Pontonema mediterranea, Warwick & Robinson, 2000

Robinson, M. Warwick J., 2000, Sibling species in the marine pollution indicator genus Pontonema (Nematoda: Oncholaimidae), with a description of mediterranea sp. nov., Journal of Natural History 34, pp. 641-662 : 658-659

Pontonema mediterranea sp. nov.

Type material

Holotype male, British Museum (Natural History) registration number 1999.880; paratypes four males and eight females, registration numbers 1999.881 ±890.

Type locality

Blanes Bay in the North Western Mediterranean Sea (41ss40’ N, 2ss48’ E). Details of the type locality are provided under the site descriptions earlier in this paper. A second population of P. mediterranea sp. nov. has also been sampled from a canal in SeÁte, south-west France. All known details of this locality are also documented earlier. Specimens from this population are available in both the authors’ collection, and in the Paris Museum of Natural History identi®ed as Pontonema sp .

Measurements Measurements are given in table 8.

Description

All observations are limited to light microscopy. Pontonema mediterranea is a very large nematode, up to 21 mm in length, with maximum diameter at mid-length. Coloration of preserved specimens is yellow/brown in males, and also in gravid and non-gravid females. The cuticle is smooth in appearance with scattered somatic setae. Head truncate with rounded margins, furnished with six short (ca 3 M m) papilliform labial sensilla and 10 long (ca 12 M m) cephalic sensilla. Amphids not discernible under light microscopy. Eight ®les of cervical setae present between buccal cavity and nerve ring, but variable in number and position. Walls of buccal cavity well-cuticularized. Located in the anterior region of the buccal cavity is one dorsal tooth, slightly anterior to which are two, equal, subventral teeth. Nerve ring ca 36% of oesophagus length from anterior. Excretory pore ca 3 buccal cavity lengths from anterior, but not clearly visible in most specimens. No oesophageal bulbs present. Ventral glands posterior to oesophago-intestina l join. Tail is short and rounded, containing three caudal glands leading to a well-developed terminal spinneret.

Males. Gonads di cult to interpret under light microscopy. Spicules equal, arcuate, and being thickest at mid-length, they are larger than observed in P. vulgare . Spicules shaped as illustrated in ®gure 5b. Although di cult to determine without dissection, gubernaculum appears to be a structure of three parts. Two ventral precloacal sensory ®elds present. First is located just anterior to cloaca, cuticularized and elevated from surrounding cuticle. Furnished with round-ended papilliform sensilla, although number and position is variable as in other congeneric species (there are four subventral pairs in the holotype, ®gure 5b). The second, anterior mid-ventral sensory ®eld is distant from the proximal end of the spicules, is very prominent, and, with heavy cuticularization, it is elevated considerably from the surrounding cuticle. Again, the furnishing of papilliform sensilla is variable. There are two subventral ®les of seven to ten smaller rounded swellings, each tipped with a pointed seta, extending forward from the cloaca (eight pairs in the holotype, ®gure 5b). A diagnostic feature of this species is a prominent ventral swelling of the tail immediately posterior to the cloaca, the surface of which is furnished with very ®ne papillae.

Females. Didelphic; ovaries opposed and reēxed. Eggs brownish. Demanian system not present.

DiOEerential diagnosis

This species belongs to group 1.1 in the key of Bett and Moore (1988); species with a short tail, two precloacal sensory ®elds, the anteriormost being distant from the proximal ends of the spicules. The group contains the North American P. vacillatum Leidy 1855 , and the north European species P. vulgare (Bastian, 1865) and P. balticum (Schulz, 1932) . These three are all very similar, although in the light of the present analysis, their synonymy as suggested by Bett and Moore (1988) is perhaps premature. Pontonema mediterranea is distinguished from these by the prominent postcloacal ventral swelling, as well as from P. vulgare by the more subtle morphometric characters detailed in this paper. Pontonema balticum also has a`postanal papilla’, but in this case it is relatively small, and positioned more than half the tail-length posterior to the cloaca.