Palicoidea, Bouvier, 1898

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 : 130-132

Superfamily Palicoidea (families Palicidae and Crossotonotidae )

Although the penis seems to emerge as a long, soft papilla from the thoracic sternum, the male gonopore is coxal, specifically coxo-sternal, as shown by our dissections ( Fig. 44B ). In Palicidae the P5 is conspicuously reduced (short and slender), dorsal, distinctly mobile, with the coxa immediately above an “episternal process” ( Castro 2000: 445, figs. 1, 16a, 17a, 18a, 20a, 22a, 23a, 24a) and reentrant, that is, not aligned with the preceding coxae, inward placed, located at mid-course in relation to near the central axis of the body, thus close to one another ( Fig. 32A ). The P5 coxa, smaller than the P2–P4 coxae, is, however, elongated; its distal margin bears a deep, wide notch to accommodate the much narrower articles of the P5 ( Fig. 32A, B ; Castro 2000: figs. 18a, 20a, 24a, 60, 61a– e). The basis is separated from the elongated ischium ( Fig. 44A ). In Crossotonotidae the P5 is smaller but roughly similar in shape and orientation to the preceding pereopods; it is slightly dorsal and not especially mobile ( Castro 2000: figs. 46, 61f). The crossotonotid P5 coxa is smaller than the P2–P4 coxae but not elongated, and its notch (visible ventrally) accommodates a short basis and a wide, not elongated ischium ( Figs. 32C, D , 44B ).

In both Palicidae and Crossotonotidae the ejaculatory duct perforates the P5 coxa, and the penis emerges at the extreme end of the slightly elongated coxo-sternal condyle (see Modalities of penis protection: Condylar protection). The gonopore is not visible dorsally. The penis is long, relatively thick, rigid, and straight. Its proximal portion is concealed by the thoracic sternum; it then protrudes on the slope of the sterno-abdominal cavity. This free portion, only covered by the abdomen, shows as a thick tube from which the often elongated or inflated papilla emerges. The emerging penis is located vertically/obliquely along the margin of the sterno-abdominal cavity and may be oriented at a conspicuous angle, as in Palicus zonatus ( Fig. 32E ). The soft papilla finally enters the lateral foramen of the G1 endopodite. This disposition of a penial tube running nearly vertically along the sternoabdominal cavity resembles that found in Dorippidae (e.g., Paradorippe granulata , Fig. 17C ). Conversely, in Crossotonotidae , the penis is straight on its entire length ( Fig. 44B ). The P5 is used for carrying behaviour in palicids ( Fig. 54 ) (as well as the P4 and P 5 in Dorippoidea ) but not in crossotonotids, in which there is a different configuration (see Carrying behaviour; Palicidae ).

In both male palicids and crossotonotids, sternite 8 is subdivided into two portions by a transversal “suture”, and shows as a double plate in dorsal view. Actually sternite 8 is transversally marked by a deep invagination resulting in a completely closed channel ( Fig. 32A–C ), named gaine pénienne (“penial sheath”) by Guinot (1979a: fig. 30G). The long penis is fully concealed within the sheath, except for its distal portion. The transversal “suture” is just the limit of the anterior and posterior portions of sternite 8, that is to say an invagination line and not a suture (specifically, not suture 7/8). Sternite 8 shows as a single plate in females ( Fig. 32D ). In male and female Palicidae , episternite 7 extends posteriorly, overhanging the P5 coxa and encircling completely sternite 8 ( Fig. 32A, B ). In male and female Crossotonotidae , conversely, episternite 7 extends posteriorly only to the level of the penis and the posterior portion of sternite 8 is not encircled by episternite 7 ( Fig. 32C, D ).

A marked modification of somite 8 involving all its components is observed in the Palicoidea : pleural, sternal, and appendicular. The same modifications are found in both Palicidae (P5 reduced and dorsal) and Crossotonotidae (P5 only slightly dorsal and reduced). The strong reduction of sternite 8 in both sexes of both families thus seems to be independent of the size and position of the P5. An additional modification, the invagination of sternite 8, is found in males of Palicidae and Crossotonotidae . Sternite 8 shows as two narrow, subequal portions in male Palicidae ( Fig. 32A, B, E ), instead of two wider, unequal portions in male Crossotonotidae ( Fig. 32C ), and as an undivided plate in female Palicidae and Crossotonotidae ( Fig. 32D ). The longer and angled penis of Palicidae , in contrast to that of Crossotonotidae , may be interpreted as linked to the dorsal insertion of the P5 as part of the modification of the last thoracic somite. The long palicoid G1 protopodite is related to the dorsal position of the first abdominal somite.

A thoracic sternum/pterygostome junction anterior to the chelipeds does not exist in the Palicoidea , the sternite 3 being incompletely extended, so the Milne Edwards openings are contiguous to the chelipeds. There is, however, a wide junction of the sternum with the branchiostegite posterior to the chelipeds, the episternite 4 being markedly extended laterally, and there is no junction posterior to the P2 and the following pereopods ( Fig. 32A; A . Milne-Edwards & Bouvier 1902: pl. 7, fig. 3; Guinot 1979a: fig. 30G; Castro 2000: fig. 2A). Both the Palicidae and Crossotonotidae have a well-marked pterygostomial lobe and a long abdomen that reaches sternite 3 ( Castro 2000: fig. 2A, C).

