Introduction

Pennellidae (Copepoda: Siphonostomatoida) consists of 25 valid genera and 148 species (Walter & Boxshall, 2023; Yumura et al., 2024) symbiotic on marine fish and mammals (Kabata, 1979; Boxshall & Halsey, 2004). Adult metamorphosed female pennellids have large bodies and lose their maxillipeds as mesoparasite adaptations (Boxshall & Halsey, 2004). These metamorphosed females exhibit variable morphology regarding for example, the structure of the cephalothorax (ranging from a simple cephalothorax to development of a cephalic holdfast organ), the trunk (varying from straight trunks to sigmoid trunks), the abdomen (varying from an indistinct abdomen to an abdomen embedded with posterior processes) and the egg strings (varying from straight egg strings to curled egg strings) (Castro-Romero, 2014).

This family has a history of intergeneric misidentifications (Kabata, 1979; Castro-Romero, 2014; Walter & Boxshall, 2023). For example, revised species of Peniculus von Nordmann, 1832 were transferred to several genera including Peniculisa Wilson C.B., 1917; Metapeniculus Castro-Romero & Baeza-Kuroki, 1985; Propeniculus Castro-Romero, 2014, and Pseudopeniculus Castro-Romero, 2014 (Wilson, 1917; Castro-Romero & Baeza-Kuroki, 1985; Castro-Romero, 2014). Similarly, several revised species of Lernaeenicus Lesueur, 1824 have already been transferred to different genera (e.g. Sarcotretes Jungersen, 1911; Protosarcotretes Ohtsuka, Lindsay & Izawa, 2018, and Cardiodectes Wilson, C.B., 1917) due to possession of morphological characters similar to those of other genera (Wilson, 1917; Ohtsuka et al., 2018).

To date, only six genera and eight species [Pennella balaenoptera Koren & Danielssen, 1877 from Balaenoptera physalus (Linnaeus); Pennella filosa (Linnaeus, 1758) from Istiompax indica (Cuvier), Mola mola (Linnaeus), Thunnus albacares (Bonnaterre), and Balaenoptera acutorostrata Lacépède; Peniculus fistula fistula von Nordmann, 1832 from Kaperangus microlepis (Norman); Peniculisa furcata (Krøyer, 1863) from Paramonacanthus frenatus (Peters); Peroderma cylindricum Heller, 1865 from Sardinella maderensis (Lowe); Cardiodectes bellottii (Richiardi, 1882) from Lampanyctodes hectoris (Günther) and Gonichthys cocco (Cocco); Lernaeenicus gonostomae Kensley & Grindley, 1973 from Sigmops elongatus (Günther); and Lernaeenicus kabatai Oldewage, 1989 from Carangoides equula (Temminck & Schlegel)] were reported from marine fish and mammals off southern Africa (Barnard, 1955; Perkins, 1983; Dippenaar, 2004).

This paper reports on the Pennellidae species collected from marine fish off Southern Africa, with re-descriptions of Sarcotretes scopeli Jungersen, 1911 and Propeniculus stromatei (Gnanamuthu, 1951). Notes are provided about the genus Lernaeenicus, with synonymizing and re-description of Lernaeenicus gonostomae Kensley & Grindley, 1973 based on voucher specimens from the Iziko South African museum. Additionally, the phylogenetic relationships between selected Pennellidae genera, using available mitochondrial COI (cytochrome oxidase I) sequences, are investigated.

Materials and Methods

Specimens collected from fish caught off the southern African coasts, from 1993 to 2019 were preserved in 70% ethanol. For morphological studies, specimens were stained with a mixture of lactic acid and a small amount of lignin pink, then examined using stereo- and compound microscopes. Some appendages were dissected and drawings were made with the aid of drawing tubes. All measurements were done using a 2 mm stage micrometer and are given as mean (range) mm. Terminology used in morphological descriptions conforms to that of Kabata (1979). Host species names were validated using Froese and Pauly (2023). Voucher specimens for Pennella instructa, Sarcotretes scopeli, S. longirostris and Propeniculus stromatei were deposited in the Iziko South African museum.

For molecular studies, DNA was extracted from Sarcotretes scopeli. Specimens were cut into small pieces and dried in 1.5 microcentrifuge tubes on a heat block at 56°C for approximately 2 hours. Genomic DNA was extracted using the Zymo Research Quick-DNA™ miniprep plus kit, following the protocol for solid tissues. Polymerase Chain Reaction (PCR) was performed to amplify a fragment of the partial mitochondrial (mtDNA) COI gene with the forward primer mICOIintF (GGWACWGGWTGAACWGTWTAYCCYCC) and reverse primer jgHCO2198 (TAIACYTCIGGRTGICCRAARAAYCA) (Geller et al., 2013; Leray et al., 2013) in the Eppendorf Mastercycler. A 25 µl PCR reaction mixture was prepared for each sample, consisting of 12 µl of OneTaq Quick-Load 2X Master Mix with Standard Buffer, 2 µl of each primer, 1-3 µl of template DNA, and double distilled water to adjust the volume. PCR cycling conditions included 94°C (3 min) initial denaturation, followed by 35 cycles of 94°C (30 sec) denaturation, 50°C (1 min) annealing and 68°C (1 min) extension, followed by 68°C (7 min) extension. Purification of PCR products was performed using exoSAP mix and incubated in Eppendorf Mastercycler at 37°C (15 min) and 80°C (15 min) for enzyme inactivation. Sanger sequencing of the purified PCR products was conducted using the Applied Biosystems™ 3730xl DNA Analyzer.

