Laophontodes gracilipes, LANG, 1936

LAOPHONTODES GRACILIPES LANG, 1936 View in CoL B

Lang (1936b) described both sexes succinctly based on material collected from muddy sediments at 50–100 m depth in the Gullmar Fjord, Sweden. Illustrations were confined to the rostrum, caudal ramus, maxilliped, P1 and female P5. Although the species did not appear to be rare at the type locality, occurring all year round ( Lang, 1948), it has been recorded from only two other localities since its original description, i.e. at 30–90 m depth in the Kandalaksha Gulf of the White Sea ( Kornev et al., 2004; Kornev & Chertoprud, 2008) and at 1259 m depth on the Anaximenes Seamount in the eastern Mediterranean Sea ( George et al., 2018). Kornev & Chertoprud (2008) provided a detailed redescription of both sexes, which forms the basis for the argumentation below.

For more than a century, Laophontodes has served as a taxonomic repository for ancorabolids that possess a rostrum, a three-segmented P1 exopod and a prehensile, two-segmented P 1 endopod with enp-1 being longer than the exopod. Although Lang (1936b) did not explicitly state his reasons, it was probably on the basis of the last combination of characters that he assumed that the appropriate generic placement of La. gracilipes was also in Laophontodes . Neither Lang (1936b, 1948) nor any subsequent workers commented on its relationships with other congeners. Gheerardyn & George (2010: 51) labelled La. gracilipes as a ‘typical’ Laophontodes , but in a subsequent paper ( George & Gheerardyn, 2015: 86) briefly hinted at the possibility of excluding it from this genus. Their amended diagnosis of Laophontodes contains two characters that are not displayed by La. gracilipes : (1) rostrum small; and (2) P1 enp-2 with one claw and one longer geniculate seta (and occasionally one minute accessory seta). Comparative morphological analysis reveals that the species exhibits a suite of mostly autapomorphic characters preventing its inclusion in Laophontodes :

(1) Rostrum very large, about two-thirds the length of the cephalic shield, sharply pointed towards the apex and markedly recurved ventrally. Large rostra have been reported in other Laophontodinae , such as Calypsophontodes macropodia ( Gee & Fleeger, 1986) , both known species of Probosciphontodes Fiers, 1988 and some members of Ancorabolina , but they are typically of a different size, shape and orientation (cf. Fiers, 1988; George & Tiltack, 2009; Gheerardyn & George, 2010; Gheerardyn & Lee, 2012).

(2) Cephalic shield, pedigerous somites and anterior half of genital double-somite (genital somite in ♂) with reticulate surface ornamentation. Some species of Laophontodes , such as Laophontodes typicus T. Scott, 1894 , Laophontodes whitsoni T. Scott, 1912 , Laophontodes sabinegeorgeae George & Gheerardyn, 2015 and Laophontodes scottorum George, 2018 , show dorsal striations near the posterior margin of the body somites (but not the cephalic shield), but their pattern, distribution and nature are different (cf. George & Gheerardyn, 2015; George, 2018).

(3) Dorsal surface of P5-bearing somite, genital double-somite (anteriorly and posteriorly) and first free abdominal somite with paired, backwardly directed, spinous projections. Comparable projections are found only in Ancorabolina spp. (see below); members of Paralaophontodes typically have paired, dorsal, sensillate processes on all somites (except the anal one), but these conspicuous protuberances are not homologous with the spiniform structures found in La. gracilipes (cf. Lang, 1965; Mielke, 1981, Fiers, 1988, George, 2017).

(4) Endopodal claw of maxilliped with long pinnules along the distal half of the inner margin. Some Laophontodes spp. , such as La. whitsoni , Laophontodes macclintocki Schizas & Shirley, 1994 , Laophontodes mourois Arroyo et al., 2003 and Laophontodes horstgeorgei George & Gheerardyn, 2015 , exhibit small spinules on the maxillipedal claw, but in most members of the genus the claw is naked (cf. Schizas & Shirley, 1994; Arroyo et al., 2003; George & Gheerardyn, 2015). Minute spinules have also been recorded in some species of Calypsophontodes and Tapholaophontodes (cf. Cottarelli & Baldari, 1987; Gheerardyn & Lee, 2012), but in all other members of the Laophontodinae the endopodal claw lacks ornamentation.

(5) P1 basis transversely prolonged in distal half, causing rami to be widely separated by its concave distal margin. In members of Laophontodes , the endopod is positioned closely and adjacent to the exopod, typically being originating from a cylindrical pedestal formed by the inner distal portion of the basis.

(6) P1 enp-2 with elongate slender claw, being almost as long as adjacent geniculate seta. Except for La. whitsoni (cf. George & Gheerardyn, 2015: fig. 21D), all species of Laophontodes have a robust, acutely curved claw that is distinctly shorter than the accompanying geniculate seta.

(7) Armature of P2–P4 enp-2 reduced to a single, extremely long apical seta.

(8) Caudal ramus seta II (and probably also seta I) positioned in proximal third of ramus. Both Lang (1936b) and Kornev & Chertoprud (2008) show only a single seta (II) along the proximal outer margin, but it is highly likely that seta I was concealed by it. In Laophontodes spp. , all caudal setae typically arise from the distal half ( Laophontodes georgei , Laophontodes gertraudae George, 2018 , La. mourois , Laophontodes sarsi George, 2018 , La. scottorum , La. typicus and La.whitsoni ) orevenquarter (Laophontodesbicornis A. Scott, 1896, La. horstgeorgei , La. macclintocki , La. sabinegeorgeae and Laophontodes spongiosus Schizas & Shirley, 1994 ). The only exception is the recently described Laophontodes monsmaris George, 2018 , in which setae I and II originate from the middle third of the outer margin (cf. George, 2018: fig. 16B). Being unique within the Ancorabolinae , the proximal displacement of setae I and II is here regarded as an autapomorphy for La. gracilipes , because in all other species of the subfamily all caudal setae arise from the distal half of the ramus, even in species of Algensiella , Calypsophontodes and Tapholaophontodes , all of which exhibit short to very short rami (cf. Soyer, 1975; Mielke, 1985; Cottarelli & Baldari, 1987; Bodiou & Colomines, 1988).

Based on the suite of autapomorphies (1–2, 4, 7–8) outlined above, La. gracilipes is here excluded from Laophontodes and fixed as the type species of a new genus to be diagnosed as follows.