Spongoclonium caribaeum (Børgesen) M.J. Wynne, 2005: 23

Mateo-Cid, Luz Elena, Mendoza-González, A. Catalina, Norris, James N. & García-López, Deisy Y., 2018, A taxonomic account of species in the tribe Spongoclonieae (Ceramiaceae, Ceramiales, Rhodophyta) reported from Atlantic and Pacific Mexico, Phytotaxa 340 (3), pp. 229-245 : 239-241

Spongoclonium caribaeum (Børgesen) M.J. Wynne, 2005: 23 , 87 ( Figs. 31–38 )

Basionym : Mesothamnion caribaeum Børgesen, 1917: 208 .

Homotypic synonym: Pleonosporium caribaeum (Børgesen) R.E. Norris, 1985: 61 .

Type locality: Annaberg, St. John, U. S. Virgin Islands [ USVI], Leeward Islands, Caribbean Sea ( Silva et al., 1996: 419).

Distribution. WESTERN ATLANTIC: Bahamas; Gulf of Mexico (Veracruz; Campeche), México; Puerto Rico; U.S. Virgin Islands, Colombia, Venezuela, and Brazil ( García and Gomez, 2007; Nunes et al., 2008; Mendoza-González et al., 2015; Ballantine et al., 2016; Wynne, 2017; herein).

Specimens studied. ATLANTIC MÉXICO. Veracruz: Escolleras de Tuxpan (97°23´57´´W, 20°57´18’’N), coll. Mateo-Cid, 19-08-2016 ( ENCB VER-16 - LE/01 ; ♂, ♀, polysporangia) ; and, Punta Puntillas (95°17´22´´W, 18°46´55´´N), coll. Mendoza-González & Mateo-Cid, 21-05-2016 ( ENCB VER-2017 / A; polysporangia) .

Habitat. Epizoic on mollusks and corals, and epiphytic on Acanthophora sp. ; intertidal.

Morphology, anatomy and reproductive structures. Thalli bushy, erect, up to 1.2 cm tall, reddish purple; primary axes ecorticate; branching principally distichous, regularly alternate, twisted, or polistichous, with several planes on the same axis; attached by a group of tangled rhizoid filaments. Branches near the apices extending and curving around the apical cell; branches of the second order generally simple, or may branch regularly alternate in distichous part and sometimes in abaxial series. Cells of main filaments terete, 160–175 μm in diameter, 110–125 μm long; middle cells 65–70 μm in diameter, 90–100 μm long; lateral branches with multicellular rhizoidal filaments from the basal cells that form a lightly rhizoidal cortication; middle of branch cells 120–130 μm in diameter, 90–120 μm long; determinate lateral branchlets usually simple, 10 cells in length, strongly curved; branchlet cells 35–40 μm in diameter, 70–80 μm long, with blunt tips (about half the dimensions of other cells).

Polysporangia sessile, ovoid to ellipsoid, about 74–80 μm in diameter (including thick hyaline cell wall), divided into eight or sixteen spores; borne in alternate groups on densely branched portions of thallus of short irregular branches. Gametangial thalli dioecious. Spermatangial clusters subcylindrical, 15–20 μm in diameter, 60–70 μm long, sessile, and adaxial on lateral branchlets. Procarp three-celled, apical on short branches, consisting of a basal cell bearing a carpogonial branch and a sterile cell, in the middle of both is the auxiliary cell and on it a sterile apical cell is formed. Trichogyne cylindrical and persistent. Cystocarps not observed.

Remarks. Mesothamnion caribaeum Børgesen (1917 ; basionym) was originally described from Annaberg, St. John, USVI, Caribbean Sea. Since then Spongoclonium caribaeum has been widely reported in temperate, subtropical to tropical regions of Eastern Atlantic, Western Atlantic, Indian Ocean, Western Pacific, Central Pacific and South Pacific ( Silva et al., 1996; Guiry and Guiry, 2017).

Our specimens generally agree with S. caribaeum as detailed by Garcia and Gomez (2007) for Venezuela, and by Secilla (2012) for Bizkaia (Biscay), Spain. Although the diameter of the cells of main filaments and the polysporangia in our Veracruz specimens are smaller than those reported by Børgesen (1917), the structure of the spermatangial clusters and the procarps agree with those of Børgesen (1917) and Norris (1985). Our specimens are the first record for Veracruz and the second report on the Mexican coast of Gulf of Mexico, Atlantic Mexico.

Figures

FIGURES 25–32. Species of Pleonosporium: Pleonosporium pygmaeum, 25) Branch of sporophyte showing sessile polysporangia (arrow). Scale bar: 90 μm. Pleonosporium rhizoideum, Puerto Peñasco, Sonora (ENCB 16338). 26) Habit of sporophyte. Scale bar: 5 mm. 27) Basal portion of the thallus; note the attachment structure (arrow). Scale bar: 280 μm. 28) Branch tip of a sporophyte with curved branchlets. Scale bar: 100 μm. 29) Group of spermatangial clusters (arrow) borne on a single branch. Scale bar: 80 μm. 30) Group of mature carposporophytes (key), with carposporangia (arrow). Scale bar: 200 μm. Species of Spongoclonium: Spongoclonium caribaeum, Escolleras Tuxpan, Veracruz (ENCB VER-2017/A). 31) Branch tips from sporophyte showing branching axis and determinate lateral branchlets. Scale bar: 600 μm. 32) Ecorticate axis and determinate lateral branches. Scale bar: 300 μm.

FIGURES 33–38. Spongoclonium caribaeum. 33) Sporophyte with numerous polysporangia. Scale bar: 450 μm. 34) Sessile mature polysporangia. Scale bar: 90 μm. 35) Sessile spermatangial cluster (arrow). Scale bar 70 μm. 36) Procarp four-celled stage (arrows). Scale bar: 75 μm. 37) Procarp at five-cell stage (arrow). Scale bar: 110 μm. 38) Young procarp with carpogonium initiating the trichogyne (arrow). Scale bar: 150 μm.