The sequences obtained from the output chromatograms were assembled using CLC genomics workbench 7 (QIAGEN) and carefully examined for nucleotide ambiguities. Forty nine pennellid COI sequences including the genera Haemobaphes Steenstrup & Lütken, 1861, Lernaeenicus, Lernaeocera Blainville, 1822, Metapeniculus, Peniculus, Pennella, Propeniculus and Trifur Wilson C.B., 1917 were downloaded from Genbank (Table 1) and compiled into a dataset with one additional generated sequence of S. scopeli (Genbank accession nr OR807153 - 365bp) with representatives of Caligidae Burmeister, 1835 (Caligus curtus Müller O.F., 1785 and C. elongates von Nordmann, 1832) as outgroup taxa according to Yumura et al. (2022) and Osuna-Cabanillas et al. (2023). Sequences were aligned with Clustal X 2.1 (Thompson et al., 1997) and converted to amino acids using MacClade (Maddison & Maddison, 2001). Furthermore, the dataset was checked for the best model of evolution for Bayesian analysis and Maximum likelihood using jModeltest (Darriba et al., 2012) [AIC = GTR+I+G (-InL = 6398.59; AIC = 13029.18)]. Maximum likelihood was performed using IQtree (Nguyen et al., 2015), with 100000 bootstrap replicates (annotated nodes with bootstrap support of >60%), while Bayesian analysis was performed using MrBayes v3.2 (Ronquist et al., 2012) (nst=6 rates=invgamma), with posterior probabilities percentage of >60% annotated on nodes. The final trees were visualized and edited using Fig tree v1.43 software (Rambaut, 2016).

Table 1 Pennellidae species used in the phylogenetic analysis with accession numbers from Genbank.
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Results and discussion

Pennella Oken, 1815

Pennella instructa Wilson C.B., 1917

Host: Seriola lalandi Valenciennes (Carangiformes: Carangidae)

Locality: West coast off South Africa

Material collected and examined: 1♀

Re-description:

Post metamorphosed females [based on one specimen, fig. 1]. Body length from tip of cephalothorax to tip of abdomen 205 mm, cephalothorax length 8 mm, width 6 mm; cephalothorax horn length 7 mm, width 2 mm; neck-like region length 113 mm, width 2 mm; trunk length 58 mm, width 5 mm; abdomen length 26 mm, width 2.7 mm. Anterior part of cephalothorax (figs. 1a, b) with papillae (p) arranged in four parentheses-like rows, cephalothorax subspherical (figs. 1a, c). Simple cephalic holdfast with two lateral horns (h) (figs. 1a, c), posterolaterally on cephalothorax. Neck-like region elongated, expanding into straight, cylindrical trunk, with elongated abdomen (ab) (fig. 1a) bearing rows of plumules laterally and elongated egg strings, with uniseriate eggs.

Fig. 1
figure 1

Pennella instructa Wilson C.B., 1917, post metamorphosed female; a. habitus, ventral view; b. cephalothorax papillae, anterior view; c. cephalothorax, dorsolateral view. Scale bars: a = 1 mm. (ab = abdomen; p = papillae; h = holdfast horn)

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Remarks:

Pennella has 10 valid species (Walter & Boxshall, 2023), known to infect a wide range of marine hosts, from teleosts to mammals. Metamorphosed females of this genus vary in total length from large (>100 mm), medium (between 50–100 mm) to small (<50 mm) (Hogans, 2017a). They have cephalothoraces with papillae of different arrangements anteriorly, simple cephalic holdfast with two posterolateral holdfast processes, sometimes with a dorsal holdfast process; a cylindrical neck-like region of varying lengths; a straight and cylindrical trunk with an abdomen of various lengths bearing plumules and elongated egg strings with uniseriate eggs (Kabata, 1979).

The collected specimen closely resembles P. instructa (Hogans, 1986) and belongs to the group of Pennella species with a large (>100 mm) total length, which also includes P. balaenoptera; P. benzi Hogans, 2017 and P. filosa. Pennella instructa differs from P. balaenoptera, P. benzi and P. filosa by possession of a cephalothorax anteriorly covered with papillae of apparently even sizes and grouped into four rows with two posterolateral holdfast horns (Hogans, 1986), whereas the others (P. balaenoptera, P. benzi, and P. filosa) possess a cephalothorax covered anteriorly with unorganized papillae of uneven sizes bearing two posterolateral holdfast horns as well as a dorsal horn of different shapes and sizes (Pillai, 1967; Hogans, 2017a).

Pennella instructa has previously been reported from Xiphias gladius Linnaeus; Istiophorus platypterus (Shaw), and Istiompax indica (Cuvier) (Wilson, 1917; Pillai, 1967; Hogans, 1986, 2017a). This is the first report of P. instructa infecting Seriola lalandi from a new geographic location i.e. the Atlantic Ocean off South Africa.


Lernaeenicus Lesueur, 1824

Lernaeenicus longiventris Wilson C.B., 1917

Host: Unknown

Locality: Off South Africa

Material collected and examined: 3♀♀ (broken)

Re-description:

Post metamorphosed females [based on three broken specimens, fig. 2]. Body length from tip of neck to tip of abdomen 45.5 mm (33.7-55.7), cephalothorax length 0.8 mm, width 2.1 mm; neck-like region length 25.2 mm (15.4-35 mm), width 0.4 mm; trunk length 6.9 mm (6.3-7.4 mm), width 1.1 mm (1-1.1 mm); abdomen length 13.3 mm (12.1-14.6 mm), width 0.32 mm (0.3-0.4 mm). Anterior part of cephalothorax (fig. 2a) with antennary appendages, antennule (a1) and antenna (a2). The ventral side of cephalothorax (fig. 2c) with mouth tube (mt) and maxillary appendages; the dorsal side (fig. 2a) armed with 3 blunt processes, 1 dorsal horn (dh) and 2 dorsolateral horns (dlh). Neck-like region elongated with four pairs of legs (l) (fig. 2c) anteriorly, expanding into straight, cylindrical trunk, elongated abdomen (ab) and elongated egg strings, with uniseriate eggs.

