Acasta sandwichi, Yu & Chan & Achituv & Kolbasov, 2017

Yu, Meng-Chen, Chan, Benny K. K., Achituv, Yair & Kolbasov, Gregory A., 2017, Four new sponge-inhabiting barnacles of the genus Acasta (Thoracica: Archaeobalanidae: Acastinae) from the Indo-Pacific, Raffles Bulletin of Zoology 65, pp. 585-615 : 606-613

Acasta sandwichi , new species

( Figs. 22–28 )

Material examined. Four specimens (holotype and paratypes) in the sponge Xestospongia testudinaria ( Lamarck, 1815) , Daping , Yeliou, Wanli, Taiwan , 25°12′45″N, 121°42′04″E, SCUBA diving, depth 18 m. The holotype (dry shell compartments, mouth parts and cirri mounted in glycerol on glass slide) and paratype (shell in EtOH) are deposited in the Zoological Museum of Moscow State University under registration numbers Mg –1228 (holotype) and Mg – 1229 (paratype). The other paratypes ( ASIZCR000378 to ASIZCR000380 ) are deposited in the Biodiversity Research Museum , Biodiversity Research Center, Academia Sinica, Taiwan .

Diagnosis. Shellwhitepinkishorwhitebrown, semitransparent, with 6 conspicuous windows between wall plates; parietes with wide radii and alae; inner lamina with longitudinal ribs; basis saucer-shaped, denticulated margin with 6 notches; scutum without distinct radial striation; spur of tergum ~1/3 width of basal margin; anterior ramus of cirrus IV with small, sharp denticles; penis with basidorsal point. Embedded in sponge Xestospongia testudinaria ( Lamarck, 1815) .

Description. (Based on holotype). Shell white pinkish or white brown, semitransparent, slightly elongated in height,

~ 5.5 mm and 4.2 mm maximal height and diameter, 3.4 mm rostro-carinal basal diameter; orifice toothed, with curved apical ends of carina and rostrum; 2.7 mm maximum length; with 6 conspicuous windows between wall plates ( Fig. 22A–C ). Basis saucer-shaped; with 6 external radial grooves; growth lines concentric; margin denticulated, with paired small teeth; often with 6 notches corresponding to windows ( Figs. 22A, B , 23I ). Parietes ( Fig. 22 ) with conspicuous, sharp external projections and fine growth lines; sheath ~2/5–1/2 total length, with horizontal striations; inner lamina beneath sheath with few long, distinct longitudinal ribs. Radii and alae wide, semitransparent, summits oblique, ~1/3–1/2 length of parietes; radii with fine, oblique and transverse external striations. Carinolatus 2 narrow, with paries ~1/5 width of carinolatus 1 ( Fig. 22A–C, F ).

Scutum ( Fig. 23A–D ) semitransparent, white, height longer than width; external growth ridges with feeble, reduced longitudinal striations; occludent margin slightly dentate. Articular ridge ~1/2 length of tergal margin, not prominent, lower end smooth, not truncated; articular furrow shallow; adductor ridge conspicuous and thick; pits for adductor and depressor muscles shallow, but visible.

Tergum ( Fig. 23E–H ) semitransparent, white, growth lines fine; apex beak-shaped, tinged with pale viole; scutal margin straight in lower and concave in upper parts; spur developed, ~1/3 half of width of basal margin, not truncated, separated from basiscutal angle; spur furrow shallow and wide. Articular ridge developed, concave, ~2/3 of scutal margin, depressor muscle crests absent.

Labrum ( Figs. 24A , 26A–C ) with deep medial notch; 3 teeth on each crest; dense, thin and small setae along margins of crests. Crests of labrum with dense ctenoid scales ( Fig. 26B ). Mandibular palps ( Figs. 24A , 26A, C ) club-shaped; with dense, long, setulate setae, small thin simple setae and ctenoid scales with long denticles on distal half; lateral surfaces with small, simple setae; rows of ctenoid scales with short denticles at base. Mandibles ( Figs. 24B, C , 26D–F ) cutting edge with 5 teeth decreasing in size from upper to lower; teeth 1–3 well separated from each other; tooth 3 bifid; tooth 4 complex, multifid; inferior angle short, with group of sharp, small denticles and setae; inner margin with long, simple setae; outer margin and upper part of blade with long, thin, omniserrate setae; lateral surface of blade with combs of dense, biserrate setae. Maxillules ( Figs. 24D, E , 26G–I ) with 10–11 cuspidate setae of different lengths along straight cutting edge; notch absent; upper and lower pairs of cuspidate setae largest; small, cuspidate setae inserted below lower pair of large setae; tuft of small, sharp, cuspidate setae on inferior angle; long, simple setae and serrate setae along outer and inner margins; biserrate setae on lateral surface. Maxillae ( Fig. 27A–D ) bilobed; dense, long, simple setae and serrate setae distally and along inner margins of upper and lower lobes; lateral surfaces of upper lobes with ctenoid scales and small, simple setae; field of stub setae in upperlateral part of lower lobe; dense carpet of sharp, biserrate setae and fine, small setae in fused basal parts.

