Acasta aspera, Yu & Kolbasov & Hosie & Lee & Chan, 2017

Yu, Meng-Chen, Kolbasov, Gregory A., Hosie, Andrew M., Lee, Tse-Min & Chan, Benny K. K., 2017, Descriptions of four new sponge-inhabiting barnacles (Thoracica: Archaeobalanidae: Acastinae), Zootaxa 4277 (2), pp. 151-198 : 155-164

Acasta aspera sp. nov.

Figs 2 ̄10

Material Examined. Holotype: ASIZCR000365, Dabaisha , Green Island (Lyudao), Taitung, Taiwan (22°38′12.03″N, 121°29′30.93″E, water depth 8 m), May 2011, coll. J.H.Y. Yu, on host sponge Iotroata sp.

Paratype: CEL-SGI20-1—data same as for holotype.

Paratype: ASIZCR000366— Gongguan , Green Island, Taitung, Taiwan (22°40′47.22″N, 121°29′29.32″E, water depth 9 m), May 2011, coll. J.H.Y. Yu, on host sponge Iotroata sp.

Paratype: WAM C58741, WAM C58742, WAM C58743, Ningaloo Homestead Beach , Ningaloo Reef, Western Australia (22°40′32.8″S, 113°41′15.7″E, 0 m) May 2010, coll. A.M. Hosie, on host sponge Crella spinulata (Hentschel, 1911) .

Paratype: WAM C55057, Roe Reef , Rottnest Island, Western Australia (31°58′25.8″S, 115°32′13.2″E, water depth 14 m), Feb. 2014, coll. A.M. Hosie and A. Hara, on host sponge Crella spinulata (Hentschel, 1911) .

Diagnosis. Shell pinkish or yellow-brown, orifice edge toothed. Basis cup-shaped with crenate edge. Radii with creased edges. Externally, parietes rugged with several irregularly spaced calcareous projections; internally, sheath extending over half of parietes with vesicular structure, inner surface below sheath with longitudinal ribs.

Scutum with feeble growth ridges and longitudinal striations, articular furrow shallow. Tergum beaked, apex tinged with red, spur truncated, width less than 1/2 of basal margin. Curved teeth on anterior ramus of cirrus IV feeble. Cirrus V protopod with vertical row of denticles on posterior edge.

Description. Shell pinkish (Taiwanese specimens) or yellow-brown (Australian specimens) when extracted from sponge, both becoming white after treatment with bleach; orifice moderately small, toothed. Basis cupshaped, rim strongly crenate ( Figs 2 ĀE, 3M, N, 4A, N). Parietes externally rugged, with horizontal growth lines and several blunt, irregularly spaced, calcareous projections; radii with inclined and horizontal striation, edges creased (Australian specimens smoother), summits oblique; internally, sheath extending just over half of parietes, with vesicular structure, surface smooth; inner lamina below with longitudinal ribs, radii with horizontal ridges, alae with horizontal striation, both not reaching to basis. Inner and outer edges of alae white, thickened ( Figs 3 ĀL, 4F̄M). Australian specimens with conspicuous slits (clefts) about 1/5 of parietal length between plates ( Fig. 4 ĀC).

Externally, scutum with feeble growth ridges forming 12̄14 teeth on occludent margin, tooth size increasing gradually from apex to basal margin, feeble longitudinal striation in basal half of valve; internally articular furrow shallow, articular ridge low, not truncated, about 1/2 of length of tergal margin, adductor ridge short, pit of adductor muscle feebly developed, pit of depressor muscle rudimentary ( Figs 2 F, G, 4D). Tergum thin, semi-transparent, beaked apex tinged with red (Taiwanese specimens), growth ridges feeble, smooth, articular ridge short, spur narrow, truncated, square shaped, width about 3/7 of basal margin, spur furrow wide, shallow, scutal margin slightly raised, crests of depressor muscles absent ( Figs 2 H, I, 4E).

