 | 1.14–1.35 | 1.00–1.37 | 1.03–1.43 | 1.03 | 1.06–1.21 | 1.10/1.13 | 1.07–1.26 | 1.42/1.44 | 1.14–1.26 | 1.15–1.30 | 1.24/1.25 |
SP exp-1:PS exp-3 | 0.85–1.11 | 0.89 | 0.89–1.00 | 0.97–1.06 | 0.93–1.03 | 0.83–1.10 | 0.97–1.03 | 0.94 | 0.88–1.00 | 1.10 | 0.83–0.85 | 1.17 | 1.07–1.31 | 1.15–1.20 | 1.14/1.35 | |
SP exp-1:ODS exp-3 | 0.83–1.03 | 0.89 | 0.87–1.05 | 0.82–1.00 | 0.83–0.95 | 0.66–0.97 | 0.94–1.11 | 0.83 | 0.77–0.94 | 0.91/0.92 | 0.81–0.83 | 1.06/1.10 | 1.00–1.06 | 1.00–1.08 | 1.07/1.09 | |
L ratio spines on P4 exp | SP exp-1:SP exp-2 | 0.90–1.18 | 0.92/1.02 | 1.01–1.12 | 0.86–1.13 | 0.94–1.06 | 0.85–1.25 | 0.96–1.17 | 0.96 | 0.88–1.21 | 1.04 | 1.05–1.19 | 1.04 | 1.04–1.08 | 1.05–1.28 | 0.81/0.83 |
SP exp-1:PS exp-3 | 0.82–1.07 | 0.73/0.90 | 0.87–1.06 | 0.80–0.93 | 0.84–0.97 | 0.86–0.93 | 0.87–1.08 | 0.86 | 0.75–0.97 | 0.92 | 0.82–1.02 | 1.10 | 1.00–1.27 | 1.00–1.17 | 0.94/1.14 | |
SP exp-1:ODS exp-3 | 0.72–0.92 | 0.69/0.79 | 0.83–0.97 | 0.70–0.93 | 0.78–0.94 | 0.72–1.04 | 0.79–1.00 | 0.78 | 0.65–0.88 | 0.76 | 0.74–0.78 | 0.91/0.93 | 0.81–0.93 | 0.78–1.00 | 0.81/0.83 | |
L ratio spines on P2 enp-3 | ODS:DS | 0.45–0.63 | 0.51/0.56 | 0.43–0.57 | 0.49–0.58 | 0.52–0.55 | 0.50–061 | 0.45–0.59 | damaged | 0.42–0.53 | 0.47/0.50 | 0.45–0.55 | 0.53/0.56 | 0.42–0.51 | 0.50–0.55 | 0.51 |
L ratio spines on P3 enp-3 | OSDS:DS | 0.39–0.56 | 0.42 | 0.37–0.48 | 0.35–0.53 | 0.47–0.53 | 0.43–0.54 | 0.39–0.56 | 0.42 | 0.34–0.52 | 0.38/0.40 | 0.32–0.43 | 0.43 | 0.38–0.43 | 0.37–0.41 | 0.37/0.41 |
ODS:DS | 0.44–0.64 | 0.42/0.51 | 0.43–0.56 | 0.42–0.55 | 0.48–0.54 | 0.42–0.51 | 0.41–0.55 | 0.45 | 0.39–0.50 | 0.40/0.46 | 0.42–0.51 | 0.51/0.52 | 0.42–0.44 | 0.42–0.50 | 0.45/0.51 | |
L ratio spines on P4 enp-3 | OSDS:DS | 0.30–0.49 | 0.38 | 0.30–0.48 | 0.28–0.45 | 0.41–0.47 | 0.30–0.47 | 0.32–0.43 | 0.37 | 0.25–0.33 | 0.27/0.34 | 0.25–0.32 | 0.34 | 0.35–0.38 | 0.34–0.38 | 0.26/0.31 |
ODS:DS | 0.36–0.50 | 0.42 | 0.32–0.48 | 0.33–0.52 | 0.42–0.51 | 0.39–0.53 | 0.36–0.48 | 0.43 | 0.29–0.38 | 0.36/0.38 | 0.28–0.41 | 0.42 | 0.39–0.41 | 0.40–0.43 | 0.34/0.37 |
Male (Figs
P5-bearing somite with paired row of midventral spinous processes (Fig.
