Biflustra perambulata, Louis, Soja, 2009

Louis, Soja, 2009, Biflustra perambulata n. sp. (Cheilostomata: Bryozoa), a new alien species from Cochin Harbour, Kerala, India, Zootaxa 2066, pp. 59-68 : 61-62

Biflustra perambulata n. sp.

( Figs 2–7 )

Material examined. Holotype. MBM-J.1.1.1 ― a colony of 10 cm diameter, collected from an oil-tanker berth in Cochin Harbour (9°58’04” N, 76°16’83” E), Kerala, India, deposited in the Marine Biodiversity Museum, Central Marine Fisheries Research Institute (Government of India), Kochi, India.

Etymology. The species name is derived from the Latin perambulatus, meaning ‘to travel over’, alluding to the capability of the genus/species to colonize contiguous marine ecosystems through transportation by natural or artificial means.

Diagnosis. Colony erect, bilamellar, from an initially encrusting base, becoming so foliaceous as to give the appearance of silky floating cloth; thin and brittle. Zooids elongate-rectangular, the distal and proximal margins slightly convex distally to almost straight, 540–600 μm long and 330–350 μm wide, arranged quincuncially with fine demarcations between them ( Fig. 3 ). Opesia oval. No gymnocyst. Cryptocyst mainly developed in the proximolateral corners of each zooid, the midproximal margin of the opesia closely approaching the proximal end of the zooid; cryptocystal surface with sparsely scattered granulations that appear as tiny denticulations along the edge of the narrow lateral cryptocyst that attenuates or disappears distally; median denticulate process absent ( Fig. 4 ). As seen in profile, the distal part of the zooid somewhat elevated to form a low-arched crest that is granular-crenulated ( Fig. 5 ). Multiporous mural septula set high in each lateral wall, 2 pairs proximolateral and 2 pairs distolateral, each with 5–9 perforations in the septulum (pore plate) ( Fig. 6 ). Small round insertion scars of parietal muscles also set fairly high in the lateral walls, with a much larger scar of operculum occlusor muscles set mid-height in the lateral wall below the distalmost septulum ( Fig. 6 ). A crescent of uniporous septula in each transverse wall; at each upturned end of the crescent is a cluster of such pores ( Fig. 7 ).

Remarks: The genus Biflustra has a concentration of species in East Asian waters. In recent decades, Xixing Liu and colleagues have described a number of them (as Membranipora ) from coastal Chinese waters ( Liu 1991, 1992; Liu & Li 1987; Liu et al. 1999, 2001; Zhang & Liu 1995), and the genus is otherwise known from Japan and the Philippines to the Red Sea ( Tilbrook 2006). Species of Biflustra can look superficially similar and be easily confused with each other, in part owing to the relative lack of morphological characters ― for example there are no zooidal polymorphs or external skeletal reproductive structures. Nevertheless, as Liu (1992) clearly demonstrated, the distribution and arrangement of septular pores in transverse and lateral walls constitute useful characters, and, as shown by Liu et al. (2001), details of the cryptocyst as revealed by scanning electron microscopy are very informative, especially if one has an ontogenetic series.

Biflustra perambulata differs from other described species of the genus in all of these characters, including from B. grandicella ( Canu & Bassler, 1929) , which it superficially resembles. As indicated in figure 8, the sizes of the zooids of these species differ (at least in New Zealand material of B. grandicella as compared with Indian material of B. perambulata , although water temperature could account in part for this) more significantly, the cryptocyst in B. grandicella is more extensive proximally, can develop coarser granulation in ephebic zooids, and produce rare spinules on the edge of the cryptocyst. None of these features is found in B. perambulata , which is a less robust, more foliaceous species that is white in the living state compared with the pale buff colour of B. grandicella .

The only other described species of Biflustra to have been recorded in Indian waters is B. savartii auctt. (as Membranipora ) (see Menon & Nair 1975 for Indian records), but the precise identity of this form with a well-developed cryptocystal process is in doubt. Flustra savartii Audouin, 1826 was first described from the Red Sea, but the illustrations executed by J. C. Savigny (1817) (see Bouchet & Danrigal 1982) plainly show the zooids as having usually a small tubercle in each proximolateral corner of the cryptocyst and no median process (d’Hondt 2006). Despite the fact that numerous authors during the past 100 years have attributed species with a median cryptocystal process to Audouin’s species, nothing precisely resembling Savigny’s illustrated material has turned up, although, if specimens of our new species were to be found with paired cryptocystal tubercles, then it could be considered as a candidate for synonymy with B. savartii sensu stricto. At present, B. savartii s.s. remains inadequately characterized and all species with a well-developed median process must be considered as belonging to some other species.

Figures

FIGURE 2. Biflustra perambulata n. sp., showing the white and foliaceous nature of the colony.

FIGURE 3. Biflustra perambulata n. sp. Autozooids, including one that has initiated a new zooid row; note the diminution of the cryptocyst midproximally in each zooid. Scale-bar: 100 μm.

FIGURE 4. Biflustra perambulata n. sp. Bifurcation of zooid rows; note the crenulations of the distal zooid rim as seen en face. Scale-bar: 100 μm.

FIGURE 5. Biflustra perambulata n. sp. Distal rim of an autozooid in a continuous zooid row; note the crenulations of the distal zooid rim as seen en face. Scale-bar: 100 μm.

FIGURE 6. Biflustra perambulata n. sp. Autozooids in lateral view, showing the interior of a lateral wall; note the high position in the wall of the pore-plates, with subjacent parietal muscle scars and the scar of the operculum occlusor muscle at right. Note also the slightly elevated distal rims of autozooids as seen in profile. Scalebar: 100 μm.

FIGURE 7. Biflustra perambulata n. sp. Distal view of the interiors of the transverse walls of three zooids, showing the arc of uniporous septula, with a cluster of such pores on each side where the arc upturns; note the crenulations in the slightly raised distal rim of each zooid. Scale-bar: 100 μm.