Report of Rhombognathus scutulatus (Acari: Halacaridae) from Goa, India

Rhombognathus scutulatus Bartsch is reported here from Goa, India. World distribution of this species is also provided.

Study area: Anjuna beach (Lat. 15° 34' 58'' N;Long. 73° 44' 28.54'' E) is located on the northern stretches of Goa state on the West Coast of India. The coast is mainly sandy and rocky shore. The rocky shore has small intertidal rock pools which are rich with diverse marine flora and fauna. The seaweed cover was seen on rocky shore and was more on seaward side represented by species of Sargassum, Hypnea, Spatoglossum, Chaetomorpha, Sphacealria, Cladophora, Dictyota, Gracillaria, Porphyra and Amphiroa. Some of the seaweeds like Sargassum sp. were found submerged in the water mainly in the splash zone area. The calcified genera include Amphiroa sp. & Cheliosporum sp. were found in abundance in the rook pool area. Whereas the rocky areas display large flank of Sargassum in rock pools & crevices. Three common seaweeds Sargassum, Ulva and Gracillaria were collected for the study of mites.
The following abbreviations are used in the text, table and figure legends: AE, anterior epimeral plate; PE, posterior epimeral plate; PGS, perigenital setae; SGS, subgenital setae.

Material Examined:
Males and females from Goa -Anjuna beach among rocky algae -Sargassum, Ulva and Gracillaria.
Brief Description: All dorsal plates fused in single shield and sculptured with foveae ( Figure 1A). Posterodorsal area with a pair of setae. All ventral plates fused to a ventral shield ( Figure 1B). AE area with 3 pairs of ventral setae plus one pair of adjunctive marginal setae. Each PE area with 3 ventral, one dorsal plus 1 adjunctive seta. Male with 11-12 pairs plumose PGS and 2 pairs SGS ( Figure 1C). Female with 5 pairs PGS and 2 pairs SGS. Gnathostoma small and compact. Palp 4-segmented. Palpal patella (P 2 ) and trochanter without any setae. Palpal telofemur with 1 seta and tibiotarsus with 3 setae. Telofemora I and II with 6 setae (2 ventral and 4 dorsal); telofemora III and IV devoid of any ventral seta and bearing 3 dorsal setae. Tibia I with 5 setae of which 2 ventral pectinate. Legs with carpite on tarsi and devoid of median claw. Lateral claw endoplanate with broad accessory process bearing about 13-15 teeth ( Figure 1D).
Distribution: This species is widely distributed in the south-western Pacific Ocean and Indian Ocean: Philippines, Singapore, Australia, Sri Lanka, India, Iran, Kenya, Mauritius and New Gunia. Table 1 and Figure 2 show the distribution of this species.
Remarks: There are six species of Rhombognathus viz. R. aspidotus Bartsch (2006), R. conjunctus Bartsch (1986), R. parvulus Viets (1939), R. peltatus Viets (1939), R. scutulatus Bartsch and R. similis Bartsch (1977) in which dorsal plates fused in single shield. R. similis was reported from Andaman & Nicobar islands (Chatterjee, 1995) as R. similis may belong to other species and should be considered at present as Rhombognathus sp. Among Rhombognathus species in which dorsal plates fused in single shield, R scutulatus and Rhombognathus sp. have been recorded from Indian Ocean.   Bartsch (2003) Singapore: Strait of Singapore, Labrador park Small brown and green rocky algae PTW: Pacific Ocean, tropical west Bartsch (2006) Srilanka: Ahangama Among Halimeda from a moderately exposed fringing reef flat ITE: Indian Ocean, tropical east Bartsch (2006) Mauritius: South of Port Louis, Flic en Flac Intertidal wave exposed rocky shore ITW: Indian Ocean, tropical west Bartsch (2009) Chatterjee (1996) reported ciliate infestation on R. Scutulatus from Kovalam beach, Kerala. Bartsch (2009) has given a comparative view on the variation in number of tines on the accessory process of lateral claws and length of idiosoma. This species exhibits wide variation in number of tines on the accessory process of lateral claws ranging from 10 to 28 (Bartsch, 2009;Abé, Etemadi, 2014).