Gaeticinae

Naruse, Tohru, 2015, Description of a new genus and a new species of gaeticine crab (Crustacea: Brachyura: Varunidae) from the Ryukyu Islands, and a review of Acmaeopleura Stimpson, 1858, and Sestrostoma Davie & N. K. Ng, 2007, Zootaxa 3925 (2), pp. 211-228 : 212-215

Gaeticinae Davie & N.K. Ng, 2007

Gaeticinae Davie & N.K. Ng, 2007: 259. Brankocleistostomidae Števčić, 2011: 127. Gopttisakini [sic] Števčić, 2011: 129.

Remarks. Davie & N.K. Ng (2007) established the subfamily Gaeticinae within the family Varunidae to accommodate Gaetice Gistel, 1848 [type genus; see Ng et al. (2008: 230) for its nomenclature] and their new genus Sestrostoma Davie & N.K. Ng, 2007 , by emphasizing characters that are related to suspension feeding, the third maxilliped and the medial sulcus on the anterior sternal plate ( Davie & N.K. Ng 2007: 260). Subsequently Gopkittisak Naruse & Clark, 2009 , was established within Gaeticinae as it shares the long setae of the palp of the third maxilliped and the fused male abdominal segments ( Naruse & Clark 2009: figs. 1c, 2a). Manning & Holthuis (1981) and Ng et al. (2008) discussed the taxonomic status of Paracleistostoma fossulum Barnard, 1955 . They considered the species is not Paracleistostoma s.s. ( Camptandriidae ), and Ng et al. (2008) placed the species in Varunidae . Števčić (2011) established the genus Brankocleistostoma Števčić, 2011, for P. fossulum and accommodated it in his new family Brankocleistostomidae. Ng (2012), however, indicated the strong similarity between Brankocleistostoma and Gopkittisak in taxonomically important characters, e.g. general pattern of carapace ridges and third maxillipeds, and transferred Brankocleistostoma to Gaeticinae . This action formally synonymized Brankocleistostomidae under Gaeticinae (Ng 2012: 62) . Although Števčić (2011) also established the tribe Gopkittisakini to accommodate Gopkittisak without any discussion, Ng (2012) also regarded it as a junior subjective synonym of Gaeticinae . Števčić (2011) spelled the tribe as “Gopttisakini”, but since the tribe name was based on an incorrect spelling of the type genus “ Gopttisak ” (correctly Gopkittisak Naruse & Clark, 2009 ), it must be corrected as Gopkittisakini (see ICZN 1999: art. 32.5.3.3 and 35.4.1).

Acmaeopleura balssi Collected from sediment in burrows of thalassinidean shrimps Unknown

Shen, 1932 and the echiurid Urechis unicinctus , but no definite

relationship can be confirmed ( Itani et al. 2002). In burrows of Upogebia major and U. issaeffi ( Marin et al. 2011) .

Acmaeopleura aff. balssi sensu Collected attached to bases of thoracic appendages of Unknown

Ghani & Tirmizi Upogebia quddusiae (cf. Ghani & Tirmizi 1991).

(1991)

Acmaeopleura sp. Clinging to abdomen of host Upogebia major (cf. Itani 2001). Feeds on host tissue (Itani

sensu Itani (2001) 2001)

Gopkittisak angustum In intertidal to subtidal burrows, in sandy substratum, no Unknown

Komai, 2011 symbiosis observed.

Proexotelson tokoroi n. sp. Burrows in subtidal sandy substratum, no symbiosis observed Unknown so far.

