Lyreididae Guinot, 1993

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 : 75-77

Family Lyreididae Guinot, 1993 new status

Lyreidinae Guinot, 1993b: 1326 .

Included subfamilies. Lyreidinae Guinot, 1993b and Marylyreidinae n. subfam.

Diagnosis. Carapace longer than wide, variously elongated; generally pyriform or fusiform, narrowing anteriorly, corresponding to elongation of pre-oral carapace region (wider anteriorly in Marylyreidus n. gen., Rogueus ). Dorsal surface smooth, grooves indistinct except for short branchiocardiac grooves. Cuticle microstructure with diverse pits, upright nodes ( Lyreidinae ) or with fungiform nodes ( Marylyreidinae n. subfam.). Anterolateral margin lacking spines, or armed with 1, 2 small spines, or strong, outwardly directed spine that may be bifurcated. Front broadly triangular or subtrapezoidal. Orbitofrontal margin generally narrow, a third to half of maximum carapace width (broad in Marylyreidus n. gen., Rogueus ). Supraorbital margin generally unarmed, with single fissure or few teeth ( Macroacaena ). Orbits directed anteriorly; eyestalk composed of one article. Antennules, antennae about same size, general shape; long, slender; both modified in relation with respiratory physiology. Antennule not folded, basal article expanded, somewhat concave internally so that, when apposed, both antennules form conduit for respiration current. Proepistome concealed, epistome narrow. Endostome strongly elongated, forwardly produced between basal articles of antennules; strongly excavated. Mxp3 long, narrow, slender, operculiform; merus longer than ischium. Pterygostome tumid, subantennary lobe developed, produced far in front of mandibles, united over long distance with edges of endostome.

Thoracic sternum long, strongly deflected behind sternite 7; anterior sternites variously developed, produced; sternite 3 crown shaped; sternite 4 slightly expanded, flat; suture 4/5 crescent shaped; sternite 5 wide; sternite 6 narrower; sternites 5, 6 with ridge ( Marylyreidinae n. subfam.); sternite 7 narrowing posteriorly; sternite 8 elongated, perpendicular to preceding ones. Medial line along sternites 7, 8. Sternum/pterygostome junction moderately developed ( Lyreidinae ) or absent ( Marylyreidinae n. subfam.). Sternum/exposed pleurites connections well-developed between P1, P2 (sternite 5 to pleurite 5); less developed between P2, P3 (sternite 6 to pleurite 6) ( Lyreidinae ) or absent between P2, P3 ( Marylyreidinae n. subfam.). Pleurites 5‒7 partially exposed, calcified, forming flat area, not overhung by branchiostegite edge. Small spermathecal apertures facing each other on opposite sides of depression (‘sunken pit’) of sternite 7, separated by medial line.

Sterno-abdominal depression present posteriorly, entirely covered by male abdomen. Abdomen freely articulated (6 somites, plus small telson), conspicuously narrow; sexual dimorphism indistinct: female abdomen only marginally wider; somites 1‒3 dorsal, in prolongation with carapace, remainder completely folded; sharp flexure at level of somite 4; somites 3‒5 may bear long, recurved spine; somite 6 long, with long ventral sockets, medially limited by thickening for locking mechanism. Locking mechanism as pair of hook-like projections arising from episternite 5, projections short, stout ( Marylyreidinae n. subfam.) or elongated, distally recurved ( Lyreidinae ); projections distally with double peg, which firmly fit into the pair of deep sockets in the latero-posterior extended corners of abdominal somite 6; locking may be effective in ovigerous females, even with large egg masses, but vestigial in large females.

Chelipeds homochelous, homodontous, may be long; basis-ischium immoveably fused with long merus; propodus short, flattened, upper margin unarmed or with single spine, lower margin with few sharp spines; dactylus long, smooth on dorsal border, bent at right angle against anterior border of palm; fixed finger conspicuously inflated; prehensile borders of both fingers with alternate, low teeth. P2‒P4 arthrodial cavities lateroventral; those of P5 subdorsal. P2‒P4 slender; merus long, slender; propodus, dactylus flattened, compressed. P2 propodus short, broad, dactylus slightly spatulate. P3 propodus longer, dactylus elongated, styliform, externally ridged. P4 carpus, propodus, dactylus variously lobate. P4 coxa subdorsally located; P5 more dorsal, strongly reduced, filiform, ending in small, flattened, elliptical dactylus.

