Acidopsidae Števčić, 2005

Ng, Peter K. L. & Rahayu, Dwi Listyo, 2014, Revision of the family Acidopsidae Števčić, 2005, and the systematic position of Typhlocarcinodes Alcock, 1900, Caecopilumnus Borradaile, 1902, and Raoulia Ng, 1987, with descriptions of two new genera and five new species (Crustacea: Brachyura: Goneplacoidea), Zootaxa 3773 (1), pp. 1-63 : 4-9

publication ID	https://doi.org/ 10.11646/zootaxa.3773.1.1
publication LSID	lsid:zoobank.org:pub:19F28753-B2D0-4D1F-9D47-88886F7333FD
DOI	https://doi.org/10.5281/zenodo.5047705
persistent identifier	https://treatment.plazi.org/id/03E287AE-5446-E233-8A9D-427DFA110A58
treatment provided by	Felipe
scientific name	Acidopsidae Števčić, 2005
status

Treatment

Family Acidopsidae Števčić, 2005 View in CoL

Acidopidae [sic] Števčić, 2005: 36

Parapilumnidae Števčić, 2005: 70 .

Raouliidae Števčić, 2005: 71 .

Typhlocarcinodidae Števčić, 2005: 62 .

Caecopilumnidae Števčić, 2011: 127 .

Diagnosis. Thoracic sternal suture 2/3 complete; only lateral part of suture 3/4 visible, short; sutures 4/5–7/8 complete, almost horizontal or with only narrow gap separating sutures 4/5; with distinct longitudinal median groove, reaching st4 sometimes extending beyond sterno-abdominal cavity. Male gonopore coxal, penis exiting anterior to coxo-sternal condyle, sitting on shallow depression on st8 at junction of suture 7/8; penis short (coxal penis condition) or long (coxo-sternal condition); lateral margin of a3 reaching to between cx4, 5; a2 reaching to base of cx5 with only small part of st8 visible when abdomen closed (coxal condition), or a3 not reaching cx4, 5; a2 well separated from cx5 with large part of st8 visible when abdomen closed (coxo-sternal condition). Male abdomen triangular, a3–5 fused, immovable but sutures may be visible at least in part. Female abdomen subovate, never completely covering thoracic sternum. Female sterno-abdominal cavity deep or shallow; vulva normally with non-movable operculum, positioned close to median longitudinal groove on thoracic sternum or on median part of st6. G1 simple, distal half with spinules or short setae, never with long setae; G2 as long or longer than G1, distal segment elongated.

Remarks. Tesch (1918: 79), with his usual insight into crab affinities, commented that Typhlocarcinodes was probably related to Acidops Stimpson, 1871 (as Epimelus A. Milne-Edwards, 1878 ), although both genera differ in the form of their eyes (structure and mobility) and third maxillipeds. The Atlantic and eastern Pacific Acidops and the closely related Pacific Parapilumnus Kossmann, 1877 , are currently in the family Acidopsidae Števčić, 2005 (= Parapilumnidae Števčić, 2005 ) (see Ng et al. 2008: 75). One species, Pilumnus alcocki Borradaile, 1902 , described from the Maldives and also reported from the Amirante Is. ( Seychelles) by Rathbun (1911), is not a pilumnid and is actually closely allied to Acidops and Parapilumnus . It is here referred to a new genus, Crinitocinus .

Guinot et al. (2013: 41, 111) discussed the systematic position of the Acidopsidae (based on Acidops and Parapilumnus ), noting that it was a basal heterotreme with a number of plesiomorphies, and summarised the key thoracic sternal, male abdominal and gonopodal characters of the family. They also discussed the systematics of Typhlocarcinodes and Raoulia , noting that they were not chasmocarcinids but uncertain of their position. Števčić (2005) had referred both genera to their respective families and superfamilies without any substantial discussion ( Guinot et al. 2013: 113). They also commented that the penis condition of members of the “ Caecopilumnidae ” was coxo-sternal ( Guinot et al. 2013: 82).