The diagnostic characters of the gaeticine genera were reexamined and summarized in Table 2. Davie & N.K. Ng (2007) linked Sestrostoma and Gaetice by the characters of the third maxillipeds and medial sulcus on the anterior sternal plate. A close examination of these two genera revealed that the ischiomerus of the third maxilliped of Gaetice is narrow and elongated, the border between the ischium and merus is obliquely steep, the dactylus is proportionally long, and the exopod is proportionally broad ( Figs. 1 a). In Sestrostoma , the ischiomerus of the third maxilliped is oblong, the border between the ischium and merus is horizontal, and the exopod is proportionally narrow ( Figs. 1 b, c). The thoracic sternite 2 of Gaetice is weakly produced medially and its anterior margin is divergent posteriorly ( Fig. 1 a), whereas that of Sestrostoma is produced entirely between the bases of the third maxillipeds ( Fig. 1 b, c), and its lateral ends of the sternite have distinct and rounded anterior projection ( Fig. 1 b, c). Furthermore, the medial sulcus of the anterior sternal plate of Gaetice is very narrow and deep on the thoracic sternites 2 and 3 ( Fig. 1 a), but in Sestrostoma , there is no obvious sulcus and is basically just a shallow depression. This depression is shallow and wide in S. balssi ( Fig. 1 b), relatively wider and deeper in S. toriumii , and very shallow and wide and only visible on sternite 2 in S. depressum ( Fig. 1 c). Besides these differences, Gaetice and Sestrostoma share important characters; the male abdominal somites 3–6 are functionally fused and the third maxilliped dactylus is attached to a subdistal portion of the outer surface of the propodus ( Fig. 2 a, b; Depledge 1989: fig. 4). It is difficult to assess whether the characters emphasized by Davie & N.K. Ng (2007) are the result of morphological adaptations for suspension feeding. Future studies of varunid genera may offer a better solution for the systematic position of the two genera. The present study tentatively retains Sestrostoma in Gaeticinae .

When Davie & N.K. Ng (2007) established the genus Sestrostoma for the three species previously placed in Acmaeopleura ( S. balssi , S. depressum and S. toriumii ), they restricted Acmaeopleura to A. parvula Stimpson, 1858 [type species] and A. rotunda Rathbun, 1909 , and left the genus in Varuninae . Since Acmaeopleura and Sestrostoma share taxonomically important characters, the present study transfers Acmaeopleura to Gaeticinae (See remarks for Acmaeopleura ).

sternite 2, 3; 2/3, suture between thoracic sternites 2 and 3.

Gaetice Acmaeopleura Sestrostoma Gopkittisak Brankocleisto-stoma Proexotelson gen. nov.

Mxp3 dactylus when Elongated, distal end Normal, distal end reaching Slightly elongated, distal Normal, distal end Normal, distal end Normal, distal end

folded reaching proximal half proximal quarter of mesial end reaching reaching distal third reaching distal end reaching proximal of mesial margin of margin of merus proximomesial corner of of mesial margin of of mesial margin of fifth of mesial ischium merus (Sd, St) or ischium ischium margin of merus distomesial corner of

ischium (Sb)

Mxp3 propodus, Setae long, reaching 2/3 Setae length moderate, Setae long, reaching S2 Setae long, reaching Setae long, which Setae length

dactylus setae reaching 2/3 (Sd) or 2/3 (Sb, St) 2/3 cover anterior S2 or moderate, reaching S3 proximomesial corner of ischium

Mxp3 propodus/ Dactylus attached to Dactylus attached to Dactylus attached to Dactylus attached to Unknown Dactylus attached to

dactylus articulation subdistal portion of subdistal portion of subdistal portion of distal end of subdistal portion of

propodus propodus propodus propodus propodus

Mxp3 ischium/ merus Oblique Horizontal Horizontal Oblique Oblique Horizontal

border

Mxp3 merus lateral Straight, oblique Almost straight Slightly convex (St) or Straight Auricular Auricular

margin weakly auricular (Sb, Sd)

Mxp3 ischium Straight, oblique Broad, shallow concavity Distinct round concavity Straight Straight Distinctround

posterior margin present present concavity present

Sternal longitudinal Deep, narrow Wide, shallow on S2 and S3 Wide, shallow on S2 and Wide, shallow on S2 Wide, shallow on S2 Wide, deep

sulcus S3 (Sb), wide, deep on S2 and S3 and S3 concavity for telson and S3 (St) or very in male, almost flat shallow, wide on S2 (Sd) in female

