Acasta fenestrata   Darwin,  1854 (Barnacle)
Organism information awaits expert curation
Class: Maxillopoda

Size: Carino-rostral diameter 2.8 mm, carinorostral basal diameter 6.3 mm; height from apex of rostral valve to bottom of basal cup 8.6 mm.

Shell: Tall globular, white, compartments with membrane covered apertures, moderately calcified quite difficult paring intact animal from host sponge; parietes with chitinous pliable spines seated on calcareous elevations; carino-lateral compartment about 1/5 in basal width of lateral compartment reaching basal cup, internally ribbed like other plates; radii, summits oblique basally terminating in a point not reaching basal cup; margin crenated. Alae summits oblique. Basal cup shallow, margin crenated; orifice narrow.
Scutum: Triangular, pointed, externally slightly concave, growth ridges pronounced marked by prominent radiating stripes; basi-tergal angle rounded off; occludent margin straight and toothed; articular ridge low but distinct; articular furrow narrow; a distinct narrow longitudinal furrow along occludent side present; pits for adductor and depressor muscles distinct.
Tergum: Triangular, apex produced, spur long transversely pointed about 1/2 the width of basal margin, fasciole shallow with prominent growth ridges; space between spur and basi-scutal angle very narrow; scutal margin straight, carinal margin slightly convex; articular ridge short and low; articular furrow narrow and shallow; crests for depressor muscles faintly indicated, inner surfaces roughened by minute points.
The numbers of segments of the cirri:
Left row:
anterior ramus: 20 - I; 12 - II; 18 - III; 19 - IV; 22 - V; 31 - VI and
posterior ramus: 7 - I; 10 - II; 14 - III; 23 - IV; 24 - V; 15 (incomplete) - VI.
Right row:
anterior ramus: 22 - I; 13 - II; 16 - III; 13 - IV; 27 - V; 30 - VI and
posterior ramus: 7 - I; 10 - II; 14 - III; 23 - IV; 30 - V; 32 - VI.
Left row:
anterior ramus: 17 - I; 9 - II; 12 - III; 17 - IV; 24 - V; 27 - VI and
posterior ramus: 6 - I; 7 - II; 9 - III; 20 - IV; 26 - V; 27 - VI.
Right row:
anterior ramus: 17 - I; 9 - II; 11 - III; 17 - IV; 24 - V; 26 - VI and
posterior ramus: 6 - I; 8 - II; 9 - III; 20 - IV; 23 - V; 23 - VI.
Anterior ramus of Cirrus I, 2-3 times longer than posterior ramus, frontal margin setose, larger setae on upper and terminal segments of posterior ramus strongly serrated like those on Cirri II and III, anterior ramus a little longer than posterior ramus. Cirri IV to VI segments elongated, intermediate ones bears 3 pairs of subequal setae, larger setae finely pinnate. In Cirrus IV basal segments of anterior ramus, except first and / or second armed with 1-3 downwardly curved hook-like teeth; few upper segments bears minute upwardly directed sharp spines similar to those on rami of Cirrus III, hook-like teeth absent on protopodite. Cirri IV to VI rami equal or unequal, frontal margin of intermediate segments bears 3 pairs of sub equal setae, proximal pair minute.
Mouth parts: Labrum with a central notch, crest hairy with 2 to 4 teeth or denticles. Mandible with 4 teeth, 2nd to 4th teeth bifid, in some only 2nd and 3rd teeth are bifid; upper margin of 4th tooth denticulate; a small tooth-like denticle is usually present on margin between 4'h tooth and inferior angle.
Maxilla with straight cutting edge bearing 6, 7 or 9 spines, 2 uppermost and 2 lowermost spines are larger than intermediate spines, some of intermediate spines in individuals with 9 spines. the 3rd, 5th, and 7th spines or in individuals with only 6 or 7 spines, only 3rd and 5th spines counting from uppermost, have its distal inferior margin pectinated. The 2 lowermost large spines are followed by few minute straight setae; inferior angle rounded. Outer maxilla bilobed, upper lobe elongated, apex more or less produced, frontal margin densely setose.
Penis very long, slender, annulated sparsely clothed with fine hairs. Basi-dorsal point present and prominent.

Ovigerous with eggs inside mantle sac cavity.

Synonym (s)
Acasta fenestrata Darwin 1854
Acasta fenestrata Hoek 1883
Acasta fenestrata Hiro 1939
Acasta fenestrata Nilsson-Cantell 1938a
Acasta fenestrata Utinomi 1958
Acasta fenestrata Rosell 1972

Common Name (s)
Economic Importance and Threats



• Madras Presidency INDIA (Record: 2006)
• INDIA (Record: 2006)

Literature Source(s)
  • Fernando, SA (2006) Monograph on Indian Barnacles Ocean science and technology Cell, Kochi 9-199 Available at - NIO, Goa
  • Society for the Management of European Biodiversity Data (2009) World Register of Marine Species (WoRMS) Available at -

Page last updated on:2012-05-22

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