Orithopsidae Schweitzer, Feldmann, Fam, Hessin, Hetrick, Nyborg & Ross, 2003

Van Bakel, Barry W. M., Guinot, Danièle, Artal, Pedro, Fraaije, René H. B. & Jagt, John W. M., 2012, A revision of the Palaeocorystoidea and the phylogeny of raninoidian crabs (Crustacea, Decapoda, Brachyura, Podotremata) 3215, Zootaxa 3215 (1), pp. 1-216 : 63-68

Family Orithopsidae Schweitzer, Feldmann, Fam, Hessin, Hetrick, Nyborg & Ross, 2003 emend.

Orithopsidae Schweitzer, Feldmann, Fam, Hessin, Hetrick, Nyborg & Ross, 2003a: 39 .

Type genus. Orithopsis Carter, 1872 (type species: O. bonneyi Carter, 1872 , by monotypy [ Glaessner 1969: R492, R627]. Since Necrocarcinus tricarinatus Bell, 1863 , is a senior synonym of O. bonneyi , the correct combination for the type species is Orithopsis tricarinata ( Bell, 1863) .

Genera included. Cherpiocarcinus Marangon & De Angeli, 1997 , Marycarcinus Schweitzer, Feldmann, Fam, Hessin, Hetrick, Nyborg & Ross, 2003 , Orithopsis Carter, 1872 , Paradoxicarcinus Schweitzer, Feldmann, Fam, Hessin, Hetrick, Nyborg & Ross, 2003 , and Silvacarcinus Collins & Smith, 1993 .

Diagnosis. Carapace subhexagonal in outline, widest about or just anterior of mid-length; surface weakly arched in all directions. Anterolateral margin relatively long, gently rounded ( Cherpiocarcinus , Paradoxicarcinus ) or moderately convex ( Orithopsis , Silvacarcinus ); with 3 or 4 teeth, long, triangular ( Cherpiocarcinus , Silvacarcinus ) or spiniform ( Orithopsis , Paradoxicarcinus ); epibranchial tooth strong ( P. nimonoides ). Posterolateral margins straight, blunt in cross section, without teeth or tubercles. Posterior margin wide, concave. Rostrum triangular; short, not extended beyond outer orbital teeth ( Cherpiocarcinus , Paradoxicarcinus , Silvacarcinus ), or long, well extended beyond outer orbital teeth ( Orithopsis ), tip as single apex, may have 1 or 2 subdistal teeth ( Orithopsis ); post-rostral slits absent. Orbitofrontal margin distinctly wide, orbital margin barely elevated, weakly concave ( Cherpiocarcinus , Paradoxicarcinus ) to concave ( Orithopsis , Silvacarcinus ). Orbits large, horizontally arranged with large plain outer orbital sockets; supraorbital margin with long flattened spines, wide open fissures. Cervical groove acute, sinuous with sharp deflections, medially interrupted by distinct gastric pits. Branchiocardiac grooves deep, diverging. Carapace surface with granular ridges (carinae); branchial ridges concave, with transverse ridge over cardiac region, or H-shaped ( C. rostratus , O. tricarinata , O. angelica , Paradoxicarcinus , S. laurae ). Antennar fossae closer to each other than antennular fossae, both situated posterior of orbits. Dorsal carapace surface with upright nodes.

Pterygostome grooved, with low blunt crest. Branchiostegite not areolated ( S. laurae ), joining coxae of pereiopods, no exposure of pleurites. Mxp3 unknown, only coxae partially preserved ( S. laurae ); wide, flabelliform, not close to each other.

Upper, lower margin of palm with anteriorly directed spiniform teeth ( C. rostratus ). P2, P3 articles oval in cross section ( O. tricarinata ). P5 reduced in size, (sub)dorsal.