Typhlocarcinodes , Caecopilumnus , Raoulia and Thecaplax gen. nov. actually share with Acidops , Parapilumnus and Crinitocinus gen. nov. a suite of key characters: male abdominal somites 3–5 are fused (even if the sutures are visible), the G1 is relatively stout and tapering towards the tip with the lateral margins of the distal half lined with spinules, without long setae; and the G2 is elongated, at least as long as G1, with a long distal segment. The male thoracic sterna in Acidops , Parapilumnus and Crinitocinus gen. nov. (notably st7 and st8) are relatively narrow, the lateral edge of a3 is between cx4 and cx5 and adjacent to the cx5, the lateral edge of a2 is adjacent to cx5, and as such, when the abdomen is closed, only a tiny part of st8 is visible ( Fig. 1A–D View FIGURE 1 ). The male opening is clearly coxal, with the short penis exiting at the base of cx5, just anterior of the condyle ( Fig. 1B, D View FIGURE 1 ). As such, the male abdomen almost completely covers the penis when closed ( Fig. 1A, C View FIGURE 1 ) (see Ng 2002; Ng & Chen 2004; Guinot et al. 2013). Compared to Acidops , Parapilumnus and Crinitocinus gen. nov., the male posterior thoracic sterna of Typhlocarcinodes , Caecopilumnus , Raoulia and Thecaplax gen. nov. are relatively broader, the lateral edge of a5 is some distance from cx4 and cx5, the lateral edge of a2 is some distance from cx5 with a large part of st8 visible even when the abdomen is closed, and the male opening is clearly coxo-sternal, with the penis longer and at least some part of it is exposed in a channel between st7 and st8 ( Fig. 1E–H View FIGURE 1 ). Of these four genera, the male posterior thoracic sternum is relatively the narrowest in Caecopilumnus . St7 and st 8 are tightly appressed along most of the length in Caecopilumnus , with only the inner part of the suture slightly divergent and exposing part of the penis externally ( Figs. 1E, F View FIGURE 1 , 29D View FIGURE 29 , 32D View FIGURE 32 ). St7 and st8 are distinctly wider in the other three genera. A narrow channel between st7 and st8, forming a channel in which the exposed penis sits ( Fig. 34D View FIGURE 34 ), is present in Thecaplax gen. nov. In Raoulia , only the outer edge of st7 and st8 are adjacent to each other, with the margins diverging towards the sterno-abdominal cavity, forming an acutely V-shaped channel in which the partially exposed penis sits ( Figs. 1G, H View FIGURE 1 , 13E View FIGURE 13 , 14D View FIGURE 14 , 18D View FIGURE 18 , 20D View FIGURE 20 ). The condition is possibly the most derived in Typhlocarcinodes , where st7 and st8 are more widely separated and there is a prominent and mobile calcified plate that sits between them. This plate is attached to (and probably derived from) the penis and moves with this structure ( Fig. 38C View FIGURE 38 ). This penial plate is different from the supplementary plate present in chasmocarcinids which is formed by an evagination of st8 and is immobile ( Fig. 2C, D View FIGURE 2 ) (see also Davie & Guinot 1996: fig. 7; Guinot et al. 2013: 111).

Two kinds of basal antennal articles (antennal article 2) are also present. In Acidops , Parapilumnus and Crinitocinus gen. nov., the basal antennal article is quadrate, being longer than wide or as long as wide ( Figs. 6A, B View FIGURE 6 , 11D View FIGURE 11 ). In Typhlocarcinodes , Caecopilumnus , Raoulia and Thecaplax gen. nov., the basal antennal article is short, being much wider than long ( Fig. 6C–F View FIGURE 6 ). There are also two kinds of arrangements of the vulvae. In Acidops , Parapilumnus and Crinitocinus gen. nov., the female sterno-abdominal cavity is relatively deep, transversely narrow, and the vulvae are positioned close to the median longitudinal groove of st6 ( Figs. 3 View FIGURE 3 , 10D View FIGURE 10 ). In Typhlocarcinodes , Caecopilumnus , Raoulia and Thecaplax gen. nov., the female sterno-abdominal cavity is relatively shallower, transversely broader, and the vulvae are positioned on median part of st6 ( Fig. 4B, D, F, H View FIGURE 4 ).

Considering the shared characters discussed above, it seems best to include Typhlocarcinodes , Caecopilumnus , Raoulia and Thecaplax gen. nov. in the Acidopsidae , but in a separate subfamily in view of their coxal-sternal male openings, structure of the basal antennal articles and position of the vulvae. The selection of a name for this subfamily poses a problem. Števčić (2005, 2011) named a large number of new suprageneric taxa for what he felt were unusual genera, often without examining material or any explanation, establishing Raouliidae Števčić, 2005 , Typhlocarcinodidae Števčić, 2005 , and Caecopilumnidae Števčić, 2011 , for Raoulia , Typhlocarcinodes and Caecopilumnus , respectively. Ng et al. (2008: 75) commented that the Raouliidae and Typhlocarcinodidae “are a problem as they do not agree well with any of the families recognised here. They may be distinct families in the Goneplacoidea as Števčić (2005) argued or merely very apomorphic genera allied to better known families in other superfamilies. For genera like these whose members are small and very poorly known, it is imperative that the original specimens are carefully re-examined, and their sternal, abdominal and gonopodal characters properly documented, before firm conclusions are made. Until we better understand their affinities, we prefer to synonymise Raouliidae and Typhlocarcinodidae with the Chasmocarcinidae for the time being”.

