Heloeciidae, H. Milne Edwards, 1852

GUINOT, DANIÈLE, TAVARES, MARCOS & CASTRO, PETER, 2013, Significance of the sexual openings and supplementary structures on the phylogeny of brachyuran crabs (Crustacea, Decapoda, Brachyura), with new nomina for higher-ranked podotreme taxa, Zootaxa 3665 (1), pp. 1-414 : 119-120

Families Heloeciidae and Ucididae

The male gonopore is sternal in Heloecius Dana, 1851 ( Heloeciidae H. Milne Edwards, 1852 ), as in Ucides Rathbun, 1897 (Ucididae) . In Heloecius ( Fig. 26 ) the gonopore opens rather close to the P5 coxa so that it could be erroneously interpreted as coxal. In Ucides ( Fig. 23C ; Guinot 1979a: 214, fig. 54E; Mota Alves 1975: fig. 1) the gonopore is relatively far from the coxa but so close to suture 7/8 that it could be interpreted as a coxo-sternal condition. Indeed, Türkay (1983b: 107, 110, figs. 2, 3) misinterpreted the male gonopore as coxo-sternal in both genera. Dissections of H. cordiformis ( Fig. 26 ) and U. cordatus revealed that the ejaculatory duct connects directly with the testis without passing via the P5 coxa, opening on sternite 8 close to suture 7/ 8 in such a way that the duct is directly in contact with the G1. Heloecius and Ucides are therefore true thoracotremes. Evidently, a coxo-sternal condition cannot exist in Thoracotremata, which exclusively shows a sternal condition, without any perforation of the P5 coxa. The coxo-sternal condition is actually coxal, since the P5 coxa is perforated by the ejaculatory duct, a condition found only in Heterotremata.

The arrangement of the penial region of Heloecius ( Fig. 26A ) is somewhat similar to that of Cardisoma ( Fig. 23A ) and Discoplax . Sternite 7 is expanded posteriorly in both genera; the small sternite 8 is covered by the abdomen, its external portion being only concealed by setae (thin in Heloecius , stiff in Cardisoma ) of the abdominal margins; the gonopore is quite close to the P5 coxa, immediately anterior to its condyle, and just at the origin of suture 7/8; there is a narrow membranous proximal penial portion (wedged between the P5 coxo-sternal condyle and sternite 7), concealed under setae along abdominal margins; a large, sclerotised, setiferous penial sheath is followed by a developed papilla; sternites 7 and 8 are only separated by the penis.

Ucides differs from Heloecius in having sternites 7 and 8 joined so that the gonopore is displaced far from the P5 coxa, and sternite 8 is exposed posteriorly. The penis has a hard basal ring, followed by a naked sclerotised sheath and a contorted papilla. In Ucides the first abdominal somite is narrow, sternite 8 is rather largely exposed (more than in Epigrapsus , where it is extended laterally), and thus there is only a superficial resemblance between Epigrapsus and Ucides in this respect.

Based on a set of characters including a supposed coxo-sternal arrangement of the male gonopore, Türkay (1983b: 108, as Heloeciinae Türkay, 1983 ) erected the subfamily Heloeciinae for Heloecius (with the provisional inclusion of Ucides ) within Ocypodidae . The taxon “Helioeciacea” H. Milne Edwards, 1852, based on Heloecius , is an available nomen that should replace Türkay’s Heloeciinae . The distinction of Heloeciinae , containing both Heloecius and Ucides , was adopted by several authors, e.g., von Sternberg & Cumberlidge (2001b: 30, 39, figs. 1, 2). The erroneous presumption of coxo-sternal gonopores ( Türkay 1983b) was repeated by Števčić (2005: 130, 131) in the diagnoses of these two subfamilies, both included by Števčić (2005) in Ocypodidae and having Heloecius and Ucides as respective type genera of Heloeciinae and Ucidinae, the later being established as a new taxon. The affinities of Ucides , for a long time assigned to Gecarcinidae , subsequently transferred to Ocypodidae (e.g., Chace & Hobbs 1969; Türkay 1983b; Tavares 1990; Oliveira-Neto et al. 2007a, b), then to Ocypodoidea , remained unclear. Based on zoeal features, adult morphology, and DNA evidence, it was suggested that Heloeciinae was a monotypic taxon separate from Ucides and other Ocypodidae sensu lato ( Fielder & Greenwood 1985b; Clark et al. 2001). Ng, Guinot & Davie (2008: 236, 244) recognised a familial rank for Heloecius and Ucides and assigned both Heloeciidae and Ucididae to Ocypodoidea . Molecular analysis by Schubart & Cuesta (2010: 295, figs. 1, 2) have shown the close relationship of Ucides and Ocypode , leading these authors to include Ucides in Ocypodidae and consider Ucididae a junior synonym of Ocypodidae . The Heloeciidae presently comprises only Heloecius , with H. cordiformis , the “semaphore burrowing crab”, as the only species ( Warren & Underwood 1986; Maitland 1990).

