Pachycerianthus delwynae Carter, 1995

Stampar, Sérgio N., Mills, V. Sadie & Keable, Stephen J., 2020, Ceriantharia (Cnidaria) from Australia, New Zealand and Antarctica with Descriptions of Four New Species, Records of the Australian Museum 72 (3), pp. 81-100 : 83

Pachycerianthus delwynae Carter, 1995

Fig. 1 A–D

Pachycerianthus delwynae Carter, 1995: 2–3 ; figs 1b, 2. Pachycerianthus longistriatus Carter, 1995: 3–4 , junior

synonym.

Specimens examined. Australian Museum (AM)— Australia, Sydney—G15399 (holotype of P. delwynae ) Port Jackson, Chowder Bay, 33°50'30"S 151°15'12"E (15/ ix/1989), depth 15 m; G15404 Port Jackson , Manly Pool, 33°50'S 151°17'E (1957) ; G14526, Port Jackson , Camp Cove, 33°50'S 151°16'E (2 specimens) ; G15808 Port Jackson , Vaucluse Bay, 33°51'S 151°16'E (many specimens) ; G15400 (paratype of P. delwynae ) Port Jackson , Bottle and Glass Rocks, 33°50'54"S 151°16'12"E (13/vii/1989), depth 5 m ; G15401 (paratype of P. delwynae ) Port Jackson , Bottle and Glass Rocks, 33°50'54"S 151°16'12"E (20/vii/1989), depth 7 m ; G12555 (paratype of P. longistriatus ) Port Jackson ; G15403 (paratype of P. longistriatus ) Port Jackson , Chowder Bay, 33°50'S 151°17'E ; G12554 (paratypes of P. longistriatus ) Port Jackson (09/1886) (5 specimens in jar but only 3 in good condition and only 3 cited by Carter (1995)) ; G15406 (paratypes of P. longistriatus ) Port Jackson , Off Dawes Point, 33°50'S 151°12'E (2 specimens) ; G12553 (paratype of P. longistriatus ) Port Jackson ; G13558 (paratype of P. longistriatus ) Port Jackson ; G13561 (paratype of P. longistriatus ) Port Jackson , G15405 (paratype of P. longistriatus ) Port Jackson , Drummoyne (viii/1963) ; G15402 (holotype of P. longistriatus ) Port Jackson , Taylors Bay, 33°50'S 151°17'E (20/vii/1989), depth 5 m.

Remarks. Closely related sympatric species always arouse much curiosity, especially regarding how the processes of speciation have occurred. However, the occurrence of two species of Pachycerianthus described from Sydney (Port Jackson) by Carter (1995) are not supported. Carter (1995) notes that separation of the two species based on anatomy is difficult because the differences in mesenterial organization are slight, but the external morphology, especially tentacle colouration, is more consistent with banded marginal tentacles in P. delwynae and with distinctive longitudinal stripes on the marginals in P. longistriatus . However, colour patterns have been shown to be highly variable in Cnidaria, especially in Ceriantharia , where numerous examples of different colour morphs have been found to represent a single species when other characters are considered (e.g., Molodtsova et al., 2011; Stampar et al., 2012 (including molecular data); Stampar et al., 2015). Some species have different colour morphs depending on the reproduction season that each polyp was produced (Stampar et al., submitted), consequently, colour is not a reliable taxonomic character in Ceriantharia . Leaving aside tentacle colouration patterns, the two main anatomical features listed by Carter (1995) that differentiate the species are not consistent, presenting variations that overlap. The first of these is the arrangement of mesenteries. Carter (1995) indicates that in P. delwynae the M2 mesentery is longer than the M1 and indicates an opposite pattern in P. longistriatus , in which mesentery M2 is shorter than M1. Observing the same specimens studied by Carter (1995) it is possible to verify this pattern is only present in some individuals, in other specimens this pattern does not exist or is not as evident as described. However, two specimens (AM G12554 and AM G15405, both nominally paratypes of P. longistriatus ) display a mixture of both morphological patterns; one side (from siphonoglyph to multiplication chamber) has mesenteries with the M2 longer than the M1, the other side has the inverse mesentery M1 is longer than the M2. The other character used to justify the separation into two species is the distribution of the insertion of the tentacles. This character is much more inconsistent than the form of the mesentery, at least four different arrangements occur. However, the most important aspect is that there is no difference in the number of pseudocycles of the tentacles of each type (marginal or labial) in all specimens. Therefore, it is not possible to keep these specimens as two separate species, Pachycerianthus delwynae is retained instead of P. longistriatus based on page precedence in Carter (1995).

Figures

Figure 1. Specimens of Pachycerianthus delwynae in New South Wales, Australia. (A, B) Tentacles with longitudinal lines and (C, D) banded tentacles. Images: Tony Strazzani.