Rhabdocoma
Rhabdocoma Cobb, 1920 (ref. ID; 3570, 7627)
Enoplida Filijev, 1929: Family Trefusiidae Gerlach, 1966: Subfamily Trefusiiniae Gelach, 1966 (ref. ID; 3570)
Family Trefusiidae (ref. ID; 7627)
ref. ID; 3570
Type species
Rhabdocoma americana Cobb, 1920 (ref. ID; 3570)
- Rhabdocoma americana Cobb, 1920 (ref. ID; 1764, 3570, 7627)
Syn; Rhabdocoma riemanni Jayasree & Warwick, 1977 (ref. ID; 1764)
- Rhabdocoma articulata Gerlach, 1955 (ref. ID; 3570)
- Rhabdocoma brevicauda Stekhoven, 1950 (ref. ID; 3570)
Syn; Rhabdocoma cylindricauda Stekhoven, 1950 (ref. ID; 3570)
- Rhabdocoma cylindricauda Stekhoven, 1950
See; Rhabdocoma brevicauda (ref. ID; 3570)
- Rhabdocoma macrura Cobb, 1920 (ref. ID; 3570, 7627)
- Rhabdocoma obtusicaudata (Chitwood, 1936) nov. comb. (ref. ID; 7627)
Syn; Cytolaimium obtusicaudatum Chitwood 1936 (ref. ID; 7627)
- Rhabdocoma riemanni (ref. ID; 1752)
See; Rhabdocoma americana (ref. ID; 1764)
Synonym
Rhabdocoma riemanni Jayasree & Warwick, 1977 (ref. ID; 1764)
Diagnosis
Rhabdocoma americana Cobb, 1920 is only described up to now from its type locality. Lorenzen (1981) found also this species in a sublittoral area of Southern Chile. Riemann (1966) described Rhabdocoma sp.1. and notes a strong relationship between his species and R. americana; the external labial setae of Rhabdocoma sp. 1 are longer than those of R. americana and therefore both species are not identical. Rhabdocoma sp. 1 had been described by Jayasree & Warwick (1977) as R. riemanni. The length of the external labial setae of the Rhabdocoma species of the Southern Bight varies between 80 to 110% of the c.b.d. No other differences could be detected between the two species; therefore, Vincx (1989) decide that R. riemanni is synonymous with R. americana. The dorsally wound amphideal fovea is also mentioned by Lorenzen (1981) for R. americana. (ref. ID; 1764)
Descriptions
Male: Body very slender with a very long filiform tail. Cuticle very faintly annulated; each annule is about 0.5-1 µm broad. Three lips are well delineated. The internal labial sensilla are 1 µm long and very thin; the six external labial sensilla are very thick setae, 12 µm long and consist of three segments each. Dentritic processes do not extend over the tip of the setae. Posteriorly from these setae the head is somewhat constricted. The four cephalic setae are thinner, 8 µm long and situated at 27 µm from the anterior end; they consist of two segments. One lateral cervical seta is present between the amphideal fovea and the nerve ring. The amphideal fovea is circular; its diameter is 9 µm of 53% of the c.b.d. Its anterior border is situated at 31 µm from the anterior end; the fovea is dorsally wound; the aperture is circular. The buccal cavity is very small and completely surrounded by the pharyngeal muscles which form a small bulb in this area. The inner cuticle lining of the dorsal sector of the pharynx is thicker in this region. The pharynx is cylindrical. Nerve ring situated at 49% of the neck length. Ventral pore situated at 39 % of the neck length; ventral gland not distinct but probably restricted to the pharyngeal region. Diorchic with outstretched testes; anterior testis at the left, posterior testis at the right of the intestine. Sperm cells 30-35 µm long and 2 µm broad. Spicules with median stiffening piece; the proximal half of the spicules is more sclerotized than the distal half. Gubernaculum very weakly sclerotized with a dorso-caudal apophysis. Musculature not obvious. Seven to eight cervical and ten to twelve preanal papillae are present at 15-20 µm from each other and each connected with a small epidermal gland cell. Tail very long and filiform with rounded end (often broken off). Caudal glands not distinct. (ref. ID; 1764)
Female: Resembles males in most aspects. Monodelphic, with only the posterior tract completely developed. The posterior ovary is antidromously reflexed to the right. The uterus consists of large wall cells and is filled with the slender sperm cells. A small prevulvar sax is present; it consists of several larger cells (with a distinct nucleus) and is connected with the vagina. This is the only remnant of the reduced anterior tract. The vagina is very much sclerotized and opens into a longitudinal structure (in lateral view) which joins the post-vaginal uterus with the prevulvar sac. (ref. ID; 1764)
Synonym
Cytolaimium obtusicaudatum Chitwood 1936 (ref. ID; 7627)
Descriptions
