06 Chthamalus stellatus

Diameter 8 mm. Tergoscutal flaps: brown mark at rostral (lower) end (1), bright orange mark at micropyle (2) and orange lobe next to rim of flap at carinal (upper) end (3). Area of light blue flap next to white rim in rostral half (4). Surrounded by smaller C. montagui (5) Portland Bill, Dorset.

 

Full SPECIES DESCRIPTION below

Sets of OTHER SPECIES at: www.flickr.com/photos/56388191@N08/collections/.

 

Chthamalus stellatus (Poli,1791) text I.F. Smith

 

Recent synonyms

Pre 1976 records include Chthamalus montagui Southward, 1976.

Vernacular names

Star barnacle, Poli’s stellate barnacle, Crachen Poli (Welsh).

 

DESCRIPTION **Glossary below.

 

opercular aperture (top opening)

Approximately broadly oval Cs1[flic.kr/p/bXnEBf], but often with tendency to flat sections of perimeter; some may approach kite-shape Cs2[flic.kr/p/bXnEHY] of C. montagui

 

opercular valves (lid plates)

Four valves, two terga and two scuta, open along longitudinal midline with a tergum and scutum each side Cs3[flic.kr/p/bXnEPE]. Whether closed or open, valves usually just below, or level with, rim of aperture, and each tergum fixed to its scutum (sometimes even after treatment with bleach) Cs4[flic.kr/p/bXnESy]). Terga fill a third or more of aperture. A few growth lines may be seen on the rostral end of the scuta Cs3[flic.kr/p/bXnEPE].

 

tergoscutal flap (membranous seal on lid plates).

Bluish; varying grey-blue, white faintly tinted blue, bright blue to entirely electric blue. Bright orange mark at micropyle Cs5[flic.kr/p/bXnEXs] Orange-brown to dark brown mark at rostral end. Bright orange longitudinal lobe at carinal end (fully exposed when valves open Cs6[flic.kr/p/bXnF4b]). Between micropyle and carina, away from the rim, the flap may be orange-brown.

wall plates

Six; delineating sutures often only visible on juveniles as usually fused Cs7[flic.kr/p/bXnFoJ] and difficult to discern on older ones. Rostral plate narrow Cs8[flic.kr/p/bXnFhu], butts onto lateral plates. Plates solid, not porose, but some holes near aperture internally Cs9[flic.kr/p/bXnFxd]. After bleaching, white with some pink-brown, especially internally near aperture. Often discoloured dull yellow in life and heavily eroded and/or punctured by Cliona celata, boring sponge Cs10[flic.kr/p/bXnFaQ].

 

profile

When isolated, low mound Cs8[flic.kr/p/bXnFhu] often very depressed. When crowded, low column about 6mm high Cs11[flic.kr/p/bXnFB3].

 

base

Black membrane. Bright orange-red Cs12[flic.kr/p/bXnFF1] flesh visible in barnacle when removed from substrate.

 

diameter & height

Usually under 10mm diameter, occasionally to 14mm. Crowded columns about 6mm high.

 

IDENTIFYING FEATURES

Aperture: Approximately broadly oval Cs1[flic.kr/p/bXnEBf], BUT can vary to rounded kite.

Tergoscutal flaps: White to blue, with bright orange at micropyle and carinal end. Cs6[flic.kr/p/bXnF4b]

Base plate: Black membrane. Bright orange flesh inside barnacle Cs12[flic.kr/p/bXnFF1]

Wall plates: Rostral plate narrow Cs8[flic.kr/p/bXnFhu] butts onto lateral plates.

Tide level: Commonest MTL to MLWS, some up to HW. Not sublittoral.

 

SIMILAR SPECIES

Chthamalus montagui

Aperture: Kite shape (not-equilateral diamond), BUT can vary to rounded kite.

Tergoscutal flaps: White to blue, with brown at micropyle and carinal end Cm1[flic.kr/p/bYFMLS].

Wall plates: Rostral plate narrow Cm, butts onto lateral plates Cm2[flic.kr/p/bYFNbS]

Base plate: Black membrane. Dull yellow flesh inside barnacle Cs12[flic.kr/p/bXnFF1]

Tide level: Commonest HWS to HWN, some down to LWN. Not sublittoral.

