Spirobranchus tetraceros (Schmarda, 1861)

Kupriyanova, Elena K., Flaxman, Beth & Burghardt, Ingo, 2022, A Puzzle No More: The Identity of Spirobranchus tetraceros (Schmarda, 1861) (Annelida, Serpulidae) is Revealed, Records of the Australian Museum (Rec. Aust. Mus.) 74 (5), pp. 201-214 : 206-209

Spirobranchus tetraceros (Schmarda, 1861)

Figs 3A–C , 4

Pomatoceros tetraceros Schmarda, 1861: 30 , pl. 21, fig. 179. [“Neu-Süd-Wales” (New South Wales). Short description with a figure; Grube, 1862: 66. [Name only]

Galeolaria?tetracerus (Schmarda) Mörch, 1863, p. 371 [no new data]; contrary to Halt et al. (2009, p. 217) neither Schmarda’s original description (operculum quadricorne, repeated in German “vier kurze, geweihartige Fortsätze”, in which four antler-like projections are visible in his fig. 179 as well), nor Mörch’s interpretation of Schmarda’s figure, can refer to Galeolaria hystrix , the taxon had been correctly attributed by Schmarda to Pomatoceros , nowadays Spirobranchus ]

Vermilia tetraceros (Schmarda) Quatrefages, 1865, p. 520 [diagnosis of Schmarda].

In part Pomatoceros elaphus Haswell, 1885, pp. 663–665 , pl. 31, fig. 7, pl. 3 2, figs 9–10 [Port Jackson, Sydney. Description; figure of operculum, peduncular wings and radioles].

In part Spirobranchus giganteus .— Dew, 1959, pp. 45–46, fig. 17 [several localities from Queensland to New South Wales (of the four specimens studied, two belonged to S. corniculatus )]

In part Spirobranchus tricornis .—Straughan, 1967, p. 244, fig. 14b–d [New South Wales —few characters]

In part Spirobranchus tetraceros .— Day & Hutchings, 1979, p. 147 [checklist of Australian records and specimens].

Material studied

Neotype: Australian Museum W. 51859, New South Wales, Port Botany , off La Perouse Point, 33°59'36"S 151°13'39"E, 1 spec. without tube.

Additional materials: Australian Museum W. 35308, NSW, Cape Three Points 33°31'55"S 151°24'57"E, 1 spec. without operculum (prepared for SEM); W.49841, Port Kembla , north east of Martin Island , 34°29'47"S 150°56'11"E, 1 spec. in tube; W.49844, NSW, Shellharbour , 34°36'12"S 150°53'42"E, 1 spec. without operculum; W.49845, NSW, Shellharbour , same as above, 1 spec. without operculum; W.51856, NSW, Port Botany , off La Perouse Point , 33°59'36"S 151°13'39"E, 1 spec. with simple conical operculum without spines; W.51858, NSW, Port Botany, La Perouse, same as above, 1 spec. without operculum .

Comparative material

Spirobranchus cf. tetraceros sp. B

Australian Museum W. 45073 Qld, Lizard Island , 14°40'46"S 145°26'49"E, 1 spec. without operculum .

Spirobranchus cf. tetraceros sp. C

Australian Museum W. 30500, Qld, Torres Strait , west of Hawkesbury Island, 10°21'44"S 142°7'4"E, 1 spec. ; W.42374, Qld, Heron Island , 23°26'30"S 151°54'2"E, 1 spec.; AM W.42391, Qld, Heron Island , 23°26'30"S 151°54'2"E, 1 spec. without operculum.

Description

Tube: attached to substrate throughout their length; tube colour predominantly pink (some parts maybe white) outside, white inside, circular in cross-section, without a tooth over entrance ( Fig. 3D, E ). Rounded in cross-section, one distinct irregular higher median keel and two or three lower slightly denticulate lateral keels and some irregular transversal ridges.

Radiolar crown: radioles arranged in two circles. Radioles square-shaped in cross-section, external side smooth, internal sides with two rows of pinnules of the same length, becoming slightly shorter towards tips of radioles. Terminal filaments without pinnules. Stylodes absent.

Interradiolar membrane: high, connecting over half of radiolar length, without lappets (processes) between radioles ( Figs 3C , 4A ).

Peduncle: nearly twice as thick as normal radioles (4A); inserted on the left of median line ( Figs 3C , 4A ), pigmented with white and blue colours ( Fig. 3A ). Lateral distal wings elongated triangular, with pointed tips and crenulated inner margins.

