Heterolaophonte discophora ( Willey, 1929 )

Heterolaophonte discophora ( Willey, 1929) View in CoL

Figs 6 View Figure 6 , 7 View Figure 7 , 8 View Figure 8 , 9 View Figure 9

Laophonte discophora Willey, 1929: 531, Abb. 2, 3, 6; Willey 1930: 607, pl. XVIII, figs 16 ~ 18 (cited from Itô 1974); Willey 1931: 5. View in CoL

Heterolaophonte discophora Lang, 1948: 1375, fig. 557-1; Lang 1965: 480, figs 262–265; Itô 1974: 628–638, figs 42–47; Song 2000: 83–86, fig. 25; Kim 2013: 25–27, fig. 9. View in CoL

Heterolaophonte rotundipes Chappuis, 1958: 420, figs 23–34. View in CoL

Material examined.

(1) • Gohado ( 34°45'56.04"N, 126°22'22.38"E), Mokpo, Jeollanam-do, marine rope debris; 01 April 2021; leg. OH Yu, SL Kim and SM Kang: 1 ♀ (MinRB-Hr 105-L 001), 3 ♀♀ ( MABIK CR 00258880 ), 1 ♂ (MinRB-Hr 105-L 002) and 3 ♂♂ ( MABIK CR 00258881 ), preserved separately in a vial with 95 % ethanol; 1 ♀ (MinRB-Hr 105-S 003), 2 ♀♀ ( MABIK CR 00258882–00258883 ), 1 ♂ ( MInRB -Hr 105-S 006) and 2 ♂♂ ( MABIK CR 00258884 –00258885), each dissected and mounted on 1 or 2 H-S slides GoogleMaps .

(2) • Naechi Beach ( 34°53'17.94"N, 126°00'05.68"E), Sinan, Jeollanam-do, expanded polystyrene buoy; 14 September 2022; leg. GH Han: 1 ♀ ( MABIK CR 00258877 ), dissected and mounted on 2 H-S slides GoogleMaps . • Same locality, fishing net; 01 February 2024; leg. SL Kim and SJ Gwak: 5 ♀♀ (MinRB-Hr 105-L 003 ), preserved in a vial with 95 % ethanol GoogleMaps .

(3) • Masan-ri ( 36°00'58.99"N, 129°29'05.55"E), Pohang, Gyeongsangbuk-do, green algae; 27 February 1997; leg. J Lee; 1 ♂ (MinRB-Hr 105-L 004 ), preserved in a vial with 95 % ethanol GoogleMaps . • Same area, coralline algae ( 36°00'59.90"N, 129°28'58.32"E); 23 April 2005; leg. J Lee: 1 ♀ ( MABIK CR 00258878 , asymmetry in the number of setae on P 2 enp - 2), dissected and mounted on 2 H-S slides and 1 ♀ ( MABIK CR 00258879 ), preserved in a vial with 95 % ethanol GoogleMaps . • Same area ( 36°00'59.90"N, 129°28'58.32"E), coralline algae; 26 April 2005; leg. J Lee: 2 ♀♀ (MinRB-Hr 105-L 005 , asymmetry in the number of setae on P 2 enp - 2), preserved in a vial with 95 % ethanol GoogleMaps .

Redescription.

Female. Body length 827–1,098 μm ( n = 17; measured from anterior margin of rostrum to posterior margin of caudal rami). Habitus slender, cylindrical, and gradually tapering posteriorly in dorsal view, separation between prosome and urosome indistinct (Fig. 6 A View Figure 6 ). Cephalothorax with diminutive spinules and several sensilla dorsally; posterior margin smooth, bearing several sensilla. Free pedigerous somites with diminutive spinular rows on dorsal surface, and one or two rows of spinules and several sensilla along posterior margin. Ventrolateral margins of cephalothorax fringed with a closely set of spinules (Fig. 6 a View Figure 6 ). Urosomites (Figs 6 A View Figure 6 , 7 G View Figure 7 ) with spinules along posterior margin (except anal somite); dorsal and ventral surfaces with patterns of diminutive spinules. Genital double-somite with a transverse spinular row dorsally and laterally, indicating original segmentation; ventrally completely fused. Genital field located near anterior margin of genital double-somite; each side covered by lobe derived from P 6, bearing one inner vestigial and one outer long seta; small triangular process present medially on each lobe. Anal somite as long as caudal rami, ornamented with tiny dorsal spinules and lateral / ventral spinules along posterior margin; semicircular operculum ornamented with marginal spinules and pair of sensilla.

