Rockacestus ottavianoi, García Facal & Ivanov & Menoret, 2024

Garcia Facal, Guillermina, Ivanov, Veronica A. & Menoret, Adriana, 2024, New species of Rockacestus (Cestoda, Phyllobothriidea) from skates of the genus Bathyraja (Rajiformes, Arhynchobatidae) in the Southwestern Atlantic Ocean with comments on the distribution of the genus, Zoosystematics and Evolution 100 (2), pp. 357-372 : 357

Rockacestus ottavianoi sp. nov.

Figs 1C , 4D, E , 6 , 7G-I

Type material.

Holotype whole mature worm, off Río Grande, Tierra del Fuego Province, Argentina (54°1.68'S, 67°6.81'W), 193 m, 2 Apr. 2012, A. Menoret leg., MACN-Pa No. 793.

Paratypes 1 whole mature worm, 1 whole mature strobila (SEM voucher), cross-section of 1 attached mature proglottid, same data as holotype, MACN-Pa Nos. 794/1-13. One whole mature worm, same data as for preceding, MLP-He No. 8100.

Description. Based on 4 specimens (3 whole mature worms, and 1 strobila without scolex), cross-sections of 1 mature proglottid, and 2 scoleces examined with SEM. Worms euapolytic, 23.1-53.1 (39.1 ± 13.8, n = 4) mm long, 124-195 (156 ± 36, n = 3) craspedote proglottids per worm (Fig. 1C ). Maximum width at level of scolex. Scolex composed of 4 bothridia, 590-750 (648 ± 70, n = 4) long, 978-1,250 (1,133 ± 36, n = 4) wide (Figs 4D , 6A ). Bothridia folded, 530-600 (570 ± 36, n = 3) long, 520-720 (613 ± 101, n = 3) wide when folded, sessile anteriorly, free posteriorly, consisting of apical sucker and marginal loculi. Posterior part of each bothridium with weak depression surrounded by circular band of muscle (Figs 4D , 6A ). Apical sucker 100-130 (113 ± 15, n = 3) long, 110-140 (125 ± 13, n = 3) wide (Figs 4D , 6A, B ). Cephalic peduncle, absent. Neck 11.6-25.3 (19.4 ± 6.0, n = 4) mm long.

Apex of scolex proper covered with acicular to capilliform filitriches (Fig. 6E ). Proximal bothridial surface covered with acicular filitriches (Fig. 6H ). Distal bothridial surface covered with acicular filitriches interspersed with lingulate spinitriches, lingulate spinitriches increasing in density posteriorly (Fig. 6F, G ). Distal surface of apical sucker covered with acicular filitriches interspersed with small lingulate spinitriches; posterior half of external rim of apical sucker with lanceolate spinitriches (Fig. 6B-D ); cilia found throughout distal surface of apical sucker. Distal surface of marginal loculi covered with acicular filitriches interspersed with short coniform spinitriches (Fig. 6I, L ). Capilliform filitriches on neck and strobila arranged in scutes (Fig. 6J, K ).

Immature proglottids wider than long, 123-179 (150 ± 28, n = 3) in number (Fig. 1C ). Mature proglottids wider than long, becoming longer than wide with maturity, 2-16 (6 ± 7, n = 4) in number (Fig. 1C ). Terminal mature proglottid longer than wide, 970-1,460 (1,220 ± 207) long, 570-760 (663 ± 81) wide, length-to-width ratio, 1.4-2.3 (1.9 ± 0.4, n = 4): 1 (Fig. 4E ).

Testes oblong, 92-152 (108 ± 39, n = 3) in total number, 55-68 (60 ± 5, n = 4) long, 43-52 (46 ± 4, n = 4) wide, extending from anterior margin of proglottid to anterior quarter of ovary; arranged in 6-7 columns anteroposteriorly and 2 layers deep in cross-section observed in anterior portion of proglottid (Figs 4E , 7G ). Cirrus sac oval, curved anteriorly, 350-395 (365 ± 26, n = 3) long, 125-165 (138 ± 23, n = 3) wide. Cirrus coiled, armed with minute spinitriches. Vas deferens highly coiled, extending anteriorly to vagina bend, overlapping medial portion of cirrus sac, anterior to cirrus sac (Fig. 4E ).

