Acutogordius finni, Schmidt-Rhaesa, Andreas & Schwarz, Christian J., 2016

Schmidt-Rhaesa, Andreas & Schwarz, Christian J., 2016, Nematomorpha from the Philippines, with description of two new species, Zootaxa 4158 (2), pp. 246-260 : 251-254

Acutogordius finni n. sp.

( Figures 4 , 5 )

Holotype. One male from type locality, to be deposited in the PNM.

Etymology. The species name “ finni ” is chosen after another son of the senior author, Finn Jaro.

Type locality. Northwest Panay Peninsula , Barangay Bulanao , Libertad, Antique, Panay Island, Philippines (11° 49' N, 121° 59' E), ~ 396 m; dry riverbed; collected by C. J. Schwarz & G. Operiano on January 14, 2012.

Paratype. One male, deposited in the Zoological Museum Hamburg, accession number V13370 . Location : Northwest Panay Peninsula , trail to Sibaliw Research Station , Barangay Bulanao, Libertad , Antique, Panay Island , Philippines (11° 48' N, 121° 58' E), ~ 290 m; dry riverbed; collected by C. J. Schwarz on October 26, 2012.

Further specimen: One male, deposited in the Zoological Museum Hamburg, accession number V13371 . Location: Northwest Panay Peninsula, Barangay Bulanao, Libertad , Antique, Panay Island , Philippines ; dry riverbed; collected by C. J. Schwarz on September 15, 2011.

Description. The holotype is 205 mm long and measures 1.2 mm in width. The paratype is 340 mm long and 1.3 mm in width, the additional specimen is 355 mm long and 1.7 mm in width. All specimens are medium brown in colour, a dark collar is present.

The body cuticle is covered by abundant fine and short bristles ( Fig. 4 A–F). The body cuticle is also structured by a system of fine grooves, which is visible under higher magnifications but varies in its extent. In the paratype there is a very clear system of anastomosing grooves ( Fig. 4 D, E); in the holotype these grooves are more shallow and less anastomosing ( Fig. 4 B, C). In some regions of the holotype and in the additional specimen the cuticle is smooth and grooves are not present ( Fig. 4 A, F). At the posterior end the tail lobes strongly taper ( Fig. 5 A, D, F). The postcloacal crescent is roughly semicircular and varies slightly in shape and position ( Fig. 5 A, D, F). In the holotype it is least curved and extends only slightly onto the tail lobes ( Fig. 5 A). In the paratype and the additional specimen it is more strongly curved and extends further onto the tail lobes ( Fig. 5 D). In the holotype the anterior margin of the postcloacal crescent is broadly serrate ( Fig. 5 A). This feature is only partly visible in the paratype ( Fig. 5 D), and not visible in the additional specimen ( Fig. 5 F), because the anterior margin is covered with material in these two specimens. The bristles present on the body cuticle are also present on the ventral side of the posterior end, and extend on the outer side of the tail lobes becoming shorter towards the tip ( Fig. 5 B). In the paratype there are more such bristles in the ventral region around the cloacal opening than in the holotype and the additional specimen. Thicker bristles, almost spines, are present on the inner side of the tail lobes ( Fig. 5 C, E, G). They extend further from the anterior side of the distal ends of the postcloacal crescent along the ventral edge of the inner side of the tail lobes to about half of their length. Much finer bristles occur in the posterior region.

Remarks. Only a few previously described Acutogordius species were investigated by SEM, and patterns of fine bristles may have escaped earlier researchers. Nevertheless, most species show a characteristic distribution of bristles at the posterior end, summarized by Schmidt-Rhaesa & Geraci (2006). A distribution of bristles (the terms “bristle” or “spine” are used by most authors more or less intuitively) as in A. finni is not present in other species. Closest in resemblance is A. sulawensis Schmidt-Rhaesa & Geraci, 2006 , which has an accumulation of bristles behind the distal tip of the postcloacal crescent ( Schmidt-Rhaesa & Geraci 2006). Bristles on the body cuticle have not been described from other species with the exception of A. americanus De Miralles & De Villalobos 1998 , where they are few, and additionally the cuticle is structured into roundish elevations called areoles ( De Miralles & De Villalobos 1998). The only other SEM documentation of the body cuticle (besides A. americanus ) is from A. sulawensis , where it is smooth ( Schmidt-Rhaesa & Geraci 2006). Given these differences, we regard A. finni as a new species.

Figures

FIGURE 4. Acutogordius finni, n. sp., cuticular structure in holotype (A – C), paratype (D – E) and additional specimen (F). All images show the spines on the cuticle and the different surface structure of the cuticle, which can be smooth (A, F), with slight (B, C) or strong (D, E) pattern of fine grooves.

FIGURE 5. Acutogordius finni, n. sp., posterior ends in holotype (A – C), paratype (D – E) and additional specimen (F – G). Position of cloacal opening (co) and postcloacal crescent (pcc) are indicated in A. Dotted squares indicate position of magnifications in figures B, C, E and G. B. Fine bristles (partly covered with dirt) on the posterior end of the tail lobes. C, E, G. Thicker bristles on the inner margin of the ventral side of the tail lobes.