Caudal rami (Figs 6 A View Figure 6 , 7 G View Figure 7 ) ~ 1.7 × longer than wide; with seven setae: seta I bare, diminutive, identified at high magnification; setae II and III bare, the former shorter than the latter; setae IV and V well-developed, fused basally to each other, and bipinnate; seta VI bare, shorter than seta II, seta VII tri-articulate, arising dorsally in distal 1 / 3 of ramus.

Rostrum (Fig. 6 A View Figure 6 ) completely defined basally, triangular, with pair of sensilla near apex; midventral tube pore in subapical position (not figured).

Antennule (Fig. 7 A View Figure 7 ) 7 - segmented; segments 1–5 covered with minute spinules on dorsal view. First segment short, with several spinular rows; second segment with outer distal spinules; third segment longest; fourth segment with one seta fused basally to an aesthetasc on a distal peduncle; seventh segment tapering distally, with apical acrothek composed of one aesthetasc and two long setae. Armature formula: 1 - [1], 2 - [8], 3 - [7], 4 - [1 + (1 + ae)], 5 - [1], 6 - [2], 7 - [7 + acro].

Antenna (Fig. 7 B View Figure 7 ) 3 - segmented, comprising coxa, allobasis, and 1 - segmented endopod. Coxa small, with a row of spinules. Allobasis with 1 abexopodal seta located approximately midway along outer margin of segment, and with long setules near base of exopod. Endopod as long as allobasis, ornamented with long spinules along inner proximal margin and rows of spinules along outer distal margin; lateral armature consisting of two pinnate spines and one slender seta; distal armature composed of two strong spines and three geniculate setae (of which most outer one basally fused to short seta). Exopod small, 1 - segmented, with three slender setae, middle one shortest inner one longest.

Mandible (Fig. 7 C View Figure 7 ). Coxa transversely elongated; gnathobase with one bicuspidate, three multicuspidate teeth, and one pinnate spine around distal margin and one pinnate seta at distal corner. Palp small, uniramous, with four bare (1 exopodal, 3 endopodal) lateral setae and one pinnate apical (basal) seta; with few small spinules present at base of proximal lateral seta.

Maxillule (Fig. 7 D View Figure 7 ). Praecoxa with a row of outer spinules; arthrite with one subdistal and eight distal elements; posterior surface with a row of spinules. Coxa with a row of long spinules on anterior surface and few spinules around inner distal margin; cylindrical endite bearing one spinulose and one slender seta. Basis with one anterior spinular row; endite with one spinulose and two slender setae. Endopod nearly incorporated into basis, represented by three bare setae, of which middle one smaller than others. Exopod small, 1 - segmented, with two long apical setae.

Maxilla (Fig. 7 E View Figure 7 ). Syncoxa with a long spinular row around outer margin and two rows of small spinules on surface; with three endites: proximal endite (praecoxal) bearing one pinnate seta; middle endite with one serrate spine and two pinnate setae, of which spine fused basally to segment; distal endite with one spine and two pinnate setae. Allobasis drawn out into a stout claw, with one spine (bearing three spinules near midlength) and two slender setae. Endopod represented by three bare setae (1 short, 2 long).