Respiratory mechanism highly specialised, both inhalant, exhalant respiratory current through modified frontal area; absence of Milne-Edwards openings (except possibly Marylyreidinae n. subfam.); presence of posterior branchial orifices and water conduits on the flanks of carapace.

Remarks. The subfamily Lyreidinae is here elevated to the family rank, as opposed to all other Raninoidea , which are referred to the family Raninidae ( Table 1). Larval characters confirm separation of Lyreididae from other Raninoidea ( Rice 1980, 1981), as do sperm characteristics ( Jamieson et al. 1994, 1995) and cuticle structure ( Waugh et al. 2009). Furthermore, Lyreididae is the only Raninoidea that lock its abdomen, as opposed to a shortened, unlocked, abdomen in Raninidae . The respiratory morphology of Lyreididae differs from that of all other Raninoidea . Two subfamilies are recognised within Lyreididae : the extinct (late Albian–early Cenomanian, c. 105– 98 Ma) Marylyreidinae n. subfam. showing several primitive characters, and Lyreidinae , which first appears during the early Turonian (c. 92 Ma).

Cuticle microstructure appears to be a reliable taxonomic tool in the study of raninid crabs. None of the Lyreididae examined here exhibit any inclined nodes, typical of Raninoidea (see Waugh et al. 2009: table 2; however, note that Raninella is now assigned to Ranininae ). The cuticle microstructure of lyreidines comprises various types of pits and small granules (i.e., upright nodes), whereas that of marylyreidines shows fungiform nodes. Both cuticle microstructural types are characteristically found in Palaeocorystoidea .

Lyreidus is probably a more exclusive back-burrower than other raninoids. It buries itself leaving the tip of its narrow, elongated anterior portion of the carapace just breaking the surface of the sand ( Bourne 1922b: 70). The long, recurved spines in the centre of abdominal somites 3–5 may be used to penetrate the sand and assure a fixed position to the crab when buried. Having no posterior branchial orifices and no Milne-Edwards openings, a lyreidid is dependent on an inhalant current in the anterior portion of the carapace (see Respiration in the Brachyura below). The exposed pleurites 5–7 form a flat plate, practically in continuity with the branchiostegite ( Figs. 46A ; 51B ), and there is no excavated area overhung by the branchiostegal edge and by the P5 as in other raninoids. Griffin (1970: fig. 6O–R) illustrated the variously produced lyreidid crown-shaped sternite 3 and the shape of sternite 4.

The lyreidid spermathecal apertures face each other on opposite sides of a depression of trough-like, although less narrow, sternite 7 in contrast to other Raninoidea such as Ranina ( Hartnoll 1979: 76, 80, figs. 1–3; Guinot 1993b: fig. 4; Guinot & Quenette 2005: 314).

While extant members of Lyreididae typically have a narrow or tapering front, their fossil representatives, assigned to a handful of genera, may show a different carapace outline as several early members (e.g., Bournelyreidus n. gen., Marylyreidus n. gen. and Rogueus Berglund & Feldmann, 1989 ) that have a much wider front than extant lyreidids. Extinct lyreidid genera recognised here are Bournelyreidus n. gen., Macroacaena Tucker, 1998 , Marylyreidus n. gen. and Rogueus . Lyreidus De Haan, 1841 , and Lysirude Goeke, 1986 , both known from the Eocene onwards (see Appendix), are the only lyreidids to survive to the present day. Here 35 fossil and 6 extant species within Lyreididae are listed. Of the latter group, one species, Lyreidus tridentatus De Haan, 1841 , is also known from the fossil record.

Figures

FIGURE 46. Exposed pleurites (gymnopleurity) in Lyreidus (Lyreididae) and Raninoides (Raninidae); A, Lyreidus tridentatus De Haan, 1841, MAB k. 2914 (male), Recent, Philippines; left lateral view; B, Raninoides bouvieri Capart, 1951, MAB k. 2919 (male), Recent, Philippines; left lateral view. og, outgrowth on exposed pleurite; P5, pereiopod 5; pl5, pl6, pl7; exposed pleurites 5, 6, 7. Scale bars: 5mm.

FIGURE 51. Orientation of P5 in Raninoidea; A, Symethis corallica Davie, 1989 (Raninidae, Symethinae), MNHN-B20795 (holotype, female), Coral Sea, Chesterfield Islands; B, Lyreidus tridentatus De Haan, 1841 (Lyreididae, Lyreidinae), MNHN- B13364 (male). Arrows indicate filiform P5. (photographs by J.-F. Dejouannet) scale bars: 5mm.