Cirrus I ( Fig. 28B–D ) with rami unequal; anterior ramus (13 annuli) twice longer than posterior ramus (7 annuli); annuli of rami with dense, serrate setae and row of ctenoid scales with long, sharp denticles along upper margins; basal annuli with ctenoid scales on lateral surfaces. Cirrus II ( Fig. 28A, E, F ) with rami unequal; anterior ramus (10 annuli) longer than posterior ramus (8 annuli); annuli of rami with long, dense simple setae and serrate setae on anterior edge, tuft of serrate setae in posterio-distal corner; groups of ctenoid scales with sharp denticles on lateral surfaces at anterior and posterior setae ( Fig. 28F ). Cirrus III ( Fig. 28G, H ) with rami subequal, with 12 annuli both; denticles absent; long, serrate setae in upper halves of anterior margins, lateral surfaces and posterio-distal corners of annuli. Cirrus IV ( Figs. 25A , 28I, J ) with posterior ramus (23 annuli) slightly longer than anterior ramus (20 annuli); proximal annuli of anterior ramus with single, sharp, straight denticle on anterior edge; middle annuli of anterior ramus with 2–3 pairs of long, middle and short serrulate setae on anterior edge; 2–3 pairs of short setae on lateral surface, tuft of simple setae on posteriodistal corner; middle annuli of posterior ramus with 3 pairs of long, middle and short serrulate setae on upper part of anterior edge, tuft of thin simple setae on posterio-distal corner, few ctenoid scales along upper margins. Cirrus V ( Fig. 28K, L ) with rami subequal (25, 26 annuli); annuli of anterior ramus without denticles; middle annuli with 3 pairs of long, middle and short serrulate setae on anterior edge, tuft of setae on posterio-distal corner; row of ctenoid scales along upper margins. Cirrus VI ( Fig. 28A ) with rami subequal (27, 26 annuli); intermediate annuli of both rami with 3 pairs of long, middle and short serrulate setae; some annuli with few long, thin setae on posterio-distal corner; inner lateral surface of coxa with dense ctenoid scales with long denticles and short serrate setae ( Fig. 27E ).

Penis ( Figs. 25B , 27E ) annulated; basidorsal point developed; gradually tapering distally; tip with few thin simple setae.

Remarks. The new species, Acasta sandwichi , is similar to the species of genus Acasta : A. armata Gravier, 1921 (= A. sinica Ren, 1984 ), Acasta crucibasis sp. nov. (herein), A. fenestrata Darwin, 1854 , A. foraminifera Broch, 1931 , A. pertusa Kolbasov, 1990 , and A. tzetlini Kolbasov, 1992 , in having conspicuous windows between the wall plates. Acasta sandwichi differs from A. foraminifera and A. crucibasis in having developed carinolatus 2 with paries reaches the basis. A new species differs from A. tzetlini in the absence of armament of recurved teeth on anterior ramus of cirrus IV. A. fenestrata and A. armata have no longitudinal ribs on inner lamina of parietes. A. pertusa has no denticles on annuli of anterior rami of cirrus IV, scutum covered with external setae and the tergal spur is about 1/2 of width of basal margin.

Etymology. We named this species after our collaborator from Green Island Marine Laboratory, Biodiversity Research Center, Academia Sinica, Taiwan, and our friend, Mr. Chang Ming-Chih, who helped us in SCUBA diving collections of sponge hosts and who preferred to use his nickname ‘Sandwich’ for specific name of this species.

Figures

Fig. 22. Acasta sandwichi sp. nov., shell, general view and compartments (holotype: A, B, D–H; paratype: C, I, J). A, B, Complete shell, left and right side, windows between wall plates indicated by arrowheads; C, Complete shell, right side, windows between wall plates indicated by arrowheads; D, E, Rostrum, external and internal surface; F, Carinolatus 2, internal surface; G, H, Carinolatus 1, internal and external surface; I, Rostrum, internal surface; J, Carina, internal surface. Abbreviations: ba = basis, ca = carina, cl1 = carinolatus 1, cl2 = carinolatus 2, r = rostrum. Scale bars in µm.

Fig. 23. Acasta sandwichi sp. nov., opercular plates and basis (holotype: A–H, paratype: I). A, B, Right scutum, external and internal view; C, D, Left scutum, external and internal view; E, F, Left tergum, external and internal view; G, H, Right tergum, external and internal view; I, Basis, internal view. Scale bars in µm.

Fig. 24. Acasta sandwichi sp. nov., mouth parts (holotype). A, Labrum and mandibular palps; B, C, Mandibles; D, E, Maxillules. Scale bars in µm.

Fig. 25. Acasta sandwichi sp. nov., cirri and penis (holotype). A, Cirrus IV, basal and middle annuli; B, Distal part of penis. Scale bars in µm.

Fig. 26. Acasta sandwichi sp. nov., mouth parts (SEM, paratype). A, Labrum and mandibular palps; B, Crests of labrum with ctenoid scales; C, Upper part of mandibular palp; D, Mandible; E, Lower part of mandible; F, Biserrate setae on lateral surface of mandible; G, Maxillule; H, Upper part of maxillule; I, Cutting edge of maxillule. Abbreviations: lb = labrum, mdp = mandibular palp. Scale bars in µm.

Fig. 27. Acasta sandwichi sp. nov., maxillae and penis (SEM, paratype). A, B, Maxillae, lateral and outer surface; C, Distal lobes of maxillae, upper parts; D, Proximal lobe of maxilla, lateral view (stub setae indicated by arrowheads); E, Basal part of penis (basidorsal point indicated by asterisk). Abbreviations: c4 to c6 = cirri IV to cirri VI, pe = penis. Scale bars in µm.

Fig. 28. Acasta sandwichi sp. nov., cirri (SEM, paratype). A, Left pairs of cirri with penis; B, Cirrus I; C, Annuli of rami of cirrus I; D, Terminal annuli of anterior ramus of cirrus I; E, Cirrus II; F, Middle annuli of cirrus II; G, Cirrus III; H, Basal and middle annuli of cirrus III; I, Cirrus IV; J, Basal and middle annuli of cirrus IV; K, Cirrus V; L, Middle annuli of cirrus V. Abbreviations: ar = anterior ramus, c2 to c6 = cirri II to cirri VI, lb = labrum, pe = penis. Scale bars in µm.