Maxilliped (Fig. 7 F View Figure 7 ) 3 - segmented, comprising syncoxa, basis, and 1 - segmented endopod. Syncoxa with two distal plumose setae and several spinular rows. Basis longer than preceding segment, outer margin slightly convex, with two rows of spinules; inner margin with a row of strong spinules in distal half. Endopod 1 - segmented, with a long, curved claw; with one short bare seta anteriorly and a tube pore posteriorly (as in P. setadefectus sp. nov., Fig. 2 F View Figure 2 ); concave inner margin bearing row of spinules.

P 1 (Fig. 8 A View Figure 8 ). Intercoxal sclerite transversely elongated and narrow. Praecoxa damaged (not shown). Coxa large, proximal outer margin protruded, with spinular rows along inner and outer margins. Basis with three spinular rows; one outer and one inner seta (displaced anteriorly). Exopod shorter than enp - 1, 3 - segmented, each segment with outer spinules; exp - 1 and exp - 2 with one outer spine; exp - 2 longest; exp - 3 with two outer spines and two geniculate apical setae. Endopod 2 - segmented, enp - 1 elongated, ~ 2 × as long as entire exopod; enp - 2 short, bearing one strong, serrate claw and one small seta, and several spinules along outer margin.

P 2 and P 3 (Fig. 8 B, C View Figure 8 ). Intercoxal sclerites subrectangular. Praecoxae transversely elongated triangular, with outer spinular rows. Coxae and bases ornamented with spinular rows along outer margin and on anterior surface. Bases each with one bare outer seta and one anterior tube pore. Exopods 3 - segmented, longer than endopods; each segment ornamented with strong spinules as illustrated; exp - 2 shortest, exp - 3 longest; exp - 1 with one outer spine; exp - 2 with one outer spine and one inner seta; exp - 3 with three outer spines, one apical spine, one apical seta, and one inner seta. Endopods 2 - segmented, enp - 1 as long as enp - 2 in P 2, but much shorter than enp - 2 in P 3, with long inner spinules and short outer spinules, with (P 2) or without (P 3) one tube pore on outer corner; enp - 2 with spinules along outer margin and on anterior surface (P 3); with one tube pore located proximally (P 2) or distally (P 3), bearing two inner (occasionally 3 in P 3), two apical and no outer (P 2) or one (P 3) outer seta.

P 4 (Fig. 8 D View Figure 8 ). Intercoxal sclerite elongated and narrow (see Fig. 9 E View Figure 9 ). Praecoxa small, transversely elongated and triangular. Coxa and basis with spinular rows along outer margins and on anterior surface. Basis with one bare outer seta and one anterior tube pore. Exopod 3 - segmented, gradually tapering distally, longer than endopod; exp - 1 broad, with several spinular rows on anterior surface; exp - 2 shortest, with one outer, slender, and elongated spine and one inner seta; exp - 3 with three outer, slender, and elongated spines, and two apical elements. Endopod 2 - segmented, enp - 1 with long inner spinules; enp - 2 ~ 2.5 × as long as enp - 1, with spinules on anterior surface, bearing one inner, two apical, and one outer seta.

Armature formula of P 1 – P 4 as follows:

P 5 (Fig. 8 E View Figure 8 ) with baseoendopod and 1 - segmented exopod, both surfaces covered with fine spinules. Baseoendopod with one bare basal seta arising from long cylindrical setophore; endopodal lobe extending to distal third of exopod, bearing spinules along inner margin, and armed with three inner and two distal bipinnate setae. Exopod widely subquadrate with slightly convex inner margin, strongly sclerotized and dented between innermost distal seta and longest seta; with three bare and three pinnate setae.

Male. Body (Fig. 6 B View Figure 6 ) generally similar to that of female, but with a more or less slender urosome. Body length 688–927 μm ( n = 15; measured in the same way as in females). Cephalothorax and pedigerous somites with ornamentation patterns as in females (Fig. 6 B, b View Figure 6 ). Sexual dimorphism in genital segmentation, antennule, P 2 – P 6.

Urosome (Figs 6 B View Figure 6 , 9 B View Figure 9 ) 6 - segmented; genital somite and first abdominal somite completely separate; ornamentation as figured.

