TRIGONOSTOMUM DENHARTOGI (KARLING, 1978) COMB. NOV.

(FIGS 8E, 11A)

Alternative species name: trigonostomum-denhartogi Proxenetes denhartogi Karling, 1978: 233, figs 35, 36.

Known distribution: Bermuda (Karling, 1978).

New localities: Kenya, Mombasa area, McKenzie Point, in shallow pool on seagrass, 30 September 1991. Curaçao (Dutch Antilles), Dam di Cabicuchi (‘Spaanse water’), on Turbinaria -like algae from exposed rocks, 14 December 1998. Curaçao (Dutch Antilles) ‘Spaanse water’, mixed sample of algae, 30 December 1998. New Caledonia, Nouméa, Nouville, on algae in a lagoon south of the asylum, 3 August 2003. New Caledonia, Nouméa, Anse Vata, on algae ( Ulva sp. and Enteromorpha sp.) from a little estuary, 22 August 2003.

Material examined: Holotype (SMNH, no. 2965). Live material and five whole mounts, one from each new locality.

Diagnosis: Trigonostomum species with very complex copulatory organ, 106–121 Mm long. Mantle with numerous folds, rods and spines, one of which has a thread-like distal part. Stylet 61–66 Mm long. Bursal appendage with a straight initial part, 22–44 Mm long, and two heavily coiled tubes.

Remarks and additional data: Karling (1978) described this species from Bermuda based on one whole mounted specimen, but without observations of live animals. On the holotype, the anterior invagination (‘proboscis’) is not visible and Karling therefore did not observe this important feature. Based on the structure of the copulatory organ he reluctantly placed the species within Proxenetes Jensen, 1878 . He explicitly mentioned, however, that the bursal appendage was very unlike that of any other species of Proxenetes, where the bursal appendage consists of a split tube, surrounded by a ring. Observations on live material clearly show that this species indeed belongs to Trigonostomum, as it has the typical anterior invagination.

The specimens from Curaçao and New Caledonia are ± 0.8 mm long. The copulatory organ is of exactly the same structure as in the specimen from Bermuda (Karling, 1978), consisting of an outer plate-like structure (Fig. 11A 1: a) that forms a broad gutter enclosing several long rods (Fig. 11A 1: e). One of these rods has a long distal thread-like point (Fig. 11A 1: e1). A second, triangular, plate-like part (Fig. 11A 1: d) surrounds the rods and carries three distal hooks (Fig. 11A 1: a1, b and c). The length of the copulatory organ (excluding the thread-like tip) is 107–111 Mm (Curaçao) and 109– 121 Mm (New Caledonia), which is almost identical to that of the holotype (115 Mm: Karling, 1978). The exact number of rods could not be determined. The tubular stylet is only clearly visible in the New Caledonian specimens (Figs 8E, 11A 3). It is 61–66 Mm long (n = 2) and rather broad, with a wide proximal funnel to which the mantle is attached. The bursal appendage of the specimens from Curaçao and New Caledonia clearly consists of two heavily coiled tubes and a proximal basal piece. This proximal part is 31 Mm and 44 Mm in the two specimens from Curaçao, 28 Mm and 36 Mm in the specimens from New Caledonia, and 22 Mm in the specimen from Bermuda (Karling, 1978). Karling (1978) could not determine the exact number of coiled tubes in the Bermuda individuals.