Counts of cirral segments given in Table 1. Cirrus I with rami unequal; serrulate and plumose setae only on posterior margin of protopod ( Fig. 5 A), serrulate and simple setae on distal margin of distal segments of posterior and anterior rami ( Fig. 5 B, C). Cirrus II longer than cirrus I; rami unequal, protopod with plumose and serrulate setae ( Fig. 5 D), distal segment of posterior ramus with serrulate setae ( Fig. 5 E). Cirrus III with unequal rami, anterior and posterior margins of protopod with serrulate and plumose setae, respectively, small denticles on anterodistal margin of basis ( Fig. 5 F), anterior and posterior rami with sharp denticles and ctenes on intermediate segments ( Fig. 5 G, H, 10A). Cirrus IV, rami subequal; anterior and posterior margins of protopod with serrulate and short simple setae, respectively ( Fig. 6 A), with few sharp denticles and short ctenes on posterodistal angle of coxa ( Fig. 6 B), lower segments of anterior ramus bearing a single, curved tooth on anterior margin in Taiwanese specimens ( Fig. 6 D, E), intermediate segments with 2 pairs of long and 1 pair of short, serrulate setae ( Fig. 6 C̄F), distal segments of anterior and posterior rami with simple and serrulate setae ( Fig. 6 G, H). Cirrus V with rami subequal; protopod with anterior and posterior margins bearing serrulate and few short simple setae, respectively ( Fig. 7 A), posterodistal surface of coxa with longitudinal row of 10-11 sharp denticles near posterior margin ( Fig. 7 B, 10C); intermediate segments of rami with 3 pairs of long, medium and short serrulate setae ( Fig. 7 C). Cirrus VI with rami unequal; protopod with few posterior short simple and anterior serrulate setae ( Fig. 7 E), intermediate segments with 3 pairs of long, medium and short serrulate setae, distal segments of anterior and posterior rami with serrulate setae ( Fig. 7 D, E).

Penis finely annulated, gradually tapering ( Fig. 7 G), tip with setae ( Fig. 7 I), basidorsal point vestigial ( Fig. 7 H, 10D).

TABLE 1. Segments count of cirral rami of five species of Acasta (* denotes broken rami).

Cirri C1 C2 C3 C4 C5 C6

A P A P A P A P A P A P A. aspera 14 6 8 6 11 9 18 18 24 25 21 27 A. huangi 15 7 10 8 4* 8 12 13 * 20 9* 8* 14 A. radenta 16 7 9 6 9 8 9* 10* 14* 14* 19* 22* A. sulcata 13 7 9 6 11 10 15 16 17 20 20 20 A. undulaterga 13 6 8 6 10 9 14 17 28 32 28 30 Maxilla bilobed, distal lobe with serrulate setae ( Fig. 8 B), basal part without setae ( Fig. 8 A); inner edge slightly concave, with dense setae ( Fig. 8 B, C). Maxillule, cutting margin straight without notch, with 10 spiniform cuspidate setae, upper and lower pairs largest ( Fig. 8 E), upper margin with 9 or 10 pairs of simple setae, lower margin with numerous simple setae ( Fig. 8 D, 10E). Mandible with 5 teeth ( Fig. 8 F, 10F), second bifid ( Fig. 8 H), inferior angle with 3 tiny denticles and stout setae, lower margin bearing simple setae ( Fig. 8 G). Mandibular palp broadly truncated ( Fig. 9 A, 10G), with dense, terminal, serrulate setae ( Fig. 9 D, E), outer margin concave ( Fig. 9 B, C). Labrum bilobed, with deep V-shaped notch, 2 small teeth on each crest ( Fig. 9 F, G,, 10H).

Remarks. This species is similar to A. sulcata ( Lamarck, 1818) in many morphological characters: i) the cupshaped basis with a crenate edge, ii) the inner longitudinal ribs of the parietes, iii) the inner sculpture of the scutum, iv) the beaked tergum with a truncate spur and wide, shallow furrow, v) the vestigial basidorsal point of the penis, and vi) the presence of curved teeth on the anterior ramus of cirrus IV. However, it differs from A. sulcata in having i) creased edges of the radii, ii) the rugged external surface of the parietes, iii) the feeble longitudinal striation in the basal part of the scutum, iv) the narrower tergal spur, and v) the less developed armament on cirrus IV. This new species is also similar to A. conica Hoek, 1913 , but differs in having more feeble longitudinal striation of the scutum, the armament of cirri III, IV and V; creased edges of the radii; and a rugged external surface of the shell plates. The denticles on the protopod of cirrus V are unique to the specimens examined in this study. On the basis of these differences, we concluded that A. aspera sp. nov. is a new species.

