Falcidens Salvini-Plawen, 1968

Genus Falcidens Salvini-Plawen, 1968 View in CoL

Subgenus Chiastofalcidens nom. nov. (pro Lepoderma Salvini-Plawen 1992 , nec Looss, 1899) Falcidens ( Chiastofalcidens) targatus Salvini-Plawen, 1992 View in CoL

( Figures 1A–C View Figure 1 , 2A–G View Figure 2 , 3A, B View Figure 3 , 4A, C) Falcidens ( Chiastofalcidens) acutargatus Salvini-Plawen, 1992 View in CoL

( Figures 1D–F View Figure 1 , 2H–J View Figure 2 , 3C View Figure 3 , 4B, D)

Chiastofalcidens is proposed to replace the species-group name (subgenus) of Lepoderma Salvini-Plawen, 1992 , which is a pre-occupied name: Lepoderma Looss, 1899 View in CoL ( Trematoda). ‘Chiastos’, derived from Greek chiasma, means intercrossed; this new name refers to the crossed sculpture of the sclerites, present in Falcidens loveni ( Nierstrasz, 1902) View in CoL , F. chiastos Scheltema, 1989 View in CoL , F. nontargatus Salvini-Plawen, 1992 View in CoL , F. targotegulatus Salvini-Plawen, 1992 View in CoL , and F. acutargatus Salvini-Plawen, 1992 View in CoL , all of them related to F. targatus View in CoL , the type species designated by Salvini-Plawen (1992) for Lepoderma .

Falcidens ( Chiastofalcidens) targatus View in CoL and F. ( Ch.) acutargatus View in CoL have an elongated body shape with three distinct regions ( Figure 1 View Figure 1 ): an anterior part, with an ‘anterium’ continuous to a neck; a trunk; and a posterium with a slender shank and a terminal knob. The collar separating the trunk from the neck is well marked in most individuals of both species. In F. ( Ch.) targatus View in CoL the neck is more prominent and the anterium can be inflated, or not ( Figures 1A–C View Figure 1 , 2A, B View Figure 2 ). Due to deposition of particles from the surrounding environment, the knob is red in almost all the individuals of this species ( Figure 1A View Figure 1 ). In some animals the gills are partially exposed because the knob is very contracted ( Figure 2C View Figure 2 ), while in others it is relaxed, showing the mantle cavity in an inflated condition ( Figure 2D View Figure 2 ). In F. ( Ch.) acutargatus View in CoL , the knob is more distinct from the shank ( Figures 1D–F View Figure 1 , 2J View Figure 2 ).

The individuals of the material from the American Museum of Natural History labelled as ‘types’, which are considered the holotypes of both species ( Boyko and Sage III 1996) are quite worn ( Figure 1C, F View Figure 1 ). The holotype of F. ( Ch.) acutargatus corresponds exactly to the specimen of figure 8 of Salvini-Plawen (1992). Most specimens of the lot of the paratypes of F. ( Ch.) targatus are well preserved and one of them is very similar to one individual from Brazil ( Figure 1A, B View Figure 1 ). The fragments of the paratypes of F. ( Ch.) acutargatus are not comparable. From external view, the animals of both species from Campos Basin are very similar to those illustrated in figures 7 and 8 of Salvini-Plawen (1992).

The sclerites extracted from Campos Basin specimens of both species and from one paratype of F. ( Ch.) targatus are illustrated in Figures 2 View Figure 2 and 3 View Figure 3 . In general, they are smaller in F. ( Ch.) targatus than in F. ( Ch.) acutargatus , being similar in shape among these species, and differing only in the some details ( Figure 3 View Figure 3 ). In the anterium, the sclerites are very small, with an elliptical shape and no ornamentation ( Figures 2E View Figure 2 , 3A, C View Figure 3 ). In the neck, trunk and shank they have a more slender shape in F. ( Ch.) targatus ( Figure 3A, B View Figure 3 ) than in F. ( Ch.) acutargatus ( Figure 3C View Figure 3 ); also, in the former species they have a tapered tip ( Figures 2F, G View Figure 2 , 3A, B View Figure 3 ), while in the latter they are more pointed distally ( Figures 2H–J View Figure 2 , 3C View Figure 3 ). In both species, the side of the sclerites facing the body is smooth (see the sclerites with an asterisk in Figure 3 View Figure 3 ), while on the opposite surface they bear the typical ornamentation originally described for the subgenus: on the proximal half of the surface there are up to eight crossed ridges. On the distal half these ridges are parallel, a median one being stronger and forming a low keel, this being particularly more evident in F. ( Ch.) acutargatus . In the neck they measure ~45 μm in F. ( Ch.) targatus and ~120 μm in F. ( Ch.) acutargatus ; in the trunk, ~100 and ~140 μm; and in the shank, ~70 and ~140 μm, respectively. Throughout the body, about 1/3 of the sclerites of F. ( Ch.) targatus also have a basal deep notch. In F. ( Ch.) acutargatus this notch is present in about 1/4 of the sclerites, and appears to be shallower. At the knob the sclerites are elongated, ~170 μm long in F. ( Ch.) targatus and ~180 μm long in F. ( Ch.) acutargatus , with the shape of long bats surrounding the mantle cavity. The extracted sclerites of the paratype of F. ( Ch.) targatus ( Figure 3B View Figure 3 ) are very similar to the ones obtained from Campos Basin’ s specimens ( Figure 3A View Figure 3 ).

