Acasta radenta Yu & Kolbasov & Hosie & Lee & Chan 2017, sp. nov.
Creators: name: Yu, Meng-Chen
name: Kolbasov, Gregory A.
name: Hosie, Andrew M.
name: Lee, Tse-Min
name: Chan, Benny K. K.
Publisher: name: Zenodo
Year: 2017
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Maxillopoda
Sessilia
Archaeobalanidae
Acasta
Acasta radenta

description: Acasta radenta sp. nov.
Figs 18 ̄24
Material examined. Holotype: ASIZCR000368, Longdong, Gongliao, New Taipei City, Taiwan (25°06′50.27″N, 121°55′13.40″E, water depth 17 m), July 2011, coll. J.H.Y. Yu, on host sponge Jaspis splendens (de Laubenfels, 1954).
Diagnosis. Shell white, tinged pinkish towards apex. Basis saucer-shaped, pointed towards center, with crenated rim. Shell with membrane-covered clefts at parietal junctions. Externally parietes smooth, internally basal longitudinal ribs feeble. Scutum with horizontal growth ridges and fine longitudinal striations. Tergum with sharp, beaked apex, spur truncated, width about 2/3 of basal margin. Teeth on anterior ramus of cirrus IV almost straight or only slightly curved.
Description. Shell white, tinged pinkish towards apex (Fig. 18 ĀD). Basis saucer-shaped, becoming pointed at central umbo, basal rim strongly crenated (Figs 18 E, 19M, N). Narrow clefts covered with membrane between basal junctions of parietes (Fig. 18 B, C). Parietes lacking external projections, with fine growth striations, radii with both inclined and horizontal striations; parietes internally with short, indistinct, longitudinal ribs on basal margin, sheath surface with slight horizontal striations except carina, sheath of carina with rugged horizontal ridges; radii with horizontal ridges, alae with horizontal striations, neither reaching to basal margin of parietes, lateral edges of alae white, thickened (Fig. 19 ĀL). Carinolaterals narrow, about 1/5 of width of laterals (Fig. 19 ḠJ).
Scutum (Fig. 18 F, G) externally with horizontal growth ridges and delicate longitudinal striation, covering the whole surface, occludent margin toothed. Internal sculpture feeble, articular ridge not prominent, not truncated, about 2/3 of length of tergal margin, adductor ridge not distinct, short, adductor pit absent, lateral depressor pit shallow. Tergum (Fig. 18 H, I) semitransparent, apex beaked, tinged with red, with fine growth lines, spur broad, truncated, square shaped, width about 2/3 of basal margin, narrowly separated from basiscutal angle, spur furrow wide, shallow; articular ridge short, reddish, crests of depressor muscles absent.
Counts of cirral segments given in Table 1. Cirrus I with rami unequal; anterior margin of protopod without setae, base of posterior margin with serrulate setae (Fig. 20 A), distal margins of terminal segments of anterior and posterior rami with simple and bifid setae (Fig. 20 B, C). Cirrus II longer than cirrus I; rami unequal, protopod anterior and posterior margins with serrulate and plumose setae, respectively (Fig. 20 D), distal segment of posterior ramus with bifid setae (Fig. 20 E). Cirrus III with rami unequal; protopod anterior and posterior margins with serrulate and plumose setae, respectively (Fig. 20 F), distal segments of rami with bifid and serrulate setae (Fig. 20 G), anterior and posterior rami with small ctenes, without denticles (Fig. 20 H). Cirrus IV with broken rami, protopod posterior margin with long plumose and short serrulate setae (Fig. 21 A). Basis bearing short, simple setae and 10 straight rather than curved teeth on anterior margin (Fig. 21 B), proximal segments of anterior ramus bearing 1̄2 similar straight teeth and row of sharp denticles on anterior edges (Fig. 21 C̄F), intermediate segments with 2 pairs of long and short serrulate setae (Fig. 21 G, H). Cirrus V with broken rami; protopod with anterior serrulate and posterior simple setae, irregular pairs (1̄3) setae on intermediate segments (Fig. 22 A, B). Cirrus VI with broken rami, anterior and posterior margins of protopod with serrulate and short simple setae respectively, intermediate segments with 2 pairs of long and short serrulate setae (Fig. 22 C, D). Penis finely annulated, gradually tapering to tip (Fig. 22 E), tip broken (Fig. 22 F), with long setae (Fig. 22 G), basidorsal point absent (Fig. 22 H).
Maxillae bilobed, oblong (Fig. 23 A), terminal part with serrulate setae, (Fig. 23 B), outer edge with short serrulate setae, inner edge straight, distal lobe with thick serrulate setae (Fig. 23 C), basal lobe with serrulate setae (Fig. 23 D). Maxillule (Fig. 23 E) straight cutting margin straight without notch, with 10 large cuspidate setae, pairs of upper and lower largest (Fig. 23 H), upper and lower margins with long simple setae (Fig. 23 F, G). Mandible with 5 teeth (Fig. 24 A), second to fourth teeth bifid, inferior angle ending in a couple of sharp denticles, lower margin with stout simple setae (Fig. 24 B), upper margin of lateral angle bears simple setae (Fig. 24 C). Mandibular palp broadly truncated (Fig. 24 D), dense serrulate setae terminally (Fig. 24 E), outer margin concave, with thick serrulate setae (Fig. 24 F). Labrum bilobed, separated by deep V-shaped notch (Fig. 24 G), crests without teeth (Fig. 24 H).
Remarks. This species also shares several common morphological characters with A. sulcata, including i) the crenate basal rim, ii) the beak-shaped tergum with a wide truncated spur, iii) the feeble inner sculpture of the scutum, and i v) the armament of teeth on the anterior ramus of cirrus IV. However, this species can be distinguished from A. sulcata in having i) a wider tergal spur (approximately 2/3 of the basal margin compared with 1/ 2 in A. sulcata), ii) the fine longitudinal striations of the scutum (absent in A. sulcata), iii) the feeble, basal, inner ribs of the parietes (ribs reaching the sheath in A. sulcata), and iv) the segments of the anterior ramus of cirrus IV bearing rather straight teeth (curved in other members of the “ sulcata species complex). This species is also similar to A. conica Hoek, 1913, in having longitudinal striations on the scutum, but differs in having a wider tergal spur, the absence of external projections on the parietes, and the straight teeth on the anterior ramus of cirrus IV. Acasta radenta sp. nov. differs from A. aspera sp. nov. in having a wider tergal spur, more feeble internal parietal ribs, and better developed armament of cirrus IV, consisting of straight teeth. Acasta radenta sp. nov. differs from A. huangi sp. nov. in having membrane-covered clefts between the shell plates and the wider spur of the tergum. The absence of teeth on the crests of the labrum also sets this species apart from others of the sulcata species complex.
Etymology. The word ‘ radenta ’ is derived from the Latin radent, meaning shave, referring to the strongly developed cirral armament used to scrape back the growing margin of the sponge.
description: Published as part of 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), pp. 151-198 in Zootaxa 4277 (2) on pages 172-179, DOI: 10.11646/zootaxa.4277.2.1, http://zenodo.org/record/809554