Longicyatholaimus maldivarum Gerlach, 1964

Balsamo, Maria, 2017, A re-description of Longicyatholaimus maldivarum Gerlach, 1964 (Nematoda, Cyatholamidae) with an emended identification key of the genus, Zootaxa 4323 (1), pp. 96-108 : 98-104

Longicyatholaimus maldivarum Gerlach, 1964

Figs. 2–6 ; Table 1

Material studied: three males, one female (mounted on glycerin slides). The material was collected by Giuseppe Baldelli on May 2005 and May 2007.

Locality: Indian Sea, Maldivian archipelago, Felidhoo, South Malé, Rasdhoo and Thooddo atolls ( Fig. 1 ).

Description. Male. Body cylindrical, slender ( Fig. 2a ). Anterior end 30–33 µm wide at the level of the outer labial sensilla. Cuticle homogeneous with transverse rows of punctuations slightly larger and more widely spaced at the anterior end. Lateral differentiation of cuticle with three rows of longitudinal punctuations starting at the end of the pharynx region, 287–308 µm from the head end ( Fig. 2d ). Cuticular pores present, but scattered in the anterior part of the body and arranged further posteriorly into rows (six in total). The three lateral rows of punctuations change their pattern in the spicular region and appear almost combined together ( Fig. 2g ). Posterior part of the pharynx: two rows of pores in correspondence of each central row of the lateral differentiation of punctuations, while the others located closely but externally to the lateral fields. Pores of the central line of the lateral differentiation more oval shaped and spaced than in the rest of the body. Six visible labial sensillae 5–8 µm long and 10 cephalic setae 11–16 µm long. Few somatic setae scattered along the body, 10–12 µm long. Amphideal fovea coiled spirally in five turns, located 7–8 µm from anterior body end ( Fig. 2b ). Amphideal fovea diameter 11– 14 µm, i.e. about 32–38% of the corresponding body diameter. Buccal cavity small, cup-shaped. Cheilostomatal walls reinforced by twelve rugae. Stoma width 20–21 µm and length 18–23 µm. Dorsal tooth 15–18 µm long and two sub-ventral teeth present ( Figs. 2c ; 4a; 5a). Pharynx cylindrical. Nerve ring at about 23–33% of the pharynx length. Cardia cells not visible. Male diorchic, gonads outstretched in opposed direction. Male spicules poorly cuticularized (45–50 µm, 1 anal body diameter) with a central lamella more visible using CLSM ( Figs. 2f , 5b ).

Gubernaculum paired, 25–32 µm long, with a distal extremity enlarged and heavily denticulate ( Figs. 2f , 5b,c ). Denticles minute. Eight-nine small pre-anal supplements, each one characterized by a conical setose structure protruding from the body of the supplementary organs ( Figs. 2e, f ; 5d, e). Distance from anus to most posterior and anterior supplements 16 µm and 80–87 µm, respectively. Tail 287–305 µm long (6 anal body diameter long) uniformly conoid to a slender cylindrical part (conical and cylindrical parts 87–92 and 197–232 µm long, respectively) ( Fig. 2a , 4g ). No terminal setae observed. Spinneret well developed.

Female. Body similar to male ( Fig. 3a ). Anterior end 32 µm wide. Cuticle homogeneous, with transverse rows of punctuations, slightly larger and more widely spaced at the anterior end. Lateral cuticular differentiation characterized by three rows of longitudinal punctuations starting at the end of the pharynx region at 322 µm from the head end ( Fig. 6c ). Cuticular pores with the same pattern as in the males ( Fig. 6d ). Multispiral amphideal fovea with four turns located 11 µm from anterior body end ( Figs. 3b , 6b ). Diameter of the amphideal fovea 14 µm i.e. 34% of the corresponding body diameter. Buccal cavity cup-shaped and characterized by a dorsal tooth 17 µm long and two sub-ventral teeth ( Figs. 3c , 6a ). Pharynx cylindrical. Nerve ring at about 34% of the pharynx length. Cardia cells not visible. Genital system didelphic, amphidelphic, gonads reflexed. Eggs observed in the uterus, the larger one is 85 µm long ( Fig. 6e ). Vulva located at 48% of the body length. Vagina surrounded by constrictor muscles ( Fig. 6f ). Tail 315 µm long with a proximal conical part 83 µm long and a distal cylindrical part 232 µm long. No terminal setae observed. Spinneret present.

Remarks: General morphology, de Man ratios and especially male copulatory system of the specimens collected in this survey perfectly matched the original description provided by Gerlach (1964). The differences noticed in some morphological details or measurements (see below) suggest only an intraspecific variation, mostly likely due to the very low number of animals collected by Gerlach, but underline also the necessity of a redescription of L. maldivarum .