Ovary lobulated, H-shaped in frontal view, X-shaped in cross-section at level of isthmus, 345-500 (408 ± 81, n = 3) long, 235-355 (292 ± 60) wide (Figs 4E , 7I ). Vagina thick-walled, extending anteriorly from the ootype region forming a seminal receptacle, to bulk of vas deferens descending laterally along anterior margin of cirrus sac to enter genital atrium anterior to cirrus (Figs 4E , 7I ). Vagina and cirrus sac join into genital atrium, 50-60 (55 ± 7, n = 2) deep. Genital pores alternate irregularly, 68-74% (71 ± 2, n = 4) of proglottid length from posterior margin of proglottid. Vitellarium follicular, follicles irregular in shape, 28-55 (39 ± 12, n = 4) long, 43-50 (46 ± 3, n = 4) wide, arranged in 2 lateral bands almost reaching the midline in anterior third of proglottid, each band consisting of multiple columns (5-6 columns anterior to cirrus sac) of follicles, extending throughout the length of proglottid, uninterrupted by ovary, interrupted partially by genital atrium (Figs 4E , 7G-I ). Uterus saccate, restricted to region between ovary and cirrus sac running anteriorly up to genital pore level, uterine duct observed (Figs 4E , 7H ). Mehlis´ gland, 90-110 (99 ± 9, n = 4) long, 63-100 (76 ± 17, n = 4) wide, posterior to ovarian isthmus (Fig. 4E ).

Host.

Bathyraja magellanica (Philippi, 1902), Magellan skate ( Rajiformes , Arhynchobatidae ) (type host). Prevalence of infection, 10% in B. magellanica (1 host infected out of 10 examined).

Etymology.

This species is named in honor of Juan Manuel Ottaviano for his genuine and loyal friendship over the years.

Distribution.

This species is known from its type locality, off Río Grande, Tierra del Fuego Province, Argentina (54°1.68'S, 67°6.81'W).

Remarks.

Rockacestus ottavianoi sp. nov. can be distinguished from R. arctowskii , R. carvajali , R. conchai , and R. magellanicus sp. nov. by having more testes (92-152 vs. 60-80, 46-55, 51-73, and 67-89, respectively) and a greater number of proglottids (124-195 vs. 24-98, 75-81, 64-105, and 61-115, respectively). Rockacestus ottavianoi sp. nov. is easily distinguished from three of its congeners by the worm length by being shorter than R. brittanicus , R. georgiensis , and R. williamsi (23.1-53.1 vs. 170-250, 60-170, and 90 mm, respectively). Rockacestus ottavianoi sp. nov. can be distinguished from three species in the genus by having different size of apical sucker. In R. rakusai and R. siedleckii , it is bigger than in R. ottavianoi sp. nov. (250-310 and 185-220 in diameter vs. 100-130 long by 110-140 wide, respectively), whereas in R. piriei it is smaller (90 in diameter vs. 100-130 long by 110-140 wide, respectively). Rockacestus ottavianoi sp. nov. has a narrower scolex (978-1,250 in scolex width) and bigger testes (43-52 long by 55-68 wide) than R. radioductus (1,800-2,000 in scolex width; 40 in testes diameter). Finally, R. ottavianoi sp. nov. is euapolytic and has testes distributed in 2 layers deep in cross-section, whereas R. blasi sp. nov. is apolytic and has testes arranged in 3-4 layers deep in cross-section.

Update of generic diagnosis and distribution of valid species of Rockacestus

The diagnosis of Rockacestus sensu Caira et al. (2021) is revised to include the three species described below from the skates of the genus Bathyraja from continental shelf waters off Argentina. The generic diagnosis is updated as follows: worms euapolytic or apolytic; scolex spinitriches lingulate, lanceolate, coniform, filitriches papilliform or acicular; genital pores lateral, in midhalf or anterior half of proglottid, irregularly alternating; testes arranged in 2-4 rows in cross-section; vagina with seminal receptacle present or absent; uteroduct present or absent.

The valid species now include, Rockacestus arctowskii (Wojciechowska, 1991), Rockacestus blasi sp. nov., Rockacestus brittanicus (Williams, 1968), Rockacestus carvajali Caira, Bueno & Jensen, 2021, Rockacestus conchai Caira, Bueno & Jensen, 2021, Rockacestus georgiensis (Wojciechowska, 1991), Rockacestus magellanicus sp. nov., Rockacestus ottavianoi sp. nov., Rockacestus piriei (Williams, 1968), Rockacestus radioductus (Kay, 1942), Rockacestus rakusai (Wojciechowska, 1991), Rockacestus siedleckii (Wojciechowska, 1991), and Rockacestus williamsi (Schmidt, 1986).