As expected, the present study shows that the Raouliidae and Typhlocarcinodidae (as well as Caecopilumnidae ) are not distinct familes (see also Guinot et al. 2013: 113) and are not related to Chasmocarcinidae . They are instead junior subjective synonyms of Acidopsidae .

As discussed earlier, chasmocarcinids differ markedly from acidopsids in several characters. The most important difference is that male chasmocarcinids possess a fused supplementary plate between st7 and st8. In addition, the basal antennular article of all chasmocarcinids completely fills the fossa and the elongated flagellum cannot retract into it (a character shared with scalopidiids). In addition, st5–8 of all male chasmocarcinids are medially interrupted with the sternites separated by a prominent channel between them. Chasmocarcinids also do not have the median longitudinal groove on st4 which is distinct in acidopsids ( Castro et al. 2010; Ng & Castro 2013).

Another issue concerns the Scalopidiidae Števčić, 2005 . Ng et al. (2008: 85) recognised this taxon as a valid family in view of the unique arrangement of its long calcified penis and coxo-sternal condition (see also Ng & Castro 2013). Comparisons of the male sternum and structure of the penis shows that the condition of the penial plate in Typhlocarcinodes (a relatively long penis covered by a narrow plate) is very similar to that observed in Scalopidia Stimpson, 1858 , in which the very long penis is surrounded by a chitinised and weakly calcified penial tube which is also mobile ( Fig. 2A, B View FIGURE 2 ). Whereas Scalopidia is superficially similar to Raoulia , Typhlocarcinodes and Caecopilumnus in the coxo-sternal form of the penis, there are substantial differences in the structures of the male thoracic sternum, antennules, antennae, male thoracic sternum and gonopods that argue against putting them in the same family. One significant difference is that male thoracic sutures 4/5, 5/6 and 7/8 are medially interrupted in scalopidiids ( Ng & Castro 2013: fig. 1) whereas these sutures are complete in acidopsids or almost so (with only a narrow gap between s4/ 5 in Acidops ) ( Fig. 1 View FIGURE 1 ). Additional differences are that in acidopsids, the antennular flagellum folds completely obliquely to almost vertically into the fossa (e.g., Fig. 6 View FIGURE 6 ) (basal antennular article completely fills fossa and the flagellum cannot fit into fossa in scalopidiids; Ng & Castro 2013: fig. 5); the anterior thoracic sternum (st1–4) is relatively narrow ( Fig. 1 View FIGURE 1 ) (transversely very broad in scalopidiids; Ng & Castro 2013: fig. 9); the G1 has scattered spinules on the distal half ( Fig. 11A, B View FIGURE 11 ) (with two dense patches of spinules on the median part in scalopidiids; Ng & Castro 2013: figs. 12, 13); G2 is as long as or longer than the G1 with an elongated distal segment ( Fig. 11C View FIGURE 11 ) (G2 about a third length of G1, with short distal segment in scalopidiids; Ng & Castro 2013: figs. 12, 13) (see also Castro et al. 2010: Table 1; Guinot et al. 2013: 118).

The present study shows that Acidopsidae Števčić, 2005 , Caecopilumnidae Števčić, 2011 , Parapilumnidae Števčić, 2005 , Raouliidae Števčić, 2005 , and Typhlocarcinodidae Števčić, 2005 , are synonyms; with all of its members belonging to a single family. Acidopsidae Števčić, 2005 , Parapilumnidae Števčić, 2005 , Raouliidae Števčić, 2005 , and Typhlocarcinodidae Števčić, 2005 , are simultaneous synonyms, as all were established in the same publication ( Števčić 2005). Ng et al. (2008: 75) highlighted this problem with Acidopsidae and Parapilumnidae , and as first revisers, chose Acidopsidae to have priority whenever the two names are treated as synonyms. The same rationale is adopted here, and as first revisers, we choose Acidopsidae Števčić, 2005 , to have priority over all other names in Števčić (2005), even if they are in the same family grouping. We here recognise two subfamily groupings within Acidopsidae ; Acidopsinae for Acidops , Parapilumnus and Crinitocinus gen. nov. (with coxal male openings); and subfamily, Raouliinae subfam. nov. for Typhlocarcinodes , Caecopilumnus , Raoulia and Thecaplax gen. nov. (with coxo-sternal male openings). As first revisers, we here select the name Raouliinae having priority over Typhlocarcinodidae Števčić, 2005 , whenever they are treated as synonyms. Caecopilumnidae Števčić, 2011 , is also a junior subjective synonym of Raouliidae Števčić, 2005 .

