Acromegalomma quadrioculatum (Willey, 1905)

(Figures 2 (a–), 3(a–f), 4(a–g))

Branchiomma quadrioculatum Willey, 1905: 307, pl. 7, figs 168–169.

Megalomma quadrioculatum .– Cantone 1976: 249, 253 (text plus table). – Cantone 1982: 134–135, 137 (throughout text and table). – Cantone 1987: 78 (table). – Henschel et al. 1990: 293, 295 (table plus text). – Knight-Jones 1997: 314 (throughout text). – Lasiaka 1999: 28–29 (text plus table). – Bailey-Brock 2003: 217 (text table). – Bu-Olayan and Thomas 2005: 96–97 (text tables). – Ramalinga Kripa 2007: 48–49 (table plus text). – Tovar-Hernández and Salazar-Vallejo 2008: 1955, 1957, 1961–1962 (throughout text and table). – Capa and Murray 2009: 217–218, 223, fig. 5f (throughout text, table). – Rajasekaran and Fernando 2012: 3, 21, 15 (tables plus text), fig. 1.2 (n). – Clavijo and Fernández 2013: 11, fig. 59. – Sivaraj et al. 2014, 2015: 65, 8 (text table). – Rajasekaran 2015: 3, 21, 15 (throughout table and text). – Clavijo 2016: 65, 67 (throughout text). – Murugesan et al. 2018: 115 (text table). – Sekar et al. 2019: 5, 26 (table plus text), fig. 25a–e (not Acromegalomma; it is a member of Notaulax).

Acromegalomma quadrioculatum . – Gil and Nishi 2017, 142 (throughout text). – Keppel et al. 2019: 63 (throughout text). – Cárdenas-Calle et al. 2020: 23 (text table). – Brusca 2020: 257, 326 (throughou text). – Balakrishnan and Tudu 2021: 152 (text table). –TovarHernández and Fitzhugh 2021: 761 (text table).

Examined material

India – Vaan Island, Gulf of Mannar, state of Tamil Nadu, district of Tuticorin, 8.841135537679804 N, 78.2219779167134 E, coral reef, seaweed and seagrass patches in sand, 0–1 m deep, 8 May 2018, 1 specimen (ZSI/ MARC / P8362) .

Type locality

Aripu (= Arippu) Coral Reef, Sri Lanka, Gulf of Manaar, Indian Ocean, (08.78N, 79.87E; estimated geolocation fide Gil and Nishi (2017).

Description

Colour, body shape and size. Radiolar crown with three purplish-brown bands at the basal half of crown (Figure 3 (a)). Dorsal collar margins with two diagonal purple lines (Figure 3 (b,c)). Ventral shields whitish (Figure 3 (a, d–e)). Rest of body pale (Figure 3 (e)). Radiolar eyes purplish-brown (Figure 3 (f)). Specimen complete, depressed. Trunk 3 cm long, 0.25 cm wide.

Radiolar crown. Length 0.5 cm. Radiolar lobes semicircular. Fourteen pairs of radioles. Outer radiolar surface flattened. Sub-distal compound eyes in dorsalmost and third dorsalmost pair (Figure 3 (f)). Eyes of dorsalmost radioles large, slightly spiralled with a short radiolar tip (shorter than 1/4 of ocular diameter) (Figure 4 (a)). Eyes from third dorsalmost radiolar pair shorter than those present in dorsalmost radioles, spherical with short radiolar tips. Dorsal lips and ventral lips not examined.

Peristomium . Anterior peristomial ring partially exposed dorsally. Caruncle present, short, triangular, 1/2 as long as second thoracic segment. Posterior peristomial ring collar with dorsal collar margins fused to faecal groove. Dorsal lappets absent, dorsal pockets present but not well developed. Ventral lappets short, triangular, with a mid-ventral incision reaching anterior margin of ventral shield of collar. Lateral collar margin oblique, not covering bases of radioles. Ventral sacs and ventral lateral lamellae present (Figure 3 (d)).

Thorax. Chaetiger 1: notochaetae only elongate and narrowly hooded; superior row longer than inferior. Ventral shield of chaetiger 1 as long as wide, with rounded anterior margin and a short, anterior medial incision (Figure 3 (d)). Chaetigers 2–8: ventral shields rectangular, wider than long, tori not contacting shields (Figure 3 (e)). Notopodial fascicles with superior group of elongate, narrowly hooded chaetae; inferior groups of chaetae Type B (with progressively tapering distal tip) (Figure 4 (b)). Uncini with main fang surmounted by several rows of numerous minute teeth; dentition covering half of main fang length, handles 2 times longer than main fang (Figure 4 (d)). Companion chaetae with teardrop-shaped membranes (Figure 4 (e)). Interramal eyespots absent.

Abdomen. Segments: 132. Neurochaetae narrowly hooded (Figure 4 (c)); chaetae in posterior rows longer than those in anterior rows. Uncini with main fang surmounted by several rows of teeth, dentition covering half of main fang length, handles as long as main fang (Figure 4 (f)). Interramal eyespots absent. Pygidium broadly rounded (Figure 4 (g)), presence of eyes unknown.

Habitat

Found embedded in dead coral masses of Acropora sp. (Figure 2 (a–)).

Remarks

Examined features of the specimen reviewed match the original description of A. quadrioculatum by Willey (1905) and comments by Tovar-Hernández and CarreraParra (2011). In the phylogenetic analysis by Tovar-Hernández and Carrera-Parra (2011), A. acrophthalmos (Grube, 1878) and A. quadrioculatum were nested within the same clade. Both species have a caruncle, but they can be differentiated based on the distribution of radiolar eyes: eyes in most radioles in A. acrophthalmos whereas eyes present only in dorsalmost and third dorsalmost radiolar pairs in A. quadrioculatum .

Acromegalomma quadrioculatum was originally described from Aripu Coral Reef in Ceylon (Sri Lanka), but Willey (1905) does not specify whether it was collected in dead coral. In the present study, A. quadrioculatum was found in dead coral Acropora sp., and it fits the original description. Other than A. quadrioculatum, only two species of Acromegalomma have been reported from dead coral blocks, as stated in the Introduction: A. interruptum (Capa and Murray, 2009) and A. circumspectum, both reported from dead blocks of Pocillopora spp .. Perhaps Acromegalomma might be common in dead coral blocks, but as their extraction post-fixation from dead coral using hammer and chisel is difficult, their presence may be unnoticed.

Acromegalomma quadrioculatum was reported from South Africa by Monro (1933, p. 504–507, figs 13–20) and Day (1967, p. 758, fig. 37.1h–o), from Guam and the Mariana islands by Bailey-Brock (1999, p. 189, 192, text plus table) and from Rio de Janeiro by Omena and Creed (2004, p. 279, table); however, all these records should be reviewed to confirm the accuracy of the identification as well as to determine whether A. quadrioculatum is endemic to the South India and Sri Lanka ecoregion or not.