Articullichirus, Poore & Dworschak & Schnabel, 2022

Poore, Gary C. B., Dworschak, Peter C. & Schnabel, Kareen E., 2022, Articullichirus, a new genus of ghost shrimp (Crustacea: Axiidea: Callichiridae) with one new species, Memoirs of Museum Victoria 81, pp. 123-133 : 123-124

Articullichirus gen. nov.

http://zoobank.org/urn:lsid:zoobank.org:act:EB81E6A6-9CF1-

4B8B-BF06-3E2440B2A6BA

Type species. Callianassa articulata Rathbun, 1906 by present designation.

Diagnosis. Anterior branchiostegal lobe sclerotised, wellproduced anteriorly beyond junction with oblique branchiostegal ridge with which it articulates by means of a virtual condyle; rostrum spine-like; anterolateral spines prominent. Pleomere 1 tergite undivided or with weak transverse step. Antennal scaphocerite acute. Maxilliped 3 ischium and merus together ovoid, axial length slightly greater than width at their articulation; crista dentata of few separate spines proximally and toothed ridge distally overlapping proximal margin of merus; propodus about as wide as long, propodus free distal margin nearly transverse. Male major cheliped merus with 3 proximal sharp oblique spines, 1 or more distally along length of lower margin; without spines on upper margin of merus and propodus or lower margin of carpus. Minor cheliped of male slightly more than half wide as major, carpus slightly shorter than palm, fingers as long as palm; merus lower margin with row of spines. Pereopod 3 propodus subpentagonal, with strong broad proximal lobe on lower margin, lower margin straight. Pereopod 4 subchelate, fixed finger shorter than dactylus. Male pleopod 1 of 2 articles. Male pleopod 2 appendix interna absent. Pleopods 3–5 appendices internae longer than broad, clearly emerging from margin of endopod. Uropodal endopod with convex anterior margin, acute-rounded apex, slightly curved posterior margin, longer than wide; exopod with elevated dorsal plate with row of setae diverging from row of setae on distal margin. Telson wider than long, convex-sided, widest near midpoint, posterior margin concave between rounded posterolateral corners, with transverse row of spiniform setae at midpoint.

Etymology. Alliteration of articulata , specific name of the type species, and Callichirus, type genus of the family.

Included species. Callianassa articulata Rathbun, 1906 ; Callianassa collaroy Poore and Griffin, 1979 ; Articullichirus chiltoni sp. nov.

Remarks. Callianassa articulata Rathbun, 1906 was provisionally included in Corallianassa by Manning (1987) and Dworschak (1992) and without qualification by Poore et al. (2019). Poupin (1998) argued for its inclusion in Cheramus Bate, 1888 , a genus now belonging in another family, Callianassidae Dana, 1852 . Sakai (1999, 2005, 2011) included the species in Glypturus Stimpson, 1866 . Dworschak (1992) noted how the telson, without a median posterior prominence, and the more operculiform maxilliped differed from other species of Corallianassa (see figures here and in Rathbun, 1906; Edmondson, 1944). Callianassa collaroy Poore and Griffin, 1979 has been variously included in Glypturus ( Sakai, 1988, 2011), Corallianassa ( Tudge et al., 2000; Davie, 2002; Komai et al., 2015; Poore et al., 2019) and Neocallichirus Sakai, 1988 ( Sakai, 1999). It was included in Komai et al.’s (2015) thorough review of differences between Glypturus and Corallianassa , but differences between C. articulata and both these genera were not commented on. The discovery of new material of C. articulata from French Polynesia, of C. collaroy in Australia, and of a similar species from New Zealand, stimulated a reappraisal of specimens from throughout the Pacific identified as one or the other of these two species. Several are misidentified and a new genus is warranted.

Articullichirus resembles Corallianassa and Glypturus (but not Neocallichirus ) in the possession of a pair of sharp anterolateral carapace spines. Articullichirus differs from both genera in the much broader oval maxilliped 3 (narrow with an oblique meral margin in Glypturus and Corallianassa ); shape of the telson (evenly convex-sided, with concave posterior margin in Articullichirus , with semicircular posterior half in Glypturus , tapering from greatest width anteriorly in Corallianassa ); and an acute scaphocerite (small in Glypturus , sometimes absent in Corallianassa ). In addition, Articullichirus , like Corallianassa , differs from Glypturus in the absence of spines along the upper margin of the chelipeds and in having a horizontal rostrum. Komai et al. (2015) noted that the combined length of pleomeres 1 and 2 of at least four species of Corallianassa is greater than or equal to the carapace length, whereas in G. armatus , Corallianassa intesi (de Saint Laurent and Le Loeuff, 1979) and Articullichirus collaroy comb. nov. pleomeres 1 and 2 are shorter than the carapace.

Calliapagurops differs from all callichirids in having exceptionally stout antennae, much more prominent than the antennules; the antennae may be used for suspension feeding ( Dworschak and Wirtz, 2010). Calliapagurops was placed in its own subfamily Calliapaguropinae by Sakai (1999) but its relationship to Callichiridae was realised by Ngoc-Ho (2002). Calliapagurops is notable for exceptionally long eyestalks with terminal cornea, differing from most callichirids that have more or less flattened eyestalks with subterminal cornea and a mesiodistal lobe ( Ngoc-Ho, 2002; Dworschak and Wirtz, 2010). While the eyestalks of species of Corallianassa , Glypturus and Articullichirus are much shorter, the cornea is terminal with only a small mesiodistal lobe. Calliapagurops and these three genera all have sharp prominent anterolateral carapace spines that, with the sharp rostrum, have more or less weakly calcified bases. Species of Articullichirus resemble the two recognised species of Calliapagurops . The oval telson with a transverse row of robust setae is similar to that of Articullichirus , quite different from those of Corallianassa and Glypturus . The chelipeds of Calliapagurops are generally similar to those of Articullichirus ; the coxae carry a pair of mesial hooks as in A. collaroy and A. chiltoni , but these are absent in A. articulatus . The uropodal endopod of Calliapagurops bears two proximal teeth on the dorsal surface similar to those seen in most species of Articullichirus , but not seen in the other two genera. The maxilliped of Calliapagurops is operculate as in Articullichirus , more so than in the other two genera. Its merus bears four distal teeth, whereas some individuals of A. articulatus and all those of A. collaroy have a single tooth or tubercle; A. chiltoni has a tubercle.