Body extremely slender, almost cylindrical throughout its length; head diameter 14-16 µm, diameter at level of amphids 17-18 µm, at end of esophagus 20-22 µm, maximum body diameter in males 22-26 µm, in females 27-30 µm (in the region of the female gonade), anal body diameter 20-23 µm in males, 16 µm in females. Cuticle very thin, smooth, devoid of somatic setae except for the cervical region, where there are some 4 µm long bristles subventrally. Hypodermis in living animals filled with highly refractive polygonal inclusions, giving the worm a glossy appearance. Head with 3 lips bearing two papillae each; 6 articulated cephalic setae, 10 µm long (0.7 head diameters) in males, 8 µm (0.6 head diameters) in females. At the level of the posterior margin of the amphid four sublateral setae, 5 µm long, which appear to be segmented too, consisting however only of two segments. Amphids circular with a break in the posterior margin of the outer contour, anterior margin 13-17 µm from the anterior end of the animal; diameter of amphids 7 µm (39% of c.b.d.) in males, 6 µm (35%) in females. Stoma conical, unarmed, esophagus cylindrical, 180-220 µm long; nerve ring at 50% of esophagus length. Tail at first conical, the second half more or less cylindrical, often obviously broken with signs of would healing. In specimens with probably complete tails they were 8-9 anal body diameters long in males, 11-12 in females. Males diorchic, testes opposed, anterior testis beginning at about 40% of body length. In one male two separate vesiculae seminalis at 50 and 60% of body length were seen, in another a 400 µm long region at about midbody was filled with the 15-17 µm long spermatozoa. Spicula weakly arcuate, with a cuticular middle rib, 30 µm (1.3-1.5 anal body diameters) measured along chord. Gubernaculum straight, with knoblike lateral projection distally, 15-17 µm long. Males with minute preanal papillae which are arranged on both sides of the ventromedian line, 8-11 were seen, but their exact number is very difficult to observe, since they only a appear distinct, when the body is bent ventrally in this region. The anteriormost papilla was seen 90-120 µm in front of the anus, the posteriormost 8-12 µm. There are also minute papillae in the cervical region, probably 8, the first 40-50 µm from the anterior end, the last approximately at the end of the esophagus. (ref. ID; 7627)
Female: Females monodelphic, vulva at 48% of body length, only the posterior gonade developed, uterus thick walled, 80-90 µm long, followed by a receptaculum seminis containing bundles of sperm, which are longer (20-23 µm) than the spermatozoa observed in the male gonade. Differences in shape and length of spermatozoa found in the male vesicula seminalis and the female receptaculum seminis has also been observed by Riemann (1966) for Trefusia longicauda. Gonade reflexed, germinative zone of the overy reaching back to approximately the receptaculum, point of inflexion at 60-65% of body length. As in R. americana there is a rudimentary anterior gonade, consisting of a 25 µm long granular structure into which a short blind extension of the vagina projects. (ref. ID; 7627)
Remarks
From the species listed under Cytolaimium and Rhabdocoma in Gerlach and Riemann 1974, R. cylindricauda Stekhoven, 1950 and R. brevicauda Stekhoven, 1950 do not belong here at all, but -as has been already suggested by Vitiello (1971)- most probably to a special group within the Siphonolaimidae lacking mouth and digestive system, a member of which will be described in a forthcoming paper by the author. Cytolaimium conicum is transferred back to its original genus Trefusia. The remaining species now can be divided into two groups:
- a) Species with paired preanal and postanal papillae on cuticular discs; no cervical papillae; spicula strong, rectangulary bent; gubernaculum distinct, with lateral plates; females didelphic - Genus Cytolaimium Cobb, 1920
- b) Species with faint preanal and cervical papillae, in single ventral row or two subventral rows very close together; no postanal papillae; spicula rather weak, arcuate; gubernaculum absent or very weak; females monodelphic - Genus Rhabdocoma Cobb, 1920. (ref. ID; 7627)
To Cytolaimium being now the type species, C. exile Cobb, 1920, which has been redescribed by Wieser and Hopper 1967 from near the type locality. C. exile sensu Gerlach, 1962 differs from this species in the length of the cephalic setae, the size of the amphid, the position of the subcepharic setae and has to be considered a new species, C. gerlachi nom. nov.; Rhabdocoma articulata Gerlach, 1955 is known from a juvenile only and thus cannot be classified easily. However already Gerlach (1962) noted the close similarity to his C. exile from the Maledive Islands, therefore I place it within the genus Cytolaimium.
