The key presented below is based on the provided by Bochert & Zettler (2009) but here the position and relative length of the first elongated chaetiger (FECH) and the number of pairs of branchiae have prevalence over chaetal types. The position of FECH in the species follows Parapar et al. (2014).
1 FECH is CH 9 ………………………………………………………………………………………2 – FECH is CH 7 or CH 8 ……………………………………………………………………………7
2. Acicular chaetae in neuropodium of CH 1 ………………………… H. catalinensis Hartman, 1944 – No acicular chaetae in neuropodium of CH 1 ………………………………………………………3
3. Eight pairs of branchiae in adults …………………………………………………………………4 – Four pairs of branchiae in adults……………………………………… H. peruana Borowski, 1994
4. FECH of almost same length as all anterior chaetigers together …… H. longissima Ehlers, 1874 – FECH clearly shorter than all anterior chaetigers together ……………………………………5
5. Capillary chaetae of elongated segments (ES) with flattened distal end ……… H. indica sp. nov. – Capillary chaetae of ES not flattened ………………………………………………………………6
6. Aristate chaetae present on elongated chaetigers ……………… H. sinica Wu & Chen, 1996 – Aristate chaetae absent on elongated chaetigers …………… H. longissima sensu Hartman 1965
7. FECH is CH 8 ………………………………………………………………………………………8 – FECH is CH 7 ………………………………………………………………………………………9
8. Five (or six) pairs of branchiae …………………………… Heterospio sp. A sensu Uebelacker 1984 – Seven pairs of branchiae ……………………… H. mediterranea Laubier, Picard & Ramos, 1973
9. One pair of branchiae ……………………………………… Heterospio sp. 1 sensu Borowski 1994 – Three pairs of branchiae …………………………………………………………………………10
10. Length of CH 8 about ½ that of all anterior chaetigers together; very long chaetae in CH 8 ………… ………………………………………………………… H. reducta Laubier, Picard & Ramos, 1973
– Length of CH 8 about ¼ that of all anterior chaetigers together; chaetae in CH 8 similar to preceeding ……………………………………………………………… H. angolana Bochert & Zettler, 2009
According to the relative size of anterior segments, Heterospio indica sp. nov. most closely resembles H. longissima (both the nominal species and H. longissima sensu Hartman 1965), H. catalinensis, H. peruana and H. sinica. In these species, the first elongated chaetiger is CH 9 while in H. mediterranea, H. reducta, H. angolana, Heterospio sp. A sensu Uebelacker 1984 and Heterospio sp. 1 sensu Borowski 1994, it corresponds to either CH 7 or CH 8 (see figs 5 and 6 in Parapar et al. 2014). In Heterospio indica sp. nov., H. longissima sensu Hartman 1965, H. peruana and H. sinica, CH 9 is about three times longer than any anterior segment ( CH 1– CH 8). By contrast, CH 9 is about as long as all anterior segments altogether in H. longissima Ehlers, 1874; H. catalinensis has a CH 9 which is slightly longer than CH 1– CH 8 and bears acicular chaetae in the neuropodium of CH 1. Heterospio peruana only bears four pairs of branchiae while H. indica sp. nov., H. longissima sensu Hartman 1965 and H. sinica bear eight pairs instead.
The flattened distal end of the capillary chaetae in the elongated segments in H. indica sp. nov. clearly distinguishes the new species from H. longissima sensu Hartman 1965 and H. sinica; in the former, both type of capillary chaetae are greatly different in size and shape while H. sinica bears aristate chaetae which are not found in the new species.
The COI and 18S SSU rDNA sequences from H. indica sp. nov. are publically available on GenBank and can be used as a reference for future molecular taxonomic and phylogenetic studies. They are the first DNA sequences published for any species of Longosomatidae.