Thoracic sternum rather long, deep sterno-abdominal cavity over complete length ( S. laurae ). Sternites 1, 2 well separated, at lower level than sternite 3 ( S. laurae ). Sternite 3 as small plate, separated by distinct groove from sternite 4, anterior side of sternite 4 as broad as sternite 3 ( O. tricarinata , S laurae ). Sternite 4 medially excavated ( O. tricarinata , S. laurae ); sternites 4‒6 equal in width; sternites 7, 8 distinctly narrower ( S. laurae ). Sternite 7 with axial part as a narrow, vertical lobe, anteriorly demarcated by a central dome ( S. laurae ), forming rather complex axial construction in same level as remainder sternites. Sternite 8 strongly tilted, perpendicular to preceding sternites, strongly reduced; medially opened forming sunken pit. Sutures 4/5–6/7 relatively long, lateral, declining in angle posteriorly; 4/5 crescent shaped: lateral part long, medial part vertical, deep ( O. tricarinata , S. laurae ); suture 5/6 with shorter lateral part, less abruptly flexed; suture 6/7 arched, anterior half deep ( S. laurae ); suture 7/8 vertical, forming long medial line ( S. laurae ). Spermathecal apertures unknown. Arthrodial cavities evenly spaced, ventro-laterally directed.

Male abdomen unknown; female abdomen completely filling laterally sterno-abdominal depression, with all abdominal somites free, first somites dorsal, somite 6 long; somites trituberculate, tubercles strong, transversely broadened, telson reaching sternite 4 ( O. tricarinata ).

Abdominal holding system present at episternite 5, assumed to have been double (see remarks for S. laurae ). Coxal structures not present, at least not on P1, P2.

Remarks. The Orithopsidae is a rather small group (10 species so far described), but with a long stratigraphic range (upper Aptian to middle Oligocene, 115–29 Ma). Cherpiocarcinus rostratus , from the middle Oligocene of northern Italy ( Fig. 20F ), is the youngest known member of the family and of the superfamily Palaeocorystoidea . The observation by Schweitzer et al. (2009a: 4) that the Orithopsidae ‘were at their peak’ during the Eocene was based on the assumption that Goniochele belonged to this family (see below).

Members of Orithopsidae have traditionally been included in Calappidae De Haan, 1833 ( Förster 1968; Wright & Collins 1972; Schweitzer & Feldmann 2000; Fraaije 2002). When the family Orithopsidae was erected, it was placed, together with Necrocarcinidae , in Dorippoidea MacLeay, 1838. This taxonomic assignment was adopted by De Grave et al. (2009: 31) and Schweitzer et al. (2010: 80, 82). The carapace has multiple anterolateral spines, narrow anterior sternites, and only the P5 is reduced; features which exclude Orithopsis , and hence Orithopsidae , from Dorippoidea.

The morphology of ventral parts in the type series of S. laurae and in a well-preserved specimen of O. tricarinata have been studied. The abdomen filling the sterno-abdominal cavity over the entire width clearly indicates that orithopsids are podotreme crabs. The tumid, bluntly crested pterygostome, the shape of sternites 3 and 4, a longer abdominal somite 6 and the absence of dorsal uropods, all match Palaeocorystoidea . The abdomen of Orithopsis , tricarinate and tuberculate, closely resembles that of cenomanocarcinids. Differences with Cenomanocarcinidae are: sternites 1 and 2 are much shorter, sternite 3 is diamond shaped, rather than crown shaped, and sternite 4 has a deep medial gutter; the size of the orbits (much larger in Orithopsidae ) and shape of branchial crests (concave in Orithopsidae , convex in Cenomanocarcinidae ).

The Orithopsidae carapace is easily recognized: moderate to large size, dorsal surface only weakly vaulted, tricarinate with concave branchial carinae; anterolateral margins rather short, spinose; orbits conspicuously large, orbitofrontal margin with strong spines. Such characters may be used to revise the taxonomic placement of genera or species (see below under O. siouxensis ). Ventral characters of Orithopsidae have so far been rarely found exposed and have not been well illustrated. The discovery of a specimen of O. tricarinata preserving ventral details confirms the similarity to S. laurae and their placement in Palaeocorystoidea . Both species show a normal-sized, a subdorsal P4 and a reduced, dorsally placed P5. The abdomen is trituberculate in Orithopsidae , with strong, thornlike tubercles ( Fig. 22D, E ); this character is shared by Cenomanocarcinidae and Orithopsidae . Abdominal somite 6 is longer than preceding somites and shows a strong central spine, the anterior corners are bulbous, corresponding to sockets ventrally. The sternal abdominal holding structure is known only in a single specimen of S. laurae ( Fig. 21F ) in which the structure is worn; its location is similar to that in Camarocarcinidae and Cenomanocarcinidae . Better preserved material is needed to examine the abdominal holding structures in detail and verify whether or not it consists of a double structure. Sternite 4 shows a deep axial gutter in Orithopsis , which is present, though less distinct, in Silvacarcinus .