Fig. 2
figure 2

Lernaeenicus longiventris Wilson C.B., 1917, post metamorphosed female; a. cephalothorax, lateral view; b. cephalothorax, ventral view; c. habitus without cephalothorax, lateral view. Scale bars a, b = 50 µm; c = 1 mm. (a1 = antennule; a2 = antenna; dh = dorsal holdfast horn; dlh = dorsolateral holdfast horn; mt = mouth tube; l = legs)

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Remarks:

Lernaeenicus currently has 31 valid species (Walter & Boxshall, 2023) known to infect marine teleosts. Metamorphosed females of this genus are mainly identified by a simple cephalic holdfast with variable lateral, dorsal or both processes of different sizes, a cylindrical neck-like region of different lengths, a straight and cylindrical trunk, with an abdomen of various lengths, and elongated egg strings, with uniseriate eggs (Kabata, 1979).

Specimens collected (figs. 2a-c) closely resemble Lernaeenicus longiventris (Knoff & Boeger, 1994) by possession of a cephalothorax with three holdfast horns (2 short dorsolateral and one long dorsal), an elongated neck-like region, a minute trunk 2 times shorter than the abdomen, and an elongated abdomen 2/3 the length of egg strings. There are twelve Lernaeenicus species with 3 cephalic horns. Lernaeenicus longiventris differs from L. sprattae (Sowerby, 1806) and L. encrasicoli (Turton, 1807) by possession of an abdomen and neck longer than the trunk and a dorsal horn longer than than the dorsolateral horns whereas L. sprattae and L. encrasicoli possess a minute abdomen, neck shorter than the trunk, longer lateral horns and the dorsal horn as a small protuberance (Kabata, 1979). Lernaeenicus longiventris differs from L. kabatai, L. neglectus Richiardi, 1877, L. vorax Richiardi, 1877, L. polynemi (Bassett-Smith, 1898), L. cerberus Leigh-Sharpe, 1927 and L. sayori Yamaguti, 1939 by possession of an abdomen longer than the trunk and a dorsal horn longer than the dorsolateral horns whereas L. kabatai, L. neglectus, L. vorax, L. polynemi, L. cerberus and L. sayori possess an abdomen shorter than the trunk and pronounced cephalic horns of the same lengths (Richiardi, 1877; Leigh-Sharpe, 1927; Pillai, 1967; Oldewage, 1989). Lernaeenicus longiventris closely resembles L. hemiramphi Kirtisinghe, 1932, L. stromatei Gnanamuthu, 1953 and L. megalepsis Aneesh, Helna, Kumar & Venmathi Maran, 2021, although it differs from them by possession of short holdfast horns, with the dorsolateral horns shorter than the dorsal horn whereas L. hemiramphi, L. stromatei, and L. megalepsis the cephalic horns are of the same lengths (Gnanamuthu, 1953; Aneesh et al., 2021).

Previous reports of L. longiventris include infection of the following fish hosts, Caranx crysos, Caranx hippos (Linnaeus), Caranx ignobilis (Forsskål), Coryphaena hippurus Linnaeus, Scomberomorus maculatus (Mitchill), Gnathanodon speciosus (Forsskål), Mugil cephalus Linnaeus, Mugil curema Valenciennes, Hyperoglyphe perciformis (Mitchill), Urophycis floridana (Bean & Dresel), Pogonias cromis (Linnaeus), Pomatomus saltatrix (Linnaeus), Rachycentron canadum (Linnaeus), Sparus aurata Linnaeus, Stolephorus commersonnii Lacepède and Atherinella brasiliensis (Quoy & Gaimard) (Wilson, 1917, 1932; Kirtisinghe, 1964; Knoff & Boeger, 1994).

Genus Lernaeenicus was inadequately described, with incomplete descriptions of different species (Raja et al., 2016; Ohtsuka et al., 2018). Thus, species of Lernaeenicus need a revision (Kabata, 1979) due to discrepancies in the identification e.g. the characteristic feature of a distinct abdomen (Boxshall & Halsey, 2004), while L. quadrilobatus Yamaguti & Utinomi, 1953 and L. gracilis (Heller, 1865) lack one. Additionally, amongst the existing species of Lernaeenicus, only L. gonostomae (see Kensley & Grindley, 1973) and L. quadrilobatus (see Yamaguti & Utinomi, 1953; Kazachenko & Avdeev, 1977) have retained vestiges of a cephalic dorsal shield similar to that in other genera (Sarcotretes, Ophiolernaea Shiino, 1958, Creopelates Shiino, 1958 and Nagasawanus Uyeno, 2015). Furthermore, L. quadrilobatus possesses features characteristic of the genus Nagasawanus Uyeno, 2015, such as possession of two pairs of cephalic lobes, mouth tube and maxillary appendages located anteriorly on the ventral surface of cephalothorax, four pairs of legs (first two biramous and last two uniramous) and a minute conical abdomen (Yamaguti & Utinomi, 1953; Kazachenko & Avdeev, 1977; Uyeno, 2015). A complete re-description of L. quadrilobatus is suggested to validate its taxonomic identity. Species of Lernaeenicus either possess cephalic holdfast, thoracic holdfast or both holdfast organs (Kabata, 1979). Species that possess a thoracic holdfast organ (including L. ater Shiino, 1958, L. nemipteri Gnanamuthu, 1953, L. affixus Wilson C.B., 1917, L. triangularis Heegaard, 1966, L. polycerus Wilson C.B., 1917 and L. ramosus Kirtisinghe, 1956) morphologically resemble each other by presence of a relatively wide abdomen (wider than the width of the neck) but shorter than the trunk and a cephalic attachment plate (see Wilson, 1917; Pillai, 1967). Phylogenetic estimation of some pennellid species (see Fig. 2, Clade III in Yumura et al. (2022)) estimates L. hemirhamphi basal to a sister grouping of Pennella sp. and L. ater/L. ramosus sister group. This may be due to L. ater, L. ramosus and Pennella sp. bearing a thoracic holdfast organ. However, the placement of Pennella sp. within the clade of Lernaeenicus species also indicates the necessity of a revision of Lernaeenicus species.