The radula of F. ( Ch.) targatus ( Figure 4A) is similar to the one of F. ( Ch.) acutargatus ( Figure 4B). A pair of sickle-shaped teeth is present in the distal end of a large cone-shaped support, and there is also a pair of lateral supports, which are approximately one third of the length of the central support in F. ( Ch.) targatus and about a half of its length in F. ( Ch.) acutargatus . A triangular plate is placed anteriorly, connected with the teeth by an apophysis of the plate.

The oral shield is U-shaped in both species ( Figure 4C, D).

From a total of about 2350 specimens of caudofoveates present in the samples collected by the Habitats Project, F. ( Ch.) targatus and F. ( Ch.) acutargatus are among the most common species, with 176 and 141 individuals, respectively ( Tables 1, 2). The former species was only collected on the shelf, represented by 17 samples from 30 to

HAB6-A07- R3 23°39 ′ 19.981 ″ S, 41°18 ′ 30.534 ″ W 732.9 25 June 2008 GoogleMaps 2

HAB3-G08- R2 22°7 ′ 19.663 ″ S, 39°52 ′ 22.613 ″ W 992.6 16 June 2008 GoogleMaps 1

HAB7-H06- R2 21°44 ′ 21.564 ″ S, 40°5 ′ 18.026 ″ W 402.7 07 July 2008 GoogleMaps 1

HAB7-H06- R3 21°44 ′ 21.493 ″ S, 40°5 ′ 18.066 ″ W 401.6 07 July 2008 GoogleMaps 1

HAB7-H07- R2 21°41 ′ 11.649 ″ S, 40°2 ′ 20.690 ″ W 699.4 07 July 2008 GoogleMaps 3

HAB4- CANG07 - R2 21°56 ′ 10.244 ″ S, 39°57 ′ 43.438 ″ W 709.7 28 May 2008 GoogleMaps 1

HAB6-B07- R1 23°13 ′ 1.396 ″ S, 40°57 ′ 36.705 ″ W 815.5 26 June 2008 GoogleMaps 1

HAB8-D06- R3 22°33 ′ 36.014 ″ S, 40°26 ′ 37.171 ″ W 383 31 January 2009 GoogleMaps 1

HAB8-E06- R3 22°25 ′ 59.389 ″ S, 40°17 ′ 33.343 ″ W 387.1 31 January 2009 GoogleMaps 2

HAB9-I07- R3 21°11 ′ 12.228 ″ S, 40°12 ′ 51.745 ″ W 683 04 February 2009 GoogleMaps 3

HAB9-H06- R1 21°44 ′ 21.608 ″ S, 40°4 ′ 59.614 ″ W 405 05 February 2009 GoogleMaps 1

HAB8-A07- R3 23°39 ′ 21.880 ″ S, 41°18 ′ 33.045 ″ W 692.7 28 January 2009 GoogleMaps 1

HAB8-A07- R1 23°39 ′ 19.742 ″ S, 41°18 ′ 28.369 ″ W 699 28 January 2009 GoogleMaps 2

HAB3-H09- R2 21°39 ′ 18.701 ″ S, 39°53 ′ 55.974 ″ W 1293.2 25 June 2008 GoogleMaps 1

HAB8-C08- R2 23°1 ′ 30.862 ″ S, 40°45 ′ 22.948 ″ W 964.8 16 January 2009 1 Mean depth 617.50 Total 156 GoogleMaps

147 m depth ( Figures 5 View Figure 5 , 6 View Figure 6 ). Most specimens and the richest samples of F. ( Ch.) targatus were obtained in the south of the area of Campos Basin, namely in transects A and B ( Figure 5 View Figure 5 ). Falcidens ( Chiastofalcidens) acutargatus is more common on the continental slope, with 53 samples obtained from 376 to 1293 m depth; this species is homogenously distributed through all of the sampling area ( Figures 5 View Figure 5 , 6 View Figure 6 ).

The mean length of F. ( Ch.) targatus is higher ( 5.34 mm), reaching up to 9.12 mm, while specimens of F. ( Ch.) acutargatus have a mean length of 4.04 mm but are up to 10.44 mm long. The t -test revealed statistical differences ( p <0.05) among species in relation to the NeL, TrL, TrW and ShW ( Table 3). Although the PoL was the only absolute measurement that can be considered similar among species ( p = 0.45), the ratio PoL/TrL was not ( p <0.05). In fact, the trunk is usually twice the length of the posterium (PoL/TrL = 0.42) in F. ( Ch.) targatus , while in F. ( Ch.) acutargatus the posterium is more distinct and longer when compared to the trunk (PoL/ TrL = 0.63). The PoL/TrL showed no correlation with the length of the body in F. ( Ch.) targatus ( r = −0.15) and in F. ( Ch.) acutargatus ( r = −0.21) ( Figure 7A View Figure 7 ).

The ratio ToL/TrW was revealed to be distinct among these species ( p <0.05). A Pearson product–moment coefficient showed a moderate correlation to the total length of the body in both F. ( Ch.) targatus ( r = 0.77) and F. ( Ch.) acutargatus ( r = 0.75). This relationship is illustrated in Figure 7B View Figure 7 .