CLADOPHORALES

Coppejans, Eric, Leliaert, Frederik, Verbruggen, Heroen, de Clerck, Olivier, Schils, Tom, de Vriese, Thomas & Marie, Daniel, 2004, The marine green and brown algae of Rodrigues (Mauritius, Indian Ocean), Journal of Natural History 38 (23), pp. 2959-3020 : 2967

CLADOPHORALES ANADYOMENACEAE Microdictyon Decaisne Microdictyon tenuius J. Gray, 1866: 69 ( figure 2 )

References: Setchell, 1929: 486–490, figures 6–9 ; Børgesen, 1940, 1946, 1954 (as M. agardhianum Decaisne ).

Type locality. Near Jeddah , Saudi Arabia .

Voucher. HEC 14849 (zF), 29 September 2001, Grand Paté (s.s. 7) .

Ecology. On coral fragments in gulleys between coral heads, mixed with other small algae; at 15 m depth.

Distribution. India, Madagascar, Mauritius ( Børgesen, 1940: 25–28, figure 7 , pl. 2, figure 1 ; 1946: 18; 1954: 5), Rodrigues ( Dickie, 1877a: 7, as M. agardhianum Decaisne ), Sri Lanka.

Note. M. tenuius is placed in the Annuliferae group, section Eumicrodictyon on account of the anastomosis of the filaments by means of smooth rings on the cell apices, the mostly opposite branching pattern and the basal attachment over a large area of the thallus ( Setchell, 1929: 478, 486). The separation between the species in the section Eumicrodictyon (and in the genus altogether) is rather ambiguous. Millar (1999: 66) argues that characters defined by Setchell (1929) are untenable and that the genus may be represented by only four of its 18 current species. Representatives of the genus in the western Indian Ocean are currently under study. We refer to Silva et al. (1996: 934–936) for a discussion of the complex nomenclature of M. tenuius .

Figures

FIGS 2–6. Chlorophyta. (2) Microdictyon tenuius, detail of branching and anastomosing patterns (HEC 14849). (3) Bryopsis pennata var. pennata, branchlets of last order contiguous and in a single plane (HEC 14796 p.p.). (4) Bryopsis pennata var. leprieurii, branchlets of last order interrupted and in a single plane (HEC 14757).(5) Bryopsis pennata var. secunda, branchlets of last order curved in one direction (HEC 14796 p.p.). (6) Chamaedoris delphinii (HEC 14617). Scale bars: 250 mm (2); 5 mm (3–5); 1 cm (6).

FIGS 7–13. Caulerpa brachypus, variation in the general morphology and margin structure of the assimilators. (7) Large growth form collected in grooves between bumps of coral rubble, frequently branching and with secondary stolons (HEC 14867). (8) Intermediately large growth form with wide assimilators (HEC 14769). (9) Intermediately large growth form with relatively narrow assimilators (HEC 14656a). (10) Typical specimen with simple or scarcely branched assimilators (HEC 14612). (11) Assimilator with smooth margin (HEC 14612). (12) Assimilator with coarsely dentate margin (HEC 14656a). (13) Assimilator with densely dentate margin (HEC 14718). Scale bars: 2 cm (7–10); 1 mm (11–13).

FIG. 1. Sampling stations. See table 1 for a list of the stations and their GPS coordinates. Map redrawn from Wells (1988). The outer grey line represents the fringing reef.