Falcaustra hinkeli, Jackson, 2000

Jackson, J. A., 2000, Two new Falcaustra Lane, 1915 species (Nematoda: Kathlaniidae) from African pipids (Anura), Journal of Natural History 34 (5), pp. 663-677 : 664-670

Falcaustra hinkeli n. sp.

(®gures 1±16)

Type-host and locality

Xenopus (Xenopus) fraseri Boulenger-like species at Ebisha, near Irangi research station, Democratic Republic of the Congo ( DRC).

Other host and locality records

From X. fraseri -like species: Boende, Tshuapa river, DRC (1); Boteka, DRC (2); Olonou, Cameroon (3); Mieri, Duome river, Cameroon (4). From X. (Xenopus) pygmaeus Loumont : Kisangani, DRC (5).

Site Lower intestine and rectum.

Material studied

Holotype NHM 1998.12.21 .1 (male), allotype NHM 1998.12.21 .2 (female), 18 paratypes NHM 1998.12.21.3 ±12, MRAC 37.428 ±429 and 10 non-type specimens from type-locality, F, hosts collected by Dr H. Hinkel, November, 1991; one specimen (1), P, host from MRAC 75-035 -B-0850-0854; two specimens (2), P, hosts from MRAC 85-030 -B-0023-0032; two specimens (3), P, hosts from RUCA 1269 ; one specimen (4), P, host from MRAC 76-014 -B-0084-0091; two specimens (5), P, hosts from RUCA S (7).

Description

General. Body long, cylindrical. Three anterior labia, one dorsal, two ventrolateral, with 12 labial papillae (six inner, six outer). Each labial papilla associated with ramus from one of six bifurcate hypodermal peduncles (two peduncles extending into each lip). Outer peduncle rami (associated with outer labial papillae) thicker than inner rami (associated with inner labial papillae). Lateral hypodermal peduncles with distally sub-branched outer rami: outer sub-branches associated with conspicuous amphids, thin inner sub-branches bearing lateral outer labial papillae. Three valve-like lamellae (one internal to each labium) delimiting buccal cavity, fused proximally, supported internally by lightly sclerotized plate with diOEerentially thickened margins. Lamellae originating on inner surface of buccal cavity and fused with labia in their midline. (Note: outward folding of distal buccal lamellae in some specimens may be a ®xation-related artefact). Complex sclerotized cheilostomal ring with thickened prominences and dagger-like, posteriorly directed projections in sectors between labia. Thin, shield-like sclerotized pieces arising on anterior surface of cheilostomal ring in labial sectors. Three arch-like thickenings on anterior external surface of oesophageal pharynx supporting cheilostomal ring in labial sectors. Oesophageal zones immediately internal to sclerotized arches with prominent anteriorly directed radial muscle ®bres, distinct from main muscle series of oesophageal pharynx. Three small sclerotized projections of oesophageal origin at base of buccal cavity. Oesophagus long, composed of short, tubular anterior pharyngeal region, long cylindrical corpus, short, slightly expanded isthmus and well-developed posterior bulb with valvular lumen enclosing three thickened, anteriorly directed plates. Three posteriorly directed, triangular projections at junction of intestine with oesophageal bulb. Anterior nerve ring associated with prominent ventral and lateral ganglia. Minute deirids approximately level with mid-oesophagus. Prominent, ventral, ovoid excretory vesicle just anterior to, or level with, oesophageal isthmus, connecting with four wide canals, two anteriorly and two posteriorly directed; excretory pore minute, level with anterior third of vesicle. Three large nuclei associated with basal area of excretory canals: one dextral, two sinistral. Small nucleus associated with posterior of excretory vesicle. Alae absent. Tail tapering to ®ne, extended point.

Male. Measurements or counts for holotype precede mean and/or range for 10 worms from type-locality (in parentheses).

Body length 6520 (6480, 4570±10 060), width 210 (260, 190±440). Oesophageal pharynx 70 (74, 65±87) long, corpus 1080 (1040, 890±1260) long, isthmus 111 (110, 93±144) long by 78 (87, 67±109) wide, bulb 130 (139, 122±174) long by 146 (150, 133±167) wide. Nerve ring, deirids and excretory pore, respectively, 320 (320, 290±400), 660 (680, 600±800) and 780 (860, 740±1170) from anterior. Testis in middle third of body. Caudal region with weak ventrad curvature; pseudosuckers absent, 34 and 31 precloacal muscle blocks on left and right respectively (25±34). Complex, equal, alate spicules, 417 (450, 390±520) long. Gubernaculum Y-shaped, complex: heavily sclerotized distal base 56 (54, 44±65) long, with thickened distal apex; proximal regions, including anterior wing-like formations, weakly sclerotized. Five pairs of subventral precloacal papillae: anterior three pairs widely spaced; posterior two pairs in close proximity, just anterior to level of cloaca. Large, unpaired ventral papilla in midline just anterior to cloacal opening. Six pairs of postcloacal papillae: two subventral pairs, just posterior to cloacal opening; two lateral pairs, one just posterior to level of cloaca and one just over one-third distance from cloaca to tip of tail; two subventral pairs, in close proximity, just under half distance from cloaca to tip of tail. Phasmids near posteriormost lateral papilla pair. Tail 510 (550, 470±740) long.