Spinoncaea ivlevi (Shmeleva, 1966), male (northwestern equatorial Pacific) A habitus, dorsal (caudal seta V on left side missing) B maxilliped, posterior C maxilliped, anterior, syncoxa missing D urosome, dorsal (caudal seta IV on left side and seta V on right side missing, seta VII on left side omitted) E urosome, lateral F urosome, ventral (caudal seta IV on left side and seta V on right side missing, seta IV on right side and seta V on left side omitted) G antennule. Scale bars in μm.
Caudal rami (Fig.
Dorsal surface of genital somite ornamented with pattern of minute denticles or spinules (Fig.
Antennule (Fig.
Antenna (not figured) with variation in length to width ratio of distal endopod segment similar to female (Table
Maxilliped (Fig.
Swimming legs 1–4 with armature and ornamentation as in female. Variability in length ratios of outer spine on exp-1 relative to outer spines on exp-2 and exp-3 of P2–P4, and length ratios of outer subdistal spine and outer distal spine relative to distal spine on enp-3 of P2–P4 given in Table
P5 (Fig.
P6 (Fig.
Spinoncaea ivlevi (Shmeleva, 1966), female, robust form (Korea Strait) A antenna [a: first endopod segment of right antenna, additional broad spinules arrowed] B maxilla, long setule arrowed C labrum, anterior, additional setules arrowed D P5-bearing somite, ventral, midventral spinous processes and weakly pronounced ventrolateral lobes arrowed. Scale bars in μm.
Some other differences between our study and Böttger-Schnack’s redescription were detected in the presence of few long fine setules on the intercoxal sclerite of P1 in both sexes (Figs
Additional or different ornamentation details found in the Pacific specimens of S. ivlevi, not mentioned and/or not figured by
Despite the ornamentation differences between the redescription (
In addition, the results of the molecular genetic analysis, which are presented, also supports this opinion, and is briefly discussed below.
Similar to the report from the Red Sea (
Spinoncaea ivlevi (Shmeleva, 1966), female, elongate form, general (northwestern equatorial Pacific) A urosome, dorsal, caudal seta V on both sides missing; elongate form, aberrant (northeastern equatorial Pacific) B P4-bearing somite and urosome, ventral, showing ornamentation on P4 and P5-bearing somites and genital double-somite, ventrolateral lobes arrowed, caudal seta V on left side missing C P5-bearing somite and genital double-somite, lateral, showing 2 long setules on ventral side of double-somite, midventral spinous process and ventrolateral lobe arrowed. Spinoncaea ivlevi (Shmeleva, 1966), female, robust form, variation, (northwestern equatorial Pacific) D setular patch on tip of cephalosome, dorsal E setular patch on cephalosome, lateral. Scale bars in μm.
In the Pacific, individual variation between specimens was found e.g., in the number of midventral spinous processes on the P5-bearing somite, either two or three in both sexes, and some individuals also had different numbers between left and right side (Fig.
A number of morphological aberrations found in some specimens of S. ivlevi were summarized in Table
The morphological abnormalities of S. ivlevi from three locations in the Pacific Ocean Abbreviations: RF1, RF2 = female robust form; EF1, EF2, female elongate form; M = male; for abbreviation of locations see Tables
Specimens | Figure | Morphological abnormalities or variation |
---|---|---|
WP-RF1 | Fig. |
- a patch of long setules on the anterior part of the cephalosome - the reduced length on both enp-3 of P1 with modified setae |
WP-RF2 | Fig. |
- a patch of long setules on the anterior part of the cephalosome |
WP-RF3 | not figured | - a long setule (or a seta) on the dorsal anterior surface of the genital double-somite |
WP-M1 | not figured | - reduced length of both enp-3 of P4 with modified spines and OSDS absent |
EP-EF1 | Fig. |
- two pairs of extremely long setules on both sides of the P4-bearing somite in ventral view |
- two extremely long setules on the ventral anterior surface of the genital double-somite | ||
EP-EF2 and EP-EF3 | Fig. |
- two pairs of extremely long setules on both sides of the P4-bearing somite in ventral view |
KS-RF1 | not figured | - one inner seta and one outer spine absent on the right exp-3 of P2 |
KS-M1 | not figured | - abnormal shape of distal endopod segment on the antenna with aberrant setae |
Spinoncaea tenuis Böttger-Schnack, 2003: 215–225, figs 12–16 (Red Sea, Mediterranean, Arabian Sea, Pacific Ocean).