The thoracic sternum of Ocypode ( Guinot 1979a: pl. 18, figs. 7, 8; Guinot & Bouchard 1998: fig. 24B) is distinguished from that of Heloecius and Ucides by the wide and laterally exposed sternite 8, in contrast to the narrow sternite 8 that is almost completely concealed by the male abdomen in Ucides and Heloecius . Ocypode , Heloecius , and Ucides show a similar thoracic sternal pattern 5, subpattern 5c ( Fig. 56I ) with interrupted sutures 4/ 5 – 7/8 and a median line extending along sternites 5 – 8. The median line and median plate are, nonetheless, different in these genera. In Ocypode ( Fig. 57A ) the median line is continuous along sternites 5–8 and, accordingly, there is a continuous, high median plate (the two laminae may be separated). In contrast, Ucides ( Fig. 57B ) has a discontinuous median line, with an externally visible interruption at the suture 6/7 level (showing as a narrow transverse bridge connecting the two posterior halves of sternite 7) as well as a discontinuous median plate forming a single plate along sternites 5, 6, and a separate plate on sternite 7, where it connects to a thick sella turcica. In Heloecius the median line shows a slight interruption at suture 6/7 level that corresponds to a change of the median plate, low along sternite 5, then vertically oriented and becoming progressively higher at sternites 6–8 level (see Evolution of the thoracic sternum in the Eubrachyura and its patterns).

There is no socket and no press-button for locking mechanism in Heloeciidae and Ucididae , both of which have a deep, well-developed sterno-abdominal cavity and a wide, long male abdomen, without a rigorous correspondence between abdominal somite 6 and thoracic sternite 5.

Figures

FIGURE 23. Sternal male gonopores in Thoracotremata. A, Cardisoma carnifex (Herbst, 1796) (Gecarcinidae), male, Madagascar (MNHN-B29589); B, Plagusia depressa (Fabricius, 1775) (Plagusiidae), male 40.0 × 44.0 mm, Senegal (MNHN- B11693): schematic view (see Fig. 33A) (abdomen indicated by dotted line); C, Ucides cordatus (Linnaeus, 1763) (Ucididae), male 70.0 × 93.0 mm, Brazil (MNHN-B13237) (abdomen indicated by dotted line); D, Grapsus grapsus (Linnaeus, 1758) (Grapsidae), male 57.0 × 60.0 mm, Clipperton I. (MNHN-B11538): schematic representation after dissection; E, F, Ocypode cursor (Linnaeus, 1758) (Ocypodidae), male 38.0 × 49.0 m, Senegal (MNHN): E, before dissection along dotted line; F, after dissection showing ejaculatory duct perforating somite 8, instead of P5 coxa. c, P5 coxo-sternal condyle; cx5, P5 coxa; e.d., ejaculatory duct; e7, episternite 7; g, gonopore; p, penis; p5, pereopod 5; 7, 8, sternites 7, 8; 7/8, thoracic sternal suture 7/8.

FIGURE 26. Thoracotreme condition in Heloecius cordiformis (H. Milne Edwards, 1837) (Heloeciidae). A, male 15.0 × 23.0 mm, Australia, New South Wales (MNHN-B21489): male gonopore sternal, with penis emerging close to P5 coxa; B, dissected male (same data, approximately same size): P5 (left) with penis protruding from sternite 8. c, P5 coxo-sternal condyle; cx5, P5 coxa; c.p., slightly sclerotised proximal portion of penis; pa, papilla; 8, sternite 8.

FIGURE 56. Diagrammatic representation of patterns of thoracic sternal sutures 4/5–7/8 and modalities of median line (median plate not taken into account) in Eubrachyura. A, pattern 1: sutures 4/5–7/8 complete (uninterrupted), median line along sternites 5–8, may extend on sternite 4; B, pattern 2: only suture 4/5 interrupted, median line along sternites 6–8; C, pattern 3: sutures 4/5, 5/6 interrupted, median line along sternites 7, 8; D, pattern 4: sutures 4/5–6/7 interrupted, median line on sternite 8; E, generalised pattern 5: sutures 4/5–7/8 incomplete, median line variable among subpatterns a-f; F, pattern 6: sutures 4/5–7/8 interrupted, suture 6/7 complete, median line along sternites 7, 8; G, subpattern 5a: sutures 4/5–7/8 interrupted, median line absent; H, subpattern 5b: sutures 4/5–7/8 interrupted, median line along sternites 3–8; I, subpattern 5c: sutures 4/5–7/8 interrupted, median line along sternites 5–8, sometimes partially on sternite 4; J, subpattern 5d: sutures 4/5–7/8 interrupted, median line along sternites 5–7; K, subpattern 5e: sutures 4/5–7/8 interrupted, median line along sternites 7, 8; L, subpattern 5f: sutures 4/5–7/8 interrupted, median line on sternite 4. Each thoracic sternum with same width; all sutures represented parallel, equidistant, and similar. Some additional patterns are not figured.

FIGURE 57. Axial skeletons. A, Ocypode sp. (Ocypodidae), male (MNHN): median plate continuous; B, Ucides cordatus (Linnaeus, 1763) (Ucididae), female (MNHN): discontinuous median plate along sternites 5–7. e, epimere; m, median plate; p, pleurites; s, sella turcica. Skeletons prepared by S. Secretan.