Sarcotretes Jungersen, 1911

Sarcotretes scopeli Jungersen, 1911

Host: Nansenia tenera Kawaguchi & Butler (Argentiniformes: Microstomatidae)

Locality: Off Namibia (Atlantic Ocean)

Material collected and examined: 6♀♀

Voucher material: 2♀♀ (SAMC-A096498) from Nansenia tenera deposited in the Iziko South African Museum, Cape Town, South Africa

Re-descriptions:

Post metamorphosed females [based on six specimens, fig. 3]. Body length from tip of cephalothorax to the tip of the abdomen 36.7 mm (33.6–38.9 mm), cephalothorax length 2.6 mm (2.1–3.1 mm), width 0.8 mm (0.7–1.0 mm); cephalothorax horn length 1.4 mm (1.0–1.6 mm), width 1.1 mm (0.8–1.4 mm); neck-like region length 14.8 mm (14.0–16.8 mm), width 1.2 mm (0.8–1.3 mm); trunk length 19.4 mm (16.8–21 mm), width 2.5 mm (2.1–2.8 mm); egg-sac length 45.4 mm, width 1.0 mm (0.7–1.1 mm). Cephalothorax (figs. 3a, b) anteriorly soft, longitudinally elongated, with protrusible proboscis (pb), posterior part heavily sclerotized, with lateral cephalothorax horns (h) (figs. 3a, b) extending posteriorly. Cylindrical neck-like region (fig. 3a) with three pairs of legs (l) anteroventrally (fig. 3b). Trunk cylindrical (fig. 3a), with a short abdomen terminally with uniseriated eggs. Antennary appendages (fig. 3a) dorsally on cephalothorax with maxillary appendages anteroventrally on cephalothorax (fig. 3b). Antennule (a1) (fig. 3c) lateral to antenna (a2), 3-segmented, basal segment with 12 setae of different lengths (eight short and four long setae), medial segment with two short setae, terminal segment with 12 apical setae of different lengths (seven short and six long setae). Antenna (fig. 3d) indistinctly 3-4 segmented, first segment robust, with sclerotised ridge; second segment robust, with dentiform process in distal corner accommodating tip of curved claw. Mandible (mn) (fig. 3e) 2-segmented, elongated, with dentiferous margin apically, with about five teeth. Maxillule (mx1) (figs. 3b, 3f) lateral to mouth tube (mt), bilobed, endite with two elongated setae; palp bulbous, with slender apical seta. Maxilla (mx2) (fig. 3g) 2-segmented, lacertus elongated, with stout protuberance medially; brachium slender, with short, plumose clavus at the base of calamus, calamus curved, with several horizontal rows of spiniform setules. Maxilliped absent. Three pairs of legs observed, second leg (fig. 3h) biramous, 2-segmented, endopod first segment armed with a short spine distolaterally, second segment with seven observed setae, exopod first segment unarmed, second segment with only three observed setae.

Fig. 3
figure 3

Sarcotretes scopeli Jungersen, 1911, post metamorphosed female; a. habitus, cephalothorax dorsal view and trunk lateral view; b. cephalothorax, ventral view; c. antennule; d. antenna; e. mandible; f. maxillule; g. maxilla, h. second leg. Scale bars: a = 1 mm; b, h = 50 µm; c-g = 10 µm. (a1 = antennule; a2 = antenna; ds = dorsal shield rudiment; mt = mouth tube; mn = mandible; mx1 = maxillule; mx2 = maxilla; pb = proboscis; h = holdfast horn; l = legs)

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Remarks:

Currently Sarcotretes has only four species, namely Sarcotretes eristaliformis (Brian, 1908); S. scopeli Jungersen, 1911; S. longirostris Ho, Nagasawa & Kim I.H., 2007, and S. umitakae Uyeno, Wakabayashi & Nagasawa, 2012 (Walter & Boxshall, 2023). Sarcotretes species are parasitic on teleosts. Post metamorphosed female species of this genus are characterized by a longitudinally elongated cephalothorax with a protrusible proboscis and lateral cephalothorax horns of different lengths extending posteriorly; a cylindrical neck-like region with three pairs of legs (both S. eristaliformis and S. umitakae with vestiges of leg four) anteroventrally; cylindrical trunk with a short abdomen terminally and uniseriate eggs (Cherel & Boxshall, 2004; Ho et al., 2007; Uyeno et al., 2012).

Sarcotretes scopeli differs from the other Sarcotretes species by having a relatively shorter body length (<45 mm) (Hogans, 1988) compared to other Sarcotretes species (>45 mm) (Cherel & Boxshall, 2004; Ho et al., 2007; Uyeno et al., 2012). Sarcotretes scopeli possesses a neck-like region shorter than the trunk (Hogans, 1988) while S. eristaliformis possesses a neck-like region of the same length as the trunk (Cherel & Boxshall, 2004) and both S. longirostris and S. umitakae possess neck-like regions which is longer than the trunk (Ho et al., 2007; Uyeno et al., 2012).

This is the first report of S. scopeli infecting N. tenera, which constitutes a new geographical record off the Namibian coast (Atlantic Ocean). Previously S. scopeli has been reported from Benthosema glaciale (Reinhardt); Cyclothone atraria Gilbert; Diogenichthys atlanticus (Tåning); Electrona carlsbergi (Tåning); Gonichthys cocco (Cocco); Gymnoscopelus nicholsi (Gilbert); Gymnoscopelus piabilis (Whitley); Hymenogadus gracilis (Gilbert & Hubbs); Krefftichthys anderssoni (Lönnberg); Lampichthys procerus (Brauer); Melanocetus johnsonii Günther; Metelectrona ventralis (Becker); Symbolophorus evermanni (Gilbert); Myctophum punctatum Rafinesque; Notoscopelus resplendens (Richardson); Polyipnus asteroides Schultz; Protomyctophum bolini (Fraser-Brunner); Protomyctophum choriodon Hulley; Protomyctophum tenisoni (Norman); Maurolicus muelleri (Gmelin); Scopeloberyx malayanus (Weber); Scopeloberyx opisthopterus (Parr); Scopeloberyx robustus (Günther); and Sternoptyx diaphana Hermann (Wilson, 1917; Kazachenko & Avdeev, 1977; Boxshall, 1989, 1998; Cherel & Boxshall, 2004).