Female. Measurements of allotype precede mean and range for 15 worms from type-locality (in parentheses).

Body length 13 680 (9470, 5390±13 680), width 530 (340, 210±530). Oesophageal pharynx 100 (88, 72±100) long, corpus 1560 (1310, 1030±1580) long, isthmus 189 (135, 117±189) long by 152 (113, 80±152) wide, bulb 212 (159, 129±212) long by 220 (175, 144±220) wide. Nerve ring, deirids and excretory pore, respectively, 420 (380, 300±420), 1040 (830, 710±1040) and 1460 (1060, 870±1460) from anterior. Vulva 61% (60, 58±64) of total body length from anterior, slightly raised from general body surface; vagina running posteriorly towards vulva, with muscular proximal region and shorter, cuticle-lined distal region. Sinuous uteri and ovaries extending from just posterior to oesophageal bulb to about 70±80% of body length from anterior; anterior ovary with blind end in anterior third of body, posterior ovary with blind end posterior to vulva. Oviducts thin-walled proximally, thickened distally at junction with spermathecata. Tail 1050 (820, 560±1060) long. Phasmids about one-third of tail length from cloaca. Distal eggs in each uterus, respectively, 107 and 122 long, by 78 and 70 wide.

Variation in male caudal papilla pattern

Variation can occur in the exact disposition of the three posterior postcloacal papilla pairs (compared to that illustrated in ®gures 12, 13). In some specimens an individual papilla may be absent or both posterior lateral papillae may be present on one side. There is also variation in the relative positions of the phasmids and posterior lateral papilla pair, although these are always close together.

Remarks

Falcaustra hinkeli n. sp. is distinguished from the majority of its congeners by the absence of a precloacal pseudosucker in males. Other Falcaustra species sharing this character state form a heterogeneous grouping, including taxa from North American and Asian amphibians, a South American saurian, African, Madagascan and Asian ®shes, and chelonians from Asia and the Caribbean. Amongst those occurring in Africa or Madagascar, F. hinkeli diOEers from Falcaustra piscicola (Linstow, 1907) (= Falcaustra congolense (Taylor, 1925) , see Inglis, 1959), Falcaustra verbekei Campana-Rouget, 1961 and Falcaustra therezieni Petter, 1979 in tail shape and in the pattern of male caudal papillae (see below). It also shows shorter male spicule length than F. piscicola and more anterior phasmids in females than F. therezieni .

Several features of F. hinkeli appear to be unique. The cheilostomal ring and its accessory sclerotized structures apparently distinguish this species from any existing member of Falcaustra , although the anterior morphology of many congeners is not well characterized. Very detailed studies have been carried out on two examples from chelonians: Falcaustra stewarti Baylis and Daubney, 1922 (see Inglis, 1966) and Falcaustra duyagi (Tubangui and Villaamil, 1933) (see Berry, 1984). In both forms, sclerotized elements (cheilostomal struts) are associated with the cheilostomal ring in labial regions. These structures may be homologous with the shield-like, labial sclerotized pieces found in F. hinkeli but diOEer markedly in form, and, in the case of the dorsal`strut’, show a central aperture. Another chelonian species, Falcaustra pelusios Baker, 1983 , has been described with an accessory sclerotized ring, supporting the cheilostomal ring, which arises from the surface of the oesophageal pharynx ( Baker, 1983). This secondary ring could be homologous with thickenings on the anterior oesophagus surface found in F. hinkeli . However, in several morphological features these species are highly divergent. Other representatives of Falcaustra from amphibians display a single cheilostomal ring (e.g. Baker, 1986), apparently without cheilostomal struts or projections. Falcaustra hinkeli is further characterized by the pattern of male caudal papillae, and the relative position of the phasmids (®gures 12, 13) (although it is important to note that the usual disposition of the three posterior papilla pairs may be modi®ed in some specimens, see above). The arrangement is similar and probably derived from a distribution found, with minor variations, in many Falcaustra species. This is: three pairs of subventral papillae well anterior to the cloaca, a single papilla in the midline just anterior to the cloaca, three subventral pairs and one lateral pair at around the level of the cloaca, and two subventral pairs and one lateral pair on the mid- to posterior tail region. In F. hinkeli the posterior lateral pair are very near to the phasmids, an extra subventral pair is present in the region of the cloaca and the three anteriormost pairs are very widely spaced.

Buccal lamellae of the kind occurring in F. hinkeli have not been clearly described in other Falcaustra species [and are not mentioned in the histological studies of Inglis (1966) and Berry (1984)]. However, SEM studies of Falcaustra sp. and Falcaustra sudanensis Khalil, 1962 (see Gibbons, 1986) appear to show lamellae externally similar to those in F. hinkeli (Gibbons noted these as producing`divided lips’ in F. sudanensis ). Comparable structures ( Moravec and Thatcher, 1996) may also be present in the neotropical kathlaniid Myleusnema bicornis Moravec and Thatcher, 1996 . The lamellae cannot be identi®ed with the tooth-like projections or onchia, of oesophageal origin, described in some Falcaustra species , as they arise more anteriorly, from the surface of the buccal cavity.

Etymology

This species is named for Dr H. Hinkel in recognition of his work on the central African ¯ora and fauna.