Antennule (Fig. 9 A View Figure 9 ) 8 - segmented, subchirocer, geniculate between segments 5 and 6. First segment with several spinular rows; fourth segment very small; fifth segment swollen; eighth segment triangular. Armature formula: 1 - [1], 2 - [9], 3 - [8], 4 - [2], 5 - [8 + 1 pinnate + 2 modified + 2 teethlike elements + (1 + ae)], 6 - [3 elements], 7 - [1], 8 - [8 + acro].

P 2 – P 3 (Fig. 9 C, D View Figure 9 ). Exopods broader than in females; exp - 3 considerably shorter, with thicker spines. P 2 endopod: enp - 1 slightly longer than enp - 2, with long spinules along inner and outer margin, and one large pore near distal corner; enp - 2 with long spinules along outer margin, one tube pore on proximal anterior surface, and inner element modified as strong bare spine. P 3 endopod: enp - 1 as in females; enp - 2 ornamented with long inner spinules and stout spinules along outer margin proximally; bearing one short apophysis on outer lateral margin, two inner and two distal setae (shorter than in females) and one tube pore on distal anterior surface; apophysis weakly curved outwardly at distal tip, bearing one stout and one small strengthen spinules (protuberance?) near its base.

P 4 (Fig. 9 E View Figure 9 ). Exopod considerably longer than in females, with thicker spines. Endopod as in females, except enp - 2 bearing tube pore on distal anterior surface.

P 5 (Fig. 9 B View Figure 9 ). Left and right baseoendopods medially fused, baseoendopod and exopod fused, forming small lobe bearing seven setae, of which two inner ones diminutive; posterior margin with four tube pores.

P 6 (Fig. 9 B View Figure 9 ) symmetrical, represented by small lobe bearing one median spine and one outer seta, and ornamented with spinular row along distal margin.

Variability.

Previous descriptions of H. discophora (e. g., Lang 1965: fig. 263 i; Itô 1974: fig. 44.3) report three inner setae on the female P 3 enp - 2. However, examination of 17 Korean specimens revealed notable variation in thoracopod setal armature. Thirteen specimens from Gohado and Naechi exhibited only two inner setae on both left and right rami (Fig. 8 C View Figure 8 ). In contrast, left – right asymmetry in the number of inner setae was found exclusively in specimens from Masan-ri, where three of the four individuals examined showed this trait (Fig. 8 F View Figure 8 ), indicating significant intraspecific variability within the species.

Abnormality.

In a female specimen from Gohado, caudal seta IV on the right caudal ramus was underdeveloped and deeply embedded within the ramus (Fig. 7 G View Figure 7 ). Additionally, another female specimen exhibited an abnormal P 4 exopod. Compared to the normal morphology of P 4 (Fig. 8 D View Figure 8 ), the distal segment of the abnormal exopod was markedly shortened and bore five spines / setae, with two distal spines fused together (Fig. 8 G View Figure 8 ).

Remarks.

Heterolaophonte discophora ( Willey, 1929) was originally described by Willey (1929) based on a female specimen collected from St. Andrews, New Brunswick, Canada. The male was subsequently reported from Passamaquoddy Bay, New Brunswick, by Willey (1931). However, these initial descriptions and illustrations were brief and provided limited morphological details, particularly regarding the P 5 of both sexes and the P 2 – P 4. Lang (1965) later provide a detailed redescription based on specimens collected from Monterey Bay, near Hopkins Marine Station, and treated H. rotundipes Chappuis, 1958 , (originally described from Puget Sound near Seattle, Washington, USA) as a junior synonym of H. discophora . Following Lang’s taxonomic revision, Itô (1974) also redescribed the species based on male and female specimens from Hokkaido, Japan. Given the incompleteness of the original description, the present comparison of the Korean material relies primarily on the comprehensive accounts by Lang (1965) and Itô (1974).

