Spinoncaea humesi Boettger-Schnack , 2003

Cho, Kyuhee, Park, Chailinn & Boettger-Schnack, Ruth, 2021, Taxonomy of three species of the genus Spinoncaea (Copepoda, Oncaeidae) in the North Pacific Ocean with focus on morphological variability, ZooKeys 1043, pp. 147-191 : 147

publication ID	https://dx.doi.org/10.3897/zookeys.1043.64438
publication LSID	lsid:zoobank.org:pub:E4AD2746-040E-4CD6-ABCA-5806FFA422CF
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scientific name	Spinoncaea humesi Boettger-Schnack , 2003
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Treatment

Spinoncaea humesi Boettger-Schnack, 2003 View in CoL Figs 12 View Figure 12 , 13 View Figure 13 , 14 View Figure 14 , 15 View Figure 15

Spinoncaea humesi Böttger-Schnack, 2003: 208-215, figs 8-11 (Red Sea, Mediterranean, Indian and Pacific oceans).

Material examined.

(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 NIBR. (2) Northwestern Pacific (a) 13°23'46.44"N, 143°55'0.60"E (WP-1), 27 March 2016: Two males dissected on one or three slides, respectively. All dissected specimens (NIBRIV0000882799-882800) were deposited in the NIBR. (b) 13°20'3.42"N, 144°20'2.7"E (WP-2), 4 April 2016. One undissected male in alcohol (NIBRIV0000882801) was deposited in the NIBR. (3) Korea Strait, 33°44'50.50"N, 128°15'39.02"E (KS), 7 October 2008: One dissected male (NIBRIV0000882802) on H-S slide, and one undissected female and one undissected male in alcohol vial (NIBRIV0000882803) were deposited in the NIBR GoogleMaps .

Description.

Female (Figs 12 View Figure 12 - 14 View Figure 14 , Tables 3 View Table 3 , 4 View Table 4 ). Body length in lateral view (telescoping of somites not considered) (Fig. 12B View Figure 12 ) 344-348 µm in northeastern Pacific (Table 3 View Table 3 ), somewhat larger than in the Red Sea (310-320 µm, Böttger-Schnack 2003: 208).

Prosome 1.7 × length of urosome, excluding caudal rami, 1.3-1.4 × urosome length including caudal rami (Fig. 12B View Figure 12 , Table 3 View Table 3 ), for comparison with Red Sea see under “Remarks”. Integumental pores on prosome difficult to discern, not figured.

P5-bearing somite with three paired midventral spinous processes (Fig. 12D View Figure 12 ), no variation in number found (but see under “Male”).

Genital double-somite (Fig. 12C, D, E View Figure 12 ) 2 × as long as maximum width in specimen figured (measured in dorsal aspect) and ~ 1.5 × as long as postgenital somites combined; variation in length to width ratio given in Table 3 View Table 3 , respective ratios from Red Sea specimens fit into this range; ornamentation of dorsal and ventral surfaces (Fig. 12D, E View Figure 12 ) as for Red Sea specimens, including weakly developed undulate hyaline frill on posterior margin of genital double-somite and postgenital somites, as well as absence of pores on lateral surface of postgenital somites (Fig. 12E View Figure 12 ).

Anal somite (Fig. 12C View Figure 12 ) with length to width ratio 1.2-1.3 (Table 3 View Table 3 ), similar to Red Sea, but slightly different from other areas reported in Böttger-Schnack's account (1.0-1.2:1, Böttger-Schnack 2003: table 7). One pair of secretory pores present dorsally near posterior margin (Fig. 12C View Figure 12 ), second pair reported for Red Sea specimens not discerned. Other ornamentation as figured (Fig. 12C-E View Figure 12 ).

Caudal ramus (Fig. 12A, C View Figure 12 ) 2.3-2.5 × longer than wide measured along inner margin and ~ 2.8-3.1 × longer than wide measured along outer margin (Table 3 View Table 3 ), range of variation similar to ratios reported for Red Sea and other regions ( Böttger-Schnack 2003: table 7). Length ratios among setae II, III, and IV with ranges in Pacific specimens given in Table 3 View Table 3 , Red Sea data fit into these ranges; seta V missing on both sides of specimen figured (measurements taken from undissected specimen as follows: seta V ~ 2.7 × longer than seta IV, 1.5 × longer than seta VII).

Antennule (Fig. 13A View Figure 13 ) with armature formula as for S. ivlevi . Ornamentation along inner non-setiferous margin of segments 2 and 3 absent, as specified for Red Sea specimens.

Antenna 3-segmented, armature and ornamentation as figured (Fig. 13B View Figure 13 ). Endopod segments ~ equal in length (but in Fig. 13B View Figure 13 , the proximal endopod segment looks shorter than the distal one, due to its orientation on the slide); distal endopod segment ~ 4 × longer than wide, variation given in Table 3 View Table 3 , Red Sea data fit into these ranges; armature and ornamentation as in S. ivlevi , except for seta II slightly longer than seta I (for numbering of elements see Fig. 3B View Figure 3 ).

Labrum with ornamentation as figured (Fig. 13G View Figure 13 ) including difference to S. ivlevi in size of four marginal teeth along distal (ventral) margin on each lobe being smaller than in S. ivlevi . Posterior face with two secretory pores on each lobe, which are difficult to discern. Anterior surface of labrum not observed in detail, but overlapping rows of fine spinules covering median concavity on anterior side visible from Fig. 13G View Figure 13 .

Mandible with armature and ornamentation as figured (Fig. 13C View Figure 13 ), small element D on gnathobase absent, as typical for the species.

