Two new species of philometrid nematodes (Philometridae),
- marine fish
- Atlantic Ocean
- North America
Nematodes of the dracunculoid family Philometridae Baylis et Daubney, 1926 represent a large group of important fish parasites many species of which occur in marine fishes. The taxonomy of these histozoic parasites is complicated by their marked sexual dimorphism in which females are highly modified and considerably larger than the males. In contrast to conspicuous, large-sized and often red-coloured philometrid females, conspecific minute males pass usually unnoticed during routine examinations of fish and that is why the males of many philometrids remain unknown (Moravec, 2006).
Needlefishes (Beloniformes: Belonidae) have frequently been reported as hosts of philometrid nematodes. They are small to medium sized, torpedo-shaped, predominantly piscivorous, sur-
face-oriented species prized in some areas as food fish or bait for large offshore predators like marlin (Istiophoridae) (Collete, 2016). The common name for the family is derived from members’ needle-like toothy beaks. Moravec
Regarding previous records of philometrids from
Records of philometrids from other congeneric hosts include that of Linton (1907) reporting female specimens of
Fish were collected in lower Tampa Bay (Fig. 1) during routine fish population monitoring conducted by the Florida Fish and Wildlife Conservation Commision’ Fish and Wildlife Research Institute (FWRI). Haul seines, 183 m in length, were deployed along the shoreline from net wells of mullet skiffs (see Wessel & Winner, 2003). Captured fish were bagged in plastic and immediately packed in ice until crews returned at the end of field days to FWRI Headquarters in St. Petersburg Florida for further processing (time on ice < 12 hrs).
In the laboratory, fish were measured for standard length, and examined for parasites. Gonad-infecting philometrids were surveyed and fixed for morphological study in 5 % formalin by methods of Moravec
For light microscopical examination, the nematodes were cleared by use of glycerine. Drawings were made with the aid of a Zeiss drawing attachment. Specimens used for scanning electron microscopy (SEM) were postfixed in 1 % osmium tetroxide (in phosphate buffer), dehydrated through a graded acetone series, critical-point-dried and sputter-coated with gold; they were examined with a JEOL JSM-7401F scanning electron microscope at an accelerating voltage of 4 kV (GB low mode). All measurements are in micrometres unless otherwise indicated. The fish nomenclature adopted follows FishBase (Froese & Pauly, 2021).
All applicable institutional, national and international guidelines for the care and use of animals were followed.
Family Philometridae Baylis et Daubney, 1926
Description: Male (1 specimen, holotype): Body filiform, whitish, 2.69 mm long, maximum width 36; anterior part of body somewhat narrowed towards cephalic extremity (Fig. 2A). Maximum width/ body length ratio 1:18. Cuticle smooth. Cephalic end rounded, 27 wide. Oral aperture small, circular. Fourteen minute cephalic papillae arranged in 2 circles present: external circle formed by 4 sub-median pairs of papillae; internal circle by 4 submedian and 2 lateral papillae. Small lateral amphids just posterior to lateral papillae of internal circle (Figs. 2B, 3A,B). Oesophagus 432 long, comprising 16 % of body length, with inflation at anterior end measuring 27 × 12; posterior part of muscular oesophagus overlapped by well-developed oesophageal gland with large cell nucleus; maximum width of gland 18 (Fig. 2A). Small ventriculus present, its length 6, width 9. Nerve ring and oesophageal nucleus 96 and 267 from anterior extremity, respectively (Fig. 2A). Excretory pore 162 from anterior end. Testis extending anteriorly approximately to level of oesophago-intestinal junction, overlapping posterior portion of oesophagus (Fig. 2A). Posterior end of body blunt, 39 wide, provided with broad U-shaped mound situated laterally and dorsally to cloacal opening (Figs. 2F, 3C,D). At least 2 adanal pairs of very flat, hardly visible caudal papillae present between ventral ends of cloacal aperture and caudal mound (Figs. 2F, 3C). Pair of small phasmids present dorsoventrally on caudal mound (Figs. 2F, 3C,D). Caudal mound with pair of minute circular depression (Figs. 2F, 3C,D). Cloacal aperture oval, markedly dorsoventrally elongated (Figs. 2F, 3C). Spicules sickle-shaped in lateral view, equally long, with somewhat expanded proximal and sharply pointed, ventrally oriented distal tips (Fig. 2C,D, 4); in ventral view, middle portion of spicules markedly broad, 9 wide (Fig. 2D); length of spicules 101, representing 3 % of body length. Gubernaculum 57 long, with narrow, weakly-sclerotized tubular proximal portion; distal portion of gubernaculum broad, heavily sclerotized, wedge-shaped in lateral view, its distal tip rounded, dorsally curved (Fig. 2C,E, 4). Length ratio of gubernaculum and spicules 1:1.42. Spicules and gubernaculum well sclerotized, brownish (Fig. 4).
Female: Not known.