Sarcotretes longirostris Ho, Nagasawa & Kim I.H., 2007

Host: Centrolophus niger (Gmelin) (Scombriformes: Centrolophidae)

Locality: off the West coast of South Africa (Atlantic Ocean)

Material collected and examined: 3♀♀ from Centrolophus niger and 3♀♀ from unknown hosts off the south coast (Atlantic Ocean, South Africa)

Voucher material: 1♀ (SAMC-A096499) from Centrolophus niger deposited in the Iziko South African Museum, Cape Town, South Africa.

Re-descriptions:

Post metamorphosed females [based on three specimens, fig. 4]. Body length from tip of cephalothorax to tip of abdomen 59.6 mm (48.3–79.8 mm), cephalothorax length 5.6 mm (4.2–8.4 mm), width 1.4 mm (1.12–1.54 mm); cephalothorax horn length 4.9 mm (4.2–5.6 mm), width 1.4 mm; neck-like region length 28.9 mm (19.6–44.8 mm), width 1.0 mm (0.8–1.1 mm); trunk length 21.7 mm (21–22.4 mm), width 3.72 mm (2.8–4.2 mm). Cephalothorax (figs. 4a-c) anteriorly soft, longitudinally elongated, with protrusible proboscis (pb), posterior part heavily sclerotized, with lateral cephalothoracic horns (h) (figs. 4a-c) extending posteriorly. Cylindrical neck-like region (fig. 4a) extending into a cylindrical trunk (fig. 4a), bearing short abdomen terminally with egg strings with uniseriated eggs.

Fig. 4
figure 4

Sarcotretes longirostris Ho, Nagasawa & Kim I.H., 2007, post metamorphosed female; a. habitus, cephalothorax anteroventral view and trunk lateral view; b. cephalothorax, posterodorsal view; c. cephalothorax, anteroventral view. Scale bars: a-c = 1 mm. (ds = dorsal shield rudiment; mt = mouth tube; pb = proboscis; h = holdfast horn)

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Remarks:

Material collected (fig. 4) closely resemble those studied in Ho et al. (2007) as S. longirostris. Sarcotretes longirostris differs from both S. eristaliformis and S. scopeli by possessing a neck-like region which is longer than the trunk (see fig. 4a), while that of S. eristaliformis is the same length as the trunk (Cherel & Boxshall, 2004) and that of S. scopeli is shorter than the trunk (Hogans, 1988). Sarcotretes longirostris differs from S. umitakae by possessing lateral horns (h) of the holdfast of the same width throughout, tapering at tips (Ho et al., 2007) (figs. 4b, c), whereas that of S. umitakae are proximally bulbous, constrict midway and tapering into slender horns (Uyeno et al., 2012).

This is the first report of S. longirostris infecting Centrolophus niger off the South African coasts. Previously, it has been reported from Globicephala macrorhynchus Gray (Ho et al., 2007).


Sarcotretes gonostomae (Kensley & Grindley, 1973) n. comb.

Syn: Lernaeenicus gonostomae Kensley & Grindley, 1973

Host: Sigmops elongatus (Günther)

Locality: Off Mozambique (Indian Ocean)

Material examined: 2♀♀ from Iziko South African Museum (Iziko South African Museum voucher numbers A11751 & A13031)

Re-description:

Post metamorphosed female [based on one specimen, fig. 5]. Body length from tip of cephalothorax to the tip of the abdomen 26.74 mm, cephalothorax length 4.34 mm, width 1.4 mm; cephalothorax horn length 4.2 mm, width 1.12 mm (1.12 mm bulbous process and 0.14 mm slender process); neck-like region length 12.6 mm, width of 0.56 mm; trunk length 9.8 mm, width 2.1 mm; egg-sac width 0.28 mm. Cephalothorax (figs. 5a-d) anteriorly soft, longitudinally elongated, with protrusible mouth tube (mt), posterior part heavily sclerotized, with lateral holdfast horns (h) (figs. 5a-d), each with a bulbous base and a slender elongation extending posteriorly. Cylindrical neck-like region (figs. 5a-d) with three pairs of legs (l) anteroventrally (fig. 5d), fourth pair not observed. Trunk cylindrical, fusiform (figs. 5a, b), with a short abdomen terminally (figs. 5a, b, e) and egg strings with uniseriated eggs (fig. 5e). Antennary appendages (fig. 5c) dorsally on cephalothorax. Maxillary appendages situated anteroventrally on cephalothorax (fig. 5d), maxillules (mx1) on each side of the mouth tube and maxilla at the base of the proboscis.

Fig. 5
figure 5

Sarcotretes gonostomae (Kensley & Grindley, 1973), post metamorphosed female; a. habitus, cephalothorax dorsal view and trunk ventral view; b. habitus, cephalothorax lateral view and trunk dorsal view; c. cephalothorax, dorsal view; d. cephalothorax, lateral view; e. abdomen, ventral view. Scale bars: a, b = 1 mm; c-e = 50 µm. (a2 = antenna; ds = dorsal shield rudiment; mt = mouth tube; mn = mandible; mx1 = maxillule; mx2 = maxilla; pb = proboscis; h = holdfast horn; l = legs)

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Remarks:

Post metamorphosed females of Lernaeenicus as described by Kabata (1979), are characterized by a distinct abdomen of variable length, straight trunk, neck-like region of variable lengths, four thoracic legs and cephalothorax with various holdfast organs made up of processes ranging from only 1 to about 5. Sarcotretes gonostomae n. comb. differs from Lernaeenicus species by possession of a cephalothorax which extends into the elongated proboscis, distinct terga segments on the dorsal side of the cephalothorax, a neck-like region of variable width and a minute abdomen (see figs. 5a-d).