Operculum: very variable, without prominent basal ampulla; endplate circular with thickened brim, slightly concave (AM W.51856 with simple conical operculum). In the centre opercular endplate bearing three groups of dichotomously branching (antler-like) spines ( Fig. 3C–E ); one group positioned medio-ventrally and two groups latero-dorsally. The most complex opercula showing one medio-ventral spine split thrice and two latero-dorsal spines split twice to thrice, with medial spinules irregularly placed.

Collar and thoracic membranes: short, covering only the bases of radioles ( Fig. 3C ); tri-lobed, with a larger ventral and two smaller lateral lobes. Tonguelets present between lateral and ventral lobes. Lateral lobes continuing into thoracic membranes producing a ventral apron reaching to the second abdominal chaetiger ( Fig. 4A ). Bundle of collar chaetae large, distinct, situated at some distance anterior to remaining thoracic chaetae ( Fig. 4A ). Collar chaetae of two types: special Spirobranchus - type bearing basal bosses covered with minute denticles and simple limbate ( Fig. 4B ).

Thorax: with seven thoracic chaetigers, including six uncinigerous ( Fig. 4A ). Thoracic chaetae simple limbate of two sizes ( Fig. 4C ), Apomatus chaetae absent. Uncini saw-shaped with 12–14 teeth in profile, anterior peg flat, nearly triangular-shaped (dorsal uncini of second thoracic chaetiger, Fig. 3D ). Ventral ends of thoracic uncinigerous tori widely separated anteriorly, gradually approaching one another towards the end of thorax, thus leaving a triangular depression.

Abdomen: abdominal chaetae long (approximately the same length as thoracic chaetae) throughout the abdomen, not becoming significantly longer towards pygidium; true trumpet-shaped with two rows of teeth ( Fig. 3F ). Uncini saw-shaped throughout the length of abdomen, with 11–12 teeth per row, anterior pegs flat, nearly triangular ( Fig. 4E ).

Colour of preserved specimens: anterior end of thorax, distal ends of radioles, peduncle, and opercular endplate blue or white with blue specks ( Fig. 3C–E ).

Remarks

For a Spirobranchus cf. tetraceros population from Eilat, Perry et al. (2018) mention the inter-radiolar membrane with lappets between radioles and so does Palero et al. (2020) for the specimens from Spain. Moreover, ten Hove (1970) also included lappets (processes) between radioles in his composite description based on specimens from the Caribbean, Iranian Gulf, Banda Sea, and Philippines. The neotype and additional specimens of Spirobranchus tetraceros , however, lack such inter-radiolar lappets altogether. Ironically, although Schmarda (1861) named his species “ tetraceros ” because of four short, antler-shaped extensions (spines) in the centre of the operculum ( Fig. 3A ), none of the specimens examined in this study show such opercula, they rather have three groups of branching spines very similar to the operculum of Pomatoceros elaphus Haswell, 1885 ( Fig. 3B ).

Interestingly, while Schmarda’s figure appears to illustrate four unbranching opercular spines figure, high magnification of the drawings shows at least three spines with a terminal bifurcation. Confusingly, Schmarda drew two spines turning away from the opercular endplate and crossing two others more or less parallel to the endplate, which might be interpreted as bifid. The total number in this figure would have been four, thus justifying the name “tetraceros ”. However, if the right “horizontal spine” is merely reflecting a shadow on the endplate seen by Schmarda, the remaining arrangement of two more or less erect spines turning away from the distal plate and one projecting in between conform the general observed pattern of two latero-dorsal and one medio-ventral groups of spines. Also, in Schmarda’s figure the edge of the opercular ampulla is apparently shown as being “toothed”. One wonders whether the colour patterns as in Fig. 3C, E might have led Schmarda, with either poor illumination or bad optics, to such an interpretation of the opercular edge shape.

As Schmarda did not leave any collections and thus the type material of Pomatoceros tetraceros is not available, here we designated a neotype in accordance with the International Code of Zoological Nomenclature ( ICZN 1999 ), Article 75.3 .

Figures

Figure 3. Photographs of the neotype and additional specimens of Spirobranchus tetraceros sensu stricto. (A) original drawings of Pomatoceros tetraceros by Schmarda (1861); (B) original drawing of Pomatoceros elaphus by Haswell (1885); (C) neotype of S. tetraceros W.51859; (D) specimen W.49841 in tube; and (E) specimen W.49844, operculum (left), a tube fragment (right).

Figure 4. Scanning electron microscopic micrographs of S. tetraceros sensu stricto W.35308. (A) lateral view of the anterior part of the paratype; (B) collar chaetae bundle with special Spirobranchus-type chaetae; (C) thoracic chaetae; (D) thoracic uncini; (E) anterior abdominal uncini; (F) anterior abdominal chaetae.