In detail, the total body length of the observed males was higher than in the type specimens (1936–2063 µm vs. 1330 µm long) with a consequent variation of the a-ratio (22–28 vs. 27). The oval multispiral amphideal fovea of the males showed five turns in the studied specimens vs. four turns in the type species, and its diameter was 0.3–0.4 vs. 0.4 of corresponding body diameter, while the width was 11–14 µm vs. 14. Furthermore, Gerlach (1964) did not notice the presence of sub-ventral teeth that were documented in the present specimens. According to the genus diagnosis, Longicyatholaimus has only one dorsal tooth, but already Hopper (1972) mentioned one dorsal tooth and the presence in some species of reduced sub-ventral teeth (i.e. L. egregius , L. falcatus , L. marilynae ).

The copulatory apparatus of L. maldivarum males appeared poorly cuticularized and diaphanous as in the original description; nevertheless, it showed an evident central lamella along the spicules mainly under CLSM – detail previously undocumented and very difficult to see using the interferential contrast. The spicule length appeared slightly shorter than in the type specimen (45–50 vs. 51 µm), as well as the spicule length divided by anal body diameter is lower (1 vs. 1.4).

Gubernaculum that envelops about one-half of the spicule length was 25–32 vs. 25 µm long.

The distal extremity appeared exactly like in the type species: enlarged and completely covered by minute denticles. The information on the pre-cloacal supplements provided by Gerlach is limited and no details of their structure is present in the iconography. A difference in the overall number was observed, 8–9 supplements in the present specimens vs. 7 in the original description. Hopper (1972), who had the opportunity to re-examine the type species, described the presence of stout and conical setae protruding from cup-shaped structures in L. maldivarum . The combination of cup-shaped supplements and protruding setae are unique to our knowledge not only within this genus, but also within this sub-family. However, pre-anal supplements are often inconspicuous in Longicyatholaimus and often unnoticed or reported with few details, especially in the old descriptions, which limits their value as a diagnostic character (Semprucci 2015). The tail length showed variations (287–305 in the newly found species vs. 270 µm in the original description) as well as its total length divided by anal body diameter (6 in the newly found species vs. 7–8 in the original description).

A comparison between the female found by Gerlach (1964) and the new one is complicated by the very scarce information reported in the original description and especially by the complete absence of illustrations. However, it can be observed that the total body length of the female recently collected in Maldives was higher than in the type species (1999 in the newly found species µm vs. 1870 in the original description µm long; a-ratio 25 vs. 26, respectively), but overall the differences detected in these parameters were less pronounced than those found when comparing the males. Gerlach (1964) did not report information about the female amphideal fovea that in the present specimens showed four turns. Instead, the tail was rather different with a total length of 232 µm in the newly found species vs. 370 µm in the original description and a ratio of the total tail length divided by anal body diameter 6 vs. 8.2, respectively.

Figures

FIGURE 1. Map of the central part of the Maldivian archipelago including the sites in which Longicyatholaimus maldivarum Gerlach, 1964 was collected in the 2005 and 2007.

FIGURE 2. Longicyatholaimus maldivarum Gerlach, 1964. Drawings of the male. a) Habitus; b) Amphideal fovea and cephalic ornamentation; c) Buccal cavity; d) Lateral differentiation of the cuticular ornamentation in the middle of the body; e) Detail of the pre-cloacal supplements; f) Copulatory apparatus; g) Lateral differentiation of the cuticular ornamentation in the spicule region. Scale bars: a = 50 µm; b, c, f = 30 µm; d, e, g = 10 µm.

FIGURE 3. Longicyatholaimus maldivarum Gerlach, 1964. Drawings of the female. a) Habitus; b) Amphideal fovea; c) Buccal cavity. Scale bars: a = 100 µm; b- = 30 µm.

FIGURE 4. Longicyatholaimus maldivarum Gerlach, 1964. Light micrographs of the male. a) Detail of the buccal cavity; b) Amphideal fovea and cuticle ornamentation in the cephalic region; c) Lateral differentiation of the cuticular ornamentation in the middle of the body; d) Starting point of the pore rows; e) Cuticular ornamentation in the spicular region; f) Precloacal supplements; g) Tail region. Scale bars: a, b, d = 5 µm; c, e – g = 10 µm.

FIGURE 5. Longicyatholaimus maldivarum Gerlach, 1964. Confocal laser scanning micrograph of the male. a) 3 Dreconstruction of the buccal cavity; b) 3 D-reconstruction of the copulatory apparatus; c) 3 D-reconstruction of the gubernaculum; d) View of the precloacal supplements; e) Detail of their structure. Scale bars: a – e = 10 µm.

FIGURE 6. Longicyatholaimus maldivarum Gerlach, 1964. Light micrographs of the female. a) Buccal cavity; b) Amphideal fovea and cuticle ornamentation in the cephalic region; c) Lateral differentiation of the cuticular ornamentation in the middle of the body; d) Detail of the central cuticular pores in the lateral fields; e) Mid-body region showing eggs in the uterus; f) Detail of the vagina. Scale bars: a, b = 5 µm; c, d, f = 10 µm; e = 25 µm.