2 lateral end No projection Weakly produced Distinctly produced No projection No projection Distinctly produced

Male abdominal Fused, sutures visible Fused, sutures visible Fused, sutures visible Fused, sutures Unknown Fused,sutures

somites 3–6 visible only for visible somites 3 and 4

1 Stout,straight,with Stout, straight, with Stout, straight, with Stout, straight, with Unknown Slender,sinuous, chitinous distal beak, not chitinous distal beak, not chitinous distal beak, not chitinous distal distal end thin, bent exposed from telson exposed from telson exposed from telson beak, not exposed 90˚, exposed from from telson telson

Male Not entering into buccal Not entering into buccal Not entering into buccal Not entering into Unknown Entering into buccal

sternoabdominal cavern cavern cavern buccal cavern cavern

cavity and telson

There is two more gaeticine genera, Gopkittisak Naruse & Clark, 2009 , and Brankocleistostoma Števčić, 2011. Naruse & Clark (2009) indicated that Gaetice and Gopkittisak share an oblique border between the third maxilliped ischium and merus, which is unique in Grapsoidea MacLeay, 1838. Gopkittisak , however, differs from Gaetice by the characters that are related to suspension feeding; length of the palp and setae of the third maxilliped is proportionately shorter in Gopkittisak ( Naruse & Clark 2009: fig. 1c, Komai 2011: fig. 2E) than in Gaetice ( Fig. 1 a), the third maxilliped dactylus is developed from the distal end of propodus in Gopkittisak ( Fig. 2 e), but it is from the subdistal portion of the outer surface of the propodus in Gaetice ( Fig. 2 a), and the anterior thoracic sternum is widely and shallowly depressed on the sternites 2 and 3 in Gopkittisak ( Komai 2011: fig. 2F), but it is very narrow and deep on the sternites 2 and 3 in Gaetice ( Fig. 1 a). Brankocleistostoma agrees with Gopkittisak in the above-mentioned characters (Ng 2012: figs. 3D, E, 5B). The systematic positions of Gopkittisak and Brankocleistostoma also need to be reassessed.

Genera included. Gaetice Gistel, 1848 [type genus, by original designation]; Acmaeopleura Stimpson, 1858 ; Brankocleistostoma Števčić, 2011; Gopkittisak Naruse & Clark, 2009 ; Sestrostoma Davie & N.K. Ng, 2007 ; and Proexotelson n. gen. (this study).

Figures

FIGURE 1. Anterior thoracic sternum and third maxillipeds. a, Gaetice depressus (De Haan, 1835) (RUMF-ZC- 1814, male, 24.0 × 29.3 mm); b, Sestrostoma balssi (Shen, 1932) (CBM ZC 8146, male, 9.2 × 12.1 mm); c, Sestrostoma depressum (Sakai, 1965) (CBM ZC 7012, male, 5.0 × 6.1 mm); d, Acmaeopleura parvula Stimpson, 1858 (RUMF-ZC- 2939, male, 6.9 × 8.5 mm). 2 / 3, suture between thoracic sternites 2 and 3; G 1, male first gonopod; ms, median sulcus; S 2 l, lateral end of thoracic sternite 2; S 3, 4, thoracic sternite 3 and 4.

FIGURE 2. Palp of left third maxilliped in anterior view. a, Gaetice depressus (De Haan, 1835) (RUMF-ZC- 1814, male, 24.0 × 29.3 mm); b, Sestrostoma balssi (Shen, 1932) (CBM ZC 8146, male, 9.2 × 12.1 mm); c, Proexotelson tokoroi n. sp. (holotype, RUMF-ZC- 3669, male, 3.0 × 3.8 mm); d, Acmaeopleura parvula Stimpson, 1858 (neotype, RUMF-ZC- 2939, male, 6.9 × 8.5 mm); e, Gopkittisak angustum Komai, 2011 (RUMF-ZC- 3673, female, 5.5 × 10.0 mm). Ca, carpus; Da, dactylus; Pr, propodus; Pr-d, distal end of propodus.