The palicoid axial skeleton is peculiar. The phragmae consist medially in low, attenuated parallel endosternites, with the remaining portion laterally confined, thus leaving a large, empty central space, only occupied by a raised and long longitudinal septum, the median plate. The median line, which only extends on the sternal surface along sternites 5–7, is narrow and difficult to be discerned dorsally, although corresponding to a high median plate that also extends along sternites 5–7 before connecting to the sella turcica ( Figs. 32A, E , 45A ). The median line and median plate patterns of Palicoidea , similar in Palicidae and Crossotonotidae , is peculiar, perhaps unique. The palicoid sternal pattern represents pattern 5, subpattern 5d ( Fig. 56J ); the sella turcica is very narrow (see Carcinisation and its outcomes: Evolution of the thoracic sternum in the Eubrachyura and its pattern; Evolution of the axial skeleton in the Eubrachyura).

The interlocking mechanism between the carapace and the cephalothorax in Palicoidea involves the thoracic pleurites at the P2–P5 levels, which laterally form a crest, with the carapace lying in the groove against the sloping side of this crest. The wide first abdominal somite is transversally excavated to receive the carapace. The relationships between the carapace, thoracic pleurite 8, sternite 8, and the first abdominal somite are complex in Palicoidea and deserve a more thorough investigation. In female Palicoidea the thoracic sternum and the abdomen are coadapted to form a brood cavity in the form of a closed box, with pleurite 8 and the first abdominal somites being involved in water draining for egg ventilation. Another unique adaptation of Palicoidea is the anterior displacement of the vulvae to the fused median portion of the thoracic sternum, although they remain still dependent on sternite 6 ( Hartnoll 1968a: fig. 14C; Guinot 1979a: fig. 31, pl. 24, fig. 10; Guinot & Richer de Forges 1997: fig. 2D, F; Castro 2000: 44; Guinot & Quenette 2005: 334; Naruse, Ng & Guinot 2008: figs. 1a, 6a, 9a, table 1; see Female sternal gonopores, or vulvae).

The coxo-sternal condition of Palicoidea had already been observed by Bouvier (1942: 40) and Balss (1944: 604), described by Guinot (1978a, 1979a), Guinot & Bouchard (1998), and pointed out by Castro (2000: 444): “sperm ducts under sternal plates, penis soft, curved, free on inner side of coxae”. Moosa & Serène (1981: 23), nevertheless, stated that “ Palicidae is typical sternotremen Brachyura : the male opening is completely sternal, the male conducts are running under the sternal plates, the penis are [sic] free far away from the coxae”. Thus, several authors assigned palicids to Catometopa, i.e., crabs with sternal male gonopores (e.g., Calman 1900: 29 under Palicus ; Alcock 1900b: 285, 450, as Palicidae ; Borradaile 1907: 482, as Palicidae ; Rathbun 1918: 15, 182, as Cymopoliidae ; Bouvier 1940: 303; 1942: 41, 46; Balss 1957: 1633, 1661, as Cymopoliidae ) or to Thoracotremata (e.g., Schram 1986: 308; Martin & Davis 2001: 56, 75; Felder et al. 2009: 1087). Palicids also appeared in the literature grouped next to the thoracotremes (e.g., Monod 1956: 387; Serène 1965: 29, 1968: 96; Sakai 1976: 592; Manning & Holthuis 1981: 191). Alternatively, the Palicidae was included in a new taxon, the Neobrachyura Brösing, Richter & Scholtz, 2007, which was based mostly on foregut characters and that included the entire Thoracotremata plus some heterotreme families, the latter being considered basal ( Brösing et al. 2007: 27, figs. 1, 2; Brösing 2008: 279, 281, fig. 2). Brösing (2008: 281) regarded the palicid male gonopores described by Castro (2000) as “clearly sternal”, which is a misinterpretation, and suggested “sister group relationship of the Palicidae to the Thoracotremata”, with the foregut characters recovering the Palicidae as a basal thoracotreme.

A heterotreme status is assumed here for the Palicoidea , which is recognised as a basal, deeply rooted eubrachyuran lineage, exhibiting a carrying behaviour in Palicidae ( Fig. 54 ). Insights on its affinities are proposed below (see Affinities between Palicoidea , Retroplumoidea , and Hexapodoidea ; Concealment behaviour: Carrying behaviour: Family Palicidae ).