(1) Northeastern Pacific (a) 10°30'N, 131°20'W (EP-1), 21 August 2009: One female (habitus of S. tenuis female in Fig.
Spinoncaea tenuis Böttger-Schnack, 2003, female (northeastern equatorial Pacific) A habitus, dorsal (outer basal seta and exopodal seta of P5 on right side damaged, caudal seta V on left side missing) B habitus, lateral C urosome, dorsal (outer basal seta and exopodal seta of P5 on right side missing, caudal seta V on left side missing) D urosome, lateral, midventral spinous processes and ventrolateral lobe arrowed E urosome, ventral, midventral spinous processes and ventrolateral lobes arrowed (caudal setae IV and VI on left side omitted and seta V missing). Scale bars in μm.
Female (Figs
Prosome 1.7 × length of urosome, excluding caudal rami, 1.5 × urosome length including caudal rami in specimens figured (Fig.
P5-bearing somite with paired midventral spinous processes variable in number (two or three processes) and one pair of ventrolateral lobate processes (arrowed in Fig.
Genital double-somite (Fig.
Anal somite (Fig.
Caudal ramus (Fig.
Antennule 6-segmented (Fig.
Antenna 3-segmented, armature and ornamentation as figured (Fig.
Labrum with ornamentation as figured (Fig.
Mandible with armature and ornamentation as figured. (Fig.
Maxillule (Fig.
Maxilla (Fig.
Maxilliped as figured (Fig.
Swimming legs 1–4 (Fig.
Exopods with variability of proportional spine lengths given in Table
Endopods. Length ranges of outer subdistal spine and outer distal spine relative to distal spine on P2–P4 enp-3 as given in Table
P5 (Fig.
P6 (Fig.
Male (Fig.
P5-bearing somite with paired row midventral spinous processes variable in number as in female and one pair of ventrolateral lobate processes (Fig.
Spinoncaea tenuis Böttger-Schnack, 2003, male (northeastern equatorial Pacific) A habitus, dorsal (outer basal seta on left side of P5-bearing somite missing) B urosome, dorsal (P5 and the outer seta of P5-bearing somite on left side missing, caudal seta V on both sides missing) C urosome, ventral, ventrolateral lobes on P5-bearing somite arrowed (P5 and the outer seta of P5-bearing somite on left side missing, caudal seta V on both sides missing) D maxilliped, anterior E antennule F P5 exopod and outer basal seta, lateral G Anal somite and caudal ramus of another specimen, ventral. seta IV on left side and seta V on right side omitted. Scale bars in μm.
Caudal rami (Fig.
Antennule (Fig.
Antenna (not figured) with variation in length to width ratio of distal endopod segment similar to female (Table
Maxilliped (Fig.
Swimming legs 1–4 with armature and ornamentation as in female. Variability in proportional spine lengths on rami given in Table
P5 (Fig.
P6 (Fig.
In terms of ornamentation details, which are described for the typical form only, our Pacific specimens differed from the typical S. tenuis mainly by some details such as: (1) (1a) on the syncoxa of the maxilla and (1b) on the proximal element of the maxilliped; (2) short spinule(s) on the inner margin of bases on P2 and P3; (3) ornamentation with few minute spinules along the medial margin of CR seta III; and (4) variable number of midventral spinous processes on the P5-bearing somite.
Unlike the females, males of S. tenuis could not clearly be classified into form types in Böttger-Schnack’s account. When compared to the typical form from the Red Sea, specimens from the equatorial Pacific are similar in morphology, except for some minor differences including (1) the length to width ratio of the genital somite, which is longer than in our specimens (1.8–2.0 ×) than in the Red Sea specimens (1.7 ×), (2) the caudal rami (inner 1.9–2.2 ×, outer 2.2–2.6 ×) were slightly longer than in the Red Sea specimens (inner 1.9 ×, outer 2.3 ×), and (3) the length ratio of caudal setae VII and IV, respectively, with seta VII being 1.6–1.9 × longer than seta IV in the Pacific specimens, whereas seta VII is only 1.4 × the length of seta IV in the Red Sea specimens. Also, the number of paired midventral spinous processes on the P5-bearing somite differs, showing only two processes in the Pacific, as compared to three processes in the Red Sea specimens. However, as the male specimen from the Korea Strait also showed three paired processes (not figured), and differences among individuals of S. tenuis females (two or three processes) were apparent, this ornamentation seems to be due to individual variation, and cannot be regarded as a regional difference.
