Holocentricola rufus, Cutmore & Cribb, 2021

Cutmore, Scott C. & Cribb, Thomas H., 2021, A new order of fishes as hosts of blood flukes (Aporocotylidae); description of a new genus and three new species infecting squirrelfishes (Holocentriformes, Holocentridae) on the Great Barrier Reef, Parasite (Paris, France) 28 (76), pp. 1-17 : 6-9

Holocentricola rufus n. sp. ( Figs. 2A , 3A )

urn:lsid:zoobank.org:act:89CB178C-58C2-431D-AC9AB4AC0B96C3A7

Type host: Sargocentron rubrum (Forsskål) , Red squirrelfish ( Holocentriformes : Holocentridae ).

Type locality: Off Heron Island (23 ° 27 0 S, 151 ° 55 0 E), southern Great Barrier Reef, Australia .

Other locality: Off Lizard Island (14 ° 40 0 S, 145 ° 27 0 E), northern Great Barrier Reef, Australia .

Site in host: Ventricle, branchial arteries, vessels of liver, wash of head split, wash of body split.

Prevalence: 14 of 17 Heron Island (adult worms in 11); 1 of 2 Lizard Island (no adult worms).

Intensity: 1–12 worms per fish (mean 4.27), when adult worms were detected.

Type material: Holotype ( QM G239429 ) and 24 paratypes ( QM G239430–239453 ), including nine hologenophores.

Representative DNA sequences: Partial cox 1 mtDNA, 16 sequences (seven submitted to GenBank, OK421322– OK421328); ITS2 rDNA, three identical sequences (two submitted to GenBank, OK422500–OK421301); partial 28S rDNA, one sequence (submitted to GenBank, OK422504).

Etymology: This species is named from the Latin rufus (red) for the type and only host, the Red squirrelfish.

Description [based on 25 specimens, including nine hologenophores]: Body lanceolate, ventrally concave, broadest at level of testis or caeca, 976–1290 × 142–222 (1093 × 182), 4.4–7.6 (6.1) times longer than wide; notch usually noticeable at level of male genital pore, sometimes indistinct; distinct terminal notch at posterior end; distinct bulge sometimes present at level of uterus. Tegumental spines arranged in ventro-marginal transverse rows for entire body length, 7–8 long, straight for most of body length, those in final 5–10 rows slightly curved with small hook on tip, 10–11 long. First spine row with 3–4 spines, increasing in number prior to dorsal nerve commissure, 8–9 spines per row for most of body length, decreasing in number posterior to testis, 3 spines in final row; spine rows 14–21 (18) wide in anterior third of body, 17–22 (19) wide in middle third of body, and 11–28 (14) wide in posterior third of body; rows spaced 4 apart. Dorsal nerve commissure 34–54 (46) across, 87–134 (112) from anterior extremity. Nerve cords well-defined, 6–9 (7) in diameter, run length of body, 30–52 (41) from body margin at midbody. Oral sucker poorly delineated, weakly muscularised, 14–28 × 15–22 (16 × 19), bearing concentric rows of fine spines in some specimens, number of rows undetermined. Mouth a simple pore, ventrally subterminal, 6–9 (7) from anterior extremity. Oesophagus almost straight to gently sinuous, thick-walled, 433–597 (480) long. Oesophageal glands enveloping oesophagus posterior to dorsal nerve commissure, thickening and forming distinct glandular bulb immediately anterior to anterior caeca. Caeca form X-shape; intestinal bifurcation in middle third of body, 435–602 (480), or 39.5–48.2% of total body length, from anterior extremity. Anterior caeca equal to subequal in length, shorter than posterior caeca; left anterior caecum 64–94 (77); right anterior caecum 65–100 (79); longer anterior caecum occupying 6.1–8.8% of total body length. Posterior caeca equal to subequal in length, 1.3–2.9 (2.1) times longer than anterior; left posterior caecum 111–222 (157); right posterior caecum 123–213 (162); longer posterior caecum occupying 9.5–19.5% of total body length. Total caecal length 204–308 (245), occupying 16.0–27.1% of body length.