Fossil Palicidae . Several fossil Palicidae are known: † Eopalicus Beschin, Busulini, De Angeli & Tessier, 1996 , with three species (Eocene and Oligocene). Miocene species were attributed to the extant genus Palicus by Van Straelen (1938) and Müller (1984a) (see Beschin & De Angeli 2003). We agree that the transverse ridges in † E. squamosus Beschin, Busulini, De Angeli & Tessier, 1996 ( Beschin et al. 1996: pl. 1), with a typically palicid- like carapace, are reminiscent of the “terraces” found in some raninids and indicate a similar adaptation for burying. According to Beschin & De Angeli (2003: 7–12, figs. 2–4), the Eocene (Lower Lutetian) fossil palicine † Spinipalicus italicus Beschin & De Angeli, 2003 , with a broad carapace and inflated, tuberculated dorsal regions, shows some similarities with retroplumids, in particular with † Archaeopus Rathbun, 1908 , a genus that had been suggested as not belonging in Retroplumidae ( Glaessner 1969; Saint Laurent 1989; McLay 2006a). See Fossil Retroplumidae . The thoracic sternum, abdomen, and the fragile, reduced P5 are unfortunately unknown in fossil Palicidae .

Figures

FIGURE 17. Coxo-sternal condition in Dorippidae. A, B, Dorippe tenuipes Chen, 1980. A, male 21.0 × 25.0 mm, South China Sea (MNHN-B8937). B, male 19.0 × 20.0 mm, holotype of Dorippe miersi Serène, 1982, Vietnam (MNHN-B7279): A, genital region covered by abdomen; B, genital region uncovered by abdomen, penis covered by sternite 8. C, Paradorippe granulata (De Haan, 1841), male 11.0 × 11.0 mm, Japan (MNHN-B11181): genital region. D, Philippidorippe philippinensis Chen, 1985, male 25.0 × 30.0 mm, Philippines (MNHN-B18913): genital region covered by abdomen. a1–a3, abdominal somites 1–3; b, sclerotised bulb; c, coxo-sternal condyle; ca, carapace; cx4, cx5, P4, P5 coxae; e7, episternite 7; pa, papilla; td, distal portion of penial tube; tp, inclined proximal portion of penial tube; 6–8, thoracic sternites 6–8; 6/7, 7/8, sternal sutures 6/7, 7/8. Scale bars: 5 mm (A, D); 3 mm (B, C).

FIGURE 32. Coxo-sternal condition in Palicidae (A, B, E), Crossotonotidae (C, D), schematic representation. A, B, Palicus caronii (Roux, 1830), male 9.0 × 11.0 mm, Canary Is. (MNHN-B16335). A, thoracic sternum and abdomen in situ; B, detail of A. C, D, Crossotonotus spinipes (de Man, 1888), New Caledonia (MNHN-B26811): detail of sternites 7 and 8. C, male 36.0 × 44.0 mm; D, female 29.0 × 32.0 mm. E, Palicus zonatus (Rathbun, 1893), male 10.0 × 13.0 mm, Gulf of California (MNHN- B26745): ventral view, abdomen removed; invaginated sternite 8 has been partially cut to expose underlying penis (left). a1, abdominal somite 1; b, press-button; cx4, cx5, P4, P5 coxae; e3–e7, episternites 3–7; l, invagination line of sternite 8; m.l., median line; p, penis (schematically represented too thin, straight in A and B, correctly represented thick and at an angle in Fig. E); p5, pereopod 5; 6, 7, thoracic sternites 6, 7; 8, thoracic sternite 8 in the form of double plate. Scale bar: 3 mm (E).

FIGURE 44. P5 ischium, long in Palicidae (A) and Retroplumidae (C), short in Crossotonotidae (B). A, Palicoides longimanus (Miyake, 1936), female 14.7 × 17.0 mm, New Caledonia (MNHN-B26791); B, Crossotonotus spinipes (de Man, 1888), male 36.9 × 43.3 mm, New Caledonia (MNHN-B26803): penis emerging from P5 coxo-sternal condyle and pulled out from sternite 8 invagination; basis-ischium concealed under coxa. C, Retropluma quadrata Saint Laurent, 1989, with attached ciliates (after Saint Laurent 1989: fig. 9; unknown size). b, basis; c, coxo-sternal condyle; cx5, P5 coxa; i, ischium; p, penis; pa, papilla. Scale bars: 3 mm (A); 1 cm (B).

FIGURE 45. Skeletons with parallel endosternites and narrow sella turcica. A, Pseudopalicus declivis Castro, 2000 (Palicidae), male, New Caledonia (MNHN-B30492): medially attenuated endosternites, remaining lateral portions covered by pleurites; marked median plate; B, Bathypluma spinifer Saint Laurent, 1980 (Retroplumidae), male, Philippines (MNHN-B37017): cx5, P5 coxa; m, median plate; p, pleurite; P5, pereopod 5; s, sella turcica; s.c., convexity of sterno-abdominal cavity; t, endosternite.

FIGURE 54. Carrying behaviour among palicid crabs. A, Exopalicus maculatus (Edmondson, 1930) carrying a foraminiferan shell (Marginopora sp.): both P5 visible, with dactyli holding camouflaging shell. B, C, Palicoides whitei (Miers, 1884): B, carrying fragment of coral rubble: dactyli of both P5 only slightly visible; C, carrying small pebble: clearly visible right P5. A, B in situ, C in aquarium, Okinawa, Japan. Photographs by Y. Fujita.

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.