Amongst all Pennellidae genera, the possession of an elongated proboscis occurs only in Sarcotretes, Ophiolernaea and Metapeniculus (Uyeno et al., 2012). Ophiolernaea is identified by variable bulbous processes of the holdfast organ on each side of the neck-like region or cephalothorax, four legs and an elongated proboscis, which is longer than the length of the neck-like region and trunk combined (Shiino, 1958; Ho, 1966; Kabata, 1979). The studied specimens possess a proboscis shorter than the neck-like region and trunk. Metapeniculus species are characterized by a cephalothorax without a holdfast but with or without anterolateral processes (Castro-Romero & Baeza-Kuroki, 1985) which differs from the current specimens due to the presence of a holdfast. Sarcotretes species also possess an elongated mouth cone, but the cephalothorax has lateral holdfast horns extending posteriorly (Wilson, 1917). Thus, the studied specimens belong to Sarcotretes with a cephalothorax consisting of two portions, the smooth proboscis-like mouth cone and a heavily sclerotized basal portion, with holdfast organ laterally that extend posteriorly. Additionally, the first two pairs of legs are biramous and leg 3 uniramous, while the neck-like region expands into the elongated trunk with a small, distinct abdomen.

Sarcotretes gonostomae n. comb. differs from S. scopeli by possessing an elongated proboscis, elongated holdfast horns, and a neck-like region longer than the trunk, whereas S. scopeli possesses a relatively short proboscis, short holdfast horns and a neck-like region which is shorter than the trunk. These two species are smaller in total length than the other species. Sarcotretes gonostomae n. comb. differs from S. eristaliformis by possessing an elongated oral cone, elongated holdfast horns, and a neck-like region longer than the trunk, whereas S. eristaliformis possesses a relatively short proboscis, short holdfast horns and a neck-like region of the same length as the trunk (Cherel & Boxshall, 2004). The total length of S. eristaliformis is about 44.5-58 mm (Cherel & Boxshall, 2004), whilst that of S. gonostomae n. comb. is 26.76 mm. Sarcotretes gonostomae n. comb. differs from S. longirostris by possessing holdfast horns with bulbous bases, thinning posteriorly whereas S. longirostris has holdfast horns without bulbous bases (Ho et al., 2007). The total length of S. longirostris is 41.4-74.4 mm (Ho et al., 2007), whereas that of S. gonostomae n. comb. is 26.76 mm. Both S. gonostomae n. comb. and S. longirostris have elongated holdfast horns and a longer proboscis, but can be distinguished based on the shape of the holdfast horns and the size. Sarcotretes gonostomae n. comb. closely resembles S. umitakae with a neck-like region which is longer than the trunk and each holdfast horn with a bulbous base with thin processes extending posteriorly (Uyeno et al., 2012). The total length of S. gonostomae n. comb. is 26.74 mm versus 30.26-50.12 mm in S. umitakae. The neck-like region is 1.3 times the trunk length in S. gonostomae n. comb. versus 3 times the trunk length in S. umitakae. The neck-like region of S. umitakae has a posterior bulge and constriction not observed in S. gonostomae n. comb. Sarcotretes gonostomae n. comb. has a small abdomen while that of S. umitakae is minute (Uyeno et al., 2012). Thus, S. gonostomae n. comb. differs from all the existing species of Sarcotretes.


Cardiodectes Wilson C.B., 1917

Cardiodectes bellottii (Richiardi, 1882)

Host: Lampanyctodes hectoris (Günther) (Myctophiformes: Myctophidae)

Locality: Off the coast of South Africa

Material collected and examined: 34♀♀

Voucher material: 2♀♀ (SAMC-A096500) deposited in the Iziko South African Museum, Cape Town, South Africa

Re-description:

Post metamorphosed females [based on eight specimens, fig. 6]. Body length from tip of cephalothorax to tip of abdomen 6.8 mm (5.1–7.6 mm), cephalothorax length 1.3 mm (1.1–1.5 mm), width 0.6 mm (0.5-0.7 mm); neck-like region length 1.0 mm (0.8–1.4 mm), width 0.3 mm (0.3-0.4 mm); trunk length 4.3 mm (3.3–5.1 mm), width 1.1 mm (0.9–1.3 mm); abdomen length 0.3 mm (0.2–0.3 mm). Anterior part of cephalothorax (figs. 6a-c) with papillae (p), cephalothorax with simple cephalic lobes (cl) (figs. 6a-c). Neck-like region short, with neck lobe (nl) anteriorly, expanding into a cylindrical trunk, with a minute unilobed abdomen (fig. 6a), and egg strings with uniseriate eggs.

Fig. 6
figure 6

Cardiodectes bellottii (Richiardi, 1882), post metamorphosed female; a. habitus, lateral view; b. cephalothorax, anterior view; c. cephalothorax, lateral view. Scale bars: a = 1 mm; b, c = 50 µm. (p = papillae; cl = cephalic lobe; nl = neck lobe)

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Remarks:

Cardiodectes has 17 valid species (Walter & Boxshall, 2023), infecting marine fishes and with molluscs as intermediate hosts (Ho, 1966; Perkins, 1983; Boxshall, 2000). Females of Cardiodectes are mainly characterized by a cephalothorax with branched papillae anteriorly (figs. 6a-c), with or without cephalic lobes, a neck-like region of variable lengths, a cylindrical trunk of variable length and width, with or without a distinct abdomen, and straight or spiral egg strings with uniseriate eggs. Adult females are divided into two groups, i.e. medusaeus (including Cardiodectes bellottii (Richiardi, 1882); C. anchorellae Brian & Gray, 1928; C. frondosus Schuurmans Stekhoven J.H. Jr, 1937; C. cristatus Shiino, 1958, and C. longicervicus Shiino, 1958) and rubosus (including C. rubosus Leigh-Sharpe, 1934; C. hardenbergi Markevich, 1936; C. krishnai Sebastian, 1968; C. rotundicaudatus Izawa, 1970; C. boxshalli Bellwood, 1981; C. spiralis Bellwood, 1981; C. asper Uyeno & Nagasawa, 2010; C. bertrandi Uyeno & Nagasawa, 2010; C. bellwoodi Uyeno, 2013; C. shini Uyeno, 2013; C. roatanensis Suárez-Morales, Vásquez-Yeomans & Vidotto, 2022, and C. vampire Aneesh, Helna, Kumar & Venmathi Maran, 2023). Members of the medusaeus group are known for possession of a distinct abdomen whereas those of the rubosus group lack a distinct abdomen.