The genus Rhabdocoma now comprises the type species R. americana Cobb, 1920, furthermore R. macrura Cobb, 1920 (which however is insufficiently described), and R. obtusicaudata (Chitwood, 1936) nov. comb. I found the latter species rather abundant in the sulfide system along the coast of North Carolina, but identified it as C. exile Cobb (Ott 1972; Ott and Schiemer 1973), accepting the synonymisation of Gerlach 1962, which is based on Chitwood's text and on the recognition, that the shape of the tail is not a taxonomically valid character in this genus. It is however evident from Chitwood's figure (Chitwood 1936, Fig.3J) that the articulate setae are only about 60% of the head diameter, whereas they are about 1 head diameter in Cobb's and Wieser and Hopper's specimen and even longer in Gerlach's. Futhermore in my male specimen the arrangement and shape of the spicula agree very closely with Rhabdocoma americana Cobb. (ref. ID; 7627)
Key to the species of Cytolaimium Cobb, 1920
1. Cephalic setae 0.8-1.0 head diameter long, amphids 26-30% of corresponding body diameter, subcephalic setae posterior to amphid - C. exile Cobb, 1920, nec C. exile in Ott & Schiemer 1973, nec C. exile in Ott 1972, nec C. exile in Ott & Schiemer 1973, nec C. obtusicaudatum Chitwood.
2. Cephlic setae 1, 3 head diameters long, amphids in males 50% of corresponding body diameter, subcephalic setae on level of posterior margin of amphid -C. gerlachi nom. nov., Syn C. exile sensu Gerlach, 1962
3. Cephalic setae 2 head diameters long (adults not known) - C. articulatum nov. comb. Syn. Rhabdocoma articulat Gerlach, 1955 (ref. ID; 7627)
Key to the species Rhabdocoma Cobb, 1920
1. Subcephalic setae anterior to amphid - R. americana Cobb, 1920
2. Subcephalic setae on level with posterior margin of amphid - R. obtusicaudata (Chitwood, 1936) nov. comb Syn. Cytolaimium obtusicaudatum Chitwood, 1936, Syn. C. exile in Ott 1972, Syn. C. exile in Ott & Schiemer 1973, nec C. exile sensu Gerlach, 1962, nec C. exile sensu Wieser & Hopper, 1967. (ref. ID; 7627)
Deposited materials
Homoeotypes (male): U.S.N.M. Nr.54000-54002 L: 2.32-2.54 mm a: 98-108 b: 11.3-12.9 c: 12.9-13.9. (ref. ID; 7627)
Homoeotypes (female): U.S.N.M. Nr.54003-54004 L: 2.26-2.41 mm a: 83.5-85.1 b: 12.5-12.8 c: 12.5-13.1. (ref. ID; 7627)
See
Rhabdocoma americana (ref. ID; 1764)
Descriptions
Marine species. (ref. ID; 1752)