Dorippoidea, MacLeay, 1838

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 : 221-224

publication ID	https://doi.org/ 10.11646/zootaxa.3665.1.1
publication LSID	lsid:zoobank.org:pub:8358B363-BEE3-416D-96CA-8614E38B61D5
persistent identifier	https://treatment.plazi.org/id/03BB9C75-FF35-FF4D-FF78-FBCEFEF1FD0F
treatment provided by	Felipe
scientific name	Dorippoidea
status

Treatment

Affinities between Dorippoidea View in CoL and Hymenosomatoidea

The relationships between hymenosomatoids and dorippoids presently appear unambiguous, being supported by various types of strong evidence (see Monophyletic Heterotremata: Superfamily Hymenosomatoidea ). The most reliable morphological trait shared by the two groups is the axial skeleton. Odiomaris pilosus and Amarinus lacustris , the most basal hymenosomatoids, show: (1) a parallel arrangement of phragmae in an anteroposterior plane, resulting in a regular, symmetrical partition ( Fig. 47D – F View FIGURE 47 ); (2) an exceptionally regular division into compartments dorsal and ventral to the strong junction plate (a plate formed by the spreading of the extremities of the endopleurites and endosternites at the level of their fusion underneath), thus a dorsoventral bipartition; (3) a sella turcica that is the only transversally binding, the remaining part of the body being empty ( Fig. 47D–F View FIGURE 47 ; Guinot 1979a: 261, pl. 20, figs. 9–11; Guinot & Richer de Forges 1997: 477, figs. 1B, 2C, E, 6F; Secretan 1998: 1763, figs. 17–20, under Amarinus ).

The regularly compartmented skeleton of the Dorippidae ( Figs. 46 View FIGURE 46 , 47A, B View FIGURE 47 ) shows an arrangement similar to that of Odiomaris and Amarinus . In O. pilosus ( Fig. 47D–F View FIGURE 47 ) and A. lacustris , the phragmae are laterally shifted (as in Ethusidae ), the large empty and smooth median space being only occupied by the convexity formed by the sterno-abdominal cavity.

The large number of traits shared by dorippids and hymenosomatoids was reviewed by Guinot & Richer de Forges (1997): (1) the arrangement of the cephalic appendages, with unfolded antennules and antennae, both close to the eyestalks, the three being lodged in a unique fossa ( Ihle 1916: fig. 41 for dorippid disposition; Lucas 1980: figs. 1D, 5D for hymenosomatoid disposition); (2) the shape of the first thoracic sternites, forming a developed shield (in particular sternite 3, which reaches the pterygostome) in Dorippidae , more flattened in hymenosomatoids; (3) sternal suture 3/4 short but very deep, corresponding to a thick endosternal phragma, ending by a marked depression, even showing as a perforation in the thoracic sternum of Dorippidae ( Fig. 42C View FIGURE 42 ; Guinot 1979a: 103, fig. 28A), this deep suture 3/4 ending by a perforation being already visible in the first juvenile crab ( Quintana 1987: fig. 8E); (4) a thoracic sternum/pterygostome junction, complete and involving sternite 3 ( Dorippidae , Fig. 42C View FIGURE 42 ) instead of varying from incomplete to complete in Hymenosomatoidea (e.g., complete in Trigonoplax H. Milne Edwards, 1853 ) because of a variously extended sternite 4 ( Figs. 42B View FIGURE 42 , 43C View FIGURE 43 ); (5) the Milne Edwards openings as pterygostomial slits entirely separated from the chelipeds in Dorippidae ( Fig. 42C View FIGURE 42 ), posteriorly limited by a variously developed sternum/pterygostome junction, always filled by a developed, largely exposed mxp3 coxa in Hymenosomatoidea ; (6) G1 and G2 with wide base, occupying a short sterno-abdominal cavity; (7) P5 coxa dorsal (also P 4 in Dorippidae ).

Despite the fact that the Hymenosomatoidea is characterised by distinctive features (“grooved” carapace dorsal surface; hymenosomian rim; pleotelson) that are absent in Dorippoidea , and that Dorippoidea has dorsal, mobile, P4, P5 (involved in carrying behaviour) and an oxystome condition (more developed in Dorippidae than in Ethusidae ) missing in Hymenosomatoidea , the groundplan could be understood as similar at a higher rank. It is not plausible to conclude to a convergence.

A thoracic sternum/pterygostome junction in Brachyura (see Axial skeleton; Thoracic sternum: Thoracic sternum/pterygostome junction) is generally linked to a specialised respiratory system, frequently in burying, “oxystome” crabs as the Raninoidea ( Fig. 42E View FIGURE 42 ) and Leucosiidae ( Fig. 42D View FIGURE 42 ). The oxystome condition that is complete in Dorippidae or partial as in Ethusidae ( Fig. 42A, C View FIGURE 42 ) does not occur in Hymenosomatoidea , characterised by a variously developed sternum/pterygostome junction, often unspecialised mouthparts, and mxp3 varying from pediform to operculiform and tightly sealed by a long, flabelliform, calcified mxp3 coxa, to which the epipod is fused ( Figs. 42B View FIGURE 42 , 43C View FIGURE 43 ; Melrose 1975: 20, figs. 3A, 5; Guinot & Richer de Forges 1997: fig. 3; Guinot 2011a: fig. 1B, C; 2011b: fig. 1B). The disposition of the Milne Edwards openings anterior to the chelipeds, without a sternum/pterygostome junction, is as usual in Ethusidae ( Fig. 42A View FIGURE 42 ). These respiratory dispositions are adaptations to burying behaviour ( Dorippidae , Ethusidae ) or to concealment ( Hymenosomatoidea ) (see Concealment behaviour; Burying and burrowing in the Eubrachyura below).

