Plumatella testudinicola Annandale, 1912

Wood, Timothy S., 2022, Phylactolaemate bryozoans at the Zoological Survey of India and a taxonomic key to Indian Phylactolaemata, Zootaxa 5200 (2), pp. 401-435 : 411

Plumatella testudinicola Annandale, 1912

( Fig. 8 )

Original description. Plumatella (Afrindella) testudinicola: Annandale 1912, p. 147 –150, pl. 13.

Material examined. ZEV5065 /7 (holotype), “on carapace of Kachingga lineata, R. Ganges, Rajmahal , collected by B. L. Chadhuri, March, 1912.” Also ZEV 5023 /7 (paratype, designated here) collected from the River Ganges by B.L.Choudhury, March, 1912 .

Description. Colonies from ZEV 5065/7 flat with closely appressed lines of zooids radiating outwards towards the periphery ( Fig. 8a ); zooids densely arranged, leaving no exposed substratum, most zooids exhibiting a faintly defined raphe. Floatoblasts absent, but sessoblasts abundant, positioned end to end in long strings throughout the length of many colony branches ( Fig. 8b ), the sessoblasts variably shaped, each with a narrow annulus, the frontal valve covered with small, faint tubercles.

Zooids of ZEV 5023/7 similar to those of ZEV 5065, but sessoblast frontal valves covered with a fine reticulation with single tubercles emerging from deep interstices ( Fig. 8c, d ).

Status. ZEV 5065/7 is Plumatella casmiana Oka, 1907 ; ZEV 5023/7 is Plumatella bombayensis Annandale, 1908 .

Remarks. The only known specimens were reported from the plastrons of freshwater tortoises: Hardella thurjii ( Gray, 1831) , Batagur dhongoka ( Gray, 1834) , and Batagur kachuga ( Gray, 1831) . According to Annandale (1912) the tortoises had been out of the water for at least 24 hours before the bryozoans were discovered.Annandale (1912) provided a detailed description of the bryozoans, accompanied by two photos illustrating a flattened colony with its radiating lines of zooids. Wiebach (1974) offered a second description along with commentary and photos of sessoblast valves. There is also a published SEM micrograph of several sessoblasts ( Wiebach 1975, reproduced here in Fig. 8b ).

The ZSI holotype ( ZEV 5065 /7) includes three pieces of turtle plastron: a large one bearing colonies (the designated lectotype) and two smaller ones with statoblasts only. The colonies consist only of frayed ectocyst and numerous sessoblasts. In areas where colony tissue is missing, the lines of contiguous sessoblasts show where colony branches once had been. The additional specimen, ZEV/7 5023, has been stored separately from the holotype. It consists of sessoblasts and pieces of colony scraped free of the substratum, which was presumably also a turtle plastron, although this cannot be confirmed .

Annandale placed the species within his new subgenus, Afrindella Annandale in Annandale & Kemp (1912), apparently based on an abrupt termination of the stiffened ectocyst near the tip of each zooid. Wiebach (1974) agreed, describing the species as Afrindella testudinicola .

However, I disagree. The designated holotype, ZEV 5065/7, labeled Plumatella (Afrindella) testudinicola is almost certainly synonymous with Plumatella casmiana Oka, 1907 . This opinion is supported by several observations:

1. The narrow sessoblast annulus and the relatively small, faint, tubercles on the frontal valve are both diagnostic features of the sessoblast of P. casmiana ( Fig. 8c, d );

2. The colonies, described by Annandale as “flat, oval or circular lichenoid patches” would easily match any description of P. casmiana growing unobstructed on a wide, flat surface, such as lotus leaves or tortoise plastrons.

3. Annandale’s description of sessoblasts “arranged in moniliform series” is a feature commonly occurring in P. casmiana .

Moreover, in his description of Plumatella persica , now recognized as P. casmiana, Annandale (1919, p. 92) wrote, “This species closely resembles the Gangetic Plumatella testudinicola but is differentiated by the possession of free as well as fixed statoblasts and by the more elongate form of the latter.” I would note that sessoblast shape can be variable and is seldom used in the diagnosis of plumatellid species.

Specimen ZEV 5023/7 is clearly different. Having been scraped from the substratum the colony structure is difficult to reconstruct, but the sessoblasts are not those of Plumatella casmiana . The small, deep interstices on the frontal valve coupled with a single tubercle in the center of each are features unique to P. bombayensis .

As for a sclerotized ectocyst that would warrant the Afrindella designation, this feature is not uncommon among P. casmiana colonies in warm parts of the world. In temperate regions the ectocyst of P. casmiana is normally thin and flexible, but in the tropics it can become well sclerotized and stiff ( Agrawal & Rao 1981). Similarly, this is a feature that commonly occurs in P. bombayensis .

Figures

FIGURE 8. Plumatella testudinicola, now recognized as two species: P. casmiana and P. bombayensis. (a) A portion of turtle plaston from ZEV 5065 showing parallel lines of zooids, scale bar = 1 cm; (b) Sessoblasts from ZEV 5065 from a SEM micrograph by Wiebach 1975, modified by the addition of a 400 µm scale bar; (c) Sessoblast from ZEV 5023 showing interstitial reticulation characteristic of P. bombayensis, scale bar = 100 µm; (d) enlarged portion of Figure 8c showing the strong reticulation, with tubercles present but less apparent than in Figure 4d.