Testis single, roughly rectangular, with margins irregularly lobed, immediately posterior to posterior ends of posterior caeca, extends laterally beyond lateral nerve cords and posteriorly to anterior margin of ovary, 100–233 × 77–154 (171 × 120), occupying 10.1–18.9% of total body length; post-testicular space 250–351 (296), or 25.2–29.2% of body length. Vas deferens originates medially from posterior margin of testis, passing ovary and uterus ventrally, widening posteriorly in some specimens, entering cirrus-sac dorso-anteriorly. External seminal vesicle absent. Cirrus-sac retort-shaped, rounded anteriorly, dramatically narrowed posteriorly; anterior rounded portion 46–79 × 30–55 (62 × 43), contains seminal vesicle and pars prostatica; posterior narrow portion 81–108 (92) long, notably thickened at marginal genital pore, contains ejaculatory duct (un-everted cirrus; everted cirrus not observed), 5–9 (6) wide at midpoint, 8–12 (10) wide at marginal thickening. Seminal vesicle round to ovoid, 25–69 × 26–53 (43 × 39), restricted to anterior, rounded portion of cirrus-sac, joining coiled pars prostatica; prostatic cells not observed. Ejaculatory duct long. Male genital pore on sinistral margin at distinct to indistinct marginal notch, 66–96 (79), or 6.5–8.3% of body length, from posterior extremity.

Ovary wedge-shaped to oblong, medial, with margins irregularly lobed, immediately posterior to testis, sometimes extending laterally beyond lateral nerve cords, 38–74 × 84–154 (58 × 119), 216–301 (249), or 21.4–24.3% of total body length, from posterior extremity. Oviduct originates from posterior margin of ovary, passes posteriorly dorsal to vitelline duct, dextro-lateral and sometimes partially dorsal to ascending portion of uterus, posteriorly curving sinistrally to meet oötype, usually filled with sperm. Oötype posterior to rest of genitalia, medial to submedial, surrounded by Mehlis’ gland, 81–138 (102) from posterior extremity. Uterus weakly convoluted, passing anteriorly between oviduct and dextral side of cirrus-sac, ventrally overlapping posterior portion of ovary, then passing posteriorly, sinistral to cirrus-sac, to female genital pore; distal portion of uterus often forming egg reservoir, creating distinct marginal bulge. Female genital pore dorsal, sinistro-submedial, separate from and anterior to male pore, just posterior to level of constriction dividing anterior and posterior portions of cirrus-sac, 33–51 (39) from sinistral margin, 104–163 (133) from posterior extremity. Eggs in utero ovoid to subspherical, very thin-shelled, anoperculate, 22–29 × 12–24 (25 × 17). Vitellarium follicular, distributed from just posterior to dorsal nerve commissure to posterior half of testis, laterally exceeding nerve cords, largely confluent anterior to testes, sometimes interrupted by ends of caeca and oesophageal gland, interrupted partially by testis ventrally and dorsally. Vitelline duct passes ovary ventrally, passing posterio-dextrally to oötype, ventrally overlaps oviduct and sometimes part of ascending portion of uterus, posteriorly curving sinistrally to meet oötype.

Excretory vesicle small, saccular; paired collecting ducts not traceable. Excretory pore at apex of terminal notch.

Remarks

Holocentricola rufus was found in all body sites examined, with adult worms in the heart (specifically the ventricle), branchial arteries of the gills, the major vessels of the liver, as well as in the wash of head split (gills already removed), and wash of entire body split (head and gills removed); however, specimens of this species were most commonly found infecting the branchial arteries. cox 1 sequence data were generated for samples from all five infections sites and from eggs lodged in the tips of gill filaments; all sequences form a strongly supported clade in the neighbor-joining analysis, with no division by infection location. No adults were recovered from the single infection from Lizard Island but an ITS2 sequence was generated from eggs lodged in gill tissue; this sequence is identical to those from adult samples from Heron Island.

Figures

Figure 2. Species of Holocentricola from Great Barrier Reef Holocentridae, whole worms, ventral views. (A) Holocentricola rufus n. sp. ex Sargocentron rubrum from off Heron Island (holotype, QM G239429); (B) Holocentricola exilis n. sp. ex Neoniphon sammara from off Lizard Island (paratype, QM G239111); (C) Holocentricola coronatus n. sp. ex Sargocentron diadema from off Lizard Island (holotype, QM G239125). Scale-bars: A–C, 200 µm.

Figure 3. Species of Holocentricola from Great Barrier Reef Holocentridae, terminal genitalia, dorsal views; spines illustrated are ventral. (A) Holocentricola rufus n. sp. ex Sargocentron rubrum from off Heron Island (paratype, QM G239440); (B) Holocentricola exilis n. sp. ex Neoniphon sammara from off Lizard Island (paratype, QM G239119); (C) Holocentricola coronatus n. sp. ex Sargocentron diadema from off Lizard Island (paratype, QM G239126). Abbreviations: CS, cirrus-sac; ER, egg reservoir; FGP, female genital pore; MGP, male genital pore; Od, oviduct; Oö, oötype; Ov, ovary; PP, pars prostatica; SV, seminal vesicle; Ut, uterus; VD, vas deferens; VitD, vitelline duct. Scale-bars: A–C, 100 µm.