According to
The female of S. tenuis can easily be confused with the elongate form of female S. ivlevi from the Pacific Ocean, due to the shape of the genital double-somite. However, as
Spinoncaea humesi Böttger-Schnack, 2003: 208–215, figs 8–11 (Red Sea, Mediterranean, Indian and Pacific oceans).
(1) Northeastern Pacific, 9°52'1.38"N, 131°45'38.28"W (EP-2), 19 March 2019. Three females dissected on three or seven slides, respectively. Two dissected females (NIBRIV0000882796–882797) and two undissected females (in alcohol, NIBRIV0000882798) were deposited in the
Female (Figs
Prosome 1.7 × length of urosome, excluding caudal rami, 1.3–1.4 × urosome length including caudal rami (Fig.
Spinoncaea humesi Böttger-Schnack, 2003, female (northeastern equatorial Pacific) A habitus, dorsal (caudal seta V missing on both sides) B habitus, lateral C urosome, dorsal, (caudal seta V missing on both sides) D urosome, ventral, (caudal seta V missing on both sides) E urosome, lateral. Scale bars in μm.
P5-bearing somite with three paired midventral spinous processes (Fig.
Genital double-somite (Fig.
Anal somite (Fig.
Caudal ramus (Fig.
Antennule (Fig.
Spinoncaea humesi Böttger-Schnack, 2003, female (northeastern equatorial Pacific) A antennule (segments 4–6 drawn from another specimen) B antenna C mandible D maxillule E maxilla, arrows indicating spinules F maxilliped, anterior G labrum, posterior, showing some ornamentation on anterior side. Scale bars in μm.
Antenna 3-segmented, armature and ornamentation as figured (Fig.
Labrum with ornamentation as figured (Fig.
Mandible with armature and ornamentation as figured (Fig.
Maxillule (Fig.
Maxilla with armature and ornamentation as figured (Fig.
Maxilliped with armature and ornamentation as figured (Fig.
Swimming legs (Fig.
Exopods with variability of proportional spine lengths in Pacific specimens given in Table
Endopods with length ranges of outer subdistal spine and outer distal spine relative to distal spine on P2 and P4 given in Table
P5 (Fig.
P6 (Fig.
Male (Fig.
P5-bearing somite with paired midventral spinous processes variable in number (two or three processes) (Fig.
Spinoncaea humesi Böttger-Schnack, 2003, male (northwestern equatorial Pacific) A habitus, dorsal (caudal seta V on right side missing) B habitus, lateral C urosome, dorsal (caudal seta V on right side missing) D urosome, ventral (caudal seta V on right side missing) E urosome, lateral F antennule G maxilliped, anterior H maxilliped, middle. Scale bars in μm.
Caudal rami (Fig.
Antennule (Fig.
Maxilliped (Fig.
Swimming legs 1–4 with the value ranges in spine lengths on rami given in Table
P5 (Fig.
P6 (Fig.
The morphology of both sexes of S. humesi from the Pacific agrees in most parts with the original description of the species by
The male of S. humesi from the Korea Strait agreed in almost all morphological characters with the specimens from the northwestern equatorial Pacific. But it exhibited individual variabilities in the length to width ratio of caudal ramus, the relative length ratio of caudal setae, and the length to width ratio of the genital somite (cf. Tables
Spinoncaea humesi can easily be distinguished from the other two species of Spinoncaea by the number of spines on P2 exp-3, showing two outer spines in S. humesi, but three spines in S. ivlevi and S. tenuis. Also, the outer basal seta of P5 is extremely long, extending beyond the posterior margin of the genital double-somite in the female, and the shape of genital double-somite is different, being barrel-shaped in S. humesi. Other additional characters for species segregation are not further mentioned in the present study because they are described in detail in the remarks section of S. humesi by
1 | P2 exp-3 with 2 outer spines; genital double-somite barrel-shaped in female | S. humesi |
– | P2 exp-3 with 3 outer spines; genital double-somite oval-shaped or elongate oval-shaped in female | 2 |
2 | Md with 5 elements; undulate or lobate hyaline frill at posterior margin of urosomites strongly pronounced; inner margin of caudal ramus with row of setules; modified seta III (spine) on caudal ramus very strong | S. ivlevi |
– | Md with 4 elements; undulate hyaline frill at posterior margin of urosomites weakly pronounced; inner margin of caudal ramus naked; modified seta III (spine) on caudal ramus less strong | S. tenuis |
The difference described for the mandible is not noticeable without difficult preparation of the mouthparts. Thus, this character is not included in the general identification key for Oncaeidae “OncIdent” of
Spinoncaea ivlevi (Shmeleva, 1966), female, robust form (northwestern equatorial Pacific) A labrum, anterior, white arrow indicating setules (in square), black arrows indicating three marginal teeth (in circle) B maxillule, inset showing enlarged second element on outer lobe C intercoxal sclerite on P1, black arrows indicating ornamentation with long, fine setule, inset showing enlarged setules D posterior part of genital double-somite and postgenital somites showing undulate hyaline frill. Spinoncaea ivlevi (Shmeleva, 1966), male (northwestern equatorial Pacific) E caudal ramus seta II, inset showing enlarged seta II ornamented with a single long spinule.