Material collected (figs. 6a-c) closely resembles those studied by Shiino (1958), Boxshall (2000) and Hogans (2017b) as C. bellottii. Cardiodectes bellottii differs from C. anchorellae by possessing a unilobed abdomen (fig. 6a) whereas that of C. anchorellae is bilobed (Pillai, 1967) and from C. longicervicus by possessing a neck-like region which is shorter than the trunk (fig. 6a) whereas that of C. longicervicus is the same length as the trunk (Shiino, 1958). Additionally, C. bellottii differs from C. cristatus and C. frondosus by possessing a short abdomen (fig. 6a) whereas those of C. cristatus (see Abb 3 in Shiino (1958)) and C. frondosus (see FIGS 1 and 7 in Schuurmans Stekhoven (1937)) are elongated.


Propeniculus Castro-Romero, 2014

Propeniculus stromatei (Gnanamuthu, 1951)

Host: Pomadasys commersonnii (Lacepède) (Eupercaria: Haemulidae)

Material collected and examined: 3♀♀ from Pomadasys commersonnii from the Indian Ocean, South Africa and 1♀ from Rhabdosargus holubi (Steindachner, 1881) (Eupercaria: Sparidae) from the Indian Ocean, South Africa

Voucher material: 1♀ (SAMC-A096501) from Pomadasys commersonnii deposited in the Iziko South African Museum, Cape Town, South Africa

Re-description:

Post metamorphosed females [based on four specimens, fig. 7]. Body length from tip of cephalothorax to tip of abdomen 9.5 mm (9.1–9.8 mm), cephalothorax length 0.7 mm (0.7–0.8 mm), width 0.4 mm (0.4 mm); neck-like region length 1.0 mm (0.8–1.1 mm), width 0.1 mm (0.1 mm); fourth segment length 0.14 mm (0.14 mm), width 0.28 mm (0.28 mm); trunk length 8.1 mm (7.6–8.8 mm), width 1.2 mm (1.0–1.4 mm); abdomen length 0.3 mm (0.2–0.3 mm); egg-sac length 9.8 mm, width 1.0 mm.

Fig. 7
figure 7

Propeniculus stromatei (Gnanamuthu, 1951), post metamorphosed female; a. habitus, cephalothorax lateral view and trunk ventral view; b. cephalothorax, dorsal view; c. cephalothorax, ventral view; d. mandible; e. maxillule; f. maxilla; g. abdomen, lateral view. Scale bars: a = 1 mm; b, c, g = 50 µm; d = 5 µm; e, f = 10 µm. (ap = antennary process; mt = mouth tube; mx1 = maxillule; mx2 = maxilla; ps = posterior swelling)

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The tip of the cephalothorax (figs. 7a-c) bifid, dorsal side (fig. 7b) sclerotized, with raised surface, ventral surface (fig. 7c) sclerotized anteriorly, posteriorly soft, with swelling (ps). Neck-like region cylindrical (fig. 7a), divided into four somites (figs. 7a-c) (each somite with a pair of legs). Trunk (fig. 7a) elongated and cylindrical, with visible abdomen (figs. 7a, g). Egg strings (fig. 7a) elongate, with uniseriate eggs.

Antennary appendages not observed. Maxillary appendages situated on the ventral side of the cephalothorax (fig. 7c). Mouth tube (mt) protrusible (fig. 7c). Mandible (mn) (fig. 7d) with curving tip without noticeable teeth. Maxillule (mx1) (fig. 7e) situated posterolateral to the mouth tube, 1-segmented, endite with two apical setae of different lengths, palp with single seta. Maxilla (mx2) (fig. 7f) 2-segmented, lacertus robust, with stout protuberance medially; brachium slender, bearing denticles on the posterodistal margin, calamus claw-like, with rows of spiniform setules. Maxilliped absent. Rudiments of four pairs of legs observed. Abdomen (fig. 7g) slightly elongated.

Remarks:

According to Castro-Romero (2014), Propeniculus species closely resemble Peniculus species, but possess features primitive compared to Peniculus species, including aspects of the cephalothorax (e.g. buccal structure and posterior swelling), a reinforced neck-like region with somites (with exception to Peniculus communis Leigh-Sharpe, 1934) and the attachment of egg strings to the abdomen aided by several flanges. Propeniculus species are mainly characterized by a simple cephalothorax, a short segmented neck-like region with four segments of different sizes, a straight trunk with a simple abdomen (Castro-Romero, 2014). Propeniculus consists of five species, namely Propeniculus sciaenae (Gnanamuthu, 1951); P. scomberi (Gnanamuthu, 1951); P. stromatei (Gnanamuthu, 1951); P. theraponi (Gnanamuthu, 1951); and P. trichiuri (Gnanamuthu, 1951) (Walter & Boxshall, 2023).

Females of Propeniculus species can be differentiated from one another by the length of the cephalothorax relative to the neck-like region and trunk lengths, the cephalothorax shape, the length of the neck-like region and the width of the fourth somite in relation to the trunk width and the length of the abdomen (Gnanamuthu, 1951, 1952; Castro-Romero, 2014).

