Desmodora nini ( Inglis, 1963 )

Larrazábal-Filho, Alexandre L., Silva, Maria Cristina Da & Esteves, André M., 2015, Four new species of free-living marine nematodes of the family Desmodoridae (Nematoda: Desmodorida) and a redescription of Desmodora nini (Inglis, 1963) from the continental shelf off northeastern Brazil, Zootaxa 4021 (1), pp. 63-92 : 84-90

Re-description of Desmodora nini ( Inglis, 1963)

(Measurements Table 6 , Figs 14 , 15,16).

Material: Male adult LMZOO 186 (03°00’00”S, 038°45’00”W) collected in June 2009 from the Potiguar Basin, between 45 and 100 m. Sediment: fine to coarse bioclastic sand.

Female adult LMZOO 187 (04°45’00”S, 036°45’00”W) from the Potiguar Basin, between 20 and 25 m. Sediment: coarse lithoclastic sand.

Re-description. Male ( Figs 14 , 16 ) Body long and cylindrical, yellowish brown in colour, with strong cephalic capsule and conical tail. Cuticle strongly annulated except on cephalic capsule and non-annulated tail end. Anterior body annulation 2.5 µm, median region 2 µm, and posterior region 1 µm. Short somatic setae arranged in six longitudinal rows; two dorsal, two lateral and two ventral. Setae beginning on cephalic capsule and extending to caudal region. Some specimens with head invaginated, as in the original description. Cephalic capsule 22 µm in diameter. A slender lip region separated with sutura from the cephalic capsule. Fovea amphidialis large and multispiral (1.4 turns), with a plate. Buccal cavity with one dorsal tooth and two ventro-sublateral teeth. Six lips with 12 folds. Anterior sensilla arrangement: six inner papillae, six outer setae and four cephalic setae located at midlevel of fovea amphidialis. Subcephalic setae absent. Cylindrical pharynx with rounded endbulb, with sclerotized lumen divided into distinct regions. Nerve ring observed. Ventral gland and secretory-excretory pore not observed. Cardia inserted in intestine. Reproductive system with outstretched testis. Spicules arched and slender, with hooked capitulum and broad velum. Gubernaculum laminar in form; positioned dorsally, without apophysis. Three caudal glands. Tail conical with setae distributed irregularly, and distal portion without annulations. Spinneret conical.

Female ( Figs 14 , 15 ) Similar to male. Reproductive system with two opposite and reflexed ovaries. Vulva a broad, transverse slit. Vagina vera short, vagina uterina with sphincter muscle. Egg found in oviduct ( Fig. 14 D). Globular sperm cells present in uterus.

Juveniles 14 juveniles were found, all in the first stage of development. Identical to adults, but smaller ( Fig. 16 ).

Additional diagnosis and relationships. The main characteristics of Desmodora nini ( Inglis 1963) are the arrangement of the short somatic setae on the head (6+6+4), the longitudinal row of setae along the body, the teeth, and the proportion of the fovea amphidialis relative to the head capsule diameter. Besides these features, the morphometric measurements of the specimens from the Potiguar Basin ( Table 6 ) are within the range given by Inglis (1963) (even though some measurements exceed these values, such as v (%), (%) amph, and the index (c); see Table 7 ). We conclude that the values that exceed those provided by Inglis (1963) extend the range of measurements of D. nini , as additionally described here.

This species was originally described as the type of the genus Bla by Inglis (1963), who considered it similar to Xenodesmodora Wieser, 1951 and Croconema . Lorenzen (1994) placed Xenodesmodora as a subgenus of Micromicron Cobb, 1920 , which in turn was synonymized with Pseudochromadora by Andrássy (1959). Croconema was long considered a subgenus of Desmodora but elevated to genus rank by Verschelde et al. (1998). Bla nini was transferred by Wieser & Hopper (1967) to Desmodora . Recently, Tchesunov (2014) confirmed the synonymization of Micromicron with Pseudochromadora , and also synonymized Bradylaimoides Timm, 1961 with the same genus. Tchesunov (2014) also synonymized the genus Xenodesmodora with Croconema . Desmodora nini has characters more related to the genus Desmodora than to Croconema .

Members of Croconema often have ornamentation on their cuticle, with ridges or spines. Croconema also has numerous subcephalic setae arranged in three or more circles. Another point is the position of the fovea amphidialis, which is located anteriorly on the cephalic capsule. None of these characters are observed in the species described by Inglis (1963).

Zalonema vicentei sp. n. and Zalonema mariae sp. n. have ventral ala and lateral alae. These structures can be represented by ridges or projections that form longitudinal expansions ( Chitwood & Chitwood 1977). Within the genus Zalonema , these structures were also observed in Zalonema myrianae Verschelde & Vincx, 2006 and Zalonema ditlevseni ( Micoletzky 1922) . A ventral ala has also been recorded in Desmodora , Psammonema Verschelde & Vincx, 1995 ; Desmodorella Cobb, 1933 and Pseudochromadora Daday, 1889 .

Both juveniles and adults of Z. mariae sp. n. have two successive dorsal teeth. When viewed in juveniles, these seem to be replacement teeth, as e.g., in members of the family Ironidae ( Smol & Coomans 2006) . Decraemer et al.