All three species of Spinoncaea, including also the two forms of female S. ivlevi, were analyzed for mtCOI and 12S srRNA sequences during the present study, but only the 12S srRNA sequences of S. ivlevi (robust form) and of S. humesi were successfully obtained (Table
Molecular analysis of three Spinoncaea species from the northeastern (NE) and northwestern (NW) equatorial Pacific: Collection region, number of individuals analyzed (N), number of DNA successfully isolated (n), and GenBank accession numbers of specimens successfully used for molecular analysis.
Species | N | n | Marker | GenBank accession no. | Collection region |
---|---|---|---|---|---|
Spinoncaea ivlevi (robust form) | 14 | 2 | 12S | MN714703, MN714705 | NE Pacific |
12 | 0 | COI | – | ||
5 | 2 | 12S | MN714704, MN714706 | NW Pacific | |
Spinoncaea ivlevi (elongate form) | 3 | 0 | COI | – | NE Pacific |
6 | 0 | 12S | – | ||
4 | 0 | 12S | – | NW Pacific | |
Spinoncaea humesi | 3 | 1 | 12S | MN714702 | NE Pacific |
3 | 0 | 12S | – | NW Pacific | |
Spinoncaea tenuis | 10 | 0 | 12S | – | NE Pacific |
9 | 0 | COI | – | ||
10 | 0 | 12S | – | NW Pacific |
Maximum-likelihood tree from 12S sequences of two Spinoncaea species from the Pacific (WP, EP) and species of a clade including Monothula and the ivlevi-tregoubovi lineage as defined by
Spinoncaea species are supposed to have a wide geographical distribution in warm-temperate and tropical areas, as they were described from various regions, such as the Mediterranean Sea (including the Adriatic Sea), the Red Sea, the Indian and the Pacific Oceans (
Apart from the detailed morphological/taxonomical analysis and documentation (figures) of Spinoncaea species from the open equatorial Pacific, for the first time individual variation of numerous morphometric characters was analyzed for all three species, including proportions of body somites (e.g., anal somite, genital (double-)somite) and armature elements, such as the proportional lengths of endopodal and exopodal spines on the swimming legs, which have been found as limited but useful characters for differentiation between species of other oncaeid genera (e.g., Triconia Böttger-Schnack, 1999) (
Intraspecific variation among the three species was also found for ornamentation details, such as the number of midventral spinous processes on the P5-bearing somite in both sexes, which, however, is considered a commonly occurring variation in nature.
The morphological descriptions of Spinoncaea species by
Some specimens of S. ivlevi in the present study did not only show abnormal ornamentation items on the cephalosome or the genital double-somite (cf. Fig.
The present study included molecular genetic analyses with the aim of overcoming taxonomic problems related to morphological variation. The sequence of the mtCOI region could not successfully be obtained for any of the three species of Spinoncaea analyzed, supporting previous findings that for oncaeid copepods the 12S gene is a better tool for use in DNA barcoding than the COI gene (
Recently, there was incongruence between the identified species of Paracalanus parvus complex through a comprehensive analysis of progressive molecular method and conventional morphology (
The constructive comments of two reviewers are gratefully acknowledged. This research was supported by the Center for Women In Science, Engineering and Technology (WISET) and WISET Regional Agency of PKNU Grant funded by the Ministry of Science and ICT(MSIT) under the Program for Returners into R&D (Returners into R&D program of Dongnam regional agency No. 2020-008) to K Cho. This research was part of the project titled ‘Aquisition of marine bioresources from the high seas and screening of biological potency’, funded by the Ministry of Oceans and Fisheries, Korea and by a research program (Contract No. PE99924) of the Korea Institute of Ocean Science and Technology (KIOST).