Anoplodactylus Wilson, 1878

Lucena, Rudá Amorim & Christoffersen, Martin Lindsey, 2018, Anoplodactylus (Pycnogonida: Phoxichilidiidae) from Brazil, new records and two new species, Turkish Journal of Zoology 42 (4), pp. 372-388 : 374-375

Genus Anoplodactylus Wilson, 1878

Type species: Anoplodactylus lentus Wilson, 1878 , by original designation.

Diagnosis: see Child (1998a).

Remarks: Anoplodactylus is the largest and the most abundant genus of Phoxichilidiidae . It is among the three most numerous genera of Pycnogonida, with 134 species. It is considered a shallow-water genus, having a pantropical distribution. Bamber (1998) proposed that Anoplodactylus has species that disperse passively in the plankton, riding on medusae, thus explaining their wide global distribution ( Bamber and Costa, 2009).

Wilson (1878), in the original description, stressed that the main diagnostic characters of Anoplodactylus are the ovigers, with 6 articles, and the absence of auxiliary claws. However, for Marcus (1940) the only distinctive character of the group is the elongation of the neck over the proboscis. This applies particularly after the synonymization of Halosoma Cole, 1904 , a genus with specimens having 5 articles in the oviger, the discovery of a new species, and the transfer of species of Phoxichilidium Milne Edwards, 1840 to Anoplodactylus . The latter species are distinguished only by the position of the auxiliary claws (reduced and basal in relation to the main claw in Anoplodactylus , long and terminal in Phoxichilidium ) ( Child, 1995).

Despite being considered a stable, morphologically homogeneous ( Arango and Maxmen, 2006), and monophyletically robust group ( Arango and Wheeler, 2007), as suggested by the absence of palps and ovigers in the females, and by a stable number of segments in the ovigers of males ( Hedgpeth, 1948; Child, 1998a; Arango and Maxmen, 2006; Lucena et al., 2015), the species of Anoplodactylus display large variations in the structure of the cement glands, in body shape and segmentation, and in the size and shape of the proboscis ( Arango, 2002).

According to Hedgpeth (1948), the species of Anoplodactylus form a variable group whose identification is uncertain. That is because their distinction is based on a set of one or two distinct characters, or by a unique combination of distinct characters, particularly of the male ( Arango and Krapp, 2007). This situation indicates the necessity for a revision of the group, as is pointed out by Williams (1941), Hedgpeth (1948), Arango and Maxmen (2006), and Müller and Krapp (2009).

Given the large morphological variations and high number of described species, taxonomic groups were proposed on the basis of species distributions and morphological characters ( Arango and Krapp, 2007). A series of species-complexes were recognized: A. pygmaeus ( Stock, 1974) , A. insignis ( Stock, 1974) , A. robustus ( Stock, 1979) , A. gestiens ( Nakamura and Child, 1991) , A. californicus-digitatus ( Arango and Maxmen, 2006) , A. tenuicorpus ( Arango and Krapp, 2007) , and A. angulatus (Krapp et al., 2008; Lucena et al., 2015).

We point out the great difficulty in defining species in the genus ( Arango and Krapp, 2007), resulting from incomplete diagnoses, absence of illustrations ( Sawaya 1949), and similarity among species due to lack of variations in some characters ( Child, 1998a). Furthermore, the males have the main diagnostic characters: the ovigers and the cement gland. Females are impossible to identify when not accompanied by males ( Nakamura and Child, 1991; Child, 1998a). As a consequence, a large number of species remain to be named ( Williams, 1941; Hedgpeth, 1948).

To date, this is the only genus of Phoxichilidiidae recorded from Brazil, being one of the most abundant genera in shallow waters in all regions of Brazil.

Key to the Brazilian species of Anoplodactylus (adult specimens)

1. Oviger with 5 articles .................................................. 2

− Oviger with 6 articles ................................................... 3

2. Trunk partially segmented, segmentation absent between segments 3 and 4. Chelae well developed. Fingers with teeth ......................................................... A. monotrema

− Trunk without segmentation. Chelae with movable finger well developed, immovable finger reduced. Fingers without teeth .......................................................... A. marcusi

3. Segments 1 and 2 of trunk with a bifid tubercle near margin of segment ................................................ A. evelinae

− Segments of trunk without ornamentation ............... 4

4. Proboscis styliform, with terminal region directed upwards. Tube of cement gland with transverse rings .......... ............................................................................ A. batangensis

− Proboscis not styliform. Tube of cement gland without transverse rings ....................................................... 5

5. Animal with very small trunk, less than 0.6 mm ..... 6

− Animal with trunk not very small, larger than 0.6 mm .......................................................................................... 8

6. Lateral processes contiguous. Movable finger of chela reduced ................................................................. A. marcusi

− Lateral processes not contiguous. Movable finger of chela equal to fixed finger ..................................................... 7

7. Trunk segmentation present between segments 1–2 and 2–3 ............................................................... A. brasiliensis

− Trunk segmentation completely absent ........ A. mirim

8. Ocular tubercle low or absent, eyes absent or very small and unpigmented ........................................ A. typhlops

− Ocular tubercle regular, eyes present and pigmented .. ................................................................................................... 9

9. Lateral processes smooth or ornamented only with setae ...................................................................................... 10

− Lateral processes ornamented with tubercle; with or without setae ........................................................................ 14

10. Tube of cement gland long and narrow, extended forwards. Lateral processes with small dorsal spine and two smaller lateral spines ...................................... A. aragaoi

− Tube of cement gland short ....................................... 11

11. Trunk without segmentation ................ A. maritimus

− Trunk with segmentation complete or absent between segments 3 and 4 .................................................................. 12

12. Trunk very long. Lateral processes separated by twice their diameter. Legs with long dorsal spores on femur and tibia 1 .......................................... A. massiliformis

− Trunk short. Lateral processes separated at most by their diameter. Legs without dorsal spores ....................... 13

13. Coxa 2 of all legs with long spurs on ventral region in males. Lateral processes with three long dorsal setae ....... .................................................................................. A. eroticus

− Coxa 2 of legs 3 and 4 with spurs not very long, remaining legs with very short spur. Lateral processes with many small setae .................................................... A. ricardoi

14. Lateral processes with large, triangular or elongate tubercles ............................................................................... 15

− Lateral processes with small, rounded tubercles ....... 17

15. Third article of oviger with a small hook directed backwards, near base ..................................... A. ganchiformis

− Third article of oviger straight, without a hook ...... 16

16. Chelifore with anterior tubercle. Opening of cement gland elongate ........................................................ A. insignis

− Chelifore without tubercle, but with many setae. Tube of cement gland robust, conical large, directed obliquely to distal region ............................................................. A. spurius

17. Trunk not segmented .............................. A. petiolatus

− Trunk partially or completely segmented ................ 18

18. Ocular tubercle conical. With a small rounded tubercle on lateral processes. A small constriction present near base of third article of oviger ........................... A. stictus

− Ocular tubercle rounded. With small rounded tubercles dorsally on lateral processes. No constriction at the base of third article of oviger ..................... A. californicus