Lacinularia Schweigger, 1820

Genus Lacinularia Schweigger, 1820 View in CoL

Lacinularia is composed of seven morphospecies, which can be misidentified as members of the genus Sinantherina . This means that at least two errors were made. (1) The gelatinous matrix present in Lacinularia was overlooked. (To avoid confusion presence of the matrix may be demonstrated by using methylene blue, which stains the boundary of the jelly.) (2) A region of the foot was mistaken for an oviferon. Additionally, in certain Sinantherina species, the presence of warts or spines were overlooked (see below).

Etymon of genus name (L., Lacin, a flap) is obscure, but may refer to the corona.

Diagnosis. Corona round or heart-shaped (kidney-shaped). Ventrolateral antennae short. Animals forming spherical to elliptical colonies (usually 20 to>100 individuals per colony, but occasionally many more) with a flocculent gelatinous matrix, often embedded with algae and other debris. Sessile species may form continuous mats over the substratum. Oviferon absent, eggs held within a gelatinous matrix. Oviparous. Planktonic or sessile.

Bhardwaj and Dattagupta (1984) provide information on colony formation in Lacinularia racemovata Thorpe, 1893 and Lacinularia flosculosa (O.F. Müller, 1773) . The species named Lacinularia causeyae ( Vidrine et al. 1985) was relocated to a new genus in the Conochilidae : Conochilopsis causeyae ( Segers & Wallace 2001) . All species inhabit a gelatinous matrix (tube), which becomes a confluent matrix in the six species forming colonies; Lacinularia megalotrocha Thorpe, 1893 is solitary. When compared to other sessile species (e.g., Floscularia ), all species of Lacinularia possess small ventral antennae. Table 2 View TABLE 2 provides a compilation of the important characteristics of this genus.

Dichotomous key to species of genus Lacinularia

1 Planktonic (colonies infrequently attached to substratum)..................................................... 2

1’ Sessile............................................................................................. 3

2(1) Corona circular, with shallow ventral sinus, slightly wider than body, dorsal gap present; body constricted at base; two eyespots present; colonial (prolate spheroid); total body length 450–750 µm. ( Fig. 2A–C View FIGURE 2 )............... racemovata Thorpe, 1893 [Colonies of ~150 individuals attached to central rod of firm gelatinous material. Colony length is 2x width and rotates about its long axis. An adult and trophi are illustrated by Banik (1996), but reported as L. elliptica , a junior subjective synonym.]

2’ Corona nearly circular to oval-shaped, slightly flattened ventrally; dorsal gap tiny; two eyespots present; colonial (spherical); total body length 700–900 µm. ( Fig. 2D–G View FIGURE 2 )...................................... ismailoviensis ( Poggenpol, 1872) [The trophi are sketched by Poggenpol (1872), Dioni (1966), and Kutikova (2007). Kutikova (2007) illustrated the male and resting eggs and notes that colonies may attach to a substratum. The corona depicted in Figure 4 View FIGURE 4 by Poggenpol (1872) is more elliptical than circular as is illustrated in Figure 5 View FIGURE 5 of Kutikova (2007) and Figure 2 View FIGURE 2 of Vidrine et al. (1985).]

3(1’) Dorsal gap in corona present (small or distinct)............................................................. 4

3’ Dorsal gap absent; corona with shallow ventral sinus; colonies attached to the substratum by a long stalk (peduncle)...... 6

4(3) Corona heart to kidney shaped with deep ventral sinus....................................................... 5

4’ Corona oval- to spherical shape, slightly wider than the body, with short axis held at right angles to trunk; ciliated between trochus and cingulum; dorsal gap distinct; body narrow, elongate; long foot (⅔ whole length); eyespots absent; colonial; total body length 800–1000 µm. ( Fig. 3A–C View FIGURE 3 )................................................ elongata Shephard, 1896 [ Shephard (1896) reports that this species may form spherical colonies or assemble into a continuous cluster resembling a “thick felt” (i.e., a mat). Shephard attributes that the “dirty brown colour” of the colonies may be characteristics of the species, but this may be a matter of the water conditions. Shephard’s rudimentary illustration of the trophi shows them to be asymmetrical.]

5(4) Corona , deep ventral sinus; dorsal gap small; eyespots absent; solitary; total body length ~1000 µm. ( Fig. 3D View FIGURE 3 )......................................................................................... megalotrocha Thorpe, 1893

5’ Corona broad, deep ventral sinus; dorsal gap small; eyespots absent; colonial; total body length ≤ 2000 µm. ( Fig. 4 View FIGURE 4 )...................................................................................... flosculosa (Müller, 1773) [Depending on the substratum to which it attaches, colonies of L. flosculosa are more-or-less spherical, but as in L. elongata this species may colonize substrata forming a massive continuous mat: see Figure 1 View FIGURE 1 in Pourriot et al. (1972). Koste et al. (1995) illustrates the adult, trophi, and colony form, as well the males, apparently with eyespots.]

6(5) Corona as wide as body, with very shallow ventral sinus; no dorsal gap; body ovoid; foot long, ca. ⅘ of body length; eyespots placed close to coronal edge; total body length ≤ 2600 µm; colonial. ( Fig. 5A–C View FIGURE 5 )............... striolata Shephard, 1899 [A detailed anatomy is illustrated by ( Shephard 1899), who also notes the following features. (1) The integument is striated. (2) Corona moderately inclined to body forming a 45° ancle with the axis of the body. (3) The peduncle (stalk), which increases in length (≤ 12 mm) as the animals age, anchors the colony to its substratum. It is formed from the combined secretions of all members of the colony. (4) Shephard estimates that the spherical colonies of 5 mm in diameter may have>3600 individuals.] (5) Gut is absent in the male, but possesses two eyespots, dorsal antenna, and a ciliated cup near the posterior. (6) The larvae aggregate into groups, thereby forming colonies of the same age; this behavior is termed geminative colony formation ( Wallace et al. 2015). However, colony formation by the stem female was not described. (7) While feeding individuals in L. striolata colonies apparently arrange themselves into arrays, as has been described by Wallace (1987) in S. socialis . (8) Shepard hints at amphoteric reproduction.]

6’ Corona ~2–3x body width, with very shallow ventral sinus; trochus and cingulum widely separated; two eyespots, ½ way down the corona, close to trochus; foot <⅘ of body length; peduncle long; total body length 750–1000 µm; colonial. ( Fig. 5D–E View FIGURE 5 )............................................................................... pedunculata Hudson, 1889