Key to genera

1. Third maxilliped merus with angular or subauriculiform anterolateral margin ( Fig. 5A, B View FIGURE 5 ); basal antennal article quadrate, at least as long as wide ( Fig. 6A, B View FIGURE 6 ); penis coxal, exiting cx5 directly into sterno-abdominal cavity, protected by a3 when abdomen closed ( Fig. 1B, D View FIGURE 1 ); male st8 visible only as a small plate when abdomen closed ( Fig. 1A, C View FIGURE 1 ); vulvae closed to median longitudinal groove of st6 ( Fig. 3 View FIGURE 3 ) [ Acidopsinae View in CoL ]............................................................ 2

- Third maxilliped merus with rounded, convex anterolateral margin ( Fig. 5C–L View FIGURE 5 ); basal antennal article rectangular, much wider than long ( Fig. 6C–F View FIGURE 6 ); penis coxo-sternal, exiting cx5 directly under or on groove between st7, 8, at least part of penis exposed, unprotected by sternites or abdomen ( Fig. 1F, H View FIGURE 1 ); male st8 visible as large rectangular to subrectangular plate even when abdomen closed ( Fig. 1E, G View FIGURE 1 ); vulvae located on median parts of st6 ( Fig. 4 View FIGURE 4 ) [ Raouliinae View in CoL ]................................. 4

2. Fingers of chelae with blade-like cutting edges ( Fig. 8B View FIGURE 8 ) (Indo-West Pacific)........................... Parapilumnus View in CoL

- Cutting edges of fingers of chelae dentate ( Fig. 7F View FIGURE 7 ) (circumtropical)............................................. 3

3. Male anterior thoracic sternum (st1–4) relatively wide ( Fig. 9B View FIGURE 9 ); eyes with prominent cornea, as wide as peduncle ( Fig. 12A View FIGURE 12 ); dactylar finger of major chela with prominent basal cutting tooth ( Fig. 9D View FIGURE 9 ) (Indo-West Pacific)...... Crinitocinus View in CoL gen. nov.

- Male anterior thoracic sternum (st1–4) relatively narrow ( Fig. 7E View FIGURE 7 ); eyes pear-shaped, cornea reduced ( Fig. 12D View FIGURE 12 ); cutting edges of major chela with large and small teeth but never with basal cutting tooth ( Fig. 7F, G View FIGURE 7 ) (Atlantic and Tropical Eastern Pacific )............................................................................................. Acidops View in CoL

4. Eyes mobile; epistome only partially sunken ( Fig. 38B View FIGURE 38 ); penis protected by mobile plate which sits in groove between st7, 8 -

Eyes fused to orbits, immobile; epistome prominently sunken ( Fig. 13D View FIGURE 13 ); at least part of penis exposed in groove between st7, 8 ( Fig. 1E–H View FIGURE 1 ) (Indo-West Pacific)........................................................................ 5

5. Thoracic sternum relatively narrow ( Fig. 29B View FIGURE 29 ); male and female a1 subrectangular, with lateral margins straight or gently convex ( Fig. 1E View FIGURE 1 ); penis partially covered by st7, st8 near junction with cx5, exposed on short groove between st7, 8 ( Fig. 1E, F View FIGURE 1 )....................................................................................... Caecopilumnus

- Thoracic sternum relatively wide ( Fig. 13C View FIGURE 13 ); male and female a1 very narrow, with lateral margins tapering to form acutely triangular structure ( Fig. 1G View FIGURE 1 ); penis partially covered by st7, st8 near junction, exposed on long groove between st7, 8, or completely exposed ( Fig. 1G, H View FIGURE 1 )............................................................................. 6

6. Anterolateral margin subcristate, entire, without trace of teeth, spines or lobes ( Fig. 13A View FIGURE 13 ); penis initially partially covered by st7, 8 near junction but exposed for the greater length between st7, 8 ( Fig. 1G, H View FIGURE 1 ); G1 with stout basal half, distal half sharply tapering to form narrow structure with scattered spinules on subdistal surface ( Fig. 16D–G View FIGURE 16 ).................... Raoulia

- Anterolateral margin with distinct granuliform lobes ( Fig. 34A View FIGURE 34 ); penis completely exposed in groove between st7, 8 ( Fig. 34D View FIGURE 34 ); G1 gradually tapering towards tip, with numerous spinules on subdistal surface ( Fig. 35D–G View FIGURE 35 ).... Thecaplax View in CoL gen. nov.