(2014) discussed two types of teeth: i) a replacement tooth, positioned behind the functional tooth and occurring in juvenile stages and ii) where there are no replacement teeth. In this study, the adults still have two teeth in the same position, and these are here considered as true dorsal teeth.

Another taxonomic character for the new species is the sexual dimorphism, present in both Zalonema mariae sp. n. (turns of the fovea amphidialis) and Croconema fortis sp. n. (percentage of the fovea amphidialis in relation to corresponding body diameter). Sexual dimorphism occurs very rarely in the subclass Chromadoria ( Lorenzen 1981, 1994). Lorenzen (1981, 1994) also stated that when this occurs, the type of dimorphism is generally linked to the size of the fovea, being larger in males than in females. Croconema and Zalonema have some cases of sexual dimorphism (e.g. Croconema floriani and Zalonema megalosoma ), and in the family Desmodoridae this type of dimorphism also exists in Desmodora , Desmodorella , Pseudochromadora and Metachromadora Daday, 1889 . Thus, sexual dimorphism in this family is not uncommon.

It is of interest that D. nini was the most abundant species among the specimens studied here. It was first described from South Africa ( Inglis 1963) and this is the first record of it from Brazil. Desmodora nini was found in sediment fine to coarse bioclastic sand. There are no data in the original description about sedimentology or the abiotic environment, that would enable a comparison between the environments studied.

Figures

FIGURE 14. Desmodora nini (Inglis, 1963). A: overview (male). B: tail region. C: copulatory apparatus. D and E: dorsal tooth (cephalic region of male and female). F: tail region (female). G: overview (female). H: vulva opening.

FIGURE 15. Desmodora nini (Inglis, 1963) Female - A: overview. B: anterior region. C: head region. D: ovary and vulva opening. E: tail region.

FIGURE 16. Desmodora nini (Inglis, 1963). Male—A and E: head region. B: overview. C: tail region. D: copulatory apparatus. F: anterior region. Juvenile I—G: overview. H: head region.

Tables

TABLE 6. Measurements (µm) of Desmodora nini (Inglis, 1963) in the Potiguar Basin, Brazil. n = number of specimens; * = not applied. Abbreviations as in Table 1.

L	Male n = 10 1425 (1144–2085)	Female n = 10 1395 (1001–2115)	Juvenile n = 10 (620–1275)
ph	175 (178–241)	196.5 (135–241)	(120–177)
mbd	46 (40–55)	52.5 (62.5–79.5)	(31–54)
abd	43 (37–52.5)	31.5 (31.5–48)	(19–44)
t	114 (108–141)	100.5 (69–136.5)	(87–119)
tf	42 (39–54)	51 (30–67.5)	(41–62)
hd	43.5 (25.5–49.5)	33 (33–49.5)	(16–42)
cap.ceph	28 (25.5–40)	19.5 (19.5–40)	(10–21)
spic	58 (60–84)	*	*
gub	22 (22–34)	*	*
Velum	58.5 (40.5–57)	*	*
nr	114 (100–141)	117 (102–136.5)	(73.5–120)
ext. lab.	4 (3–5.5)	5 (3–5.5)	(3–8.5)
cs	4 (5.5–8.5)	6.5 (5–7)	(3–7)
subc s.	7 (5.5–7)	5.5 (5–6)	(4–11)
som. s.	6.5 (5.5–7)	6.5 (3.5–7)	(5–6.5)
s.pre.c.l	84 (81–109)	*	*
s.pre.c.	6.5 (6.5–12)	*	*
T	957 (602–1024)	*	*
spin	6.5 (6.5–9)	9 (6.5–10)	(5–8.5)
annul	2.5 (2.5)	2.5 (2.5–3.5)	(3–4)
% bulb	60 (62–78)	57 (57–76)	(58–74)
% amph	47 (50–68)	40 (30–50)	(41–65)
ov	*	321 (202–651)	*
v	*	825 (449–1155)	*
v (%)	*	59 (45–74)	*
a	34 (28.5–36)	26.5 (19–30)	(15–28)
b	9 (6–8)	7 (7–9)	(5–7.5)
c	13.5 (11–14.5)	14 (13–23)	(6–11)
c'	2.5 (2–3)	3 (2–3.5)	(2–5)

TABLE 7. Measurements (µm) of Desmodora nini obtained by Inglis (1963), from South Africa. n = number of specimens; * = not applied. Abbreviations as in Table 1.

L	Male n = 2 1600(1800)	Female n = 2 1600(1700)	Juvenile n = 1 1400
ph	230 (210)	200 (230)	180
mbd	52 (46)	55 (54)	43
abd	49 (44)	43 (46)	42
t	86 (93)	115 (103)	114
tf	30 (31)	54 (44)	34
hd	24 (22)	20 (23)	23
spic	47 (47)	*	*
gub	18 (19)	*	*
% amph	54 (54)	13 (13)	10
V	*	612 (588)	*
V (%)	*	38 (34.5)	*
a	30.8 (39.1)	29.1 (32.7)	32.6
b	7 (8.6)	8 (7.4)	7.8
c	18.6 (19.4)	13.9 (15.5)	12.3
Discussion