Halicarcinus White 1846

Halicarcinus White, 1846 sensu stricto

Hymenosoma (Halicarcinus) White, 1846: 178.

Halicarcinus— White 1847: 33. — Dana 1851: 379. — Lucas 1980: 176 –178 (for synonymy).

Liriopea Nicolet, 1849 (type species, Hymenosoma leachii Guérin, 1832, in Guérin-Méneville 1829 – 1837, by subsequent designation).

Hymenicus Dana, 1851 (type species, Hymenicus varius Dana, 1851, by subsequent designation).

Hombronia Lucas, 1853 (type species, Hymenosoma tridentata Jacquinot & Jacquinot, 1846, by monotypy). See Holthuis (2002) for authorship of species.

Type species. Cancer planatus Fabricius, 1775, by original designation.

Diagnosis. Rostrum a median tubercle similar in males, females, 0.05–0.2 times carapace length; apex without long setae. Supraocular eave obsolete, defined anteromedially by conical or ridge-like tubercle (pseudorostral element); postocular margin an obsolete, rounded vertical ridge without spine. Subhepatic region with obsolete ridges. Carapace about as long as wide; with moderately to well-developed gastro-cardiac, thoracic grooves; with short longitudinal cardiac groove; hymenosomian groove completely surrounding dorsum, isolating rostrum. Thoracic sternum of male with pleonal cavity defined laterally, anteriorly by sharp rim, about 0.8 of sternal length; with locking button on sternite 6. Male pleomeres 1–5 free, pleotelson free; pleomere 1 wider than pleomere 2, laterally swollen; pleonal margin tapering most strongly at pleomere 3. Thoracic sternum of female with paired vulvae anteriorly on membranous medial area; with paired branchiosternal canal apertures on posterior ventral face of sternite 8. Pleon of ovigerous female discoid, pleomeres 1–5, pleotelson free. Antennule with basal article evenly tapering; antennules separated by broad flat septum (proepistome). Epistome flat, almost vertical or obliquely sloping posteriorly, anterior margin ridge-like under eyes, antennae, posterior margin with 2 submedial lobes separated by median notch. Eyestalks compact, without tubercle on anterior margin. Maxilliped 3 endopod, exposed exopod covering most of lateral width of buccal cavern when closed; ischium mesially expanded; axial length of ischium-merus 1.5–1.8 maximum ischium width; merus with moderately expanded anterolateral lobe. Cheliped in male with grossly swollen barrel-like propodus, fingers with finely denticulate cutting edges, gape without felt of setae (except in H. varius); dactylus with square proximal tooth. Ambulatory legs moderate to long (pereopod 2 2–3 times as long as carapace length); merus usually without distal tubercle on upper margin; with articulation between propodus, dactylus supported by short narrow plate on each side; dactyli evenly curved with 1 or 2 rows of short blunt teeth along most of flexor margin, most distal 2 sometimes longer than others. Gonopod 1 with swollen base tapering to finer distal part strongly, evenly curving dorsally through>120°, with acute apex directed ventrally, sitting in pocket on lateral ventral face of pleotelson when pleon closed. Gonopod 2 with triangular base, mesiodistal lobe about one-third length of base. Female pleopods 2–5 biramous.

Included species. Halicarcinus cookii (Filhol, 1885) (ex Hymenicus); H. ovatus Stimpson, 1858; H. planatus (Fabricius, 1775) (ex Cancer); H. quoyi (H. Milne Edwards, 1853); H. tongi Melrose, 1975; H. varius (Dana, 1851) (ex Hymenicus); H. whitei (Miers, 1876) (ex Elamena).

Distribution. Subantarctic islands, southern New Zealand (Melrose 1975), southern South America (Tavares & Santana 2015, Aronson et al. 2015), southern Australia (Poore 2004).

Remarks. The critical characters diagnosing Halicarcinus are the rostrum being slightly longer but often shorter than the lateral preocular (pseudorostral) pair, the three combined on a triangular base, the strongly curved gonopod 1, and free pleomeres, the pleon in the female being discoid and not swollen. Pereopodal dactylar teeth are much shorter in species of Halicarcinus than in other genera; they align in two alternating parallel rows in H. cookii, H. ovatus and H. planatus. In H. quoyi the last two teeth are longer than the rest. The epistome of H. planatus and H. quoyi is more vertical (see Melrose 1975: figs 9G, 9H,12D–F) than that of H. cooki, H. ovatus and H. varius (Melrose 1975: figs 10D, 10E, 14D, 17C, 17D, 26C). Melrose (1975) described and illustrated all species in detail; her key to species remains useful although two of its species are now included in other genera.

The type species of Liriopea (Hymenosoma leachii Guérin, 1832, in Guérin-Méneville 1829 – 1837) and type species of Hombronia (Hymenosoma tridentata Jacquinot & Jacquinot, 1846) are both subjective junior synonyms of the type species of Halicarcinus. Having the same type species, three genera are therefore subjective synonyms. The type species of Hymenicus, Hymenicus varius Dana, 1851, is also a member of Halicarcinus s.s. so this genus too is a junior subjective synonym. Some species remaining in Halicarcinus present nomenclatural and taxonomic challenges. Each is discussed in context below.

Species of Halicarcinus are distributed in southern South America, subantarctic islands, New Zealand and southern Australia.