Propeniculus stromatei differs from P. sciaenae and P. theraponi by possession of a prominent posterior swelling, with a short, protrusible mouth tube whereas P. sciaenae and P. theraponi possess a less prominent posterior swelling, but larger mouth cone (see Figs. 12 and 14 in Gnanamuthu (1951)). Propeniculus stromatei differs from P. scomberi in the structure of the cephalothorax, with P. stromatei with a symmetrical cephalothorax with a posterior swelling and even anteroventral surface whereas the cephalothorax of P. scomberi is asymmetrical, without a posterior swelling, but with a swollen ventral surface (see Figs. 2a-g in Gnanamuthu (1952)). Propeniculus stromatei resembles P. trichiuri. However, the cephalothorax of P. stromatei has a less protruding posterior swelling ventrally and is flattened dorsally, with a neck-like region longer than the cephalothorax (Gnanamuthu, 1952) whereas P. trichiuri (see Figs. 1 and 4 in Gnanamuthu (1951)) possesses a more protruding posterior swelling on the ventral side of the cephalothorax as well as a protruding dorsal side and has a neck-like region shorter than the cephalothorax. Additionally, the trunk of P. stromatei is approximately eight times longer than the neck-like region (Gnanamuthu, 1952) whereas that of P. trichiuri is more than eleven times the neck-like region (Fig. 1 in Gnanamuthu, 1951).

Previously, P. stromatei has been reported from Parastromateus niger (Bloch) (Gnanamuthu, 1952). Both P. niger and Pomadasys commersonii are reef-associated while Rhabdosargus holubi is demersal (Froese & Pauly, 2023). Other Propeniculus species were reported from several different fish species, namely P. sciaenae from Daysciaena albida (Cuvier), P. scomberi from Rastrelliger kanagurta (Cuvier), P. theraponi from Terapon jarbua (Forsskål) and P. trichiuri from Trichiurus lepturus Linnaeus, Lepturacanthus savala (Cuvier), and Eupleurogrammus muticus (Gray) (Gnanamuthu, 1951, 1952; Castro-Romero, 2014).

Phylogenetic analysis

Results and discussion:

The complete dataset consists of 54 sequences including nine genera belonging to Pennellidae and two Caligidae species as outgroup taxa. The sequences are 507-683 base pairs long except that of S. scopeli which is only 365 base pairs long. Even though the COI gene is not ideal for estimating relationships among genera it still provides an hypothesis of relationships to be tested using more suitable slower-evolving genes.

Both the maximum likelihood and Bayesian analyses of the COI dataset estimated Pennellidae as a highly supported monophyletic group (fig. 8). Even though most genera included in the dataset with more than one sequence (Trifur, Metapeniculus, Pennella, Peniculus, Haemobaphes and Lernaeocera) form highly supported monophyletic groups, it may be due to most sequences possibly being conspecific (except for those of Pennella and Haemobaphes). Sarcotretes scopeli (although a much shorter sequence of only 365 bp) is basal to all other genera from node D supporting the estimated morphological phylogeny in Boxshall (1986) (see Fig. 5 in Boxshall (1986)). According to Castro-Romero (2014), the structure of the mouth tube of Propeniculus is primitive to all pennellids which attach to the host fins, including Peniculus, Metapeniculus and Peniculisa. In the estimated phylogram (fig. 8) Propeniculus is estimated as the basal group to all the remaining genera and not only to Peniculus and Metapeniculus, while Metapeniculus and Pennella form an unsupported sister grouping (node J) with Peniculus (and Pennellidae species) basal to this grouping (node I). Further support for the previous morphological estimation (specifically regarding the possession of a sigmoid trunk) (Boxshall, 1986) is the well supported sister grouping of Haemobaphes and Lernaeocera. Notably in the estimated phylogeny (fig. 8) is the species of Lernaeenicus which are polyphyletic with a well-supported clade formed by L. seeri Kirtisinghe, 1934 and L. alatus Rangnekar, 1962 basal to all included genera (node B), L. sprattae (Sowerby, 1806) as a sister group of Trifur sp. (node H) and L. radiatus as a sister group of the Haemobaphes/Lernaeocera sister group (node F). Thus, it seems that some Lernaeenicus species were misidentified or rather that Lernaeenicus is in serious need of revision. According to Boxshall (1986), Lernaeenicus can be distinguished by their possession of an elongated body which is similar to other Pennellidae genera including Sarcotretes, Peniculus, Propeniculus, Pennella, Exopenna Boxshall, 1986, Metapeniculus, Pseudopeniculus and Peniculisa. Furthermore, distinguishing features mentioned by Kabata (1979) include many possible variations which are also shared by other genera. Regarding the estimated relationships in this study, L. sprattae and Trifur sp. share morphological similarities including the possession of three holdfast horns on the cephalothorax (2 lateral and 1 dorsal) and the possession of an abdomen shorter than the trunk. Furthermore, Lernaeenicus radiatus, Lernaeocera branchialis (Linnaeus, 1767), Haemobaphes pannosus Kabata, 1979 and H. diacerus Wilson C.B., 1917 share the possession of holdfast organs situated in a horizontal plane at the base of the cephalothorax, posterior holdfast organ (on neck-like region) and an abdomen shorter than the trunk. Therefore, even though more data is needed for a more conclusive estimation of the relationships amongst the genera of Pennellidae, it is clear that specifically Lernaeenicus is in need of thorough revision of all current species.

Fig. 8
figure 8

The estimated phylogram of some Pennellidae genera with representatives of Caligus as outgroup taxa, using maximum likelihood and Bayesian inference of the partial COI (cytochrome oxidase I) gene. Values above the lines indicate bootstrap support (%) of the ML analysis while those below the lines indicate the posterior probabilities (%) of the Bayesian analysis.

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Conclusions

New geographical records are reported for Pennella instructa, Propeniculus stromatei, S. scopeli, S. longirostris, and L. longiventris from southern African waters with new host records for P. instructa on Seriola lalandi, P. stromatei on Rhabdosargus holubi and Pomadasys commersonnii, S. scopeli on Nansenia tenera and S. longirostris on Centrolophus niger. Re-descriptions are provided for P. stromatei and S. scopeli and S. gonostomae n. comb. (synonymy L. gonostomae) from Iziko South African Museum. Additionally, an estimation of the phylogenetic relationships amongst some of the Pennellidae genera was attempted using COI sequences available on Genbank with the addition of a generated sequence for S. scopeli. This estimation emphasizes the need of revising the species of Lernaeenicus specifically due to their polyphyletic grouping in the phylogram.