Heterolaophonte discophora was first reported from Korea in the doctoral dissertation by Song (2000). In that study, Song identified specimens collected from macroalgae at Masan-ri, Pohang, as H. discophora , providing a brief species description, with the setal formula of P 2 – P 4 and illustrations of the female P 1, P 4, P 5, the A 2 exopod, the caudal ramus, and the male P 5. He noticed that the Korean H. discophora machted Itô’s (1974) redescription in all characters except for the relative lengths of the two short inner setae on the male P 5. We obtained Korean specimens of H. discophora from MPD stranded along the coasts of Gohado, Mokpo, and Naechi Beach, Sinan, as well as Masan-ri. Contrary to Song’s (2000) observations, our examination of these newly collected Korean specimens reveals additional morphological differences not previously reported.

One of the diagnostic traits of H. discophora is the shape of the P 4 exp - 3, which is slender and elongated, gradually broadening distally in its proximal part ( Willey 1929: fig. 2; Lang 1965: fig. 264 a). However, this characteristic appears less pronounced in Japanese specimens ( Itô 1974: fig. 264 a, a. 1) and in the Korean material examined here (Fig. 8 D View Figure 8 ). Nonetheless, the markedly large and broad P 4 exp - 1 in H. discophora , relative to exp - 2 and exp - 3, may represent a more reliable diagnostic feature of this species than the morphology of exp - 3 when compared to congeners.

Comparative analysis of the Korean specimens with previous records of H. discophora reveals four distinct morphological traits. Lang (1965) reported four setae on the endopodal lobe of the female P 5, whereas Chappuis (1958) and Itô (1974) described five; the Korean specimens also possess five setae on this lobe. It is possible that Lang (1965) observed a variable condition of the female P 5, considering that most Heterolaophonte species have five setae on the corresponding segment, except for H. exigua (Scott, 1912) , H. norvegica Drzycimski, 1968 , and H. tupitskyi Chislenko, 1976 . In the male P 5, Lang (1965) and Willey (1931) described five elements, whereas Chappuis (1958) and Itô (1974) noticed seven elements, including two additional small inner setulae — features also observed in the Korean material. It appears that these two inner ornamentations were interpreted as armatures by earlier authors. Regarding the female P 3 endopod, Itô (1974) reported three inner setae on the enp - 2; however, most Korean specimens only have two, with occasional asymmetry (bearing 2 or 3 inner setae) between the left and right rami (see variability above). Lang (1965) described the male P 3 endopod as three-segmented, and Itô (1974) referred to a tripartite condition, though with indistinct boundaries. Conversely, the Korean specimens consistently exhibit a two-segmented endopod, although a posterior suture line is variably developed — absent in some individuals, faint in others, and distinctly visible in a few — potentially leading to interpretative ambiguity. Similar variable chaetotaxy has occasionally been reported in laophontid copepods, particularly in the genus Quinquelaophonte , which is closely related to Heterolaophonte ( Willen 1996; Kim and Lee 2023). Finally, Itô (1974) noted a single triangular, spur-shaped protuberance on the outer distal corner of the male P 3 enp - 2, which, unfortunately, was not mentioned by Lang (1965). In contrast, the Korean specimens exhibit two triangular, strengthened spinules (protuberances?) of unequal size in the same position, with a similar row of strong spinules also present proximally along the outer margin. This ornamentation was probably overlooked by earlier authors.

In addition, the Korean specimens exhibit several minor differences from previous accounts. They have three setae on the endopod of the maxilla, whereas Lang (1965) described two, and Itô (1974) reported only one. In the female P 5 exopod of the Korean material, only three of the five setae are bare, whereas all were described as bare in previous accounts. In the male P 4 exopod, the terminal segment is similar in length to the second segment, but it is slightly longer in Lang’s (1965) and Itô’s (1974) material. In the male P 2 enp - 2, the apical outer seta is longer than the inner distal seta, whereas the reverse condition was described previously. Except for the first difference, these minor disparities are considered herein as intraspecific variability.