The genus is widespread among temperate waters of the East Pacific and Atlantic Oceans, with R. brittanicus , R. piriei , and R. williamsi inhabiting the Northeast Atlantic Ocean; R. radioductus in the Northeast Pacific Ocean, R. carvajali from off Chiloé Island in the Southeast Pacific Ocean, and R. conchai off Malvinas Islands in the SWA. A subset of Rockacestus species also inhabits sub-Antarctic and Antarctic waters, with R. georgiensis from off South Georgia Island, R. rakusai registered off the Antarctic Peninsula, and records of R. arctowskii and R. siedleckii off the Antarctic Peninsula and the Weddel Sea. Rockacestus blasi sp. nov., R. magellanicus sp. nov. and R. ottavianoi sp. nov. are restricted to the Magellanic Province sensu Sabadin et al. (2020) in the SWA. The finding of the new species increases the species richness from two to five in marine waters around South America. Thus, the known latitudinal range of the genus in the Northern Hemisphere covers from 48°N to 58°N whereas in the Southern Hemisphere Rockacestus now ranges between 37 to 74°S (Fig. 9 ).

Figures

Figure 1. Light micrographs of whole worms of Rockacestus from the Southwestern Atlantic Ocean. A. Rockacestus blasi sp. nov. (holotype MACN-Pa No. 783) from Bathyraja macloviana; B. Rockacestus magellanicus sp. nov. (holotype MACN-Pa No. 789) from Bathyraja magellanica; C. Rockacestus ottavianoi sp. nov. (holotype MACN-Pa 793) from Bathyraja magellanica.

Figure 4. Line drawings of species of Rockacestus from the Southwestern Atlantic. A-C. Rockacestus magellanicus sp. nov. from Bathyraja magellanica; A. Bothridium (paratype MLP-He No. 8099); B. Detail of ootype region, mature proglottid (paratype MACN-Pa No. 790 / 4); C. Terminal mature proglottid (paratype MLP-He No. 8098); D-E. Rockacestus ottavianoi sp. nov. from Bathyraja magellanica; D. Bothridium (paratype MACN-Pa No. 794 / 1); E. Terminal mature proglottid (holotype MACN-Pa No. 793).

Figure 6. Rockacestus ottavianoi sp. nov. from Bathyraja magellanica, scanning electron micrographs. A. Scolex, small letters indicate the location of details shown in; B. Apical sucker, small letters indicate the location of details shown in Fig. 6 C, D; C. Surface of the external apical sucker rim, acicular filitriches and small lingulate spinitriches; D. Detail of distal apical sucker surface, lingulate spinitriches; E. Apex of scolex, acicular to capilliform filitriches; F, G. Distal bothridial surface, acicular filitriches and lingulate spinitriches; H. Proximal bothridial surface, acicular filitriches; I. Distal surface of marginal loculi, acicular filitriches and short coniform spinitriches; J, K. Scutes on surface of neck; L. Detail of microtriches on marginal loculi.

Figure 7. Light micrographs of cross-sections of mature proglottids of species of Rockacestus off Argentina. A-C. Rockacestus blasi sp. nov.; A. At the level of the testes, anterior to the cirrus sac; B. At the level of the cirrus sac; C. At the level of ovarian isthmus; D-F. Rockacestus magellanicus sp. nov.; D. At the level of the testes, anterior to the cirrus sac; E. At the level of the cirrus sac; F. At the level of ovarian isthmus; G-I. Rockacestus ottavianoi sp. nov; G. At the level of the testes, anterior to the cirrus sac; H. At the level of the cirrus sac; I. At the level of ovarian isthmus; cs - cirrus sac; oc - ovicapt; ov - ovary; sr - seminal receptacle; t - testes; u - uterus; ut - uteroduct; vd - vas deferens; vf - vitelline follicle; vg - vagina; vod - ventral osmoregulatory duct.

Figure 9. Geographic distribution of the valid species of Rockacestus from the Southern Hemisphere. Symbols: red dot: new records; blue dot: previous records; Rar - Rockacestus arctowskii; Rbl - Rockacestus blasi sp. nov.; Rca - Rockacestus carvajali; Rco - Rockacestus conchai; Rge - Rockacestus georgiensis; Rma - Rockacestus magellanicus sp. nov.; Rot - Rockacestus ottavianoi sp. nov.; Rra - Rockacestus rakusai; Rsi - Rockacestus siedleckii.