Through similarities of their orbital construction, carapace outline, nature of anterolateral teeth and anterior carapace areolation, Orithopsidae is considered here to be most closely related to Palaeocorystidae .

Schweitzer et al. (2003a: 39) included Goniochele Bell, 1858 in the Orithopsidae . Larghi (2004: 530) stated that Goniochele was perhaps related to Cherpiocarcinus , which he placed in Necrocarcinidae . Schweitzer & Feldmann (2011: 5) erected Goniochelidae as a new dorippoid family to contain Goniochele .

Figures

FIGURE 20. A, E, Silvacarcinus laurae Collins & Smith, 1993 (Orithopsidae), IRScNB TCCI 6119 (paratype; indeterminate sex), lower Eocene (Ypresian), Brussels (Belgium); frontal view showing huge orbits, and dorsal view of carapace; B–D, G, Silvacarcinus laurae Collins & Smith, 1993, IRScNB TCCI6115 (holotype; indeterminate sex); dorsal view of carapace; frontal view; left lateral view, and detail of frontal region; F, Cherpiocarcinus rostratus Marangon & De Angeli, 1997 (Orithopsidae), middle Oligocene, northern Italy; reconstruction of carapace after type material (drawing by A. De Angeli). bs, branchiostegite; ia1, insertion of antennule; ia2, insertion of antenna; o, orbit; P1, P2, P3, pereiopods 1, 2, 3; ps, pterygostome. Scale bars: A- F: 5mm; G: 2mm.

FIGURE 21. Silvacarcinus laurae Collins & Smith, 1993 (Orithopsidae), lower Eocene (Ypresian), Brussels (Belgium). A, B, D, F, IRScNB TCCI 6115 (holotype; indeterminate sex); ventral view showing thoracic sternum; posterior view; detail of posterior view, and detail of thoracic sternum; C, IRScNB TCCI 6119 (paratype; indeterminate sex); ventral view showing thoracic sternum; E, MAB k. 2881 (ex Tak Collection; indeterminate sex), lower Eocene (Ypresian), Egem, northwestern Belgium; ventral view showing thoracic sternum. 2, 3, 4, 5, 6, 8, thoracic sternites 2, 3, 4, 5, 6, 7, 8; 4/5, 5/6, 6/7, 7/8, thoracic sternal sutures 4/5, 5/6, 6/7, 7/8; aP3, aP4, aP5, arthrodial cavities of P3, P4, P5; b, bulge; c, buccal collar of pterygostome; cmxp3, coxa of mxp3; cx1, P1 coxa; e4, e5, e6, e7, episternites 4, 5, 6, 7; in, intestinal canal; pt, pterygostome. Scale bars: 5mm.

FIGURE 22. A, B, D, E, Orithopsis tricarinata (Bell, 1863) (Orithopsidae), NHM In.30297 (female), Albian, Folkestone (southern England); ventral view; posterior view showing abdomen; detail of abdomen, anterior portion of thoracic sternum and bases of pereiopods, and detail of abdomen and pereiopods in posterior view; C, F, Orithopsis tricarinata (Bell, 1863), IRScNB unnumbered [Van Straelen Collection; indeterminate sex], upper Albian Cambridge Greensand, Cambridge (southern England); dorsal view of carapace, and ventral view showing anterior part of thoracic sternum; G, Orithopsis angelicus (Fraaije, 2002), MAB k. 2548 (holotype; indeterminate sex), upper Maastrichtian, Maastricht, the Netherlands; dorsal view of carapace (composite photograph). 1, 2, 3, 4, thoracic sternites 1, 2, 3, 4; 4/5, thoracic sternal suture 4/5; a2, a3, a4, a5, a6; abdominal somites 1, 2, 3, 4, 5, 6; cx1, cx2, cx3, cx4, cx5, P1-P5 coxae; e4, e5, episternites 4, 5; g1, gynglyme for P1 coxa. Scale bars: 5mm.