The wide diversity of the G1s present in Dorippidae ( Holthuis & Manning 1990: 6; Sin et al. 2009: fig. 4) is similar to that of Hymenosomatidae , varying in both families from simple to variously twisted and complex, with apical processes. The plesiomorphic hymenosomatoid state is represented in Amarinus by a short, straight, spindlelike G1 ( Lucas 1980: fig. 10A, D–F; Ng & Chuang 1996: figs. 2E, 3F) and in Odiomaris by a more slender G1, with distal lobes and subterminal tufts of setae ( Ng & Richer de Forges 1996: fig. 7D) whereas strongly curved G1s characterise more derived taxa ( Lucas 1980: figs. 9, 10H, I; see also Melrose 1975). The G2 approximately measures half the length of the G 1 in Dorippidae ( Figs. 15B View FIGURE 15 , 16C, E View FIGURE 16 , 18C View FIGURE 18 ) and is much longer than the G 1 in Ethusidae ( Figs. 20B, D View FIGURE 20 , 22C View FIGURE 22 ) whereas it is short and without flagellum in Hymenosomatidae .

The short “setting gutter” of Dorippoidea , with exposed pleurites 5–7 ( Figs. 42C View FIGURE 42 , 46A, B View FIGURE 46 , 47A, B View FIGURE 47 ), is somewhat comparable to the gutter present at the pleurites 5–8 levels of Inachoididae ( Fig. 47G View FIGURE 47 ), in which the last pleurite (pleurite 8) is exposed with regards to the lateral orientation of the P5 (in contrast to a dorsal P 5 in Dorippoidea ). These peculiar organisations bring to mind the “hymenosomian rim” of Hymenosomatoidea ( Fig. 47D, E View FIGURE 47 ). Two ongoing taxonomic studies on the Dorippidae (Guinot & Lai, study in progress) and on the Hymenosomatoidea (Naruse, Guinot & Ng, study in progress) stress the extraordinary diversity of cephalic appendages, mouthparts, thoracic sternum, male and female abdomens, G1, and vulvae within each superfamily. A long evolutionary history is inferred for both, although the fossil record does not yet provide any evidence, no fossil hymenosomatoids being so far known due to their small size, flat body, and poorly calcified carapace.

According to Rice (1980: 319) who did not mention a doprippid megalopa, the degree of “advancement” of the zoeae and their unique combination of characters place the Dorippoidea apart from all other brachyurans. The megalopae of three Japanese dorippid species reared and described by Quintana (1987) do not greatly differ from the first crab stages. This dorippid megalopa has dorsal and subchelate P4 and P5 (thus devoid of the usual long setae, the feelers, at the end of the dactyli) that are able to hold camouflaging material on the back (see Carrying behaviour). Thus carrying behaviour is acquired precociously in the dorippid ontogeny, more precocious than in dromioids or homoloids. The dorippid megalopa is not an active swimmer and was even observed not swimming at all in Paradorippe granulata despite the presence of pleopods on somites 2–5 ( Quintana 1987: 265). Pleopod buds appear in the zoea IV ( Rice 1980; Terada 1981) or zoea III ( Bourdillon-Casanova 1960). A megalopa was not described in Ethusa microphthalma Smith, 1881 , by Martin & Truesdale (1989) nor in Medorippe lanata by Paula (1991). Quintana (1987: 267, figs. 5C, 9G, H, 17G–J) considered the possibility that in dorippids the zoea moults directly to a first crab stage instead of a megalopa, but he abandoned this idea because of the presence of pleopods in the megalopa. Nonetheless, the appearance of such traits in dorippoid megalopae demonstrates the presence of an unusual phase that could be lost in an ulterior evolutionary state, as in the case of the Hymenosomatoidea , which metamorphose directly from the zoea to the first crab stage, by dispensing with the megalopa. The absence of uropods recorded in the megalopa of Paradorippe granulata ( Quintana 1987: 260) must be verified in other dorippoids.

A main difference between Dorippoidea and Hymenosomatoidea refers to the location of the male gonopore and penis: a coxal to coxo-sternal condition in Dorippoidea , with the penis exiting from the P5 coxa at the suture 7/ 8 level ( Figs. 15–22 View FIGURE 15 View FIGURE 16 View FIGURE 17 View FIGURE 18 View FIGURE 19 View FIGURE 20 View FIGURE 21 View FIGURE 22 ), and a “sternitreme” arrangement in Hymenosomatoidea , with the penis exiting in a posteriormost location on sternite 8, distant from suture 7/8 ( Figs. 29A, B View FIGURE 29 , 58A, B, E View FIGURE 58 ; Guinot 1979a: figs. 30A, 53F; 2011b: fig. 1A).

The Inachoididae View in CoL is also probably closely linked to the Hymenosomatidae View in CoL ( Guinot 2011 a, 2011b; see Affinities between Hymenosomatoidea View in CoL and Inachoididae View in CoL below), Inachoididae View in CoL being itself closely related to the Inachidae View in CoL and, thus, to the other Majoidea View in CoL (see Affinities between Inachoididae View in CoL and Inachidae View in CoL below).

The extreme carcinisation of Hymenosomatoidea View in CoL has resulted in a major modification of the male duct that abridges its trajectory and thus perforates the thoracic sternum as in the Thoracotremata, whereas the Dorippoidea View in CoL displays multiple modalities of coxo-sternal condition (see Coxo-sternal condition; Modalities of penis protection: Coxo-sternal penial tube; Monophyletic Heterotremata: Superfamily Dorippoidea View in CoL ; Superfamily Hymenosomatoidea View in CoL ; Position of the Dorippoidea View in CoL within the Brachyura ; Position of the Hymenosomatoidea View in CoL within the Brachyura ).