Because the radii and alae are not in contact with the basis, membrane-covered windows or clefts are often present between the shell plates. These are not conspicuous in all specimens. A close examination of the growth lines on the shell plates can indicate where these clefts may form. The mechanism underlying the variability of this character is unknown.

Etymology. The word ' aspera ' is derived from the Latin asper - asperous, rugged or rough.

Figures

FIGURE 2. Acasta aspera sp. nov. Complete shell, scuta and terga (Holotype). A, view from rostrum; B, view from lateral; C, view from carina; D, top view showing whole shell; E, view from basis; F, external view of scuta; G, internal view of scuta; H, external view of terga (one with broken basal part); I, internal view of terga (one with broken basal part);. Abbreviations: R, rostrum; CL, carinolateral; C, carina; S, scuta; T, terga. Scale bars = 1 mm.

FIGURE 3. Acasta aspera sp. nov. Disassembled shell after bleach treatment showing separated plates and basis (Holotype). A, B, external and internal view of rostrum; C, E, external view of laterals; D, F, internal view of laterals; G, I, external view of carinolaterals; H, J, internal view of carinolaterals; K, L, external and internal view of carina; M, N, external and internal view of basis. Scale bar = 1 mm.

FIGURE 4. Acasta aspera sp. nov. Complete shell, scuta, terga and disassembled shell. A, B and F ̅ M are specimen WAM- C 58741 (Paratype); C ̅ E and N are specimen WAM-C 55057 (Paratype). A, view from lateral; B, Close up of membranecovered clefts; C, view from lateral without basis, showing the clefts; D, external view of scuta; E, internal view of terga; F, G, external and internal view of rostrum; H, I, external and internal view of laterals; J, K, external and internal view of carinolaterals; L, M, external and internal view of carina; N. external view of basis. Scale bars = 1 mm.

FIGURE 5. Acasta aspera sp. nov. Cirri I (A ̅ C), II (D ̅ E) and III (F ̅ H) (Holotype). A, cirrus I; B, distal segments of posterior ramus; C, terminal segment of anterior ramus; D, cirrus II; E, bifid setae on anterior ramus; F, cirrus III; G, intermediate segments of anterior rami, denticles on anterior edge enlarged in rectangle area; H, intermediate segments of posterior rami, sharp denticles and ctenes on posterior edge enlarged in rectangle areas, respectively. Scale bars in µm.

FIGURE 6. Acasta aspera sp. nov. Cirrus IV (Holotype). A, Cirrus IV; B, posterior of protopod, small denticles and short ctenes on posterior surface of coxa enlarged in rectangle area; C, intermediate segments of posterior ramus; D, E, curved teeth on anterior ramus; F, serrulate setae on posterior ramus; G, H, terminal segments of anterior and posterior rami, serrulate setae on segments, enlarged in rectangle areas, respectively.. Scale bars in µm.

FIGURE 7. Acasta aspera sp. nov. Cirri V (A ̅ C), VI (D ̅ F) and penis (G ̅ I) (Holotype). A, cirrus V; B, posterior of protopod, denticles on posterior surface of coxa enlarged in rectangle area; C, 3 pairs of anterior setae on intermediate segments; D, cirrus VI; E, protopod; F, terminal segment of anterior ramus; G, penis; H, basal part of penis, showing rudimentary basidorsal point; I, tip of penis showing setae on tip. Scale bars in µm.

FIGURE 8. Acasta aspera sp. nov. Maxillae (A ̅ C), maxillule (D, E) and mandible (F ̅ H) (Holotype). A, maxillae; B, terminal parts of maxillae; C, inner edges of maxillae; D, maxillule; E, straight cutting margin showing 10 spiniform cuspidate setae; F, mandible; G, inferior angle showing 3 tiny denticles and stout setae; H, upper half showing bifid second tooth. Scale bars in µm.

FIGURE 9. Acasta aspera sp. nov. Mandibular palp (A ̅ F) and labrum (F ̅ H) (Holotype). A, mandibular palp; B, C, inner margin showing outer margin concave; D, E, terminal part showing serrulate setae in distal lobe; F, labrum; G, teeth on each crest of labrum; H, basal part of labrum. Scale bars in µm.