Type host: Hound needlefish
Site of infection: Ovary.
Type locality: Tampa Bay, Florida, Rattlesnake Key at mouth of Terra Ceia Bay (27.5474, -82.633250), USA (collected 7 November 2017).
Prevalence and intensity: 1 fish infected/5 fish examined); 1 nematode.
Type specimen: Male holotype (mounted on SEM stub) in the Helminthological Collection of the Institute of Parasitology, BC CAS, České Budějovice, Czech Republic (Cat. No. N–1229).
Etymology: The specific name
In having ventrally curved, sickle-shaped spicules, the distal tip of the gubernaculum oriented dorsally and the cloacal aperture markedly dorsoventrally elongate, this nematode belongs to the philometrid genus
smooth, dorsally curved distal tip vs. proximal end of the gubernaculum narrowed, strongly curved dorsally, distal tip smooth, laterally expanded, with a minute terminal digital projection in
Worth noting, however, is that three sphyraenids occur sympatrically with
Description: Male (6 specimens; measurements of holotype in parentheses): Body filiform, whitish, 2.19 – 3.81 (3.44) mm long, maximum width at middle of body 33 – 48 (48); anterior part of body tapering to anterior extremity, with slightly outlined constriction just posterior to cephalic end (Fig. 5A). Maximum width/body length ratio 1:66 – 94 (1:72). Cuticle smooth. Cephalic end rounded, 21 – 33 (33) wide, width at cephalic constriction 18 – 30 (30). Small oral aperture surrounded by 14 cephalic papillae arranged in 2 circles and pair of amphids, as in males of all other philometrid species (cephalic ends used for SEM proved to be very damaged and unsuitable for illustrations). Oesophagus 282 – 441 (441) long, comprising 7 – 13 (13) % of body length, with slight inflation at anterior end measuring 21 – 36 × 12 – 21 (36 × 21); posterior part of muscular oesophagus overlapped by well-developed oesophageal gland with large cell nucleus; maximum width of gland 15 – 21 (21) (Fig. 4A). Ventriculus small, 6 – 15 (15) long, 9 – 18 (18) wide. Nerve ring and oesophageal nucleus 126 – 198 (198) and 201 – 327 (327), respectively, from anterior extremity. Excretory pore 171 – 216 (216) from anterior end. Posterior end of body blunt, 30 – 45 (45) wide, with broad caudal mound formed by 2 lateral reniform portions well separated dorsally (Figs. 5D, 6A,B). Four pairs of small adanal papillae present in space between caudal mound and cloacal aperture: 2 pairs of small, markedly elevated papillae situated closely to cloacal aperture and 2 pairs of very flat, hardly visible papillae located externally to them; pair of small phasmids present dorsoventrally on caudal mound (Figs. 5D, 6B – F). Each portion of caudal mound with 1 subdorsal, minute circular depression (Figs. 5D, 6B). Spicules needle-like, equally or nearly equally long, with somewhat expanded proximal and sharply pointed distal tips (Fig. 5B,C); length of spicules 105-117 (117), maximum width 6 (6); length ratio of spicules 1:1.00-1.03 (1:1.00); spicules representing 2.9 – 4.8 (3.4) % of body length. Gubernaculum narrow, 78 – 90 (90) long, with anterior portion somewhat dorsally bent; length of anterior bent part 45 – 57 (48), comprising 53 – 63 (53) % of entire gubernaculum length (Fig. 5B,C,E – G).
In lateral view, distal tip of gubernaculum with 2 smooth, reflexed dorsal barbs (1 large and 1, more distal barb small) and with several transverse, dorsally uninterrupted lamellae in region anterior to barbs; proper extremity of gubernaculum posterior to barbs rounded (Figs. 5F,G, 6C – F). Length ratio of gubernaculum and spicules 1:1.23 – 1.35 (1:1.30). Spicules and gubernaculum well sclerotized, yellowish, anterior part of gubernaculum and proximal ends of spicules colourless.
Female: Not known.
Type host: Hound needlefish
Type locality: Tampa Bay (27.632516, -82.574166), Gulf of Mexico, USA (collected 9 December 2019).
Other locality: Tampa Bay (27.588783, -82.602266; 27.5474, -82.633250), Gulf of Mexico, USA (collected 15 September and 7 November 2017).
Prevalence and intensity: 4 fish infected/5 fish examined; 1 – 4 nematodes per fish.
Type specimens: Holotype and 2 paratypes in the Smithsonian National Museum of Natural History, Washington, USA (Cat. Nos. USNM 1640967 and USNM 1640968, respectively); 2 paratypes in the Helminthological Collection of the Institute of Parasitology, BC CAS, České Budějovice, Czech Republic (Cat. No. N–1230).
Etymology: The specific name
The males of this new species are morphologically and biometrically very similar to those of
One male of
While the morphology of
This indicates a possibility that the location of large, subgravid and gravid females of
The present description of