 

Semibalanus balanoides (some juveniles in wave exposed positions)

Aperture: Oval.

Tergoscutal flaps: Whitish to grey with white rim, brown/blackish at rostral end, brown at micropyle, but white at carinal end Sb10[ flic.kr/p/bFdLky].

Wall plates: Lateral plates butt onto wide rostral plate Sb4[flic.kr/p/bFdL67].

Profile: Depressed.

Base plate: Membranous.

 

ECOLOGY

Stenohaline, full salinity. Commonest MTL to MLWS, some up to HW, not sublittoral. On rock and live limpets Cs13[flic.kr/p/bXnFPY] exposed to strong and very strong wave action, where it is may be the dominant littoral barnacle. Usually overlaps with shore zones of Balanus semibalanoides and Chthamalus montagui. In Britain, breeds April to September, cyprids settle July to December.

Masses of Chthamalus near high water mark on shores exposed to strong waves are a favoured habitat of the isopod Campocea hirsuta and juveniles of the gastropod Melarhaphe neritoides Cs2[flic.kr/p/bXnEHY].

 

DISTRIBUTION

N.E. Atlantic coasts from Shetland to Azores, Canaries and N.W. Africa, and into Mediterranean and Black seas. See GBIF map www.gbif.org/species/2115620

British coasts westwards from Isle of Wight to Scilly and thence north to Shetland. Most Irish coasts, except Larne to Dublin. Southward (2008) wrote, “It straggles down the east coast of Scotland in small numbers, mostly in cryptic situations [deep cracks in rock], as far as Stonehaven. - - It is missing from the north Wales coast east of Holyhead, and from Lancashire, Cumbria, the Galloway peninsula and the Clyde Sea”. Records of it on NBN from these areas of reported absence require evidence of the tergoscutal flap for substantiation as the shell and aperture can overlap in appearance with that of C. montagui which is often mistaken for it. Those in situations of low wave action are especially suspect . See NBN map at species.nbnatlas.org/species/NBNSYS0000174548

 

CURRENT TAXONOMY

World Register of Marine Species www.marinespecies.org/aphia.php?p=taxdetails&id=106231

 

Glossary

ala – (pl. alae) side flange of wall plate, overlapped by radius of next plate.

carina – posterior wall plate adjoining the smaller pair of lid plates (terga). carinal – (adj.) of the carina.

cirri – (sing. cirrus) feather-like thoracic limbs used in filter feeding.

cypris – (pl. cyprids) final larval bivalved stage in barnacle development.

euryhaline – tolerant of wide range of salinities.

HW- high water level.

HWS- level of high water spring tide.

lateral plates - wall plates other than end plates (depending on sp., strictly may be rostro-lateral or carino-lateral).

LWN- level of low water neap tide.

micropyle – small breathing/sensing hole between tergoscutal flaps, sometimes visible when operculum shut. Found on spp. that are left out of water for long periods.

MLWS- level of mean low water spring tide.

MTL – mid-tide level.

opercular – (adj.) of the operculum (aperture lid).

operculum – moveable lid-like structure used to close the aperture.

paries – ( pl. parietes) central section of wall plate, flanked by alae and radii.

ppt – parts per thousand (of salt in water).

radius – (pl. radii) side flange of wall plate, overlaps ala of adjacent plate.

right – on right when barnacle viewed from above with rostrum at 12 o’clock.

rostral - (adj.) of the rostrum.

rostrum - anterior wall plate adjoining larger pair of lid plates (scuta). (Lost on Elminius and balanoids; place taken by fused rostro-laterals; referred to as rostrum for simplicity.)

scuta – (sing. scutum) the larger plates of the operculum (lid).

sessile – (adj.) permanently attached to substrate (of immobile organism).

stenohaline – unable to tolerate much variation in salinity.

terga – (sing. tergum) the smaller plates of the operculum (lid).

tergoscutal flaps - membranous “lid seals", (most visible as valves start to open).

 

 

References & links

 

Rainbow, P.S., 1984. An introduction to the biology of British littoral barnacles. Field studies 6: 1-51.

fsj.field-studies-council.org/media/350581/vol6.1_161.pdf

 

Southward, A.J., 2008. Barnacles. London, Linnean Society.

 

 

Done