Maxillule (Fig. 13D View Figure 13 ) similar to S. ivlevi , except for middle element on outer lobe naked.

Maxilla with armature and ornamentation as figured (Fig. 13E View Figure 13 ), additional ornamentation on syncoxa in Pacific specimens arrowed in Fig. 13E View Figure 13 .

Maxilliped with armature and ornamentation as figured (Fig. 13F View Figure 13 ), similar to Red Sea specimens, including small ornamentation details, such as proximal element on basis unornamented.

Swimming legs (Fig. 14A-D View Figure 14 ), with armature as in S. ivlevi except for spine count on distal exopod segment of P2, showing only two outer spines (Table 2 View Table 2 ). Intercoxal sclerites unornamented (missing in specimen figured). Surface of coxae and bases with sparse surface ornamentation as figured, outer basal seta on P4 very long, reaching as far as tip of distal exopod segment (Fig. 14D View Figure 14 ), as typical for the species.

Exopods with variability of proportional spine lengths in Pacific specimens given in Table 4 View Table 4 , respectively values from Red Sea generally fit into these ranges, except proportional spine lengths on P2 larger than in the Red Sea specimens.

Endopods with length ranges of outer subdistal spine and outer distal spine relative to distal spine on P2 and P4 given in Table 4 View Table 4 generally similar to Red Sea specimens, except for outer distal spine relative to distal spine on P2 (0.45-0.51) and P3 (0.42-0.44) smaller than Red Sea (0.56 on P2 and 0.48 on P3, calculated from Böttger-Schnack 2003: fig. 10B, C).

P5 (Fig. 12C, E View Figure 12 ) with exopod 1.4 × longer than wide, shorter than in Red Sea (1.7:1; cf. Böttger-Schnack 2003: 208, fig. 8H, I), armature and ornamentation as figured.

P6 (Fig. 12C View Figure 12 ) as figured, armature (short spinule) difficult to discern.

Male (Fig. 15 View Figure 15 , Tables 3 View Table 3 , 4 View Table 4 ). Body length 285-295 µm (Table 3 View Table 3 ). Sexual dimorphism in antennule, maxilliped, P6, and in genital segmentation, slight modification in setal length of P5. Pore pattern on prosome not discerned.

P5-bearing somite with paired midventral spinous processes variable in number (two or three processes) (Fig. 15D View Figure 15 ).

Caudal rami (Fig. 15A, C, D View Figure 15 ) with length to width ratio 2.1-2.5 measured along inner margin and 2.6-3.2 measured along outer margin (Table 3 View Table 3 ), [single value from Korea Strait larger than those from western equatorial Pacific,] respective values from Red Sea and other areas ( Böttger-Schnack 2003: table 7) fit into this range. Ornamentation details as figured, similar to Red Sea specimens, including absence of surface ornamentation on genital somite (Fig. 15C, D View Figure 15 ).

Antennule (Fig. 15F View Figure 15 ) with armature as for S. ivlevi . Segments 2 and 3 without ornamentation.

Maxilliped (Fig. 15G, H View Figure 15 ) 3-segmented, syncoxa missing in specimen figured. Basis and endopod (claw) with armature and ornamentation similar to Red Sea specimen, including ornamentation detail on claw, with pinnules only along distal half of concave margin.

Swimming legs 1-4 with the value ranges in spine lengths on rami given in Table 4 View Table 4 not significantly different from female, except for the values of the endopodal spines on P4 from Korea Strait smaller than those of females.

P5 (Fig. 15B, E View Figure 15 ) with exopodal seta and outer basal seta shorter than in female, outer basal seta also much shorter than in Red Sea specimens ( Böttger-Schnack 2003: fig. 11D-F).

P6 (Fig. 15D View Figure 15 ) with ornamentation as figured.

Remarks.

The morphology of both sexes of S. humesi from the Pacific agrees in most parts with the original description of the species by Böttger-Schnack (2003). As stated above, the Pacific specimens differ only in a few characters, such as in (1) a somewhat larger body size in the female and (2) the length ratio of the prosome to the urosome in the female, which appears to be slightly larger in the Pacific specimens (1.7:1 and 1.3-1.4:1, excluding and including caudal rami, respectively) as compared to the Red Sea specimens (1.5:1 excluding caudal rami and 1.2:1 including caudal rami, calculated from Böttger-Schnack (2003: fig. 8A). Note, that in the text of Böttger-Schnack (2003: 208) the proportions of the prosome to the urosome are given as 2.0:1 and 1.7:1, respectively, but these were calculated by a different method taking into account the telescoping of somites, while the telescoping of somites was not considered in the present study. Also, some additional ornamentations were found in the Pacific specimens, such as on the syncoxa of the maxilla of both sexes, the additional ornamentation on the inner portion of the basis of P2-P4 in our Pacific specimens or the number and size of spatulated spinules between proximal seta and articulation with endopod on the maxilliped in female, which are smaller and more numerous than in the specimen from the Red Sea.

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 3 View Table 3 , 4 View Table 4 ). An additional variation in the male from the Korea Strait was found in the number of midventral spinous processes on the P5-bearing somite, with three paired processes (not figured), as in female, while in the male of the northwestern Pacific only two paired processes were found, as in the male from the Red Sea ( Böttger-Schnack 2003: fig. 11E). The number of midventral spinous processes on the P5-bearing somite seems to be a common individual variation seen within both sexes among Spinoncaea species.

Spinoncaea humesi can easily be distinguished from the other two species of Spinoncaea by the number of spines on P2exp-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 Böttger-Schnack (2003: 214-215).